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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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18 pages, 4444 KB  
Article
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 2768
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 KB  
Article
Na0.76V6O15/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 12 | Viewed by 2896
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, Na0.76V6O15 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 KB  
Article
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 4 | Viewed by 2572
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 KB  
Article
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 4523
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 KB  
Article
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 22 | Viewed by 3796
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 KB  
Article
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 18 | Viewed by 3788
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 KB  
Article
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 3543
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 KB  
Article
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 30 | Viewed by 4119
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 KB  
Article
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 5872
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 KB  
Review
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 26 | Viewed by 5585
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 KB  
Article
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 67 | Viewed by 6252
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 KB  
Article
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 2942
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 KB  
Article
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 3551
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 KB  
Article
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 4872
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 KB  
Article
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 3484
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 KB  
Article
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 26 | Viewed by 3816
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 KB  
Article
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 3755
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 βf = 10 to 15°, βn = 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 KB  
Article
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 12 | Viewed by 3056
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 KB  
Article
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 3057
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 KB  
Article
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 3701
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 KB  
Article
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 2898
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 KB  
Article
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 31 | Viewed by 5434
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 KB  
Article
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 21 | Viewed by 3323
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 KB  
Article
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 3037
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 KB  
Article
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 4493
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 (Csp) of 557.4 Fg−1 and areal capacitance (Careal) 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 KB  
Article
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 2760
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 KB  
Article
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 2496
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 KB  
Article
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 3237
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 KB  
Article
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 2795
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 KB  
Review
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 3860
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 KB  
Article
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 3241
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 KB  
Article
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 8 | Viewed by 2833
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 KB  
Article
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 3766
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 KB  
Article
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 14 | Viewed by 2694
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 KB  
Article
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 2867
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 vc and depth of cut ap 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 KB  
Review
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 42 | Viewed by 6267
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 KB  
Article
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 15 | Viewed by 5387
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 KB  
Article
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 25 | Viewed by 3244
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 (σ0.2) 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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16 pages, 2956 KB  
Article
A Proposal of a Method for Ready-Mixed Concrete Quality Assessment Based on Statistical-Fuzzy Approach
by Izabela Skrzypczak, Wanda Kokoszka, Joanna Zięba, Agnieszka Leśniak, Dariusz Bajno and Lukasz Bednarz
Materials 2020, 13(24), 5674; https://doi.org/10.3390/ma13245674 - 12 Dec 2020
Cited by 13 | Viewed by 3858
Abstract
Control of technical parameters obtained by ready-mixed concrete may be carried out at different stages of the development of concrete properties and by different participants involved in the construction investment process. According to the European Standard EN 206 “Concrete–Specification, performance, production and conformity”, [...] Read more.
Control of technical parameters obtained by ready-mixed concrete may be carried out at different stages of the development of concrete properties and by different participants involved in the construction investment process. According to the European Standard EN 206 “Concrete–Specification, performance, production and conformity”, mandatory control of concrete conformity is conducted by the producer during production. As shown by the subject literature, statistical criteria set out in the standard, including the method for concrete quality assessment based on the concept of concrete family, continue to evoke discussions and raise doubts. This justifies seeking alternative methods for concrete quality assessment. This paper presents a novel approach to quality control and classification of concrete based on combining statistical and fuzzy theories as a means of representation of two types of uncertainty: random uncertainty and information uncertainty. In concrete production, a typical situation when fuzzy uncertainty can be taken into consideration is the conformity control of concrete compressive strength, which is conducted to confirm the declared concrete class. The proposed procedure for quality assessment of a concrete batch is based on defining the membership function for the considered concrete classes and establishing the degree of belonging to the considered concrete class. It was found that concrete classification set out by the standard includes too many concrete classes of overlapping probability density distributions, and the proposed solution was to limit the scope of compressive strength to every second class so as to ensure the efficacy of conformity assessment conducted for concrete classes and concrete families. The proposed procedures can lead to two types of decisions: non-fuzzy (crisp) or fuzzy, which point out to possible solutions and their corresponding preferences. The suggested procedure for quality assessment allows to classify a concrete batch in a fuzzy way with the degree of certainty less than or equal to 1. The results obtained confirm the possibility of employing the proposed method for quality assessment in the production process of ready-mixed concrete. Full article
(This article belongs to the Special Issue Testing of Materials and Elements in Civil Engineering)
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16 pages, 6289 KB  
Article
Photocurable Polymeric Blends for Surgical Application
by Teresa Cernadas, Marta Santos, Sónia P. Miguel, Ilídio J. Correia, Patrícia Alves and Paula Ferreira
Materials 2020, 13(24), 5681; https://doi.org/10.3390/ma13245681 - 12 Dec 2020
Cited by 4 | Viewed by 2483
Abstract
The preparation of photocrosslinkable bioadhesives synthesized from oligomers of lactic acid and polycaprolactone (PCL), both functionalized with 2-isocyanoethyl acrylate (AOI), were studied. The obtained modified macromers of LA-AOI (mLA) and PCL-AOI (mCL) were chemically characterized by 1H NMR and used to formulate [...] Read more.
