Materials

12 pages, 6841 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Selective Extraction of Nonfullerene Acceptors from Bulk-Heterojunction Layer in Organic Solar Cells for Detailed Analysis of Microstructure

by Masahiro Nakano, Akira Takahara, Kenji Genda, Md. Shahiduzzaman, Makoto Karakawa, Tetsuya Taima and Kohshin Takahashi

Materials 2021, 14(9), 2107; https://doi.org/10.3390/ma14092107 - 21 Apr 2021

Cited by 3 | Viewed by 2795

Abstract

Detailed analyses of the microstructures of bulk-heterojunction (BHJ) layers are important for the development of high-performance photovoltaic organic solar cells (OSCs). However, analytical methods for BHJ layer microstructures are limited because BHJ films are composed of a complex mixture of donor and acceptor [...] Read more.

Detailed analyses of the microstructures of bulk-heterojunction (BHJ) layers are important for the development of high-performance photovoltaic organic solar cells (OSCs). However, analytical methods for BHJ layer microstructures are limited because BHJ films are composed of a complex mixture of donor and acceptor materials. In our previous study on the microstructure of a BHJ film composed of donor polymers and fullerene-based acceptors, we analyzed donor polymer-only films after selectively extracting fullerene-based acceptors from the film by atomic force microscopy (AFM). Not only was AFM suitable for a clear analysis of the morphology of the donor polymers in the BHJ film, but it also allowed us to approximate the acceptor morphology by analyzing the pores in the extracted films. Herein we report a method for the selective extraction of nonfullerene acceptors (NFAs) from a BHJ layer in OSCs and provide a detailed analysis of the remaining BHJ films based upon AFM. We found that butyl glycidyl ether is an effective solvent to extract NFAs from BHJ films without damaging the donor polymer films. By using the selective extraction method, the morphologies of NFA-free BHJ films fabricated under various conditions were studied in detail. The results may be useful for the optimization of BHJ film structures composed of NFAs and donor polymers. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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17 pages, 4928 KiB

Open AccessEditor’s ChoiceArticle

An Electrochemical and Spectroscopic Study of Surfaces on Bronze Sculptures Exposed to Urban Environment

by Dajana Mikić, Helena Otmačić Ćurković, Tadeja Kosec and Neven Peko

Materials 2021, 14(8), 2063; https://doi.org/10.3390/ma14082063 - 20 Apr 2021

Cited by 8 | Viewed by 3368

Abstract

Polluted urban environment enhances dissolution of patina and underlying bronze material of recent and historical bronze sculptures exposed outdoors. In this work, two bronze statues, situated in one of the most polluted Croatian cities, were examined in order to characterize composition of patina [...] Read more.

Polluted urban environment enhances dissolution of patina and underlying bronze material of recent and historical bronze sculptures exposed outdoors. In this work, two bronze statues, situated in one of the most polluted Croatian cities, were examined in order to characterize composition of patina and its electrochemical stability. The composition of patina on several positions on each sculpture was determined by EDS, Raman spectroscopy, and FTIR measurements. Electrochemical impedance spectroscopy measurements were conducted in order to evaluate the corrosion stability of both patina and underlying bronze. Results obtained in this work show that the two examined bronze sculptures were covered with patina layer that was mainly composed of copper sulfides and sulphates, which is in accordance with the high concentrations of H₂S and SO₂ in the atmosphere. However, the variations in the appearance of FTIR and Raman spectra revealed that the amount of each species differed from spot to spot, as well as the fact that other compounds, such as carbonates, were present at some areas. This difference in patina composition was reflected in electrochemical behavior as observed by electrochemical impedance spectroscopy. Full article

(This article belongs to the Special Issue Surface Modification of Metallic Materials)

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11 pages, 3884 KiB

Open AccessEditor’s ChoiceArticle

Methodology for Selecting the Operating Conditions of a Vibration Generator Used in the Hot-Dip Galvanizing Process

by Wojciech Kacalak, Igor Maciejewski, Dariusz Lipiński and Błażej Bałasz

Materials 2021, 14(8), 2042; https://doi.org/10.3390/ma14082042 - 19 Apr 2021

Viewed by 2550

Abstract

A simulation model and the results of experimental tests of a vibration generator in applications for the hot-dip galvanizing process are presented. The parameters of the work of the asynchronous motor forcing the system vibrations were determined, as well as the degree of [...] Read more.

A simulation model and the results of experimental tests of a vibration generator in applications for the hot-dip galvanizing process are presented. The parameters of the work of the asynchronous motor forcing the system vibrations were determined, as well as the degree of unbalance enabling the vibrations of galvanized elements weighing up to 500 kg to be forced. Simulation and experimental tests of the designed and then constructed vibration generator were carried out at different intensities of the unbalanced rotating mass of the motor. Based on the obtained test results, the generator operating conditions were determined at which the highest values of the amplitude of vibrations transmitted through the suspension system to the galvanized elements were obtained. Full article

(This article belongs to the Special Issue Computational and Experimental Mechanics of Engineering Materials and Structures)

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12 pages, 944 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Silica and Silica–Titania Xerogels Doped with Iron(III) for Total Antioxidant Capacity Determination

by Maria A. Morosanova, Ksenia V. Chaikun and Elena I. Morosanova

Materials 2021, 14(8), 2019; https://doi.org/10.3390/ma14082019 - 17 Apr 2021

Cited by 6 | Viewed by 2155

Abstract

In order to design a sensor material for total antioxidant capacity determination we have prepared silica and silica–titania xerogels doped with iron(III) and modified with 1,10-phenanthroline. Titanium(IV) tetraethoxyde content in the precursors (titanium(IV) tetraethoxyde and tetraethyl orthosilicate) mixtures has been varied from 0 [...] Read more.

In order to design a sensor material for total antioxidant capacity determination we have prepared silica and silica–titania xerogels doped with iron(III) and modified with 1,10-phenanthroline. Titanium(IV) tetraethoxyde content in the precursors (titanium(IV) tetraethoxyde and tetraethyl orthosilicate) mixtures has been varied from 0 to 12.5% vol. Iron(III) concentrations in sol has been varied from 1 to 100 mM. The increase of titanium(IV) content has led to a decrease in BET surface area and average pore diameter and an increase of micropore surface area and volume, which has resulted in better iron(III) retention in the xerogels. Iron(III), immobilized in the xerogel matrix, retains its ability to form complexes with 1,10-phenanthroline and to be reduced to iron(II). Static capacities for 1,10-phenanthroline have been determined for all the iron(III) doped xerogels (0.207 mmol/g–0.239 mmol/g) and they are not dependent on the iron(III) content. Sensor materials—xerogels doped with iron(III) and modified with 1,10-phenanthroline—have been used for antioxidants (catechol, gallic and ascorbic acids, and sulphite) solid phase spectrophotometric determination. Limits of detection for catechol, gallic and ascorbic acids, and sulphite equal 7.8 × 10⁻⁶ M, 5.4 × 10⁻⁶ M, 1.2 × 10⁻⁵ M, and 3.1 × 10⁻⁴ M, respectively. The increase of titanium(IV) content in sensor material has led to an increase of the reaction rate and the sensitivity of determination. Proposed sensor materials have been applied for total antioxidant capacity (in gallic acid equivalents) determination in soft beverages, have demonstrated high stability, and can be stored up to 6 months at room temperature. Full article

(This article belongs to the Special Issue Sol-Gel-Derived Materials)

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14 pages, 5343 KiB

Open AccessEditor’s ChoiceArticle

Fracture Parameters and Cracking Propagation of Cold Recycled Mixture Considering Material Heterogeneity Based on Extended Finite Element Method

by Lei Gao, Xingkuan Deng, Ye Zhang, Xue Ji and Qiang Li

Materials 2021, 14(8), 1993; https://doi.org/10.3390/ma14081993 - 16 Apr 2021

Cited by 6 | Viewed by 2086

Abstract

Cold recycled mixture (CRM) has been widely used around the world mainly because of its good ability to resist reflection cracking. In this study, mixed-mode cracking tests were carried out by the designed rotary test device to evaluate the cracking resistance of CRM. [...] Read more.

