Materials

14 pages, 7597 KiB

Open AccessEditor’s ChoiceArticle

Effect of Equal Channel Angular Pressing on the Dynamic Softening Behavior of Ti-6Al-4V Alloy in the Hot Deformation Process

by Zhiyong Zhao, Jun Gao, Yaoqi Wang, Yanling Zhang and Hongliang Hou

Materials 2021, 14(1), 232; https://doi.org/10.3390/ma14010232 - 5 Jan 2021

Cited by 7 | Viewed by 3099

Abstract

To investigate the effect of equal channel angular pressing (ECAP) on the deformation of Ti-6Al-4V alloy at a higher temperature, hot compression tests were conducted on alloys having two different initial microstructures (the original alloy (Pre-ECAP) and ECAP-deformed alloy (Post-ECAP)). Post-ECAP, the alloy [...] Read more.

To investigate the effect of equal channel angular pressing (ECAP) on the deformation of Ti-6Al-4V alloy at a higher temperature, hot compression tests were conducted on alloys having two different initial microstructures (the original alloy (Pre-ECAP) and ECAP-deformed alloy (Post-ECAP)). Post-ECAP, the alloy showed a higher degree of dynamic softening during the hot deformation process due to its finer grain size and higher distortion energy. The flow stress of Post-ECAP alloy was higher than the Pre-ECAP alloy at 500 °C when

\dot{ε} = 0.003 s^{- 1}

. However, the stress of the Post-ECAP alloy decreased rapidly with increasing temperature and strain rate, until the stress value was much lower than that of Pre-ECAP at 700 °C when

\dot{ε} = 0.03 s^{- 1}

. The value of the dynamic softening coefficient revealed that the dynamic softening behavior of Post-ECAP was more pronounced than that of Pre-ECAP in the hot compression deformation process. The main dynamic softening mechanism of Pre-ECAP is dynamic recovery, while the dynamic recrystallization process plays a more important role in the deformation process of Post-ECAP alloy. The microstructures observation results showed that dynamic recrystallization was more likely to occur to Post-ECAP alloys under the same deformation condition. Almost fully dynamic recrystallization had occurred in the deformation process of Post-ECAP at 700 °C and a strain rate of

\dot{ε} = 0.01 s^{- 1}

. The grains of Post-ECAP alloys were further refined. The Post-ECAP alloy exhibits better plastic deformation at temperatures higher than 600 °C due to its significant dynamic recrystallization. Full article

(This article belongs to the Special Issue Metal Forming: Processes and Analyses)

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13 pages, 2365 KiB

Open AccessEditor’s ChoiceArticle

Natural Building Materials for Interior Fitting and Refurbishment—What about Indoor Emissions?

by Matthias Richter, Wolfgang Horn, Elevtheria Juritsch, Andrea Klinge, Leon Radeljic and Oliver Jann

Materials 2021, 14(1), 234; https://doi.org/10.3390/ma14010234 - 5 Jan 2021

Cited by 23 | Viewed by 4756

Abstract

Indoor air quality can be adversely affected by emissions from building materials, consequently having a negative impact on human health and well-being. In this study, more than 30 natural building materials (earth dry boards and plasters, bio-based insulation materials, and boards made of [...] Read more.

Indoor air quality can be adversely affected by emissions from building materials, consequently having a negative impact on human health and well-being. In this study, more than 30 natural building materials (earth dry boards and plasters, bio-based insulation materials, and boards made of wood, flax, reed, straw, etc.) used for interior works were investigated as to their emissions of (semi-)volatile organic compounds ((S)VOC), formaldehyde, and radon. The study focused on the emissions from complete wall build-ups as they can be used for internal partition walls and the internal insulation of external walls. Test chambers were designed, allowing the compounds to release only from the surface of the material facing indoors under testing parameters that were chosen to simulate model room conditions. The emission test results were evaluated using the AgBB evaluation scheme, a procedure for the health-related evaluation of construction products and currently applied for the approval of specific groups of building materials in Germany. Seventeen out of 19 sample build-ups tested in this study would have passed this scheme since they generally proved to be low-emitting and although the combined emissions of multiple materials were tested, 50% of the measurements could be terminated before half of the total testing time. Full article

(This article belongs to the Special Issue Measurement of the Environmental Impact of Materials)

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20 pages, 5548 KiB

Open AccessEditor’s ChoiceReview

Applications of Hydrogel with Special Physical Properties in Bone and Cartilage Regeneration

by Hua Lin, Cuilan Yin, Anchun Mo and Guang Hong

Materials 2021, 14(1), 235; https://doi.org/10.3390/ma14010235 - 5 Jan 2021

Cited by 52 | Viewed by 8777

Abstract

Hydrogel is a polymer matrix containing a large amount of water. It is similar to extracellular matrix components. It comes into contact with blood, body fluids, and human tissues without affecting the metabolism of organisms. It can be applied to bone and cartilage [...] Read more.

Hydrogel is a polymer matrix containing a large amount of water. It is similar to extracellular matrix components. It comes into contact with blood, body fluids, and human tissues without affecting the metabolism of organisms. It can be applied to bone and cartilage tissues. This article introduces the high-strength polymer hydrogel and its modification methods to adapt to the field of bone and cartilage tissue engineering. From the perspective of the mechanical properties of hydrogels, the mechanical strength of hydrogels has experienced from the weak-strength traditional hydrogels to the high-strength hydrogels, then the injectable hydrogels were invented and realized the purpose of good fluidity before the use of hydrogels and high strength in the later period. In addition, specific methods to give special physical properties to the hydrogel used in the field of bone and cartilage tissue engineering will also be discussed, such as 3D printing, integrated repair of bone and cartilage tissue, bone vascularization, and osteogenesis hydrogels that regulate cell growth, antibacterial properties, and repeatable viscosity in humid environments. Finally, we explain the main reasons and contradictions in current applications, look forward to the research prospects in the field of bone and cartilage tissue engineering, and emphasize the importance of conducting research in this field to promote medical progress. Full article

(This article belongs to the Special Issue Dental Materials and Devices)

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12 pages, 14590 KiB

Open AccessEditor’s ChoiceArticle

Effect of Periodic Water Clusters on AISI 304 Welded Surfaces

by Madhulika Srivastava, Akash Nag, Lucie Krejčí, Jana Petrů, Somnath Chattopadhyaya and Sergej Hloch

Materials 2021, 14(1), 210; https://doi.org/10.3390/ma14010210 - 4 Jan 2021

Cited by 10 | Viewed by 2708

Abstract

This study compared the effect of the interaction time of periodic water clusters on the surface integrity of AISI 304 tungsten inert gas (TIG) welded joints at different excitation frequencies, as the effect of the technological parameters of pulsating water jet (PWJ) on [...] Read more.

This study compared the effect of the interaction time of periodic water clusters on the surface integrity of AISI 304 tungsten inert gas (TIG) welded joints at different excitation frequencies, as the effect of the technological parameters of pulsating water jet (PWJ) on the mechanical properties of TIG welded joints are under-researched. The TIG welded joints were subjected to different frequencies (20 and 40 kHz) and traverse speeds (1–4 mm/s) at a water pressure of 40 MPa and a standoff distance of 70 mm. The effect of the interaction of the pulsating jet on the material and the enhancement in its mechanical properties were compared through residual stress measurements, surface roughness, and sub-surface microhardness. A maximum enhancement in the residual stress values of up to 480 MPa was observed in the heat-affected zone, along with a maximum roughness of 6.03 µm and a maximum hardness of 551 HV using a frequency of 40 kHz. The improvement in the surface characteristics of the welded joints shows the potential of utilizing pulsed water jet technology with an appropriate selection of process parameters in the treatment of welded structures. Full article

(This article belongs to the Collection Machining and Manufacturing of Alloys and Steels)

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16 pages, 7314 KiB

Open AccessEditor’s ChoiceArticle

Immobilization of Heavy Metals in Boroaluminosilicate Geopolymers

by Piotr Rożek, Paulina Florek, Magdalena Król and Włodzimierz Mozgawa

Materials 2021, 14(1), 214; https://doi.org/10.3390/ma14010214 - 4 Jan 2021

Cited by 15 | Viewed by 3842

Abstract

Boroaluminosilicate geopolymers were used for the immobilization of heavy metals. Then, their mechanical properties, phase composition, structure, and microstructure were investigated. The addition of borax and boric acid did not induce the formation of any crystalline phases. Boron was incorporated into the geopolymeric [...] Read more.

Boroaluminosilicate geopolymers were used for the immobilization of heavy metals. Then, their mechanical properties, phase composition, structure, and microstructure were investigated. The addition of borax and boric acid did not induce the formation of any crystalline phases. Boron was incorporated into the geopolymeric network and caused the formation of N–B–A–S–H (hydrated sodium boroaluminosilicate) gel. In the range of a B/Al molar ratio of 0.015–0.075, the compressive strength slightly increased (from 16.1 to 18.7 MPa), while at a ratio of 0.150, the compressive strength decreased (to 12 MPa). Heavy metals (lead and nickel) were added as nitrate salts. The loss of the strength of the geopolymers induced by heavy metals was limited by the presence of boron. However, it caused an increase in heavy metal leaching. Despite this, heavy metals were almost entirely immobilized (with immobilization rates of >99.8% in the case of lead and >99.99% in the case of nickel). The lower immobilization rate of lead was due to the formation of macroscopic crystalline inclusions of PbO·xH₂O, which was vulnerable to leaching. Full article

(This article belongs to the Special Issue Recent Developments in Geopolymers and Alkali-Activated Materials)

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20 pages, 4719 KiB

Open AccessEditor’s ChoiceArticle

Deformation Characteristics and Constitutive Equations for the Semi-Solid Isothermal Compression of Cold Radial Forged 6063 Aluminium Alloy

by Yongfei Wang, Shengdun Zhao, Yi Guo, Kuanxin Liu and Shunqi Zheng

Materials 2021, 14(1), 194; https://doi.org/10.3390/ma14010194 - 3 Jan 2021

Cited by 12 | Viewed by 2874

Abstract

Al-Mg-Si based alloys are popular alloys used in the automotive industry. However, limited studies have been performed to investigate the microstructure, deformation characteristics, and deformation mechanism for the semi-solid 6063 alloys. In this study, the cold radial forging method and semi-solid isothermal treatment [...] Read more.

Al-Mg-Si based alloys are popular alloys used in the automotive industry. However, limited studies have been performed to investigate the microstructure, deformation characteristics, and deformation mechanism for the semi-solid 6063 alloys. In this study, the cold radial forging method and semi-solid isothermal treatment (SSIT) are proposed in the semi-solid isothermal compression (SSIC) process to fabricate high-quality semi-solid 6063 billets. The effects of deformation temperature, strain rate, and strain on the microstructure, deformation characteristics, and deformation mechanism of the SSIC of cold radial forged 6063 alloys were investigated experimentally. Constitutive equations were established based on the measured data in experiments to predict the flow stress. Results show that an average grain size in the range from 59.22 to 73.02 μm and an average shape factor in the range from 071 to 078 can be obtained in the microstructure after the cold radial forged 6063 alloys were treated with SSIT process. Four stages (i.e., sharp increase, decrease, steady state, and slow increase) were observed in the true stress- true strain curve. The correlation coefficient of the constitutive equation was obtained as 0.9796 while the average relative error was 5.01%. The deformation mechanism for SSIC of cold radial forged aluminum alloy 6063 mainly included four modes: The liquid phase flow, grain slide or grain rotation along with the liquid film, slide among solid grains, and the plastic deformation of solid grains. Full article

(This article belongs to the Special Issue Hot Deformation and Microstructure Evolution of Metallic Materials)

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13 pages, 2560 KiB

Open AccessEditor’s ChoiceArticle

Performance Assessment of Minimum Quantity Castor-Palm Oil Mixtures in Hard-Milling Operation

by Binayak Sen, Munish Kumar Gupta, Mozammel Mia, Danil Yurievich Pimenov and Tadeusz Mikołajczyk

Materials 2021, 14(1), 198; https://doi.org/10.3390/ma14010198 - 3 Jan 2021

Cited by 39 | Viewed by 3153

Abstract

The necessity to progress towards sustainability has inspired modern researchers to examine the lubrication and cooling effects of vegetable oils on conventional metal cutting operations. Consequently, as an eco-friendly vegetable product, castor oil can be the right choice as Minimum quantity lubrication (MQL) [...] Read more.