The preparation of photocrosslinkable bioadhesives synthesized from oligomers of lactic acid and polycaprolactone (PCL), both functionalized with 2-isocyanoethyl acrylate (AOI), were studied. The obtained modified macromers of LA-AOI (mLA) and PCL-AOI (mCL) were chemically characterized by 1H NMR and used to formulate polymeric blends with different mass proportions, 1:1, 1:2 and 2:1, respectively. Subsequently, the produced blends were crosslinked, considering two UV irradiation times: 30 and 120 s. After their production, the thermal and mechanical properties of bioadhesives were assessed, where upon the rheology, gel content, hydrolytic degradation and dynamic contact angles were determined. Furthermore, the cytotoxic profile of bioadhesives was evaluated in contact with human dermal fibroblasts cells, whereas their antibacterial effect was studied monitoring Escherichia coli and S. aureus growth. Overall, flexible and resistant films were obtained, presenting promising features to be used as surgical bioadhesives. Full article
(This article belongs to the Special Issue Synthesis, Properties and Applications of Polymer Blends)
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12 pages, 9268 KB  
Article
Modification of Structural Properties Using Process Parameters and Surface Treatment of Monolithic and Thin-Walled Parts Obtained by Selective Laser Melting
by Krzysztof Grzelak, Janusz Kluczyński, Ireneusz Szachogłuchowicz, Jakub Łuszczek, Lucjan Śnieżek and Janusz Torzewski
Materials 2020, 13(24), 5662; https://doi.org/10.3390/ma13245662 - 11 Dec 2020
Cited by 17 | Viewed by 2311
Abstract
Additive manufacturing is one of the most popular technological processes and is being considered in many research works, a lot of which are related to thin-walled parts analysis. There are many cases where different part geometries were manufactured using the same process parameters. [...] Read more.
Additive manufacturing is one of the most popular technological processes and is being considered in many research works, a lot of which are related to thin-walled parts analysis. There are many cases where different part geometries were manufactured using the same process parameters. That kind of approach often causes different porosity and surface roughness values in the geometry of each produced part. In this work, the porosity of thin-walled and monolithic parts was compared. To analyze additively manufactured samples, porosity and microstructural analyses were done. Additionally, to check the influence of process parameter modification on the manufactured parts’ properties, hardness and roughness measurements were made. Surface roughness and the influence of surface treatment were also taken into account. Porosity reduction of thin-walled parts with energy density growth was observed. Additionally, a positive influence of slight energy density growth on the surface roughness of produced parts was registered. Comparing two extreme-parameter groups, it was observed that a 56% energy density increase caused an almost 85% decrease in porosity and a 45% increase in surface roughness. Additional surface treatment of the material allowed for a 70–90% roughness reduction. Full article
(This article belongs to the Special Issue Microstructural and Mechanical Properties Investigation of Alloy Prepared by Additive Manufacturing Technology)
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18 pages, 22445 KB  
Article
Features of Electrostatic Fields and Their Force Action When Using Micro- and Nanosized Inter-Electrode Gaps
by Nikolai Pshchelko and Ekaterina Vodkailo
Materials 2020, 13(24), 5669; https://doi.org/10.3390/ma13245669 - 11 Dec 2020
Cited by 1 | Viewed by 1731
Abstract
The present work is devoted to assessing the influence of discreteness of electric charge distribution in the double electric layer on the characteristics of the electric fields and their force action in capacitor structures with small interelectrode gaps. Due to the fact that [...] Read more.