Cold recycled mixture (CRM) has been widely used around the world mainly because of its good ability to resist reflection cracking. In this study, mixed-mode cracking tests were carried out by the designed rotary test device to evaluate the cracking resistance of CRM. Through the finite element method, the heterogeneous model of CRM based on its meso-structure was established. The cracking process of CRM was simulated using the extended finite element method, and the influence of different notch lengths on its anti-cracking performance was studied. The results show that the mixed-mode fracture test method can effectively evaluate the cracking resistance of CRM by the proposed fracture parameters. The virtual tests under three of five kinds of mixed-cracking modes have good simulation to capture the cracking behavior of CRM. The effect of notch length on the initial crack angle and the crack propagation process of the CRM is mainly related to the distribution characteristics of its meso-structure. With the increase of the proportion of Mode II cracking, the crack development path gradually deviates, and the failure elements gradually increase. At any mixed-mode level, there is an obvious linear relationship between the peak load, fracture energy, and the notch length. Full article

(This article belongs to the Special Issue Temperature Reduction Technologies Meet Asphalt Pavement: Green and Sustainability)

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13 pages, 4037 KiB

Open AccessEditor’s ChoiceArticle

Ultraviolet Luminescence of ZnO Whiskers, Nanowalls, Multipods, and Ceramics as Potential Materials for Fast Scintillators

by Ivan D. Venevtsev, Andrey P. Tarasov, Arsen E. Muslimov, Elena I. Gorokhova, Ludmila A. Zadorozhnaya, Piotr A. Rodnyi and Vladimir M. Kanevsky

Materials 2021, 14(8), 2001; https://doi.org/10.3390/ma14082001 - 16 Apr 2021

Cited by 13 | Viewed by 2354

Abstract

The presented work is dedicated to the study and comparison of scintillating properties of zinc oxide samples prepared in different morphologies: whiskers, nanowalls, multipods, and ceramics. It was shown that total transmittance, photo- and radioluminescence spectra, and radioluminescence kinetics can vary significantly depending [...] Read more.

The presented work is dedicated to the study and comparison of scintillating properties of zinc oxide samples prepared in different morphologies: whiskers, nanowalls, multipods, and ceramics. It was shown that total transmittance, photo- and radioluminescence spectra, and radioluminescence kinetics can vary significantly depending on sample structure and preparation conditions. The highest total transmittance was registered for ZnO ceramics (>50% at 0.5 mm thickness). Differences in the transmittance of whiskers, nanowalls, and multipods can be attributed to their shape and thickness which affects the amount of light refraction and scattering. The study of radioluminescence demonstrated that all samples, except undoped ceramics and air annealed whiskers, have predominantly fast luminescence with a decay time <1 ns. High transmittance of ceramics opens the way for their use in the registration of high energy X-ray and gamma radiation, where a large volume of scintillators is required. In cases, where large scintillator thickness is not a necessity, one may prefer to use other ZnO structures, such as ensembles of whiskers and nanowalls. Studies of near-band-edge luminescence components at low temperatures showed that the structure is quite similar in all samples except Ga doped ceramics. Full article

(This article belongs to the Special Issue ZnO Materials: Synthesis, Properties and Applications)

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12 pages, 11588 KiB

Open AccessEditor’s ChoiceArticle

Preparation and Thermal Conductivity of Epoxy Resin/Graphene-Fe₃O₄ Composites

by Zhong Wu, Jingyun Chen, Qifeng Li, Da-Hai Xia, Yida Deng, Yiwen Zhang and Zhenbo Qin

Materials 2021, 14(8), 2013; https://doi.org/10.3390/ma14082013 - 16 Apr 2021

Cited by 11 | Viewed by 3253

Abstract

By modifying the bonding of graphene (GR) and Fe₃O₄, a stable structure of GR-Fe₃O₄, namely magnetic GR, was obtained. Under the induction of a magnetic field, it can be orientated in an epoxy resin (EP) [...] Read more.

By modifying the bonding of graphene (GR) and Fe₃O₄, a stable structure of GR-Fe₃O₄, namely magnetic GR, was obtained. Under the induction of a magnetic field, it can be orientated in an epoxy resin (EP) matrix, thus preparing EP/GR-Fe₃O₄ composites. The effects of the content of GR and the degree of orientation on the thermal conductivity of the composites were investigated, and the most suitable Fe₃O₄ load on GR was obtained. When the mass ratio of GR and Fe₃O₄ was 2:1, the thermal conductivity could be increased by 54.8% compared with that of pure EP. Meanwhile, EP/GR-Fe₃O₄ composites had a better thermal stability, dynamic thermomechanical properties, and excellent electrical insulation properties, which can meet the requirements of electronic packaging materials. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics)

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15 pages, 2696 KiB

Open AccessEditor’s ChoiceArticle

3D PCL/Gelatin/Genipin Nanofiber Sponge as Scaffold for Regenerative Medicine

by Markus Merk, Orlando Chirikian and Christian Adlhart

Materials 2021, 14(8), 2006; https://doi.org/10.3390/ma14082006 - 16 Apr 2021

Cited by 20 | Viewed by 5599

Abstract

Recent advancements in tissue engineering and material science have radically improved in vitro culturing platforms to more accurately replicate human tissue. However, the transition to clinical relevance has been slow in part due to the lack of biologically compatible/relevant materials. In the present [...] Read more.

Recent advancements in tissue engineering and material science have radically improved in vitro culturing platforms to more accurately replicate human tissue. However, the transition to clinical relevance has been slow in part due to the lack of biologically compatible/relevant materials. In the present study, we marry the commonly used two-dimensional (2D) technique of electrospinning and a self-assembly process to construct easily reproducible, highly porous, three-dimensional (3D) nanofiber scaffolds for various tissue engineering applications. Specimens from biologically relevant polymers polycaprolactone (PCL) and gelatin were chemically cross-linked using the naturally occurring cross-linker genipin. Potential cytotoxic effects of the scaffolds were analyzed by culturing human dermal fibroblasts (HDF) up to 23 days. The 3D PCL/gelatin/genipin scaffolds produced here resemble the complex nanofibrous architecture found in naturally occurring extracellular matrix (ECM) and exhibit physiologically relevant mechanical properties as well as excellent cell cytocompatibility. Samples cross-linked with 0.5% genipin demonstrated the highest metabolic activity and proliferation rates for HDF. Scanning electron microscopy (SEM) images indicated excellent cell adhesion and the characteristic morphological features of fibroblasts in all tested samples. The three-dimensional (3D) PCL/gelatin/genipin scaffolds produced here show great potential for various 3D tissue-engineering applications such as ex vivo cell culturing platforms, wound healing, or tissue replacement. Full article

(This article belongs to the Special Issue Organic Nanofibers: Fabrication, Properties and Applications)

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16 pages, 4932 KiB

Open AccessEditor’s ChoiceArticle

A Model Procedure for Catalytic Conversion of Waste Cotton into Useful Chemicals

by Michal J. Binczarski, Justyna Malinowska, Andrei Stanishevsky, Courtney J. Severino, Riley Yager, Malgorzata Cieslak and Izabela A. Witonska

Materials 2021, 14(8), 1981; https://doi.org/10.3390/ma14081981 - 15 Apr 2021

Cited by 6 | Viewed by 2859

Abstract

Cotton is grown in about 90 countries and accounts for 24% of the fibers used in the global production of textiles. In 2018/2019, 25.8 Mt of cotton were produced around the world. Since this natural product consists mainly of cellulose, it can be [...] Read more.