The necessity to progress towards sustainability has inspired modern researchers to examine the lubrication and cooling effects of vegetable oils on conventional metal cutting operations. Consequently, as an eco-friendly vegetable product, castor oil can be the right choice as Minimum quantity lubrication (MQL) base fluid. Nonetheless, the high viscosity of castor oil limits its flowability and restricts its industrial application. Conversely, palm oil possesses superior lubricity, as well as flowability characteristics. Hence, an attempt has been made to improve the lubrication behavior of castor oil. Here, six castor-palm mixtures (varying from 1:0.5–1:3) were utilized as MQL-fluid, and the values of machining responses viz. average surface roughness, specific cutting energy, and tool wear were evaluated. Furthermore, an integrated Shannon’s Entropy-based Technique for order preference by similarity to ideal solution (TOPSIS) framework was employed for selecting the most suitable volume ratio of castor-palm oil mixture. The rank provided by the TOPSIS method confirmed that 1:2 was the best volume ratio for castor-palm oil mixture. Afterward, a comparative analysis demonstrated that the best castor-palm volume fraction resulted in 8.262 and 16.146% lowering of surface roughness, 5.459 and 7.971% decrement of specific cutting energy, 2.445 and 3.155% drop in tool wear compared to that of castor and palm oil medium, respectively. Full article

(This article belongs to the Special Issue Additive and Subtractive Manufacturing of Advanced Materials: Applications, Future Trends and Perspectives of Industry 4.0)

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15 pages, 6907 KiB

Open AccessEditor’s ChoiceArticle

Modeling of Bridging Law for Bundled Aramid Fiber-Reinforced Cementitious Composite and its Adaptability in Crack Width Evaluation

by Daiki Sunaga, Takumi Koba and Toshiyuki Kanakubo

Materials 2021, 14(1), 179; https://doi.org/10.3390/ma14010179 - 2 Jan 2021

Cited by 3 | Viewed by 3041

Abstract

Tensile performance of fiber-reinforced cementitious composite (FRCC) after first cracking is characterized by fiber-bridging stress–crack width relationships called bridging law. The bridging law can be calculated by an integral calculus of forces carried by individual fibers, considering the fiber orientation. The objective of [...] Read more.

Tensile performance of fiber-reinforced cementitious composite (FRCC) after first cracking is characterized by fiber-bridging stress–crack width relationships called bridging law. The bridging law can be calculated by an integral calculus of forces carried by individual fibers, considering the fiber orientation. The objective of this study was to propose a simplified model of bridging law for bundled aramid fiber, considering fiber orientation for the practical use. By using the pullout characteristic of bundled aramid fiber obtained in the previous study, the bridging laws were calculated for various cases of fiber orientation. The calculated results were expressed by a bilinear model, and each characteristic point is expressed by the function of fiber-orientation intensity. After that, uniaxial tension tests of steel reinforced aramid-FRCC prism specimens were conducted to obtain the crack-opening behavior and confirm the adaptability of the modeled bridging laws in crack-width evaluation. The experimental parameters are cross-sectional dimensions of specimens and volume fraction of fiber. The test results are compared with the theoretical curves calculated by using the modeled bridging law and show good agreements in each parameter. Full article

(This article belongs to the Special Issue Advances in Construction and Building Materials)

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16 pages, 2938 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Filtration Materials Modified with 2D Nanocomposites—A New Perspective for Point-of-Use Water Treatment

by Michał Jakubczak, Ewa Karwowska, Anita Rozmysłowska-Wojciechowska, Mateusz Petrus, Jarosław Woźniak, Joanna Mitrzak and Agnieszka M. Jastrzębska

Materials 2021, 14(1), 182; https://doi.org/10.3390/ma14010182 - 2 Jan 2021

Cited by 34 | Viewed by 6739

Abstract

Point-of-use (POU) water treatment systems and devices play an essential role in limited access to sanitary safe water resources. The filtering materials applied in POU systems must effectively eliminate contaminants, be readily produced and stable, and avoid secondary contamination of the treated water. [...] Read more.

Point-of-use (POU) water treatment systems and devices play an essential role in limited access to sanitary safe water resources. The filtering materials applied in POU systems must effectively eliminate contaminants, be readily produced and stable, and avoid secondary contamination of the treated water. We report an innovative, 2D Ti₃C₂/Al₂O₃/Ag/Cu nanocomposite-modified filtration material with the application potential for POU water treatment. The material is characterized by improved filtration velocity relative to an unmodified reference material, effective elimination of microorganisms, and self-disinfecting potential, which afforded the collection of 99.6% of bacteria in the filter. The effect was obtained with nanocomposite levels as low as 1%. Surface oxidation of the modified material increased its antimicrobial efficiency. No secondary release of the nanocomposites into the filtrate was observed and confirmed the stability of the material and its suitability for practical application in water treatment. Full article

(This article belongs to the Special Issue New Findings of MXenes: Preparation, Properties and Applications in Biotechnology and Catalysis)

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16 pages, 3334 KiB

Open AccessEditor’s ChoiceArticle

Towards Further Understanding the Secondary Fracture during Spaghetti Bent Break

by Long Long, Yuxuan Zheng, Fenghua Zhou and Huilan Ren

Materials 2021, 14(1), 189; https://doi.org/10.3390/ma14010189 - 2 Jan 2021

Cited by 2 | Viewed by 2950

Abstract

When a brittle thin rod, such as a dry spaghetti stick, is bent beyond its flexural limit, it often breaks into more than two pieces, typically three or more. This phenomenon and puzzle has aroused widespread interest and discussion since its first proposal [...] Read more.

When a brittle thin rod, such as a dry spaghetti stick, is bent beyond its flexural limit, it often breaks into more than two pieces, typically three or more. This phenomenon and puzzle has aroused widespread interest and discussion since its first proposal by Feynman. Previous work has partly explained the inevitability of the secondary fracture, but without any adjustable time parameter. In order to further understand this problem, especially the secondary fracture, in this paper we propose and study the dynamics of a half-infinite model to mimic the physics that a spaghetti stick is half-infinite under uniform bending. When the breaking process starts, a gradual release of initial moment of a linearly declining time at the free end, instead of a sudden release, is adopted, resulting in the introduction of a characteristic time parameter to the model and agrees better with the real situation. A specific analytical solution in terms of the excited bending moment using Euler–Bernoulli beam theory is derived, and that the gradual release of initial moment induces a burst of flexural waves, and these flexural waves locally increase the moment in the stick and progressively get to the maximum value, and then lead to the secondary fracture are concluded. The excited moment increases with time and distance, and has an asymptotic extremum value of 1.43 times initial moment. The gradual release in our model requires and gives certain distance and time when the excited bending moment reaches its extremum value, which provides a possibility to predict the detailed fracture parameters such as fragmentation length and time and thus to further understand the secondary fracture during spaghetti bent break. Full article

(This article belongs to the Section Materials Physics)

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15 pages, 3835 KiB

Open AccessEditor’s ChoiceReview

Fatigue Crack Growth and Fracture of Internal Fixation Materials in In Vivo Environments—A Review

by Kailun Wu, Bin Li and Jiong Jiong Guo

Materials 2021, 14(1), 176; https://doi.org/10.3390/ma14010176 - 1 Jan 2021

Cited by 13 | Viewed by 4812

Abstract

The development of crack patterns is a serious problem affecting the durability of orthopedic implants and the prognosis of patients. This issue has gained considerable attention in the medical community in recent years. This literature focuses on the five primary aspects relevant to [...] Read more.

The development of crack patterns is a serious problem affecting the durability of orthopedic implants and the prognosis of patients. This issue has gained considerable attention in the medical community in recent years. This literature focuses on the five primary aspects relevant to the evaluation of the surface cracking patterns, i.e., inappropriate use, design flaws, inconsistent elastic modulus, allergic reaction, poor compatibility, and anti-corrosiveness. The hope is that increased understanding will open doors to optimize fabrication for biomedical applications. The latest technological issues and potential capabilities of implants that combine absorbable materials and shape memory alloys are also discussed. This article will act as a roadmap to be employed in the realm of orthopedic. Fatigue crack growth and the challenges associated with materials must be recognized to help make new implant technologies viable for wider clinical adoption. This review presents a summary of recent findings on the fatigue mechanisms and fracture of implant in the initial period after surgery. We propose solutions to common problems. The recognition of essential complications and technical problems related to various approaches and material choices while satisfying clinical requirements is crucial. Additional investigation will be needed to surmount these challenges and reduce the likelihood of fatigue crack growth after implantation. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials)

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26 pages, 19070 KiB

Open AccessEditor’s ChoiceReview

Environmental Impact of Nanoparticles’ Application as an Emerging Technology: A Review

by Guillermo Martínez, Manuel Merinero, María Pérez-Aranda, Eva María Pérez-Soriano, Tamara Ortiz, Eduardo Villamor, Belén Begines and Ana Alcudia

Materials 2021, 14(1), 166; https://doi.org/10.3390/ma14010166 - 31 Dec 2020

Cited by 191 | Viewed by 13847

Abstract

The unique properties that nanoparticles exhibit, due to their small size, are the principal reason for their numerous applications, but at the same time, this might be a massive menace to the environment. The number of studies that assess the possible ecotoxicity of [...] Read more.

The unique properties that nanoparticles exhibit, due to their small size, are the principal reason for their numerous applications, but at the same time, this might be a massive menace to the environment. The number of studies that assess the possible ecotoxicity of nanomaterials has been increasing over the last decade to determine if, despite the positive aspects, they should be considered a potential health risk. To evaluate their potential toxicity, models are used in all types of organisms, from unicellular bacteria to complex animal species. In order to better understand the environmental consequences of nanotechnology, this literature review aims to describe and classify nanoparticles, evaluating their life cycle, their environmental releasing capacity and the type of impact, particularly on living beings, highlighting the need to develop more severe and detailed legislation. Due to their diversity, nanoparticles will be discussed in generic terms focusing on the impact of a great variety of them, highlighting the most interesting ones for the industry. Full article

(This article belongs to the Special Issue Advances in Bioactive Materials)

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18 pages, 4444 KiB

Open AccessEditor’s ChoiceArticle

Comparison of Three Manufacturing Techniques for Sustainable Porous Clay Ceramics

by Fernanda Andreola, Isabella Lancellotti, Rachele Sergi, Valeria Cannillo and Luisa Barbieri

Materials 2021, 14(1), 167; https://doi.org/10.3390/ma14010167 - 31 Dec 2020

Cited by 6 | Viewed by 2554

Abstract

This study proposes different manufacturing techniques (manual pelletization, powder pressing, and “shell scaffold”) to obtain lightweight clay ceramics containing recovery raw materials. The sintering in an electrical furnace (1000 °C, 1 h processing time) was conducted by traditional firing from room temperature, for [...] Read more.