The present work is devoted to assessing the influence of discreteness of electric charge distribution in the double electric layer on the characteristics of the electric fields and their force action in capacitor structures with small interelectrode gaps. Due to the fact that modern technologies often use submicron-sized interelectrode gaps, it is no longer possible to consider the electrodes uniformly charged because of the discreteness of the electric charge. The corresponding development of a mathematical and physical model for the study of a non-uniform electric field is suggested. Numerical calculations are carried out, expressions, criteria, and results that are convenient for practical evaluations are obtained. The physical and mathematical model for force characteristics of a non-uniform electric field is developed. With a sufficiently small size of the interelectrode gap, the integral force effect of discretely distributed charges can be significantly higher than with a uniform distribution of the same charge. At reasonable surface charge densities, these phenomena are usually observed at interelectrode gaps less than tenths of a micrometer. Full article
(This article belongs to the Section Materials Physics)
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16 pages, 3686 KB  
Article
An Experimental Assessment of the Water Permeability of Concrete with a Superplasticizer and Admixtures
by Zdzisław Skutnik, Mariusz Sobolewski and Eugeniusz Koda
Materials 2020, 13(24), 5624; https://doi.org/10.3390/ma13245624 - 10 Dec 2020
Cited by 23 | Viewed by 8147
Abstract
This study presents a flow pump technique usually used for evaluating the permeability of soils, which was, for first time, applied to measure the water permeability of concrete. Additionally, a new easy-to-apply method to determine permeability is proposed, based on a modification of [...] Read more.
This study presents a flow pump technique usually used for evaluating the permeability of soils, which was, for first time, applied to measure the water permeability of concrete. Additionally, a new easy-to-apply method to determine permeability is proposed, based on a modification of Valenta’s formula. In the calculations, the apparent air content of concrete mixes was taken into account. An additional purpose of the conducted research was to determine the influence of a new generation of polycarboxylate superplasticizer and chemically active admixtures on the permeability, compressive strength, and other properties of concrete. The following four types of concrete were tested: concrete without admixtures, concrete with an admixture to increase the compressive strength, concrete with a superplasticizer, and concrete containing two admixtures simultaneously. The results showed that the proposed method allows to obtain reliable measurements within a very short period of time. The obtained results confirmed that new method may be very useful in engineering practice, particularly in terms of the watertightness of hydrotechnical concretes and the properties of the concretes used in bridge construction, underground parts of office buildings, or sealed tanks. Full article
(This article belongs to the Special Issue Properties and Applications of Cement-based Composites)
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17 pages, 7053 KB  
Article
Analysis of Deformation and Prediction of Cracks in the Cogging Process for Die Steel at Elevated Temperatures
by Marcin Kukuryk
Materials 2020, 13(24), 5589; https://doi.org/10.3390/ma13245589 - 8 Dec 2020
Cited by 6 | Viewed by 2517
Abstract
In this paper, an analysis of a three-dimensional state of strain and stress in the case of the hot cogging process of X32CrMoV12-28 die steel with the application of the finite element method is presented. The results of the investigations connected with the [...] Read more.