Cotton is grown in about 90 countries and accounts for 24% of the fibers used in the global production of textiles. In 2018/2019, 25.8 Mt of cotton were produced around the world. Since this natural product consists mainly of cellulose, it can be used as a raw material in the so-called “sugar economy”. This paper discusses a model procedure for thermally assisted acidic hydrolysis of cotton into glucose and subsequent oxidation of the glucose into calcium gluconate over Pd-Au/SiO₂ catalyst. In the first step, H₂SO₄ was used as a catalyst for hydrolysis. The cotton hydrolysates were neutralized using CaCO₃ and applied as a substrate in the second step, where glucose was oxidized over Pd-Au/SiO₂ prepared by ultrasound assisted co-impregnation. With the appropriate Au/Pd molar ratio, small crystallites of palladium and gold were created which were active and selective towards the formation of gluconate ions. This approach to the transformation of glucose represents as a viable alternative to biological processes using fungal and bacterial species, which are sensitive to the presence of inhibitors such as furfurals and levulinic acid in hydrolysates. Full article

(This article belongs to the Special Issue Green Synthesis and Transformation in Material Science)

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22 pages, 6950 KiB

Open AccessEditor’s ChoiceArticle

Corrosion Protection of Q235 Steel Using Epoxy Coatings Loaded with Calcium Carbonate Microparticles Modified by Sodium Lignosulfonate in Simulated Concrete Pore Solutions

by Weilin Liu, Jiansan Li, Xiangqi Huang and Jinye Bi

Materials 2021, 14(8), 1982; https://doi.org/10.3390/ma14081982 - 15 Apr 2021

Cited by 25 | Viewed by 3710

Abstract

In this study, calcium carbonate (CaCO₃) microparticles having pH-sensitive properties were loaded with sodium lignosulfonate (SLS), a corrosion inhibitor. Scanning electron microscope (SEM), UV–VIS spectrophotometer (UV-vis), X-ray diffraction (XRD), and attenuated total reflection-Fourier-transform infrared spectroscopy (ATR-FTIR) were applied to evaluate the [...] Read more.

In this study, calcium carbonate (CaCO₃) microparticles having pH-sensitive properties were loaded with sodium lignosulfonate (SLS), a corrosion inhibitor. Scanning electron microscope (SEM), UV–VIS spectrophotometer (UV-vis), X-ray diffraction (XRD), and attenuated total reflection-Fourier-transform infrared spectroscopy (ATR-FTIR) were applied to evaluate the properties of the synthetic microparticles. This material could lead to the release of corrosion inhibitor under different pH conditions of the aqueous media. However, the extent of release of the corrosion inhibitor in the acidic media was higher, leading to enhanced shielding effect of the Q235 steel. These microparticles can serve as anti-corrosion additive for epoxy resin-coated Q235 steel. Electrochemical experiments were used to assess the anti-corrosive ability of the epoxy coatings in simulated concrete pore (SCP) solution, confirming the superior corrosion inhibition of the epoxy coating via incorporation of 5 wt % calcium carbonate microparticles loaded with SLS (SLS/CaCO₃). The physical properties of coating specimens were characterized by water absorption, contact angle, adhesion, and pencil hardness mechanical tests. Full article

(This article belongs to the Special Issue Corrosion of Reinforced Concrete Structures in Civil Engineering and Architecture)

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13 pages, 2888 KiB

Open AccessEditor’s ChoiceArticle

Highly Porous and Ultra-Lightweight Aero-Ga₂O₃: Enhancement of Photocatalytic Activity by Noble Metals

by Irina Plesco, Vladimir Ciobanu, Tudor Braniste, Veaceslav Ursaki, Florian Rasch, Andrei Sarua, Simion Raevschi, Rainer Adelung, Joydeep Dutta and Ion Tiginyanu

Materials 2021, 14(8), 1985; https://doi.org/10.3390/ma14081985 - 15 Apr 2021

Cited by 15 | Viewed by 3080

Abstract

A new type of photocatalyst is proposed on the basis of aero-β-Ga₂O₃, which is a material constructed from a network of interconnected tetrapods with arms in the form of microtubes with nanometric walls. The aero-Ga₂O₃ material [...] Read more.

A new type of photocatalyst is proposed on the basis of aero-β-Ga₂O₃, which is a material constructed from a network of interconnected tetrapods with arms in the form of microtubes with nanometric walls. The aero-Ga₂O₃ material is obtained by annealing of aero-GaN fabricated by epitaxial growth on ZnO microtetrapods. The hybrid structures composed of aero-Ga₂O₃ functionalized with Au or Pt nanodots were tested for the photocatalytic degradation of methylene blue dye under UV or visible light illumination. The functionalization of aero-Ga₂O₃ with noble metals results in the enhancement of the photocatalytic performances of bare material, reaching the performances inherent to ZnO while gaining the advantage of the increased chemical stability. The mechanisms of enhancement of the photocatalytic properties by activating aero-Ga₂O₃ with noble metals are discussed to elucidate their potential for environmental applications. Full article

(This article belongs to the Special Issue Properties of Interfaced Materials and Films)

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18 pages, 108991 KiB

Open AccessEditor’s ChoiceArticle

Assessment of the Dimensional and Geometric Precision of Micro-Details Produced by Material Jetting

by Miguel R. Silva, António M. Pereira, Álvaro M. Sampaio and António J. Pontes

Materials 2021, 14(8), 1989; https://doi.org/10.3390/ma14081989 - 15 Apr 2021

Cited by 8 | Viewed by 2932

Abstract

Additive Manufacturing (AM) technology has been increasing its penetration not only for the production of prototypes and validation models, but also for final parts. This technology allows producing parts with almost no geometry restrictions, even on a micro-scale. However, the micro-Detail (mD) measurement [...] Read more.

Additive Manufacturing (AM) technology has been increasing its penetration not only for the production of prototypes and validation models, but also for final parts. This technology allows producing parts with almost no geometry restrictions, even on a micro-scale. However, the micro-Detail (mD) measurement of complex parts remains an open field of investigation. To be able to develop all the potential that this technology offers, it is necessary to quantify a process’s precision limitations, repeatability, and reproducibility. New design methodologies focus on optimization, designing microstructured parts with a complex material distribution. These methodologies are based on mathematical formulations, whose numerical models assume the model discretization through volumetric unitary elements (voxels) with explicit dimensions and geometries. The accuracy of these models in predicting the behavior of the pieces is influenced by the fidelity of the object’s physical reproduction. Despite that the Material Jetting (MJ) process makes it possible to produce complex parts, it is crucial to experimentally establish the minimum dimensional and geometric limits to produce parts with mDs. This work aims to support designers and engineers in selecting the most appropriate scale to produce parts discretized by hexahedral meshes (cubes). This study evaluated the dimensional and geometric precision of MJ equipment in the production of mDs (cubes) comparing the nominal design dimensions. A Sample Test (ST) with different sizes of mDs was modeled and produced. The dimensional and geometric precision of the mDs were quantified concerning the nominal value and the calculated deviations. From the tests performed, it was possible to conclude that: (i) more than 90% of all analyzed mDs exhibit three dimensions (xyz) higher than the nominal ones; (ii) for micro-details smaller than 423 μm, they show a distorted geometry, and below 212 μm, printing fails. Full article

(This article belongs to the Special Issue Additive Manufacturing Materials and Their Applications)

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18 pages, 1551 KiB

Open AccessEditor’s ChoiceArticle

Study of Optimal Cam Design of Dual-Axle Spring-Loaded Camming Device

by David Rybansky, Martin Sotola, Pavel Marsalek, Zdenek Poruba and Martin Fusek

Materials 2021, 14(8), 1940; https://doi.org/10.3390/ma14081940 - 13 Apr 2021

Cited by 8 | Viewed by 4305

Abstract

The spring-loaded camming device (SLCD), also known as “friend”, is a simple mechanism used to ensure the safety of the climber through fall prevention. SLCD consists of two pairs of opposing cams rotating separately, with one (single-axle SLCD) or two (dual-axle SLCD) pins [...] Read more.