This study proposes different manufacturing techniques (manual pelletization, powder pressing, and “shell scaffold”) to obtain lightweight clay ceramics containing recovery raw materials. The sintering in an electrical furnace (1000 °C, 1 h processing time) was conducted by traditional firing from room temperature, for pressed and shell-scaffold samples, while the flash heating (i.e., samples directly put at 1000 °C) was used only for the pellets. The porous materials (porosity 40–80%), functionalized with nutrients (K and P) in amounts to confer the fertilizer capability, gave suitable results in terms of pH (6.7–8.15) and electrical conductivity (0.29–1.33 mS/cm). Thus, such materials can be considered as feasible lightweight clay ceramics, with a positive effect on the soil. These findings permit us to hypothesize a potential use in green roofs or in agronomic applications. Full article

(This article belongs to the Special Issue Environmentally Sustainable Materials and Fabrication Techniques)

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10 pages, 3241 KiB

Open AccessEditor’s ChoiceArticle

Na_0.76V₆O₁₅/Activated Carbon Hybrid Cathode for High-Performance Lithium-Ion Capacitors

by Renwei Lu, Xiaolong Ren, Chong Wang, Changzhen Zhan, Ding Nan, Ruitao Lv, Wanci Shen, Feiyu Kang and Zheng-Hong Huang

Materials 2021, 14(1), 122; https://doi.org/10.3390/ma14010122 - 30 Dec 2020

Cited by 11 | Viewed by 2769

Abstract

Lithium-ion hybrid capacitors (LICs) are regarded as one of the most promising next generation energy storage devices. Commercial activated carbon materials with low cost and excellent cycling stability are widely used as cathode materials for LICs, however, their low energy density remains a [...] Read more.

Lithium-ion hybrid capacitors (LICs) are regarded as one of the most promising next generation energy storage devices. Commercial activated carbon materials with low cost and excellent cycling stability are widely used as cathode materials for LICs, however, their low energy density remains a significant challenge for the practical applications of LICs. Herein, Na_0.76V₆O₁₅ nanobelts (NaVO) were prepared and combined with commercial activated carbon YP50D to form hybrid cathode materials. Credit to the synergism of its capacitive effect and diffusion-controlled faradaic effect, NaVO/C hybrid cathode displays both superior cyclability and enhanced capacity. LICs were assembled with the as-prepared NaVO/C hybrid cathode and artificial graphite anode which was pre-lithiated. Furthermore, 10-NaVO/C//AG LIC delivers a high energy density of 118.9 Wh kg⁻¹ at a power density of 220.6 W kg⁻¹ and retains 43.7 Wh kg⁻¹ even at a high power density of 21,793.0 W kg⁻¹. The LIC can also maintain long-term cycling stability with capacitance retention of approximately 70% after 5000 cycles at 1 A g⁻¹. Accordingly, hybrid cathodes composed of commercial activated carbon and a small amount of high energy battery-type materials are expected to be a candidate for low-cost advanced LICs with both high energy density and power density. Full article

(This article belongs to the Section Energy Materials)

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9 pages, 2810 KiB

Open AccessEditor’s ChoiceArticle

Fabrication of SiC Sealing Cavity Structure for All-SiC Piezoresistive Pressure Sensor Applications

by Lihuan Zhao, Haiping Shang, Dahai Wang, Yang Liu, Baohua Tian and Weibing Wang

Materials 2021, 14(1), 128; https://doi.org/10.3390/ma14010128 - 30 Dec 2020

Cited by 3 | Viewed by 2450

Abstract

High hardness and corrosion resistance of SiC (silicon carbide) bulk materials have always been a difficult problem in the processing of an all-SiC piezoresistive pressure sensor. In this work, we demonstrated a SiC sealing cavity structure utilizing SiC shallow plasma-etched process (≤20 μm) [...] Read more.

High hardness and corrosion resistance of SiC (silicon carbide) bulk materials have always been a difficult problem in the processing of an all-SiC piezoresistive pressure sensor. In this work, we demonstrated a SiC sealing cavity structure utilizing SiC shallow plasma-etched process (≤20 μm) and SiC–SiC room temperature bonding technology. The SiC bonding interface was closely connected, and its average tensile strength could reach 6.71 MPa. In addition, through a rapid thermal annealing (RTA) experiment of 1 min and 10 mins in N₂ atmosphere of 1000 °C, it was found that Si, C and O elements at the bonding interface were diffused, while the width of the intermediate interface layer was narrowed, and the tensile strength could remain stable. This SiC sealing cavity structure has important application value in the realization of an all-SiC piezoresistive pressure sensor. Full article

(This article belongs to the Special Issue Additive Manufacturing Technologies and Its Applications Using Advanced Materials)

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13 pages, 2030 KiB

Open AccessEditor’s ChoiceArticle

Mechanical and Air Permeability Performance of Novel Biobased Materials from Fungal Hyphae and Cellulose Fibers

by Inese Filipova, Ilze Irbe, Martins Spade, Marite Skute, Inga Dāboliņa, Ilze Baltiņa and Linda Vecbiskena

Materials 2021, 14(1), 136; https://doi.org/10.3390/ma14010136 - 30 Dec 2020

Cited by 29 | Viewed by 4388

Abstract

Novel biobased materials from fungal hyphae and cellulose fibers have been proposed to address the increasing demand for natural materials in personal protective equipment (PPE). Materials containing commercially available kraft fibers (KF), laboratory-made highly fibrillated hemp fibers (HF) and fungal fibers (FF) obtained [...] Read more.

Novel biobased materials from fungal hyphae and cellulose fibers have been proposed to address the increasing demand for natural materials in personal protective equipment (PPE). Materials containing commercially available kraft fibers (KF), laboratory-made highly fibrillated hemp fibers (HF) and fungal fibers (FF) obtained from fruiting bodies of lignicolous basidiomycetes growing in nature were prepared using paper production techniques and evaluated for their mechanical and air permeability properties. SEM and microscopy revealed the network structure of materials. The tensile index of materials was in the range of 8–60 Nm/g and air permeability ranged from 32–23,990 mL/min, depending on the composition of materials. HF was the key component for strength; however, the addition of FF to compositions resulted in higher air permeability. Chemical composition analysis (Fourier-transform infrared spectroscopy) revealed the presence of natural polysaccharides, mainly cellulose and chitin, as well as the appropriate elemental distribution of components C, H and N. Biodegradation potential was proven by a 30-day-long composting in substrate, which resulted in an 8–62% drop in the C/N ratio. Conclusions were drawn about the appropriateness of fungal hyphae for use in papermaking-like technologies together with cellulose fibers. Developed materials can be considered as an alternative to synthetic melt and spun-blown materials for PPE. Full article

(This article belongs to the Section Materials Chemistry)

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21 pages, 5166 KiB

Open AccessEditor’s ChoiceArticle

Numerical Investigation of Effective Thermal Conductivity of Strut-Based Cellular Structures Designed by Spatial Voronoi Tessellation

by Minghao Zhang, Junteng Shang, Shiyue Guo, Boyoung Hur and Xuezheng Yue

Materials 2021, 14(1), 138; https://doi.org/10.3390/ma14010138 - 30 Dec 2020

Cited by 20 | Viewed by 3662

Abstract

Porous materials possess light weight and excellent thermal insulation performance. For disordered porous structures, the number of seed points is an important design parameter which is closely related to the morphology and mean pore size of the structure. Based on the arrangement of [...] Read more.

Porous materials possess light weight and excellent thermal insulation performance. For disordered porous structures, the number of seed points is an important design parameter which is closely related to the morphology and mean pore size of the structure. Based on the arrangement of points in three-dimensional space, seven kinds of structures were designed by spatial Voronoi tessellation in this paper. The effect of the number of seed points on effective thermal conductivity for Voronoi was studied. Numerical simulation was conducted to research the effects of structural porosity, filling material and structural orientation on the effective thermal conductivity and heat transfer characteristics. The results showed that the effective thermal conductivity is closely related to the porosity and the matrix material. Different number and arrangement of seed points make the structure have different anisotropic performance due to different thermal paths. In addition, required the least number of seed points was obtained for the designation of isotropic random Voronoi. Full article

(This article belongs to the Section Porous Materials)

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11 pages, 4819 KiB

Open AccessEditor’s ChoiceArticle

Design of Eutectic Hydrated Salt Composite Phase Change Material with Cement for Thermal Energy Regulation of Buildings

by Niuniu Wu, Lijie Liu, Zhiwei Yang, Yifan Wu and Jinhong Li

Materials 2021, 14(1), 139; https://doi.org/10.3390/ma14010139 - 30 Dec 2020

Cited by 17 | Viewed by 3577

Abstract

An energy-efficient eutectic hydrated salt phase change material based on sodium carbonate decahydrate and disodium hydrogen phosphate dodecahydrate (SD) was prepared. Then, SD was encapsulated into expanded graphite (EG) to produce form-stable composite phase change materials (SD/E), which indicated a positive effect on [...] Read more.

An energy-efficient eutectic hydrated salt phase change material based on sodium carbonate decahydrate and disodium hydrogen phosphate dodecahydrate (SD) was prepared. Then, SD was encapsulated into expanded graphite (EG) to produce form-stable composite phase change materials (SD/E), which indicated a positive effect on preventing the leakage of SD, decreasing the supercooling and improving the thermal conductivity. SD/E was further tested for thermal efficiency by simulating the indoor environment with a house-like model which was composed of SD/E and magnesium oxychloride cement. The results showed an excellent thermal insulation effect. This exciting porous composite phase shift material reveals possible architectural applications because of the attractive thermos-physical properties of SD/E. Full article

(This article belongs to the Special Issue Advanced Materials for Thermal Energy Storage)

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20 pages, 11499 KiB

Open AccessEditor’s ChoiceArticle

Durability of Hydrophobic/Icephobic Coatings in Protection of Lightweight Concrete with Waste Aggregate

by Danuta Barnat-Hunek, Jacek Góra and Marcin K. Widomski

Materials 2021, 14(1), 101; https://doi.org/10.3390/ma14010101 - 29 Dec 2020

Cited by 20 | Viewed by 3389

Abstract

The aim of the research presented in this paper is to evaluate the feasibility of using hydrophobic agents based on organosilicon compounds for surface protection of lightweight concrete modified with waste polystyrene. The experimental part pertains to the physical and mechanical properties of [...] Read more.

The aim of the research presented in this paper is to evaluate the feasibility of using hydrophobic agents based on organosilicon compounds for surface protection of lightweight concrete modified with waste polystyrene. The experimental part pertains to the physical and mechanical properties of polystyrene-modified lightweight concrete. The concrete samples were prepared with the following ingredients: CEM I 42.5 R cement, recycled polystyrene (0–2 mm), quartz sand (0–2 mm), coarse river aggregate (2–16 mm), and water. Silane and tetramethoxysilane were employed for surface hydrophobization. Concrete with 20% polystyrene exhibits high porosity (25.22%), which is related to an increase in absorptivity (14.75%) compared to the reference concrete. The hydrophobized concrete is characterized by the lowest surface free energy (SFE) value, which is 7 or 11 times lower than the value of reference concrete, depending on the agents. The test on the contact angle (CA) was performed before and after the frost-resistance test (F–T test). Lower SFE translates into lower adhesive properties, higher resistance of the material to the infiltration of water and corrosive compounds, e.g., salts, and higher resistance to freezing and thawing cycles. Silane and tetramethoxysilane coating raised frost resistance by 54–58% compared to the reference samples. This agent reduced absorptivity by 30%. Recycled polystyrene can be successfully used to produce lightweight concrete (LC) with high durability provided by hydrophobic/icephobic coatings. Full article

(This article belongs to the Special Issue Durability of Concrete or Mineral-Asphalt Mixtures with Recycled Aggregates)

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12 pages, 2904 KiB

Open AccessEditor’s ChoiceArticle

Fabrication of Gelatin-ZnO Nanofibers for Antibacterial Applications

by Nataliya Babayevska, Łucja Przysiecka, Grzegorz Nowaczyk, Marcin Jarek, Martin Järvekülg, Triin Kangur, Ewa Janiszewska, Stefan Jurga and Igor Iatsunskyi

Materials 2021, 14(1), 103; https://doi.org/10.3390/ma14010103 - 29 Dec 2020

Cited by 27 | Viewed by 3969

Abstract

In this study, GNF@ZnO composites (gelatin nanofibers (GNF) with zinc oxide (ZnO) nanoparticles (NPs)) as a novel antibacterial agent were obtained using a wet chemistry approach. The physicochemical characterization of ZnO nanoparticles (NPs) and GNF@ZnO composites, as well as the evaluation of their [...] Read more.