In this paper, an analysis of a three-dimensional state of strain and stress in the case of the hot cogging process of X32CrMoV12-28 die steel with the application of the finite element method is presented. The results of the investigations connected with the simulation of the kinematics of metal flow and thermal phenomena are presented, accompanied by prognosing the formation of ductile fractures in the course of the hot cogging process conducted with the application of three different shape tools and of a proposed deformation criterion of the loss of cohesion. The applied anvils were found to be highly effective in the aspects of distribution of effective strains and stresses, absence of tensile stresses in the axial zones of a forging, and also of a significant thermal stability in the internal layers of a deformed material. The developed course of changes in the deformation of the damage factor in the case of forging in the investigated anvils renders it possible to predict the situation and the phase of deformation in which the loss of cohesion by a deformed material will occur. The comparison between the predicted and the experimental results showed a good agreement. Full article
(This article belongs to the Special Issue Forging Processes of Materials)
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43 pages, 8119 KB  
Review
Review on Adhesives and Surface Treatments for Structural Applications: Recent Developments on Sustainability and Implementation for Metal and Composite Substrates
by Ana C. Marques, Alexandra Mocanu, Nataša Z. Tomić, Sebastian Balos, Elisabeth Stammen, Asa Lundevall, Shoshan T. Abrahami, Roman Günther, John M. M. de Kok and Sofia Teixeira de Freitas
Materials 2020, 13(24), 5590; https://doi.org/10.3390/ma13245590 - 8 Dec 2020
Cited by 132 | Viewed by 18314
Abstract
Using adhesives for connection technology has many benefits. It is cost-efficient, fast, and allows homogeneous stress distribution between the bonded surfaces. This paper gives an overview on the current state of knowledge regarding the technologically important area of adhesive materials, as well as [...] Read more.
Using adhesives for connection technology has many benefits. It is cost-efficient, fast, and allows homogeneous stress distribution between the bonded surfaces. This paper gives an overview on the current state of knowledge regarding the technologically important area of adhesive materials, as well as on emergent related technologies. It is expected to fill some of the technological gaps between the existing literature and industrial reality, by focusing at opportunities and challenges in the adhesives sector, on sustainable and eco-friendly chemistries that enable bio-derived adhesives, recycling and debonding, as well as giving a brief overview on the surface treatment approaches involved in the adhesive application process, with major focus on metal and polymer matrix composites. Finally, some thoughts on the connection between research and development (R&D) efforts, industry standards and regulatory aspects are given. It contributes to bridge the gap between industry and research institutes/academy. Examples from the aeronautics industry are often used since many technological advances in this industry are innovation precursors for other industries. This paper is mainly addressed to chemists, materials scientists, materials engineers, and decision-makers. Full article
(This article belongs to the Special Issue Welding and Joining of Materials for Advanced Aerospace Applications)
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17 pages, 5665 KB  
Article
Use of Coal Bottom Ash and CaO-CaCl2-Activated GGBFS Binder in the Manufacturing of Artificial Fine Aggregates through Cold-Bonded Pelletization
by Dongho Jeon, Woo Sung Yum, Haemin Song, Seyoon Yoon, Younghoon Bae and Jae Eun Oh
Materials 2020, 13(24), 5598; https://doi.org/10.3390/ma13245598 - 8 Dec 2020
Cited by 13 | Viewed by 2811
Abstract
This study investigated the use of coal bottom ash (bottom ash) and CaO-CaCl2-activated ground granulated blast furnace slag (GGBFS) binder in the manufacturing of artificial fine aggregates using cold-bonded pelletization. Mixture samples were prepared with varying added contents of bottom ash [...] Read more.