The spring-loaded camming device (SLCD), also known as “friend”, is a simple mechanism used to ensure the safety of the climber through fall prevention. SLCD consists of two pairs of opposing cams rotating separately, with one (single-axle SLCD) or two (dual-axle SLCD) pins connecting the opposing cams, a stem, connected to the pins, providing the attachment of the climbing rope, springs, which simultaneously push cams to a fully expanded position, and an operating element controlling the cam position. The expansion of cams is thus adaptable to allow insertion or removal of the device into/from a rock crack. While the pins, stem, operating element, and springs can be considered optimal, the (especially internal) shape of the cam allows space for improvement, especially where the weight is concerned. This paper focuses on optimizing the internal shape of the dual-axle SLCD cam from the perspective of the weight/stiffness trade-off. For this purpose, two computational models are designed and multi-step topology optimization (TOP) are performed. From the computational models’ point of view, SLCD is considered symmetric and only one cam is optimized and smoothened using parametric curves. Finally, the load-bearing capacity of the new cam design is analyzed. This work is based on practical industry requirements, and the obtained results will be reflected in a new commercial design of SLCD. Full article

(This article belongs to the Special Issue Manufacturing and Mechanics of Materials)

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23 pages, 7050 KiB

Open AccessEditor’s ChoiceArticle

Size-Induced Constraint Effects on Crack Initiation and Propagation Parameters in Ductile Polymers

by Anja Gosch, Florian Josef Arbeiter, Silvia Agnelli, Michael Berer and Francesco Baldi

Materials 2021, 14(8), 1945; https://doi.org/10.3390/ma14081945 - 13 Apr 2021

Cited by 3 | Viewed by 2044

Abstract

Fracture mechanics are of high interest for the engineering design and structural integrity assessment of polymeric materials; however, regarding highly ductile polymers, many open questions still remain in terms of fully understanding deformation and fracture behaviors. For example, the influence of the constraint [...] Read more.

Fracture mechanics are of high interest for the engineering design and structural integrity assessment of polymeric materials; however, regarding highly ductile polymers, many open questions still remain in terms of fully understanding deformation and fracture behaviors. For example, the influence of the constraint and specimen size on the fracture behavior of polymeric materials is still not clear. In this study, a polymeric material with an elastic plastic deformation behavior (ABS, acrylonitrile butadiene styrene) is investigated with regard to the influence of constraint and specimen size. Different single-edge notched bending (SENB) specimen sizes with constant geometrical ratios were tested. The material key curve was used to investigate differences in the constraint, where changes for small and large specimen sizes were found. Based on a size-independent crack resistance curve (J–R curve), two apparent initiation parameters (J_0.2 and J_bl) were determined, namely, the initiation parameter J_ini (based on the crack propagation kinetics curve) and the initiation parameter J_I,lim (based on an ESIS TC 4 draft protocol). It was found that J_0.2 and J_bl could be used as crack initiation parameters whereby J_ini and J_I,lim are indicative of the onset of stable crack growth. Full article

(This article belongs to the Special Issue Fracture Mechanics Investigation of Polymeric Materials)

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16 pages, 7366 KiB

Open AccessEditor’s ChoiceArticle

Effect of Stirring Pin Rotation Speed on Microstructure and Mechanical Properties of 2A14-T4 Alloy T-Joints Produced by Stationary Shoulder Friction Stir Welding

by Haifeng Yang, Hongyun Zhao, Xinxin Xu, Li Zhou, Huihui Zhao and Huijie Liu

Materials 2021, 14(8), 1938; https://doi.org/10.3390/ma14081938 - 13 Apr 2021

Cited by 8 | Viewed by 2321

Abstract

In this study, 2A14-T4 Al-alloy T-joints were prepared via stationary shoulder friction stir welding (SSFSW) technology where the stirring pin’s rotation speed was set as different values. In combination with the numerical simulation results, the macro-forming, microstructure, and mechanical properties of the joints [...] Read more.

In this study, 2A14-T4 Al-alloy T-joints were prepared via stationary shoulder friction stir welding (SSFSW) technology where the stirring pin’s rotation speed was set as different values. In combination with the numerical simulation results, the macro-forming, microstructure, and mechanical properties of the joints under different welding conditions were analyzed. The results show that the thermal cycle curves in the SSFSW process are featured by a steep climb and slow decreasing variation trends. As the stirring pin’s rotation speed increased, the grooves on the weld surface became more obvious. The base and rib plates exhibit W- or N-shaped hardness distribution patterns. The hardness of the weld nugget zone (WNZ) was high but was lower than that of the base material. The second weld’s annealing effect contributed to the precipitation and coarsening of the precipitated phase in the first weld nugget zone (WNZ1). The hardness of the heat affect zone (HAZ) in the vicinity of the thermo-mechanically affected zone (TMAZ) dropped to the minimum. As the stirring pin's rotation speed increased, the tensile strengths of the base and rib plates first increased and then dropped. The base and rib plates exhibited ductile and brittle/ductile fracture patterns, respectively. Full article

(This article belongs to the Special Issue Additive Manufactured Metals, Polymers and Hybrid Materials for Engineering Applications)

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20 pages, 4285 KiB

Open AccessEditor’s ChoiceArticle

Parametric Optimization for Improving the Machining Process of Cu/Mo-SiC_P Composites Produced by Powder Metallurgy

by Emine Şap, Üsame Ali Usca, Munish Kumar Gupta, Mustafa Kuntoğlu, Murat Sarıkaya, Danil Yurievich Pimenov and Mozammel Mia

Materials 2021, 14(8), 1921; https://doi.org/10.3390/ma14081921 - 12 Apr 2021

Cited by 48 | Viewed by 3754

Abstract

The features of composite materials such as production flexibility, lightness, and excellent strength put them in the class of materials that attract attention in various critical areas, i.e., aerospace, defense, automotive, and shipbuilding. However, the machining of composite materials displays challenges due to [...] Read more.

The features of composite materials such as production flexibility, lightness, and excellent strength put them in the class of materials that attract attention in various critical areas, i.e., aerospace, defense, automotive, and shipbuilding. However, the machining of composite materials displays challenges due to the difficulty in obtaining structural integrity. In this study, Cu/Mo-SiC_P composite materials were produced by powder metallurgy with varied reinforcement ratios and then their machinability was investigated. In machinability experiments, the process parameters were selected as cutting speed (v_C), feed rate (f), depth of cut (a_P), and reinforcement ratio (R_R). Two levels of these parameters were taken as per the Taguchi’s L8 orthogonal array, and response surface methodology (RSM) is employed for parametric optimization. As a result, the outcomes demonstrated that R_R = 5%, f = 0.25 mm/rev, a_P = 0.25 mm, v_C = 200 m/min for surface roughness, R_R = 0%, f = 0.25 mm/rev and a_P = 0.25 mm and v_C = 200 m/min for flank wear and R_R = 0%, f = 0.25 mm/rev, a_P = 0.25 mm, v_C = 150 m/min for cutting temperature for cutting temperature and flank wear should be selected for the desired results. In addition, ANOVA results indicate that reinforcement ratio is the dominant factor on all response parameters. Microscope images showed that the prominent failure modes on the cutting tool are flank wear, built up edge, and crater wear depending on reinforcement ratio. Full article

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

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13 pages, 3949 KiB

Open AccessEditor’s ChoiceArticle

Giant Stress-Impedance Effect in CoFeNiMoBSi Alloy in Variation of Applied Magnetic Field

by Piotr Gazda and Michał Nowicki

Materials 2021, 14(8), 1919; https://doi.org/10.3390/ma14081919 - 12 Apr 2021

Cited by 5 | Viewed by 2216

Abstract

The article presents the stress impedance investigation of CoFeNiMoBSi alloy in variation of the applied magnetic field. In order to carry out the study, a specialized stand was developed that allows for loading the sample with stresses and simultaneous action of the DC [...] Read more.

The article presents the stress impedance investigation of CoFeNiMoBSi alloy in variation of the applied magnetic field. In order to carry out the study, a specialized stand was developed that allows for loading the sample with stresses and simultaneous action of the DC (direct current) magnetizing field. The tests were carried out for as-cast and Joule annealed samples. The significant influence of the magnetizing field acting on the sample on the stress-impedance results was demonstrated and the dependence of the maximum impedance change in the stress-impedance effect was determined, depending on the field acting. The obtained results are important due to the potential use of the stress-impedance effect for the construction of stress sensors. Full article

(This article belongs to the Collection Magnetoelastic Materials)

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20 pages, 8332 KiB

Open AccessEditor’s ChoiceArticle

Characterizing Depth of Defects with Low Size/Depth Aspect Ratio and Low Thermal Reflection by Using Pulsed IR Thermography

by Alexey I. Moskovchenko, Michal Švantner, Vladimir P. Vavilov and Arsenii O. Chulkov

Materials 2021, 14(8), 1886; https://doi.org/10.3390/ma14081886 - 10 Apr 2021

Cited by 11 | Viewed by 2471

Abstract

This study is focused on the quantitative estimation of defect depth by applying pulsed thermal nondestructive testing. The majority of known defect characterization techniques are based on 1D heat conduction solutions, thus being inappropriate for evaluating defects with low aspect ratios. A novel [...] Read more.