In this study, GNF@ZnO composites (gelatin nanofibers (GNF) with zinc oxide (ZnO) nanoparticles (NPs)) as a novel antibacterial agent were obtained using a wet chemistry approach. The physicochemical characterization of ZnO nanoparticles (NPs) and GNF@ZnO composites, as well as the evaluation of their antibacterial activity toward Gram-positive (Staphyloccocus aureus and Bacillus pumilus) and Gram-negative (Escherichia coli and Pseudomonas fluorescens) bacteria were performed. ZnO NPs were synthesized using a facile sol-gel approach. Gelatin nanofibers (GNF) were obtained by an electrospinning technique. GNF@ZnO composites were obtained by adding previously produced GNF into a Zn²⁺ methanol solution during ZnO NPs synthesis. Crystal structure, phase, and elemental compositions, morphology, as well as photoluminescent properties of pristine ZnO NPs, pristine GNF, and GNF@ZnO composites were characterized using powder X-ray diffraction (XRD), FTIR analysis, transmission and scanning electron microscopies (TEM/SEM), and photoluminescence spectroscopy. SEM, EDX, as well as FTIR analyses, confirmed the adsorption of ZnO NPs on the GNF surface. The pristine ZnO NPs were highly crystalline and monodispersed with a size of approximately 7 nm and had a high surface area (83 m²/g). The thickness of the pristine gelatin nanofiber was around 1 µm. The antibacterial properties of GNF@ZnO composites were investigated by a disk diffusion assay on agar plates. Results show that both pristine ZnO NPs and their GNF-based composites have the strongest antibacterial properties against Pseudomonas fluorescence and Staphylococcus aureus, with the zone of inhibition above 10 mm. Right behind them is Escherichia coli with slightly less inhibition of bacterial growth. These properties of GNF@ZnO composites suggest their suitability for a range of antimicrobial uses, such as in the food industry or in biomedical applications. Full article

(This article belongs to the Special Issue Advanced Antimicrobial Materials)

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27 pages, 9903 KiB

Open AccessEditor’s ChoiceArticle

Novel Low-Twist Bast Fibre Yarns from Flax Tow for High-Performance Composite Applications

by Nina Graupner, Karl-Heinz Lehmann, David E. Weber, Hans-Willi Hilgers, Erik G. Bell, Isabel Walenta, Luisa Berger, Torsten Brückner, Kay Kölzig, Herbert Randerath, Albert Bruns, Bernd Frank, Maik Wonneberger, Marc Joulian, Lisa Bruns, Friedrich von Dungern, Alexander Janßen, Thomas Gries, Stefan Kunst and Jörg Müssig

Materials 2021, 14(1), 105; https://doi.org/10.3390/ma14010105 - 29 Dec 2020

Cited by 14 | Viewed by 5651

Abstract

The use of natural fibres for components subjected to higher mechanical requirements tends to be limited by the high price of high-quality semi-finished products. Therefore, the present study deals with the development of more cost-effective staple fibre yarns made from flax tow. In [...] Read more.

The use of natural fibres for components subjected to higher mechanical requirements tends to be limited by the high price of high-quality semi-finished products. Therefore, the present study deals with the development of more cost-effective staple fibre yarns made from flax tow. In the subsequent processing stage, the yarns were processed into quasi-unidirectional (UD) fabrics. The results of the fibre characterisation along the process chain have shown that no significant mechanical fibre damage occurs after slivers’ production. Fibres prepared from yarns and fabrics show comparable characteristics. The yarns were processed to composites by pultrusion to verify the reinforcement effect. The mechanical properties were comparable to those of composites made from a high-quality UD flax roving. The fabrics were industrially processed into composite laminates using a vacuum infusion and an autoclave injection process (vacuum injection method in an autoclave). While impact strength compared to a reference laminate based on the UD flax roving was achieved, tensile and flexural properties were not reached. An analysis showed that the staple fibre yarns in the fabric show an undulation, leading to a reorientation of the fibres and lower characteristic values, which show 86–92% of the laminate made from the flax roving. Hybrid laminates with outer glass and inner flax layers were manufactured for the intended development of a leaf spring for the bogie of a narrow-gauge railroad as a demonstrator. The hybrid composites display excellent mechanical properties and showed clear advantages over a pure glass fibre-reinforced composite in lightweight construction potential, particularly flexural stiffness. Full article

(This article belongs to the Special Issue High Performance Natural Fibre Composites)

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23 pages, 21063 KiB

Open AccessEditor’s ChoiceReview

Enhancement of 3D-Printable Materials by Dual-Curing Procedures

by Xavier Fernández-Francos, Osman Konuray, Xavier Ramis, Àngels Serra and Silvia De la Flor

Materials 2021, 14(1), 107; https://doi.org/10.3390/ma14010107 - 29 Dec 2020

Cited by 23 | Viewed by 5321

Abstract

Dual-curing thermosetting systems are recently being developed as an alternative to conventional curing systems due to their processing flexibility and the possibility of enhancing the properties of cured parts in single- or multi-stage processing scenarios. Most dual-curing systems currently employed in three-dimensional (3D) [...] Read more.

Dual-curing thermosetting systems are recently being developed as an alternative to conventional curing systems due to their processing flexibility and the possibility of enhancing the properties of cured parts in single- or multi-stage processing scenarios. Most dual-curing systems currently employed in three-dimensional (3D) printing technologies are aimed at improving the quality and properties of the printed parts. However, further benefit can be obtained from control in the curing sequence, making it possible to obtain partially reacted 3D-printed parts with tailored structure and properties, and to complete the reaction by activation of a second polymerization reaction in a subsequent processing stage. This paves the way for a range of novel applications based on the controlled reactivity and functionality of this intermediate material and the final consolidation of the 3D-printed part after this second processing stage. In this review, different strategies and the latest developments based on the concept of dual-curing are analyzed, with a focus on the enhanced functionality and emerging applications of the processed materials. Full article

(This article belongs to the Special Issue Advances in Thermoset Materials)

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29 pages, 12202 KiB

Open AccessEditor’s ChoiceArticle

Femur Auxetic Meta-Implants with Tuned Micromotion Distribution

by Naeim Ghavidelnia, Mahdi Bodaghi and Reza Hedayati

Materials 2021, 14(1), 114; https://doi.org/10.3390/ma14010114 - 29 Dec 2020

Cited by 64 | Viewed by 5989

Abstract

Stress shielding and micromotions are the most significant problems occurring at the bone-implants interface due to a mismatch of their mechanical properties. Mechanical 3D metamaterials, with their exceptional behaviour and characteristics, can provide an opportunity to solve the mismatch of mechanical properties between [...] Read more.

Stress shielding and micromotions are the most significant problems occurring at the bone-implants interface due to a mismatch of their mechanical properties. Mechanical 3D metamaterials, with their exceptional behaviour and characteristics, can provide an opportunity to solve the mismatch of mechanical properties between the bone and implant. In this study, a new porous femoral hip meta-implant with graded Poisson’s ratio distribution was introduced and its results were compared to three other femoral hip implants (one solid implant, and two porous meta-implants, one with positive and the other with a negative distribution of Poisson’s ratio) in terms of stress and micromotion distributions. For this aim, first, a well-known auxetic 3D re-entrant structure was studied analytically, and precise closed-form analytical relationships for its elastic modulus and Poisson’s ratio were derived. The results of the analytical solution for mechanical properties of the 3D re-entrant structure presented great improvements in comparison to previous analytical studies on the structure. Moreover, the implementation of the re-entrant structure in the hip implant provided very smooth results for stress and strain distributions in the lattice meta-implants and could solve the stress shielding problem which occurred in the solid implant. The lattice meta-implant based on the graded unit cell distribution presented smoother stress-strain distribution in comparison with the other lattice meta-implants. Moreover, the graded lattice meta-implant gave minimum areas of local stress and local strain concentration at the contact region of the implants with the internal bone surfaces. Among all the cases, the graded meta-implant also gave micromotion levels which are the closest to values reported to be desirable for bone growth (40 µm). Full article

(This article belongs to the Special Issue Designing and Manufacturing Hard and Soft Mechanical Metamaterials)

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16 pages, 14935 KiB

Open AccessEditor’s ChoiceArticle

Effect of Ti Content on the Microstructure and High-Temperature Creep Property of Cast Fe-Ni-Based Alloys with High-Al Content

by Gokul Obulan Subramanian, Changheui Jang, Ji Ho Shin and Chaewon Jeong

Materials 2021, 14(1), 82; https://doi.org/10.3390/ma14010082 - 26 Dec 2020

Cited by 5 | Viewed by 2809

Abstract

The cast Fe-Ni-based austenitic heat-resistant alloys with 4.5 wt% Al and varying Ti content were developed for high-temperature application. With increase in Ti content, strength of model alloys increased gradually at 700 °C and 750 °C. At 750 °C, alloys with 35Ni–(2~4)Ti composition [...] Read more.

The cast Fe-Ni-based austenitic heat-resistant alloys with 4.5 wt% Al and varying Ti content were developed for high-temperature application. With increase in Ti content, strength of model alloys increased gradually at 700 °C and 750 °C. At 750 °C, alloys with 35Ni–(2~4)Ti composition showed a significant increase in creep rupture life compared to 30Ni–1Ti alloy, attributed to the increase in γ’-Ni₃(Al,Ti) precipitates due to higher Ni and Ti content. Among the 35Ni–(2~4)Ti alloys, increasing Ti content from 2 to 4 wt% gradually increased the creep rupture life in the as-cast condition. The creep rupture life was improved after solution annealing treatment, however, the beneficial effect of higher Ti content was not evident for 35Ni–(2~4)Ti alloys. After solution annealing, interdendritic phases were partially dissolved, but coarse B2-NiAl phases were formed. The size and amount of coarse B2-NiAl phases increased with Ti content. In the creep-tested specimens, creep void nucleation and crack propagation were observed along the coarse B2-NiAl phases, especially for high-Ti alloys. Therefore, the beneficial effect of the increase in γ’-Ni₃(Al,Ti) precipitates for high-Ti alloys on creep property was limited due to the detrimental effect of the presence of coarse B2-NiAl phases. Full article

(This article belongs to the Special Issue Creep and High Temperature Deformation of Steels and Alloys)

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22 pages, 4356 KiB

Open AccessEditor’s ChoiceArticle

Predictive Modelling for Concrete Failure at Anchorages Using Machine Learning Techniques

by Panagiotis Spyridis and Oladimeji B. Olalusi

Materials 2021, 14(1), 62; https://doi.org/10.3390/ma14010062 - 25 Dec 2020

Cited by 13 | Viewed by 3416

Abstract

Anchorage to concrete plays a significant role in various aspects of modern construction. The structural performance of anchors under direct tensile load can lead to failure by concrete cone breakout. Concrete related failure modes are quasi-brittle, and as such, they may develop without [...] Read more.