This study investigated the use of coal bottom ash (bottom ash) and CaO-CaCl2-activated ground granulated blast furnace slag (GGBFS) binder in the manufacturing of artificial fine aggregates using cold-bonded pelletization. Mixture samples were prepared with varying added contents of bottom ash of varying added contents of bottom ash relative to the weight of the cementless binder (= GGBFS + quicklime (CaO) + calcium chloride (CaCl2)). In the system, the added bottom ash was not simply an inert filler but was dissolved at an early stage. As the ionic concentrations of Ca and Si increased due to dissolved bottom ash, calcium silicate hydrate (C-S-H) formed both earlier and at higher levels, which increased the strength of the earlier stages. However, the added bottom ash did not affect the total quantities of main reaction products, C-S-H and hydrocalumite, in later phases (e.g., 28 days), but simply accelerated the binder reaction until it had occurred for 14 days. After considering both the mechanical strength and the pelletizing formability of all the mixtures, the proportion with 40 relative weight of bottom ash was selected for the manufacturing of pilot samples of aggregates. The produced fine aggregates had a water absorption rate of 9.83% and demonstrated a much smaller amount of heavy metal leaching than the raw bottom ash. Full article
(This article belongs to the Special Issue Sustainable Construction Materials: From Paste to Concrete)
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17 pages, 5959 KB  
Article
Comparison of Long-Term Strength Development of Steel Fiber Shotcrete with Cast Concrete Based on Accelerator Type
by Kyong Ku Yun, Seunghak Choi, Taeho Ha, Mohammad Shakhawat Hossain and Seungyeon Han
Materials 2020, 13(24), 5599; https://doi.org/10.3390/ma13245599 - 8 Dec 2020
Cited by 12 | Viewed by 2663
Abstract
This study analyzed the effect of accelerating agents, such as aluminate, cement mineral, and alkali-free accelerators, on the long-term performance of steel-fiber-reinforced shotcrete. The shotcrete performance was studied based on the type and amount of steel fiber added. Performance tests were performed to [...] Read more.
This study analyzed the effect of accelerating agents, such as aluminate, cement mineral, and alkali-free accelerators, on the long-term performance of steel-fiber-reinforced shotcrete. The shotcrete performance was studied based on the type and amount of steel fiber added. Performance tests were performed to identify the accelerator providing better long-term performance to the steel-fiber-reinforced shotcrete. Changes in strength and flexural performance over time were investigated. The compressive strength and flexural strength tests on 1-, 3-, 6-, 12-, and 24-month-old test specimens were performed, wherein 37 kg of steel fiber was added to the cement mineral and aluminate mixes, and 40 kg of steel fiber was added to the alkali-free mix. The 1-month compressive strength result of all the test variables satisfied the Korea Expressway Corporation standard. The compressive strength of the cast concrete and shotcrete specimens increased with age, demonstrating a strength reduction, particularly in the 24-month-old shotcrete specimens. Thus, the shotcrete performance may deteriorate in the long-term. In the 24-month-old specimen, substantial flexural strength reduction was observed, particularly in the aluminate and alkali-free specimens. The relative strength of the specimens was compared with that of the cast concrete mold specimens. The results suggest the use of alkali-free accelerators, considering the long-term performance of tunnels and safety of workers. Moreover, increasing the steel fiber performance rather than the amount of low-performance steel fiber must be considered. Full article
(This article belongs to the Special Issue Concrete and Construction Materials)
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17 pages, 7612 KB  
Article
Analysis on the Effects of External Temperature and Welding Speed on the Safety of EVA Waterproofing Sheet Joints by Hot Air Welding
by Wan-Goo Park, Su-Young Choi, Jin-Sang Park, Dong-Bum Kim, Xing-Yang He and Sang-Keun Oh
Materials 2020, 13(23), 5586; https://doi.org/10.3390/ma13235586 - 7 Dec 2020
Cited by 5 | Viewed by 2646
Abstract
This study analyzes the optimal seasonal ambient temperature during welding and welding speed conditions for securing high tensile strength of ethylene vinyl acetate (EVA) waterproofing sheets bonded for roofing, installed by hot air welded joints (overlaps). Seven separate ambient temperature conditions (−10, −5, [...] Read more.