This study is focused on the quantitative estimation of defect depth by applying pulsed thermal nondestructive testing. The majority of known defect characterization techniques are based on 1D heat conduction solutions, thus being inappropriate for evaluating defects with low aspect ratios. A novel method for estimating defect depth is proposed by taking into account the phenomenon of 3D heat diffusion, finite lateral size of defects and the thermal reflection coefficient at the boundary between a host material and defects. The method is based on the combination of a known analytical model and a non-linear fitting (NLF) procedure. The algorithm was verified both numerically and experimentally on 3D-printed polylactic acid plastic samples. The accuracy of depth prediction using the proposed method was compared with the reference characterization technique based on thermographic signal reconstruction to demonstrate the efficiency of the proposed NLF method. Full article

(This article belongs to the Special Issue Thermography Technique in Materials Science)

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35 pages, 4238 KiB

Open AccessEditor’s ChoiceArticle

Essential Material Knowledge and Recent Model Developments for REBCO-Coated Conductors in Electric Power Systems

by Frederic Trillaud, Gabriel dos Santos and Guilherme Gonçalves Sotelo

Materials 2021, 14(8), 1892; https://doi.org/10.3390/ma14081892 - 10 Apr 2021

Cited by 14 | Viewed by 4874

Abstract

The manufacturing of commercial REBCO tapes, REBCO referring to Rare-earth barium copper oxide, has matured enough to lead to a variety of applications ranging from scientific instruments to electric power systems. In particular, its large current density with a high n index and [...] Read more.

The manufacturing of commercial REBCO tapes, REBCO referring to Rare-earth barium copper oxide, has matured enough to lead to a variety of applications ranging from scientific instruments to electric power systems. In particular, its large current density with a high n index and low hysteresis losses make it a strong candidate for specific applications relying on the dependence of its resistance on current. Despite its advantages, there are still issues that remain to be addressed, such as the scarcity of experimental data for the basic characteristics of the superconductor over a wide range of temperature and applied magnetic field, the inhomogeneity of these characteristics along the conductor length, as well as the anisotropy of the critical current and n index with respect to the direction of the applied magnetic field. To better utilize the technology, it is therefore sensible to understand the relevancy of these issues so that one could simulate as accurately as possible the physics of the superconductor, at least the dynamics that may impact the correct operation of the superconducting device. There are different levels of modelling to achieve such a goal that can either focus on the performance of the superconductor itself, or on the whole device. The present work addresses some of the latest developments in the modelling of commercial REBCO tapes in power systems with a particular focus on the thermoelectric behavior of superconducting devices connected to external circuits. Two very different approaches corresponding to two different scales in the modelling of superconducting devices are presented: (1) analysis using equivalent models and lumped parameters to study the thermoelectric response of superconducting devices as a whole, (2) Finite Element Analysis (FEA) to compute distributed fields such as current density, magnetic flux density and local losses in tapes. In this context, this paper reviews both approaches and gives a broad variety of examples to show their practical applications in electric power systems. Firstly, they show the relevance of the technology in power systems engineering. Secondly, they allow inferring the necessary level of model details to optimize the operation of superconducting power devices in power grids. This level of details relies completely on the knowledge of some basic measurable properties of superconducting tapes (critical current and n index) and their cooling conditions. Full article

(This article belongs to the Special Issue Superconducting Materials for Applications)

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13 pages, 2688 KiB

Open AccessEditor’s ChoiceArticle

Grain-to-Grain Interaction Effect in Polycrystalline Plain Low-Carbon Steel within Elastic Deformation Region

by Hai Qiu, Rintaro Ueji, Yuuji Kimura and Tadanobu Inoue

Materials 2021, 14(8), 1865; https://doi.org/10.3390/ma14081865 - 9 Apr 2021

Cited by 2 | Viewed by 2261

Abstract

A grain is surrounded by grains with different crystal orientations in polycrystalline plain low-carbon steel. The grain is constrained by its adjacent grains in the tension process. The interaction of the grain with the adjacent grains was investigated within the elastic deformation region. [...] Read more.

A grain is surrounded by grains with different crystal orientations in polycrystalline plain low-carbon steel. The grain is constrained by its adjacent grains in the tension process. The interaction of the grain with the adjacent grains was investigated within the elastic deformation region. The following results have been obtained: (1) the Young’s modulus of a grain without consideration of grain-to-grain interaction is denoted as the inherent Young’s modulus; when the inherent Young’s modulus of a grain is equal to the Young’s modulus of the bulk material, there is almost no interaction between the grain and its adjacent grains; when a grain has a great difference between its inherent Young’s modulus and the Young’s modulus of the bulk material, its grain-to-grain interactions increase significantly; (2) the grain-to-grain interaction is mainly caused by the difference in the inherent Young’s modulus between the grain and its adjacent grains; the misorientation angle between the grain and its adjacent grains has almost no effect on the grain-to-grain interaction. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties Relationship for Metallic Materials)

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18 pages, 5086 KiB

Open AccessEditor’s ChoiceArticle

Size-Dependent Filtration Efficiency of Alternative Facemask Filter Materials

by David I. A. Dhanraj, Shruti Choudhary, Udayabhanu Jammalamadaka, David H. Ballard, Benjamin M. Kumfer, Audrey J. Dang, Brent J. Williams, Kathleen W. Meacham, Richard L. Axelbaum and Pratim Biswas

Materials 2021, 14(8), 1868; https://doi.org/10.3390/ma14081868 - 9 Apr 2021

Cited by 11 | Viewed by 5614

Abstract

The use of facemasks is proven to mitigate the spread of the coronavirus and other biological agents that cause disease. Various forms of facemasks, made using different materials, are being used extensively, and it is important to determine their performance characteristics. The size-dependent [...] Read more.

The use of facemasks is proven to mitigate the spread of the coronavirus and other biological agents that cause disease. Various forms of facemasks, made using different materials, are being used extensively, and it is important to determine their performance characteristics. The size-dependent filtration efficiency and breathing resistance of household sterilization wrap fabrics, and isolation media (American Society for Testing and Materials (ASTM)- and non-ASTM-rated), were measured in filter-holder- and mannequin-in-chamber-based systems, focusing on particles sizes between 20 nm and 2 μm. Double-layer MERV-14 (Minimum Efficiency Reporting Values with rating 14) showed the highest filtration efficiency (94.9–73.3%) amongst household filter media, whereas ASTM-rated isolation masks showed the highest filtration efficiencies (95.6–88.7) amongst all the masks considered. Filtration efficiency of 3D-printed masks with replaceable filter media was found to depend on the degree of sealing around the media holder, which depended on the material’s compressibility. Filtration efficiencies of triple-layer combinations (95.8–85.3%) follow a profile similar to single layers but with improved filtration efficiencies. Full article

(This article belongs to the Special Issue Personal Protective Materials (PPMs) re COVID-19)

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20 pages, 2329 KiB

Open AccessEditor’s ChoiceArticle

The Role of Hydrogen Bonding in Paracetamol–Solvent and Paracetamol–Hydrogel Matrix Interactions

by Marta Miotke-Wasilczyk, Marek Józefowicz, Justyna Strankowska and Jerzy Kwela

Materials 2021, 14(8), 1842; https://doi.org/10.3390/ma14081842 - 8 Apr 2021

Cited by 5 | Viewed by 2535

Abstract

The photophysical and photochemical properties of antipyretic drug – paracetamol (PAR) and its two analogs with different substituents (acetanilide (ACT) and N-ethylaniline (NEA)) in 14 solvents of different polarity were investigated by the use of steady–state spectroscopic technique and quantum–chemical calculations. As [...] Read more.