Anchorage to concrete plays a significant role in various aspects of modern construction. The structural performance of anchors under direct tensile load can lead to failure by concrete cone breakout. Concrete related failure modes are quasi-brittle, and as such, they may develop without prior warning indications of damage, while it also exposes the bearing component to damage propagation. As such, an adequate reliability assessment of anchors against concrete cone failure is of high importance, and improved precision and minimisation of uncertainty in the predictive model are critical. This contribution develops predictive models for the tensile breakout capacity of fastening systems in concrete using the Gaussian Process Regression (GPR) and the Support Vector Regression (SVR) machine learning (ML) algorithms. The models were developed utilising a set of 864 experimental anchor tests. The efficiency of the developed models is assessed by statistical comparison to the state-of-practice semi-empirical predictive model, which is embedded in international design standards. Furthermore, the algorithms were evaluated based on a newly introduced Model Explainability concept based on Analogous Rational and Mechanical phenomena (MEARM). Finally, a discussion is provided regarding the developed ML models’ suitability for use as General Probabilistic Models in a reliability framework. Full article

(This article belongs to the Special Issue Artificial Intelligence for Cementitious Materials)

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10 pages, 5370 KiB

Open AccessEditor’s ChoiceArticle

The Influence of Disorder in the Synthesis, Characterization and Applications of a Modifiable Two-Dimensional Covalent Organic Framework

by Jordan Brophy, Kyle Summerfield, Jiashi Yin, Jon Kephart, Joshua T. Stecher, Jeramie Adams, Takashi Yanase, Jason Brant, Katie Dongmei Li-Oakey, John O. Hoberg and Bruce A. Parkinson

Materials 2021, 14(1), 71; https://doi.org/10.3390/ma14010071 - 25 Dec 2020

Cited by 9 | Viewed by 4711

Abstract

Two-dimensional covalent organic frameworks (2D-COFs) have been of increasing interest in the past decade due to their porous structures that ideally can be highly ordered. One of the most common routes to these polymers relies on Schiff-base chemistry, i.e., the condensation reaction between [...] Read more.

Two-dimensional covalent organic frameworks (2D-COFs) have been of increasing interest in the past decade due to their porous structures that ideally can be highly ordered. One of the most common routes to these polymers relies on Schiff-base chemistry, i.e., the condensation reaction between a carbonyl and an amine. In this report, we elaborate on the condensation of 3,6-dibromobenzene-1,2,4,5-tetraamine with hexaketocyclohexane (HKH) and the subsequent carbonylation of the resulting COF, along with the possibility that the condensation reaction on HKH can result in a trans configuration resulting in the formation of a disordered 2D-COF. This strategy enables modification of COFs via bromine substitution reactions to place functional groups within the pores of the materials. Ion-sieving measurements using membranes from this COF, reaction of small molecules with unreacted keto groups along with modeling studies indicate disorder in the COF polymerization process. We also present a Monte Carlo simulation that demonstrates the influence of even small amounts of disorder upon both the 2D and 3D structure of the resulting COF. Full article

(This article belongs to the Special Issue Novel Covalent Organic Frameworks: Design, Synthesis and Properties)

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17 pages, 3815 KiB

Open AccessEditor’s ChoiceArticle

Applicability of Cork as Novel Modifiers to Develop Electrochemical Sensor for Caffeine Determination

by Mayra K. S. Monteiro, Djalma R. Da Silva, Marco A. Quiroz, Vítor J. P. Vilar, Carlos A. Martínez-Huitle and Elisama V. Dos Santos

Materials 2021, 14(1), 37; https://doi.org/10.3390/ma14010037 - 24 Dec 2020

Cited by 28 | Viewed by 3361

Abstract

This study aims to investigate the applicability of a hybrid electrochemical sensor composed of cork and graphite (Gr) for detecting caffeine in aqueous solutions. Raw cork (RAC) and regranulated cork (RGC, obtained by thermal treatment of RAC with steam at 380 °C) were [...] Read more.

This study aims to investigate the applicability of a hybrid electrochemical sensor composed of cork and graphite (Gr) for detecting caffeine in aqueous solutions. Raw cork (RAC) and regranulated cork (RGC, obtained by thermal treatment of RAC with steam at 380 °C) were tested as modifiers. The results clearly showed that the cork-graphite sensors, GrRAC and GrRGC, exhibited a linear response over a wide range of caffeine concentration (5–1000 µM), with R² of 0.99 and 0.98, respectively. The limits of detection (LOD), estimated at 2.9 and 6.1 µM for GrRAC and GrRGC, suggest greater sensitivity and reproducibility than the unmodified conventional graphite sensor. The low-cost cork-graphite sensors were successfully applied in the determination of caffeine in soft drinks and pharmaceutical formulations, presenting well-defined current signals when analyzing real samples. When comparing electrochemical determinations and high performance liquid chromatography measurements, no significant differences were observed (mean accuracy 3.0%), highlighting the potential use of these sensors to determine caffeine in different samples. Full article

(This article belongs to the Special Issue Environment-Friendly Electrochemical Processes)

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12 pages, 11235 KiB

Open AccessEditor’s ChoiceArticle

Effect of Phase Transformation on Stress Corrosion Behavior of Additively Manufactured Austenitic Stainless Steel Produced by Directed Energy Deposition

by Tomer Ron, Ohad Dolev, Avi Leon, Amnon Shirizly and Eli Aghion

Materials 2021, 14(1), 55; https://doi.org/10.3390/ma14010055 - 24 Dec 2020

Cited by 24 | Viewed by 3691

Abstract

The present study aims to evaluate the stress corrosion behavior of additively manufactured austenitic stainless steel produced by the wire arc additive manufacturing (WAAM) process. This was examined in comparison with its counterpart, wrought alloy, by electrochemical analysis in terms of potentiodynamic polarization [...] Read more.

The present study aims to evaluate the stress corrosion behavior of additively manufactured austenitic stainless steel produced by the wire arc additive manufacturing (WAAM) process. This was examined in comparison with its counterpart, wrought alloy, by electrochemical analysis in terms of potentiodynamic polarization and impedance spectroscopy and by slow strain rate testing (SSRT) in a corrosive environment. The microstructure assessment was performed using optical and scanning electron microscopy along with X-ray diffraction analysis. The obtained results indicated that in spite of the inherent differences in microstructure and mechanical properties between the additively manufactured austenitic stainless steel and its counterpart wrought alloy, their electrochemical performance and stress corrosion susceptibility were similar. The corrosion attack in the additively manufactured alloy was mainly concentrated at the interface between the austenitic matrix and the secondary ferritic phase. In the case of the counterpart wrought alloy with a single austenitic phase, the corrosion attack was manifested by uniform pitting evenly scattered at the external surface. Both alloys showed ductile failure in the form of “cap and cone” fractures in post-SSRT experiments in corrosive environment. Full article

(This article belongs to the Collection Microstructure and Corrosion Behavior of Advanced Alloys)

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15 pages, 10769 KiB

Open AccessEditor’s ChoiceArticle

Increasing the Accuracy of Free-Form Surface Multiaxis Milling

by Marek Sadílek, Zdeněk Poruba, Lenka Čepová and Michal Šajgalík

Materials 2021, 14(1), 25; https://doi.org/10.3390/ma14010025 - 23 Dec 2020

Cited by 13 | Viewed by 3612

Abstract

This contribution deals with the accuracy of machining during free-form surface milling using various technologies. The contribution analyzes the accuracy and surface roughness of machined experimental samples using 3-axis, 3 + 2-axis, and 5-axis milling. Experimentation is focusing on the tool axis inclination [...] Read more.

This contribution deals with the accuracy of machining during free-form surface milling using various technologies. The contribution analyzes the accuracy and surface roughness of machined experimental samples using 3-axis, 3 + 2-axis, and 5-axis milling. Experimentation is focusing on the tool axis inclination angle—it is the position of the tool axis relative to the workpiece. When comparing machining accuracy during 3-axis, 3 + 2-axis, and 5-axis milling the highest accuracy (deviation ranging from 0 to 17 μm) was achieved with 5-axis simultaneous milling (inclination angles β_f = 10 to 15°, β_n = 10 to 15°). This contribution is also enriched by comparing a CAD (Computer Aided Design) model with the prediction of milled surface errors in the CAM (Computer Aided Manufacturing) system. This allows us to determine the size of the deviations of the calculated surfaces before the machining process. This prediction is analyzed with real measured deviations on a shaped surface—using optical three-dimensional microscope Alicona Infinite Focus G5. Full article

(This article belongs to the Collection Machining and Manufacturing of Alloys and Steels)

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9 pages, 2723 KiB

Open AccessEditor’s ChoiceArticle

Morphology, Mechanical Properties and Shape Memory Effects of Polyamide12/Polyolefin Elastomer Blends Compatibilized by Glycidylisobutyl POSS

by Dong-Hun Lee, Young-Wook Chang and Keon-Soo Jang

Materials 2021, 14(1), 27; https://doi.org/10.3390/ma14010027 - 23 Dec 2020

Cited by 10 | Viewed by 2896

Abstract

Small amounts of glycidylisobutyl polyhedral oligomericsilsesquioxane (G-POSS) (up to 10 phr) were added into a immiscible polyamide12 (PA12)/polyolefin elastomer (POE) blend (70 wt%/30 wt%) by simple melt mixing. The effects of the G-POSS on phase morphology and mechanical properties were investigated by FE-SEM, [...] Read more.

Small amounts of glycidylisobutyl polyhedral oligomericsilsesquioxane (G-POSS) (up to 10 phr) were added into a immiscible polyamide12 (PA12)/polyolefin elastomer (POE) blend (70 wt%/30 wt%) by simple melt mixing. The effects of the G-POSS on phase morphology and mechanical properties were investigated by FE-SEM, tensile testing, Izod impact test and dynamic mechanical analysis. FE-SEM analysis revealed that domain size of the dispersed POE phase in matrix PA12 is decreased significantly by adding the G-POSS, indicating a compatibilization effect of the G-POSS for the immiscible PA12/POE blend. The PA12/POE blend compatibilized with POSS showed simultaneous enhancement in mechanical properties including tensile modulus, strength and toughness. Further, thermally triggered shape memory effect was observed in this compatibilized blend. Full article

(This article belongs to the Special Issue Polymer Blends: Processing, Morphology, and Properties)

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20 pages, 18613 KiB

Open AccessEditor’s ChoiceArticle

Determination of Selected Texture Features on a Single-Layer Grinding Wheel Active Surface for Tracking Their Changes as a Result of Wear

by Anna Bazan, Andrzej Kawalec, Tomasz Rydzak, Paweł Kubik and Adam Olko

Materials 2021, 14(1), 6; https://doi.org/10.3390/ma14010006 - 22 Dec 2020

Cited by 17 | Viewed by 2931

Abstract

Measurements of the active surface microgeometry of the grinding wheel by contact and optical methods are commonly used to obtain a cloud of points representing the surface of the examined tool. Parameters that can be determined on the basis of the above-mentioned measurements [...] Read more.

Measurements of the active surface microgeometry of the grinding wheel by contact and optical methods are commonly used to obtain a cloud of points representing the surface of the examined tool. Parameters that can be determined on the basis of the above-mentioned measurements can be universal parameters, which are commonly used to assess the geometric structure of a surface or parameters taking into account specific properties of the grinding wheel active surface (GWAS) structure. This article proposes a methodology for determining the average level of binder, which allows the definition the cut-off level required to separate from the measurement data: (i) the areas representing grains, (ii) the areas of gumming up of the grinding wheel, and (iii) deep cavities in approximately the same places on the investigated grinding wheel, regardless of the degree of its wear. This, in turn, allows one to track changes in characteristic parameters computed from measurements of texture in the above-mentioned areas due to different GWAS wear processes. The research was based on the analysis of data obtained from measurements of single-layer grinding wheels using the replica technique. The adopted measurement methodology enables measurement of approximately the same (94% coverage) areas of the GWAS at four stages of grinding wheel operation. Errors that were computed related to the determination of the volume of abrasive on the GWAS at various stages of wear using the developed methodology were lower, on average, by 48% compared to the automatic recognition of islands made with a commercial software. Full article

(This article belongs to the Special Issue “3D” Parametric and Nonparametric Description of Surface Topography in Manufacturing Processes)

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15 pages, 9690 KiB

Open AccessEditor’s ChoiceArticle

Skew Rolling of Bimetallic Rods

by Janusz Tomczak, Tomasz Bulzak, Zbigniew Pater, Łukasz Wójcik and Tomasz Kusiak

Materials 2021, 14(1), 18; https://doi.org/10.3390/ma14010018 - 22 Dec 2020

Cited by 15 | Viewed by 3543

Abstract

The present article reports selected results of a preliminary study of the process of skew rolling of bimetallic rods. The experiments were conducted using a numerically controlled three-roller skew rolling mill. During the tests, bimetallic rods were rolled from billets whose cores and [...] Read more.