This study analyzes the optimal seasonal ambient temperature during welding and welding speed conditions for securing high tensile strength of ethylene vinyl acetate (EVA) waterproofing sheets bonded for roofing, installed by hot air welded joints (overlaps). Seven separate ambient temperature conditions (−10, −5, and 0 °C for winter conditions, 20 °C for the normal condition, and 25, 30, and 35 °C for summer conditions) were set for the test variable and seven speed conditions (3, 4, 5, 6, 7, 8, and 9 m/min) for hot air welding. Based on these conditions, EVA sheet joint specimens were prepared, and the tensile strength of the joint sections was tested and measured. Tensile strength results, compared to normal temperature conditions (20 °C) showed an increase in the summer temperature condition but a decrease during winter temperature conditions. The analysis on the effects of the welding speed showed that in summer temperature conditions (25, 30, and 35 °C), the optimum hot air welding speed is 4.3~9.0 m/min at 25 °C, 4.7~8.7 m/min at 30 °C and 5.2~8.6 m/min at 35 °C, whereas in winter (−10, −5, and 0 °C), the optimum hot air welding temperature is 3~4.1 m/min at −10 °C, 3~4.6 m/min at −5 °C and 3~4.9 m/min at 0 °C. Research results demonstrate that it is imperative to consider the welding speed in accordance to the respective seasonal temperature conditions to secure construction quality of the EVA joints for roofing. Full article
(This article belongs to the Special Issue Concrete and Waterproofing Materials: Development of Waterproofing Technology for Buildings and Civil Concrete Structures)
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15 pages, 938 KB  
Review
A Review of Polarization-Sensitive Materials for Polarization Holography
by Yueyang Zhai, Li Cao, Ying Liu and Xiaodi Tan
Materials 2020, 13(23), 5562; https://doi.org/10.3390/ma13235562 - 6 Dec 2020
Cited by 51 | Viewed by 4838
Abstract
Polarization holography has the unique capacity to record and retrieve the amplitude, phase, and polarization of light simultaneously in a polarization-sensitive recording material and has attracted widespread attention. Polarization holography is a noteworthy technology with potential applications in the fields of high-capacity data [...] Read more.
Polarization holography has the unique capacity to record and retrieve the amplitude, phase, and polarization of light simultaneously in a polarization-sensitive recording material and has attracted widespread attention. Polarization holography is a noteworthy technology with potential applications in the fields of high-capacity data storage, polarization-controlled optical elements, and other related fields. The choice of its high-performance materials is particularly important. To further develop polarization holography applications and improve the quality of the information recorded (i.e., material sensitivity and resolution), a deeper understanding of such materials is needed. We present an overview of the polarization-sensitive materials, which introduced polarization holographic technology and the development of polarization holographic materials. The three main types of polarization holographic materials are described, including azopolymer materials, photopolymer material, and photorefractive polymer material. We examine the key contributions of each work and present many of the suggestions that have been made to improve the different polarization-sensitive photopolymer materials. Full article
(This article belongs to the Special Issue Photonic Materials and Devices)
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13 pages, 5272 KB  
Article
Characterization and Optimization of Elastomeric Electrodes for Dielectric Elastomer Artificial Muscles
by Guangqiang Ma, Xiaojun Wu, Lijin Chen, Xin Tong and Weiwei Zhao
Materials 2020, 13(23), 5542; https://doi.org/10.3390/ma13235542 - 4 Dec 2020
Cited by 11 | Viewed by 3214
Abstract
Dielectric elastomer actuators (DEAs) are an emerging type of soft actuation technology. As a fundamental unit of a DEA, the characteristics of compliant electrodes play a crucial role in the actuation performances of DEAs. Generally, the compliant electrodes can be categorized into uncured [...] Read more.
Dielectric elastomer actuators (DEAs) are an emerging type of soft actuation technology. As a fundamental unit of a DEA, the characteristics of compliant electrodes play a crucial role in the actuation performances of DEAs. Generally, the compliant electrodes can be categorized into uncured and cured types, of which the cured one commonly involves mixing conductive particles into an elastomeric matrix before curing, thus demonstrating a better long-term performance. Along with the increasing proportion of conductive particles, the electrical conductivity increases at the cost of a stiffer electrode and lower elongation at break ratio. For different DEA applications, it can be more desirable to minimize the electrode stiffness or to maximize its conductivity. In examination of the papers published in recent years, few works have characterized the effects of elastomeric electrodes on the outputs of DEAs, or of their optimizations under different application scenarios. In this work, we propose an experimental framework to characterize the performances of elastomeric electrodes with different formulas based on the two key parameters of stiffness and conductivity. An optimizing method is developed and verified by two different application cases (e.g., quasi-static and dynamic). The findings and the methods developed in this work can offer potential approaches for developing high-performance DEAs. Full article
(This article belongs to the Section Smart Materials)
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