The photophysical and photochemical properties of antipyretic drug – paracetamol (PAR) and its two analogs with different substituents (acetanilide (ACT) and N-ethylaniline (NEA)) in 14 solvents of different polarity were investigated by the use of steady–state spectroscopic technique and quantum–chemical calculations. As expected, the results show that the spectroscopic behavior of PAR, ACT, and NEA is highly dependent on the nature of the solute–solvent interactions (non-specific (dipole-dipole) and specific (hydrogen bonding)). To characterize these interactions, the multiparameter regression analysis proposed by Catalán was used. In order to obtain a deeper insight into the electronic and optical properties of the studied molecules, the difference of the dipole moments of a molecule in the ground and excited state were determined using the theory proposed by Lippert, Mataga, McRae, Bakhshiev, Bilot, and Kawski. Additionally, the influence of the solute polarizability on the determined dipole moments was discussed. The results of the solvatochromic studies were related to the observations of the release kinetics of PAR, ACT, and NEA from polyurethane hydrogels. The release kinetics was analyzed using the Korsmayer-Peppas and Hopfenberg models. Finally, the influence of the functional groups of the investigated compounds on the release time from the hydrogel matrix was analyzed. Full article

(This article belongs to the Section Materials Physics)

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15 pages, 4671 KiB

Open AccessEditor’s ChoiceArticle

Utilizing Iron Ore Tailing as Cementitious Material for Eco-Friendly Design of Ultra-High Performance Concrete (UHPC)

by Gang Ling, Zhonghe Shui, Xu Gao, Tao Sun, Rui Yu and Xiaosheng Li

Materials 2021, 14(8), 1829; https://doi.org/10.3390/ma14081829 - 7 Apr 2021

Cited by 34 | Viewed by 3766

Abstract

In this research, iron ore tailing (IOT) is utilized as the cementitious material to develop an eco-friendly ultra-high performance concrete (UHPC). The UHPC mix is obtained according to the modified Andreasen and Andersen (MAA) packing model, and the applied dosage of IOT is [...] Read more.

In this research, iron ore tailing (IOT) is utilized as the cementitious material to develop an eco-friendly ultra-high performance concrete (UHPC). The UHPC mix is obtained according to the modified Andreasen and Andersen (MAA) packing model, and the applied dosage of IOT is 10%, 20%, and 30% (by weight), respectively. The calculated packing density of different mixtures is consistent with each other. Afterwards, the fresh and hardened performance of UHPC mixtures with IOT are evaluated. The results demonstrate that the workability of designed UHPC mixtures is increased with the incorporation of IOT. The heat flow at an early age of designed UHPC with IOT is attenuated, the compressive strength and auto shrinkage at an early age are consequently reduced. The addition of IOT promotes the development of long-term compressive strength and optimization of the pore structure, thus the durability of designed UHPC is still guaranteed. In addition, the ecological estimate results show that the utilization of IOT for the UHPC design can reduce the carbon emission significantly. Full article

(This article belongs to the Special Issue Advanced Cement and Concrete Composites)

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15 pages, 1001 KiB

Open AccessEditor’s ChoiceArticle

Carbon Fiber Reinforced Polymer Composites Doped with Graphene Oxide in Light of Spectroscopic Studies

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

Materials 2021, 14(8), 1835; https://doi.org/10.3390/ma14081835 - 7 Apr 2021

Cited by 17 | Viewed by 3190

Abstract

Carbon fiber reinforced polymer composites are a dynamically developing group of lightweight composites for applications in the automotive, wind energy, aerospace, and sports sectors. Interfacial connection is the weakest place in these materials. In this study, an attempt was made to improve adhesion [...] Read more.

Carbon fiber reinforced polymer composites are a dynamically developing group of lightweight composites for applications in the automotive, wind energy, aerospace, and sports sectors. Interfacial connection is the weakest place in these materials. In this study, an attempt was made to improve adhesion between carbon fiber and epoxy resin. For this purpose, nanoparticles of graphene oxide were added to a polymer matrix. The results of the three-point bend test showed that the strength of samples with added graphene oxide increased. Improvement of adhesion between components, reduction of the pull-out effect and change in the method of crack propagation were observed. An attempt was made to explain this effect using spectroscopic methods, both IR and Raman. On the basis of the obtained results, chemical bonds between the individual components of the composites were identified. Full article

(This article belongs to the Section Advanced Materials Characterization)

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28 pages, 7535 KiB

Open AccessEditor’s ChoiceArticle

Stochastic Model for Energy Propagation in Disordered Granular Chains

by Kianoosh Taghizadeh, Rohit Kumar Shrivastava and Stefan Luding

Materials 2021, 14(7), 1815; https://doi.org/10.3390/ma14071815 - 6 Apr 2021

Cited by 6 | Viewed by 2972

Abstract

Energy transfer is one of the essentials of mechanical wave propagation (along with momentum transport). Here, it is studied in disordered one-dimensional model systems mimicking force-chains in real systems. The pre-stressed random masses (other types of disorder lead to qualitatively similar behavior) interact [...] Read more.

Energy transfer is one of the essentials of mechanical wave propagation (along with momentum transport). Here, it is studied in disordered one-dimensional model systems mimicking force-chains in real systems. The pre-stressed random masses (other types of disorder lead to qualitatively similar behavior) interact through (linearized) Hertzian repulsive forces, which allows solving the deterministic problem analytically. The main goal, a simpler, faster stochastic model for energy propagation, is presented in the second part, after the basic equations are re-visited and the phenomenology of pulse propagation in disordered granular chains is reviewed. First, the propagation of energy in space is studied. With increasing disorder (quantified by the standard deviation of the random mass distribution), the attenuation of pulsed signals increases, transiting from ballistic propagation (in ordered systems) towards diffusive-like characteristics, due to energy localization at the source. Second, the evolution of energy in time by transfer across wavenumbers is examined, using the standing wave initial conditions of all wavenumbers. Again, the decay of energy (both the rate and amount) increases with disorder, as well as with the wavenumber. The dispersive ballistic transport in ordered systems transits to low-pass filtering, due to disorder, where localization of energy occurs at the lowest masses in the chain. Instead of dealing with the too many degrees of freedom or only with the lowest of all the many eigenmodes of the system, we propose a stochastic master equation approach with reduced complexity, where all frequencies/energies are grouped into bands. The mean field stochastic model, the matrix of energy-transfer probabilities between bands, is calibrated from the deterministic analytical solutions by ensemble averaging various band-to-band transfer situations for short times, as well as considering the basis energy levels (decaying with the wavenumber increasing) that are not transferred. Finally, the propagation of energy in the wavenumber space at transient times validates the stochastic model, suggesting applications in wave analysis for non-destructive testing, underground resource exploration, etc. Full article

(This article belongs to the Special Issue Advances in Acoustic Metamaterials)

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12 pages, 4943 KiB

Open AccessEditor’s ChoiceArticle

A Pocket-Textured Surface for Improving the Tribological Properties of Point Contact under Starved Lubrication

by Wei Wang, Wenhan Zhao, Yang Liu, Hui Zhang, Meng Hua, Guangneng Dong, Hon-Yuen Tam and Kwai-Sang Chin

Materials 2021, 14(7), 1789; https://doi.org/10.3390/ma14071789 - 5 Apr 2021

Cited by 7 | Viewed by 3076

Abstract

This paper reports a novel pocket-textured surface for improving the tribological properties of point contact under starved lubrication by possibly storing and releasing oil, and homogenizing the surface contact pressure. The ball-on-disk experimental results confirmed the coefficient of friction (COF) and wear reduction [...] Read more.

This paper reports a novel pocket-textured surface for improving the tribological properties of point contact under starved lubrication by possibly storing and releasing oil, and homogenizing the surface contact pressure. The ball-on-disk experimental results confirmed the coefficient of friction (COF) and wear reduction effect of such pocket-texturing. The maximum reduction rate was 40% compared with a flat surface under the same operating conditions. Analyses on experimental results attributed the oil storage effect and enhanced the secondary lubrication effect within the starved lubrication state, to become the main mechanism. In addition, the plate elasticity and the Hertzian contact principles were employed to estimate the pressure and the load acting on the surface. The experimental results and numerical analysis substantiated the design of pocket-textured surface, making it likely to enlarge about 50% of contact surface and to reduce 90% of equivalent stress in comparison to those of conventional surfaces. Full article

(This article belongs to the Special Issue Friction and Wear of Materials Surfaces)

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15 pages, 4309 KiB

Open AccessEditor’s ChoiceArticle

Influence of Silica-Aerogel on Mechanical Characteristics of Polyurethane-Based Composites: Thermal Conductivity and Strength

by Jeong-Hyeon Kim, Jae-Hyeok Ahn, Jeong-Dae Kim, Dong-Ha Lee, Seul-Kee Kim and Jae-Myung Lee

Materials 2021, 14(7), 1790; https://doi.org/10.3390/ma14071790 - 5 Apr 2021

Cited by 23 | Viewed by 4362

Abstract

Polyurethane foam (PUF) has generally been used in liquefied natural gas (LNG) carrier cargo containment systems (CCSs) owing to its excellent mechanical and thermal properties over a wide range of temperatures. An LNG CCS must be designed to withstand extreme environmental conditions. However, [...] Read more.