The present article reports selected results of a preliminary study of the process of skew rolling of bimetallic rods. The experiments were conducted using a numerically controlled three-roller skew rolling mill. During the tests, bimetallic rods were rolled from billets whose cores and outer sleeves (bushings) were made of different types of steel. The results demonstrate that the proposed method can be successfully used in the production of bimetallic rods. However, proper fastening of the two materials depends on the geometrical parameters of the billets, and the quality of bimetallic rods depends on the heating method used. When the rods are heated without protective atmospheres, the surface layer of the core gets decarburized and the surfaces of the materials being joined together are oxidized, which hinders the welding process and adversely affects the physical and chemical properties of such products. The results of numerical modeling indicate that the material near the surface tends to flow, which may have a negative impact on the welding process. In addition, the distribution of stress in the tool–workpiece contact zone may make welding of the materials difficult. The results reported in this paper are preliminary and constitute a prelude to a more detailed analysis of bimetallic rod rolling. Full article

(This article belongs to the Special Issue Recent Advances and Trends in Metal Forming)

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20 pages, 7427 KiB

Open AccessEditor’s ChoiceArticle

Low-Cost Sensors for Determining the Variation in Interior Moisture Content in Gypsum Composite Materials

by Daniel Ferrández, Carlos Morón, Pablo Saiz, Evangelina Atanes-Sánchez and Engerst Yedra

Materials 2020, 13(24), 5831; https://doi.org/10.3390/ma13245831 - 21 Dec 2020

Cited by 1 | Viewed by 2727

Abstract

Non-destructive testing can be used to determine some of the most relevant physical properties of building materials. In this work, two low-cost measuring devices were developed capable of determining the variation in real-time of the percentage of humidity that is produced in the [...] Read more.

Non-destructive testing can be used to determine some of the most relevant physical properties of building materials. In this work, two low-cost measuring devices were developed capable of determining the variation in real-time of the percentage of humidity that is produced in the construction of gypsum and plaster during the hardening process. For this, an Arduino resistive sensor and a capacitive sensor of our design were used. The results show how it is possible to determine the variations in mixing water content during the seven days of curing established by the UNE-EN 13279-2 standard as well relate to the mechanical resistance of the test specimens with the same percentage of humidity. Additionally, the study was completed with the determination of the formation of the dihydrate compound linked to this setting process in the test specimens by conducting X-ray diffraction and thermogravimetric analysis tests at different ages of the samples. Full article

(This article belongs to the Special Issue Mechanical Characterization of Gypsum Composites)

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19 pages, 9852 KiB

Open AccessEditor’s ChoiceArticle

Effect of Natural Graphite Fineness on the Performance and Electrical Conductivity of Cement Paste Mixes for Self-Sensing Structures

by Ioanna Papanikolaou, Chrysoula Litina, Amir Zomorodian and Abir Al-Tabbaa

Materials 2020, 13(24), 5833; https://doi.org/10.3390/ma13245833 - 21 Dec 2020

Cited by 29 | Viewed by 4985

Abstract

Cementitious composites are the most widely used construction materials; however, their poor durability necessitates frequent monitoring and repairs. The emergence of self-sensing composites could reduce the need for costly and time-consuming structural inspections. Natural graphite, due to its low cost and wide availability, [...] Read more.

Cementitious composites are the most widely used construction materials; however, their poor durability necessitates frequent monitoring and repairs. The emergence of self-sensing composites could reduce the need for costly and time-consuming structural inspections. Natural graphite, due to its low cost and wide availability, is a promising additive to generate an electrically conductive network which could ultimately lead to a self-sensing mechanism. Despite several studies using natural graphite as a conductive additive, the effect of its fineness on the cementitious composite’s performance has not been explored. This study experimentally investigated the effect of three graphite products of varying fineness on the early age, mechanical, and electrical conductivity performance of cement pastes. The fluidity of the graphite-cement paste reduced significantly with increasing graphite fineness, and graphite did not affect the cement hydration. The finer the graphite, the lower the effect on the mechanical performance, as confirmed by compressive strength testing and micro-indentation. Electrical conductivity testing showed that the percolation threshold depended on the graphite fineness and was found at ~20 wt % for the fine and medium graphite, while it increased to 30–40 wt % for the coarse graphite. This is the first study that has investigated holistically the effect of graphite fineness on the performance of cement pastes and will pave the way for using this material as an additive for self-sensing structures. Full article

(This article belongs to the Special Issue Research and Development of Modified Building Materials)

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18 pages, 7373 KiB

Open AccessEditor’s ChoiceArticle

Analysis and Modeling of the Micro-Cutting Process of Ti-6Al-4V Titanium Alloy with Single Abrasive Grain

by Łukasz Rypina, Dariusz Lipiński, Błażej Bałasz, Wojciech Kacalak and Tomasz Szatkiewicz

Materials 2020, 13(24), 5835; https://doi.org/10.3390/ma13245835 - 21 Dec 2020

Cited by 20 | Viewed by 3165

Abstract

Modeling of material displacements in the microcutting zone is complex due to the number and interdependence of factors affecting the results of the process. An important problem in the modeling process is the selection of the constitutive model and its parameters, which will [...] Read more.

Modeling of material displacements in the microcutting zone is complex due to the number and interdependence of factors affecting the results of the process. An important problem in the modeling process is the selection of the constitutive model and its parameters, which will correctly describe the properties of the material under the conditions of triaxial compression, which is characteristic for the areas of the contact zone of the blade and the processed material in abrasive machining processes. The aim of the work was to develop computer models (with the use of the finite element method) of the microcutting process with a single abrasive grain, which were verified with the results of experimental tests. The paper presents the methodology of modeling the processes of microcutting with abrasive grains, whose geometrical models were created based on optical scanning methods. Observations of the microcutting process were carried out with the use of a high-speed camera and an optical profilometer. This enabled a detailed observation of the chip formation process, as well as the analysis of the surface topography of microcutting traces. The results presented in the paper indicate the convergence of the results of the numerical and experimental simulations with regard to the geometric parameters describing the scratches formed in the microcutting process and the compliance of the chip-forming process. Thus, the correctness of the selection of the constitutive model (Johnson Cook equation) and its parameters was demonstrated, as well as the correctness of the applied methodology for creating a geometric model that allowed for a reflection of the geometrical parameters of the abrasive grains that coincided with the real objects, thanks to which it was possible to reflect in detail the phenomena occurring in the vicinity of the abrasive grain tip. Full article

(This article belongs to the Special Issue Advanced Design for Manufacturing Processes)

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25 pages, 10982 KiB

Open AccessEditor’s ChoiceArticle

Numerical and Experimental Results on Charpy Tests for Blends Polypropylene + Polyamide + Ethylene Propylene Diene Monomer (PP + PA + EPDM)

by Cătălin Pîrvu, Andreea Elena Musteată, George Ghiocel Ojoc and Lorena Deleanu

Materials 2020, 13(24), 5837; https://doi.org/10.3390/ma13245837 - 21 Dec 2020

Cited by 3 | Viewed by 2944

Abstract

This paper presents results from numerical and experimental investigation on Charpy tests in order to point out failure mechanisms and to evaluate new polymeric blends PP + PA6 + EPDM. Charpy tests were done for initial velocity of the impactor of 0.96 m/s [...] Read more.

This paper presents results from numerical and experimental investigation on Charpy tests in order to point out failure mechanisms and to evaluate new polymeric blends PP + PA6 + EPDM. Charpy tests were done for initial velocity of the impactor of 0.96 m/s and its mass of 3.219 kg and these data were also introduced in the finite element model. The proposed model takes into account the system of four balls, including support and the ring of fixing the three balls and it has a finer discretization of the impact area to highlight the mechanisms of failure and their development in time. The constitutive models for four materials (polypropylene with 1% Kritilen, two blends PP + PA6 + EPDM and a blend PA6 + EPDM) were derived from tensile tests. Running simulations for each constitutive model of material makes possible to differentiate the destruction mechanisms according to the material introduced in the simulation, including the initiation and the development of the crack(s), based on equivalent plastic strain at break (EPS) for each material. The validation of the model and the simulation results were done qualitatively, analyzing the shape of broken surfaces and comparing them to SEM images and quantitatively by comparing the impact duration, energy absorbed by the sample, the value of maximum force during impact. The duration of the destruction of the specimen is longer than the actual one, explainable by the fact that the material model does not take into account the influence of the material deformation speed in Charpy test, the model being designed with the help of tests done at 0.016 m/s (1000 mm/min) (maximum strain rate for the tensile tests). Experimental results are encouraging for recommending the blends 20% PP + 42% PA6 + 28% EPDM and 60% PA6 + 40% EPDM as materials for impact protection at low velocity (1 m/s). Simulation results are closer to the experimental ones for the more brittle tested materials (with less content of PA6 and EPDM) and more distanced for the more ductile materials (with higher content of PA6 and EPDM). Full article

(This article belongs to the Special Issue Synthesis, Properties and Applications of Polymer Blends)

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20 pages, 5435 KiB

Open AccessEditor’s ChoiceArticle

Improving the Performance of a Graphite Foil/Polyaniline Electrode Material by a Thin PEDOT:PSS Layer for Application in Flexible, High Power Supercapacitors

by Zuzanna Zarach, Konrad Trzciński, Marcin Łapiński, Anna Lisowska-Oleksiak and Mariusz Szkoda

Materials 2020, 13(24), 5791; https://doi.org/10.3390/ma13245791 - 18 Dec 2020

Cited by 17 | Viewed by 4309

Abstract

In this study, we present a novel strategy for enhancing polyaniline stability and thus obtaining an electrode material with practical application in supercapacitors. A promising (graphite foil/polyaniline/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) GF/PANI/PEDOT:PSS) electrode material was characterized and used in the construction of a symmetric supercapacitor that provides [...] Read more.

In this study, we present a novel strategy for enhancing polyaniline stability and thus obtaining an electrode material with practical application in supercapacitors. A promising (graphite foil/polyaniline/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) GF/PANI/PEDOT:PSS) electrode material was characterized and used in the construction of a symmetric supercapacitor that provides an outstanding high power density. For this purpose, the electropolymerization of PANI was carried out on a graphite foil and then a thin protective layer of PEDOT:PSS was deposited. The presence of the nanometer PEDOT:PSS layer made it possible to widen the electroactivity potential range of the electrode material. Moreover, the synergy between materials positively affected the amount of accumulated charge, and thus the thin PEDOT:PSS layer contributed to enhancing the specific capacity of the electrode material. The electrochemical performance of the GF/PANI/PEDOT:PSS electrode, as well as the symmetrical supercapacitor, was investigated by cyclic voltammetry and galvanostatic charge/discharge cycles in 1 M H₂SO₄ at room temperature. The fabricated electrode material shows a high specific capacitance (C_sp) of 557.4 Fg⁻¹ and areal capacitance (C_areal) of 2600 mF·cm⁻² in 1 M H₂SO₄ at a current density of 200 mA·cm⁻² (~4 A·g⁻¹). The supercapacitor performance was studied and the results show that a thin PEDOT:PSS layer enables cycling stability improvement of the device from 54% to 67% after 10,000 cycles, and provides a high specific capacity (159.8 F·g⁻¹) and a maximum specific power (18,043 W·kg⁻¹) for practical applications. Full article

(This article belongs to the Special Issue Electrode Materials for Advanced Photo-Supercapacitors)

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19 pages, 8456 KiB

Open AccessEditor’s ChoiceArticle

The Role of Observation–Measurement Methods in the Surface Characterization of X39Cr13 Stainless-Steel Cutting Blades Used in the Fish Processing Industry

by Wojciech Kapłonek, Krzysztof Nadolny, Bartosz Zieliński, Jarosław Plichta, Danil Yurievich Pimenov and Shubham Sharma

Materials 2020, 13(24), 5796; https://doi.org/10.3390/ma13245796 - 18 Dec 2020

Cited by 5 | Viewed by 2628

Abstract

In the modern fish processing industry, flat fishes play an important role. They are processed into a final product in the form of a fillet during the skinning operation, which is carried out on machines operating in automated production lines. These machines are [...] Read more.

In the modern fish processing industry, flat fishes play an important role. They are processed into a final product in the form of a fillet during the skinning operation, which is carried out on machines operating in automated production lines. These machines are usually equipped with a single planar cutting blade or a few of such blades. The high-efficiency skinning and industrial conditions cause rapid wear of the cutting edge of the blade, which is detrimental to the quality of the final product. One of the forms of renewing the cutting ability of these types of tools is the regeneration carried out with the use of precise traverse surface grinding. The results of this process must be carefully verified for determining its correctness and possible optimization of its parameters. The main goal of this article was to characterize the usefulness of a number of observational and measuring methods to evaluate the results of the technical blade regeneration process. In this work, a number of contemporary observation–measurement methods such as optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), optical profilometry (OP), and angle-resolved scattering (ARS), supported by image processing and analysis techniques, were analyzed. The authors focused on presenting the role of the abovementioned methods in the surface characterization of planar cutting blades made of X39Cr13 chromium martensitic stainless steel before and after the technological operation of flat-fish skinning. Additionally, the surface condition after the regeneration process carried out using the five-axis CNC (computerized numerical control) grinding machine was also assessed. Numerous results of surface observations, elemental composition microanalysis, high-accuracy surface microgeometry measurements, and quantitative and qualitative analysis confirming the possibility of using the proposed methods in the presented applications are presented. Full article

(This article belongs to the Special Issue Precision and Ultra-Precision Subtractive and Additive Manufacturing Processes of Alloys and Steels)

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18 pages, 10536 KiB

Open AccessEditor’s ChoiceArticle

Tribological Properties of Ni-P/Si₃N₄ Nanocomposite Layers Deposited by Chemical Reduction Method on Aluminum Alloy AW-7075

by Kazimierz Czapczyk

Materials 2020, 13(24), 5797; https://doi.org/10.3390/ma13245797 - 18 Dec 2020

Cited by 6 | Viewed by 2411

Abstract

The article presents the results of tribological tests of Ni-P/Si₃N₄ nanocomposite and Ni-P nickel layers deposited on the AW-7075 aluminum alloy by chemical reduction method, and the AW-7075 alloy without coating. Nanocomposite layers were produced using Si₃N₄ [...] Read more.

The article presents the results of tribological tests of Ni-P/Si₃N₄ nanocomposite and Ni-P nickel layers deposited on the AW-7075 aluminum alloy by chemical reduction method, and the AW-7075 alloy without coating. Nanocomposite layers were produced using Si₃N₄ siliconnitride in the form of a polydisperse powder whose particle sizes ranged from 20 to 25 nm. The influence of the content of the dispersion phase layer material on the abrasive wear, which was determined as the “ball on disc” method, was analyzed. Surface topography was examined by the contact method using a profilometer. The purpose of introducing Si₃N₄ particles into the Ni-P layer was to increase the wear resistance of AW-7075 aluminum alloy parts with an embedded nanocomposite coating. Based on the obtained test results, it was found that the Ni-P/Si₃N₄ layers are more resistant to wear than the Ni-P layers and the AW-7075 alloy layers, and are a good barrier against abrasive wear at various loads and environmental conditions. Full article

(This article belongs to the Special Issue Precision and Ultra-Precision Subtractive and Additive Manufacturing Processes of Alloys and Steels)

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15 pages, 4102 KiB

Open AccessEditor’s ChoiceArticle

The Effects of Temperature Curing on the Strength Development, Transport Properties, and Freeze-Thaw Resistance of Blast Furnace Slag Cement Mortars Modified with Nanosilica

by Karol Federowicz, Vitoria Alves Figueiredo, Hussein Al-kroom, Hamdy A. Abdel-Gawwad, Mohamed Abd Elrahman and Pawel Sikora

Materials 2020, 13(24), 5800; https://doi.org/10.3390/ma13245800 - 18 Dec 2020

Cited by 12 | Viewed by 3059

Abstract

This investigation studies the effects of hot water and hot air curing on the strength development, transport properties, and freeze-thaw resistance of mortars incorporating low-heat blast furnace slag cement and nanosilica (NS). Mortar samples were prepared and stored in ambient conditions for 24 [...] Read more.

This investigation studies the effects of hot water and hot air curing on the strength development, transport properties, and freeze-thaw resistance of mortars incorporating low-heat blast furnace slag cement and nanosilica (NS). Mortar samples were prepared and stored in ambient conditions for 24 h. After demolding, mortar samples were subjected to two different hot curing methods: Hot water and hot air curing (40 °C and 60 °C) for 24 h. For comparison purposes, mortar reference mixes were prepared and cured in water and air at ambient conditions. Strength development (from 1 to 180 days), capillary water porosity, water sorptivity, and freeze-thaw resistance were tested after 180 days of curing. The experimental results showed that both curing regimes accelerate the strength development of mortars, especially in the first seven days of hydration. The highest early strengths were reported for mortars subjected to a temperature of 60 °C, followed by those cured at 40 °C. The hot water curing regime was found to be more suitable, as a result of more stable strength development. Similar findings were observed in regard to durability-related properties. It is worth noting that thermal curing can more efficiently increase strength in the presence of nanosilica, suggesting that NS is more effective in enhancing strength under thermal curing. Full article

(This article belongs to the Collection Advanced Civil Engineering Materials: From Synthesis to Application)

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15 pages, 8404 KiB

Open AccessEditor’s ChoiceArticle

Organic Contaminant-Triggered Self-Healing Soil Mix Cut-Off Wall Materials Incorporating Oil Sorbents

by Benyi Cao, Livia Ribeiro de Souza and Abir Al-Tabbaa

Materials 2020, 13(24), 5802; https://doi.org/10.3390/ma13245802 - 18 Dec 2020

Cited by 4 | Viewed by 2682

Abstract

Soil mix cut-off walls have been increasingly used for containment of organic contaminants in polluted land. However, the mixed soil is susceptible to deterioration due to aggressive environmental and mechanical stresses, leading to crack-originated damage and requiring costly maintenance. This paper proposed a [...] Read more.

Soil mix cut-off walls have been increasingly used for containment of organic contaminants in polluted land. However, the mixed soil is susceptible to deterioration due to aggressive environmental and mechanical stresses, leading to crack-originated damage and requiring costly maintenance. This paper proposed a novel approach to achieve self-healing properties of soil mix cut-off wall materials triggered by the ingress of organic contaminants. Oil sorbent polymers with high absorption and swelling capacities were incorporated in a cementitious grout and mixed with soil using a laboratory-scale auger setup. The self-healing performance results showed that 500 µm-wide cracks could be bridged and blocked by the swollen oil sorbents, and that the permeability was reduced by almost an order of magnitude after the permeation of liquid paraffin. It was shown by micro-CT scan tests that the network formed by the swollen oil sorbents acted as attachments and binder, preventing the cracked mixed soil sample from crumbling, and that the oil sorbents swelled three times in volume and therefore occupied the air space and blocked the cracks in the matrix. These promising results exhibit the potential for the oil sorbents to provide soil mix cut-off walls in organically-contaminated land with self-healing properties and enhanced durability. Full article

(This article belongs to the Special Issue Advances in Construction and Building Materials)

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24 pages, 3328 KiB

Open AccessEditor’s ChoiceReview

Influence of Design Parameters on Fresh Properties of Self-Compacting Concrete with Recycled Aggregate—A Review

by Rebeca Martínez-García, P. Jagadesh, Fernando J. Fraile-Fernández, Julia M. Morán-del Pozo and Andrés Juan-Valdés

Materials 2020, 13(24), 5749; https://doi.org/10.3390/ma13245749 - 16 Dec 2020

Cited by 26 | Viewed by 3675

Abstract

This article presents an overview of the bibliographic picture of the design parameter’s influence on the mix proportion of self-compacting concrete with recycled aggregate. Design parameters like water-cement ratio, water to paste ratio, and percentage of superplasticizers are considered in this review. Standardization [...] Read more.

This article presents an overview of the bibliographic picture of the design parameter’s influence on the mix proportion of self-compacting concrete with recycled aggregate. Design parameters like water-cement ratio, water to paste ratio, and percentage of superplasticizers are considered in this review. Standardization and recent research on the usage of recycled aggregates in self-compacting concrete (SCC) exploit its significance in the construction sector. The usage of recycled aggregate not only resolves the negative impacts on the environment but also prevents the usage of natural resources. Furthermore, it is necessary to understand the recycled aggregate property’s role in a mixed design and SCC properties. Design parameters are not only influenced by a mix design but also play a key role in SCC’s fresh properties. Hence, in this overview, properties of SCC ingredients, calculation of design parameters in mix design, the effect of design parameters on fresh concrete properties, and the evolution of fresh concrete properties are studied. Full article

(This article belongs to the Special Issue Recovery of Waste Materials: Technological Research and Industrial Scale-Up)

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15 pages, 38329 KiB

Open AccessEditor’s ChoiceArticle

Influence of Microstructure and Chemical Composition on Microhardness and Wear Properties of Laser Borided Monel 400

by Mateusz Kukliński, Aneta Bartkowska, Damian Przestacki and Grzegorz Kinal

Materials 2020, 13(24), 5757; https://doi.org/10.3390/ma13245757 - 16 Dec 2020

Cited by 19 | Viewed by 3075

Abstract

In this study, wear properties of Monel 400 after laser alloying with boron are described. Surfaces were prepared by covering them with boron paste layers of two different thicknesses (100 µm and 200 μm) and re-melting using diode laser. Laser beam power density [...] Read more.

In this study, wear properties of Monel 400 after laser alloying with boron are described. Surfaces were prepared by covering them with boron paste layers of two different thicknesses (100 µm and 200 μm) and re-melting using diode laser. Laser beam power density was equal to 178.3 kW/cm². Two laser beam scanning velocities were chosen for the process: 5 m/min and 50 m/min. Surfaces alloyed with boron were investigated in terms of wear resistance, and the surface of untreated Monel 400 was examined for comparison. Wear tests were performed using counterspecimen made from steel 100Cr6 and water as a lubricant. Both quantitative and qualitative analysis of surfaces after wear test are described in this paper. Additionally, microstructures and properties of obtained laser alloyed surfaces are presented. It was found that the wear resistance increased from four to tens of times, depending on parameters of the laser boriding process. The wear mechanism was mainly adhesive for surfaces alloyed with initial boron layer 100 µm thick and evolves to abrasive with increasing boron content and laser beam scanning velocity. Iron particles detached from counterspecimens were detected on each borided surface after the wear test, and it was found that the harder the surface the less built-ups are present. Moreover, adhered iron particles oxidized during the wear test. Full article

(This article belongs to the Topic Laser Surface Modification of Cemented Carbides, Superalloys, Composites, and Alloys)

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11 pages, 4927 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Baking Heat Treatment on the Fatigue Strength and Life of Shot Peened 4340M Landing Gear Steel

by Seok-Hwan Ahn, Jongman Heo, Jungsik Kim, Hyeongseob Hwang and In-Sik Cho

Materials 2020, 13(24), 5711; https://doi.org/10.3390/ma13245711 - 15 Dec 2020

Cited by 7 | Viewed by 2689

Abstract

In this study, the effect of baking heat treatment on fatigue strength and fatigue life was evaluated by performing baking heat treatment after shot peening treatment on 4340M steel for landing gear. An ultrasonic fatigue test was performed to obtain the S–N curve, [...] Read more.