Polyurethane foam (PUF) has generally been used in liquefied natural gas (LNG) carrier cargo containment systems (CCSs) owing to its excellent mechanical and thermal properties over a wide range of temperatures. An LNG CCS must be designed to withstand extreme environmental conditions. However, as the insulation material for LNGC CCSs, PUF has two major limitations: its strength and thermal conductivity. In the present study, PUFs were synthesized with various weight percentages of porous silica aerogel to reinforce the characteristics of PUF used in LNG carrier insulation systems. To evaluate the mechanical strength of the PUF-silica aerogel composites considering LNG loading/unloading environmental conditions, compressive tests were conducted at room temperature (20 °C) and a cryogenic temperature (−163 °C). In addition, the thermal insulation performance and cellular structure were identified to analyze the effects of silica aerogels on cell morphology. The cell morphology of PUF-silica aerogel composites was relatively homogeneous, and the cell shape remained closed at 1 wt.% in comparison to the other concentrations. As a result, the mechanical and thermal properties were significantly improved by the addition of 1 wt.% silica aerogel to the PUF. The mechanical properties were reduced by increasing the silica aerogel content to 3 wt.% and 5 wt.%, mainly because of the pores generated on the surface of the composites. Full article

(This article belongs to the Section Materials Physics)

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27 pages, 12188 KiB

Open AccessEditor’s ChoiceArticle

Effects of Deposition Strategy and Preheating Temperature on Thermo-Mechanical Characteristics of Inconel 718 Super-Alloy Deposited on AISI 1045 Substrate Using a DED Process

by Ho Kim, Kwang-Kyu Lee, Dong-Gyu Ahn and Hyub Lee

Materials 2021, 14(7), 1794; https://doi.org/10.3390/ma14071794 - 5 Apr 2021

Cited by 12 | Viewed by 3702

Abstract

Thermomechanical characteristics are highly dependent on the deposition strategy of the directed energy deposition (DED) process, including the deposition path, the interpass time, the deposition volume, etc., as well as the preheating condition of the substrate. This paper aims to investigate the effects [...] Read more.

Thermomechanical characteristics are highly dependent on the deposition strategy of the directed energy deposition (DED) process, including the deposition path, the interpass time, the deposition volume, etc., as well as the preheating condition of the substrate. This paper aims to investigate the effects of the deposition strategy and the preheating temperature on thermomechanical characteristics of Inconel 718 super-alloy deposited on an AISI 1045 substrate using a DED process via finite element analyses (FEAs). FE models for different deposition strategies and preheating temperatures are created to examine the thermomechanical behavior. Sixteen deposition strategies are adopted to perform FEAs. The heat sink coefficient is estimated from a comparison of temperature histories of experiments and those of FEAs to obtain appropriate FE models. The influence of deposition strategies on residual stress distributions in the designed model for a small volume deposition is examined to determine feasible deposition strategies. In addition, the effects of the deposition strategy and the preheating temperature on residual stress distributions of the designed part for large volume deposition are investigated to predict a suitable deposition strategy of the DED head and appropriate preheating temperature of the substrate. Full article

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

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16 pages, 2829 KiB

Open AccessEditor’s ChoiceArticle

Establishing the Carbonation Profile with Raman Spectroscopy: Effects of Fly Ash and Ground Granulated Blast Furnace Slag

by Yanfei Yue, Jing Jing Wang, P. A. Muhammed Basheer and Yun Bai

Materials 2021, 14(7), 1798; https://doi.org/10.3390/ma14071798 - 5 Apr 2021

Cited by 8 | Viewed by 3524

Abstract

Establishing the carbonation profile is of great significance to the prediction of the service life of reinforced concrete structures. In our previous work, Raman spectroscopy was shown to be an efficient tool for characterizing calcium carbonate (CaCO₃) polymorphs and their profile [...] Read more.

Establishing the carbonation profile is of great significance to the prediction of the service life of reinforced concrete structures. In our previous work, Raman spectroscopy was shown to be an efficient tool for characterizing calcium carbonate (CaCO₃) polymorphs and their profile in plain Portland cement (PC) matrices. However, as supplementary cementitious materials (SCMs), particularly fly ash (FA) and ground granulated blast furnace slag (GGBS), are widely used in concrete, establishing the carbonation profile without considering the possible effects of these SCMs could be of little significance to the real world. This paper, thus, investigated the effects of FA and GGBS on the working capacity and reliability of Raman spectroscopy for establishing the carbonation profile in PC blends containing SCMs. The thermogravimetry (TG) analysis was also conducted to verify the results from Raman spectroscopy. The results show that Raman spectroscopy demonstrated a good capacity for differentiating the variation of CaCO₃ contents in FA or GGBS blends. However, the incorporation of FA and GGBS into the PC system caused some adverse effects on the quantification of CaCO₃ by Raman spectroscopy, which could be attributed to the darker color and weak scatter nature of FA and the high content of glassy phases in GGBS. Full article

(This article belongs to the Section Construction and Building Materials)

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26 pages, 4262 KiB

Open AccessEditor’s ChoiceArticle

Effect of D-Mannitol on the Microstructure and Rheology of Non-Aqueous Carbopol Microgels

by Simona Migliozzi, Panagiota Angeli and Luca Mazzei

Materials 2021, 14(7), 1782; https://doi.org/10.3390/ma14071782 - 4 Apr 2021

Cited by 3 | Viewed by 4089

Abstract

D-mannitol is a common polyol that is used as additive in pharmaceutical and personal care product formulations. We investigated its effect on the microstructure and rheology of novel non-aqueous Carbopol dispersions employing traditional and time-resolved rheological analysis. We considered two types of sample, [...] Read more.

D-mannitol is a common polyol that is used as additive in pharmaceutical and personal care product formulations. We investigated its effect on the microstructure and rheology of novel non-aqueous Carbopol dispersions employing traditional and time-resolved rheological analysis. We considered two types of sample, (i) fresh (i.e., mannitol completely dissolved in solution) and aged (i.e., visible in crystalline form). The analysis of the intracycle rheological transitions that were observed for different samples revealed that, when completely dissolved in solution, mannitol does not alter the rheological behaviour of the Carbopol dispersions. This highlights that the chemical similarity of the additive with the molecules of the surrounding solvent allows preserving the swollen dimension and interparticle interactions of the Carbopol molecules. Conversely, when crystals are present, a hierarchical structure forms, consisting of a small dispersed phase (Carbopol) agglomerated around a big dispersed phase (crystals). In keeping with this microstructural picture, as the concentration of Carbopol reduces, the local dynamics of the crystals gradually start to control the integrity of the microstructure. Rheologically, this results in a higher elasticity of the suspensions at infinitesimal deformations, but a fragile yielding process at intermediate strains. Full article

(This article belongs to the Special Issue Rheology of Advanced Complex Fluids)

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24 pages, 1590 KiB

Open AccessEditor’s ChoiceArticle

Third-Order Theory for the Bending Analysis of Laminated Thin and Thick Plates Including the Strain Gradient Effect

by Michele Bacciocchi and Angelo Marcello Tarantino

Materials 2021, 14(7), 1771; https://doi.org/10.3390/ma14071771 - 3 Apr 2021

Cited by 10 | Viewed by 6973

Abstract

The aim of the paper is the development of a third-order theory for laminated composite plates that is able to accurately investigate their bending behavior in terms of displacements and stresses. The starting point is given by the corresponding Reddy’s Third-order Shear Deformation [...] Read more.