In this study, the effect of baking heat treatment on fatigue strength and fatigue life was evaluated by performing baking heat treatment after shot peening treatment on 4340M steel for landing gear. An ultrasonic fatigue test was performed to obtain the S–N curve, and the fatigue strength and fatigue life were compared. The micro hardness of shot peening showed a maximum at a hardened depth of about 50 μm and was almost uniform when it arrived at the hardened depth of about 400 μm. The overall average tensile strength after the baking heat treatment was lowered by about 80–111 MPa, but the yield strength was improved by about 206–262 MPa. The five cases of specimens showed similar fatigue strength and fatigue life in high cycle fatigue (HCF) regime. However, the fatigue limit of the baking heat treated specimens showed an increasing tendency rather than that of shot peening specimens when the fatigue life was extended to the very high cycle fatigue (VHCF) regime. The effect of baking heat treatment was identified from improved fatigue limit when baking heat was used to treat the specimen treated by shot peening containing inclusions. The optimum temperature range for the better baking heat treatment effect could be constrained not to exceed maximum 246 °C. Full article

(This article belongs to the Special Issue Damage and Mechanical Properties of Steels)

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14 pages, 5931 KiB

Open AccessEditor’s ChoiceArticle

A Rotary Compression Process for Producing Hollow Gear Shafts

by Arkadiusz Tofil, Janusz Tomczak, Tomasz Bulzak, Zbigniew Pater, Marcin Buczaj and Andrzej Sumorek

Materials 2020, 13(24), 5718; https://doi.org/10.3390/ma13245718 - 15 Dec 2020

Cited by 4 | Viewed by 3515

Abstract

This paper presents selected numerical and experimental results of a study investigating the process of forming hollow stepped gear shafts from tubes by rotary compression. The objective of the study was to determine whether the rotary compression process is an effective method of [...] Read more.

This paper presents selected numerical and experimental results of a study investigating the process of forming hollow stepped gear shafts from tubes by rotary compression. The objective of the study was to determine whether the rotary compression process is an effective method of producing hollow stepped gear shafts and to identify limitations of this manufacturing method. A theoretical analysis involved the numerical modeling of the proposed process by the finite element method (FEM). 3D simulations were performed using the commercial simulation software package Simufact Forming. The analysis involved examining the material flow pattern along with thermal and force parameters of the process. The FEM results were verified with experimental tests conducted under laboratory conditions. The experiments were performed on a machine specially designed for the rotary compression of hollow parts. Results demonstrate that it is difficult to form a stepped gear shaft in one operation. For this reason, such parts should be formed in two operations. The first operation involves the forming of a hollow stepped shaft by rotary compression, while in the second operation, a gear is formed on one of the steps of the shaft. Full article

(This article belongs to the Special Issue Recent Advances and Trends in Metal Forming)

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14 pages, 4324 KiB

Open AccessEditor’s ChoiceArticle

Experimental Study on Chloride Ion Diffusion in Concrete under Uniaxial and Biaxial Sustained Stress

by Xiaokang Cheng, Jianxin Peng, C.S. Cai and Jianren Zhang

Materials 2020, 13(24), 5717; https://doi.org/10.3390/ma13245717 - 15 Dec 2020

Cited by 11 | Viewed by 2503

Abstract

The existence of axial and lateral compressive stress affect the diffusion of chloride ions in concrete will lead to the performance degradation of concrete structure. This paper experimentally studied the chloride diffusivity properties of uniaxial and biaxial sustained compressive stress under one-dimensional chloride [...] Read more.

The existence of axial and lateral compressive stress affect the diffusion of chloride ions in concrete will lead to the performance degradation of concrete structure. This paper experimentally studied the chloride diffusivity properties of uniaxial and biaxial sustained compressive stress under one-dimensional chloride solution erosion. The influence of different sustained compressive stress states on chloride ion diffusivity is evaluated by testing chloride concentration in concrete. The experiment results show that the existence of sustained compressive stress does not always inhibit the diffusion of chloride ions in concrete, and the numerical value of sustained compressive stress level can affect the diffusion law of chloride ions in concrete. It is found that the chloride concentration decreases most when the lateral compressive stress level is close to 0.15 times the compressive strength of concrete. In addition, the sustained compressive stress has a significant effect on chloride ion diffusion of concrete with high water/cement ratio. Then, the chloride diffusion coefficient model under uniaxial and biaxial sustained compressive stress is established based on the apparent chloride diffusion coefficient. Finally, the results demonstrate that the chloride diffusion coefficient model is reasonable and feasible by comparing the experimental data in the opening literature with the calculated values from the developed model. Full article

(This article belongs to the Special Issue Corrosion Behaviour in Concrete)

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13 pages, 6998 KiB

Open AccessEditor’s ChoiceArticle

Cutting Force during Surface Layer Milling of Selected Aluminium Alloys

by Magdalena Zawada-Michałowska, Jerzy Józwik, Stanisław Legutko, Dariusz Mika, Paweł Pieśko and Jarosław Pytka

Materials 2020, 13(24), 5725; https://doi.org/10.3390/ma13245725 - 15 Dec 2020

Cited by 5 | Viewed by 2646

Abstract

This paper presents the analysis of cutting force during surface layer milling of selected aluminium alloys, which are widely used in the aviation industry. The cutting force is one of the most important parameters determining the machinability of the material and also provides [...] Read more.

This paper presents the analysis of cutting force during surface layer milling of selected aluminium alloys, which are widely used in the aviation industry. The cutting force is one of the most important parameters determining the machinability of the material and also provides important information about the course of the cutting. The study analysed the influence of the technological parameters, i.e., cutting speed v_c and depth of cut a_p as well as the relation between cutting tool feed direction and rolling direction on the value of cutting force during milling of selected aluminium alloys, i.e., EN AW-2017A T451 and EN AW-2024 T351. The material anisotropy is a very important issue, since the engineering industry faces enormous problems related to the cutting of the tested materials that are usually supplied in the form of rolled plates. The surface layer was cut due to the fact that it accumulates the greatest residual stresses. The measurement process of cutting force was performed by using 9257B Kistler piezoelectric dynamometer. As part of the analysis of the results, the measurement uncertainty was also estimated, which was determined on the basis of two components obtained by using the A and B methods, respectively. Full article

(This article belongs to the Special Issue Precision and Ultra-Precision Subtractive and Additive Manufacturing Processes of Alloys and Steels)

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32 pages, 13782 KiB

Open AccessEditor’s ChoiceReview

Doping Effect on Cu₂Se Thermoelectric Performance: A Review

by Yuanhao Qin, Liangliang Yang, Jiangtao Wei, Shuqi Yang, Mingliang Zhang, Xiaodong Wang and Fuhua Yang

Materials 2020, 13(24), 5704; https://doi.org/10.3390/ma13245704 - 14 Dec 2020

Cited by 39 | Viewed by 5855

Abstract

Cu₂Se, owing to its intrinsic excellent thermoelectric (TE) performance emerging from the peculiar nature of “liquid-like” Cu⁺ ions, has been regarded as one of the most promising thermoelectric materials recently. However, the commercial use is still something far from reach [...] Read more.

Cu₂Se, owing to its intrinsic excellent thermoelectric (TE) performance emerging from the peculiar nature of “liquid-like” Cu⁺ ions, has been regarded as one of the most promising thermoelectric materials recently. However, the commercial use is still something far from reach unless effective approaches can be applied to further increase the figure of merit (ZT) of Cu₂Se, and doping has shown wide development prospect. Until now, the highest ZT value of 2.62 has been achieved in Al doped samples, which is twice as much as the original pure Cu₂Se. Herein, various doping elements from all main groups and some transitional groups that have been used as dopants in enhancing the TE performance of Cu₂Se are summarized, and the mechanisms of TE performance enhancement are analyzed. In addition, points of great concern for further enhancing the TE performance of doped Cu₂Se are proposed. Full article

(This article belongs to the Special Issue Advances in Thermoelectric Materials)

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21 pages, 6840 KiB

Open AccessEditor’s ChoiceArticle

Pultruded GFRP Reinforcing Bars Using Nanomodified Vinyl Ester

by Shreya Vemuganti, Rahulreddy Chennareddy, Amr Riad and Mahmoud M. Reda Taha

Materials 2020, 13(24), 5710; https://doi.org/10.3390/ma13245710 - 14 Dec 2020

Cited by 13 | Viewed by 5080

Abstract

Glass fiber-reinforced polymer (GFRP) reinforcing bars have relatively low shear strength, which limits their possible use in civil infrastructure applications with high shear demand, such as concrete reinforcing dowels. We suggest that the horizontal shear strength of GFRP bars can be significantly improved [...] Read more.

Glass fiber-reinforced polymer (GFRP) reinforcing bars have relatively low shear strength, which limits their possible use in civil infrastructure applications with high shear demand, such as concrete reinforcing dowels. We suggest that the horizontal shear strength of GFRP bars can be significantly improved by nanomodification of the vinyl ester resin prior to pultrusion. The optimal content of functionalized multiwalled carbon nanotubes (MWCNTs) well dispersed into the vinyl ester resin was determined using viscosity measurements and scanning electron micrographs. Longitudinal tension and short beam shear tests were conducted to determine the horizontal shear strength of the nanomodified GFRP reinforcing bars. While the tensile strength of the GFRP reinforcing bars was improved by 20%, the horizontal shear strength of the bars was improved by 111% compared with the shear strength of neat GFRP bars pultruded using the same settings. Of special interest is the absence of the typical broom failure observed in GFRP when MWCNTs were used. Differential scanning calorimetry measurements and fiber volume fraction confirmed the quality of the new pultruded GFRP bars. Fourier-transform infrared (FTIR) measurements demonstrated the formation of carboxyl stretching in nanomodified GFRP bars, indicating the formation of a new chemical bond. The new pultrusion process using nanomodified vinyl ester enables expanding the use of GFRP reinforcing bars in civil infrastructure applications. Full article

(This article belongs to the Special Issue Advances in Construction and Building Materials)

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17 pages, 6425 KiB

Open AccessEditor’s ChoiceArticle

Anisotropic Response of CoCrFeMnNi High-Entropy Alloy Fabricated by Selective Laser Melting

by Bowen Wang, Miao Sun, Bobo Li, Lijuan Zhang and Bingheng Lu

Materials 2020, 13(24), 5687; https://doi.org/10.3390/ma13245687 - 13 Dec 2020

Cited by 24 | Viewed by 3126

Abstract

This study investigated the anisotropic characteristics of the microstructural, mechanical and corrosion properties of CoCrFeMnNi high-entropy alloy produced by selective laser melting (SLM) additive manufacturing (AM). Under the extremely high thermal gradient during the SLM process, a columnar solidification structure with a single [...] Read more.

This study investigated the anisotropic characteristics of the microstructural, mechanical and corrosion properties of CoCrFeMnNi high-entropy alloy produced by selective laser melting (SLM) additive manufacturing (AM). Under the extremely high thermal gradient during the SLM process, a columnar solidification structure with a single face-centered cubic (FCC) phase structure was formed. The crystal structure exhibited a regular checkerboard structure in the XOY plane (perpendicular to the building direction), which was composed of {110} direction and a small amount of {100} fiber texture. The cellular-dendritic sub-structures formed in the columnar crystal structure with sizes of about 500 nm in diameter. As for the mechanical properties, the XOY plane exhibited higher ultimate tensile strength and yield strength (σ_0.2) but lower elongation to failure compared to the XOZ plane (parallel to building direction), which reflected the anisotropy of the microstructure. The electrochemical test results of the different planes showed that the XOZ plane exhibited better corrosion resistance in comparison with the XOY plane in the 3.5 wt % NaCl solution, which was on account of the selective attack at the Mn-rich inter-cellular regions and the different structures of the cellular-dendritic sub-structures on different planes. Full article

(This article belongs to the Section Manufacturing Processes and Systems)

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