The aim of the paper is the development of a third-order theory for laminated composite plates that is able to accurately investigate their bending behavior in terms of displacements and stresses. The starting point is given by the corresponding Reddy’s Third-order Shear Deformation Theory (TSDT). This model is then generalized to consider simultaneously the Classical Laminated Plate Theory (CLPT), as well as the First-order Shear Deformation Theory (FSDT). The constitutive laws are modified according to the principles of the nonlocal strain gradient approach. The fundamental equations are solved analytically by means of the Navier methodology taking into account cross-ply and angle-ply lamination schemes. The numerical applications are presented to highlight the nonlocal effects on static behavior. Full article

(This article belongs to the Special Issue Modeling of Constitutive Laws for Traditional and Innovative Building Materials)

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22 pages, 1279 KiB

Open AccessEditor’s ChoiceArticle

Vegetable Fillers and Rapeseed Oil-Based Polyol as Natural Raw Materials for the Production of Rigid Polyurethane Foams

by Milena Leszczyńska, Elżbieta Malewska, Joanna Ryszkowska, Maria Kurańska, Michał Gloc, Michał K. Leszczyński and Aleksander Prociak

Materials 2021, 14(7), 1772; https://doi.org/10.3390/ma14071772 - 3 Apr 2021

Cited by 31 | Viewed by 3734

Abstract

The reported study concerns the introduction of renewable raw materials into the formulation of rigid polyurethane foams in the quest for the sustainable development of polymer composites. In this study, rigid polyurethane foam composites were prepared using 75 wt.% of rapeseed oil-based polyol [...] Read more.

The reported study concerns the introduction of renewable raw materials into the formulation of rigid polyurethane foams in the quest for the sustainable development of polymer composites. In this study, rigid polyurethane foam composites were prepared using 75 wt.% of rapeseed oil-based polyol and 15 parts per hundred parts of polyol (php) of natural fillers such as chokeberry pomace, raspberry seeds, as well as hazelnut and walnut shells. The influence of the used raw materials on the foaming process, structure, and properties of foams was investigated using a FOAMAT analyzer and a wide selection of characterization techniques. The introduction of renewable raw materials limited reactivity of the system, which reduced maximum temperature of the foaming process. Moreover, foams prepared using renewable raw materials were characterized by a more regular cell structure, a higher share of closed cells, lower apparent density, lower compressive strength and glass transition temperature, low friability (<2%), low water absorption (<1%), high dimensional stability (<±0.5%) and increased thermal stability. The proper selection and preparation of the renewable raw materials and the rational development of the polyurethane recipe composition allow for the preparation of environmentally-friendly foam products with beneficial application properties considering the demands of the circular economy in the synthesis of rigid foams. Full article

(This article belongs to the Special Issue Development of Bio-Based Composite Foams)

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16 pages, 3845 KiB

Open AccessEditor’s ChoiceArticle

Efficient Removal of Methylene Blue from Aqueous Solutions Using a High Specific Surface Area Porous Carbon Derived from Soybean Dreg

by Zhiwei Ying, Lu Huang, Lili Ji, He Li, Xinqi Liu, Chi Zhang, Jian Zhang and Guofu Yi

Materials 2021, 14(7), 1754; https://doi.org/10.3390/ma14071754 - 2 Apr 2021

Cited by 11 | Viewed by 2711

Abstract

Porous carbon material with high specific surface area was prepared from soybean dreg by a simple and effective two-step method (high temperature pyrolysis and activation). The structural characteristics of the synthesized carbon were evaluated by Brunauer–Emmett–Teller (BET), N₂ adsorption/desorption measurements/techniques, an elemental [...] Read more.

Porous carbon material with high specific surface area was prepared from soybean dreg by a simple and effective two-step method (high temperature pyrolysis and activation). The structural characteristics of the synthesized carbon were evaluated by Brunauer–Emmett–Teller (BET), N₂ adsorption/desorption measurements/techniques, an elemental analyzer (EA), scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM), an X-ray diffractometer (XRD), Raman spectroscopy (Raman), a Fourier transform infrared spectrometer (FTIR), and X-ray photoelectron spectroscopy (XPS). The specific surface area of SDB-6-K was 2786 m² g⁻¹, the pore volume was 2.316 cm³ g⁻¹, and the average pore size was 3.326 nm. The high specific surface area and effective functional groups of carbon material promoted the adsorption of methylene blue. The maximum adsorption capacity of SDB-6-K to methylene blue was 2636 mg g⁻¹ at 318 K. The adsorption kinetic and isotherm data were most suitable for pseudo-second-order and Langmuir equations. The results showed that the adsorbent had excellent adsorptive ability and had good practical application potential in the field of dye wastewater treatment in the future. Full article

(This article belongs to the Special Issue Adsorbents and Their Applications)

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15 pages, 6130 KiB

Open AccessEditor’s ChoiceArticle

Hierarchical Microtextures Embossed on PET from Laser-Patterned Stamps

by Felix Bouchard, Marcos Soldera, Robert Baumann and Andrés Fabián Lasagni

Materials 2021, 14(7), 1756; https://doi.org/10.3390/ma14071756 - 2 Apr 2021

Cited by 16 | Viewed by 3324

Abstract

Nowadays, the demand for surface functionalized plastics is constantly rising. To address this demand with an industry compatible solution, here a strategy is developed for producing hierarchical microstructures on polyethylene terephthalate (PET) by hot embossing using a stainless steel stamp. The master was [...] Read more.

Nowadays, the demand for surface functionalized plastics is constantly rising. To address this demand with an industry compatible solution, here a strategy is developed for producing hierarchical microstructures on polyethylene terephthalate (PET) by hot embossing using a stainless steel stamp. The master was structured using three laser-based processing steps. First, a nanosecond-Direct Laser Writing (DLW) system was used to pattern dimples with a depth of up to 8 µm. Next, the surface was smoothed by a remelting process with a high-speed laser scanning at low laser fluence. In the third step, Direct Laser Interference Patterning (DLIP) was utilized using four interfering sub-beams to texture a hole-like substructure with a spatial period of 3.1 µm and a depth up to 2 µm. The produced stamp was used to imprint PET foils under controlled temperature and pressure. Optical confocal microscopy and scanning electron microscopy imaging showed that the hierarchical textures could be accurately transferred to the polymer. Finally, the wettability of the single- and multi-scaled textured PET surfaces was characterized with a drop shape analyzer, revealing that the highest water contact angles were reached for the hierarchical patterns. Particularly, this angle was increased from 77° on the untreated PET up to 105° for a hierarchical structure processed with a DLW spot distance of 60 µm and with 10 pulses for the DLIP treatment. Full article

(This article belongs to the Special Issue Laser Applications in Micromachining and Surface Functionalization of Materials)

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17 pages, 29943 KiB

Open AccessEditor’s ChoiceArticle

Zinc-Containing Effluent Treatment Using Shewanella xiamenensis Biofilm Formed on Zeolite

by Inga Zinicovscaia, Nikita Yushin, Dmitrii Grozdov, Daler Abdusamadzoda, Alexey Safonov and Elena Rodlovskaya

Materials 2021, 14(7), 1760; https://doi.org/10.3390/ma14071760 - 2 Apr 2021

Cited by 15 | Viewed by 2352

Abstract

The sorption properties of Shewanella xiamenensis biofilm formed on zeolite (mineral-organic sorbent) as a sorbent have been investigated aiming to determine its suitability for complex zinc-containing effluent treatment. The optimum conditions for metal sorption from synthetic solutions were evaluated by changing the pH, [...] Read more.

The sorption properties of Shewanella xiamenensis biofilm formed on zeolite (mineral-organic sorbent) as a sorbent have been investigated aiming to determine its suitability for complex zinc-containing effluent treatment. The optimum conditions for metal sorption from synthetic solutions were evaluated by changing the pH, zinc concentration, temperature, and time of sorption. The highest removal of metal ions was attained at pH range 3.0–6.0 within 60–150 min of sorbent-sorbate contact. The results obtained from the equilibrium studies were described using the Langmuir, Freundlich, and Temkin models. Maximum sorption capacity of the sorbent calculated from the Langmuir model changed from 3.4 to 6.5 mg/g. High coefficient of determination values calculated for pseudo-second-order and Elovich models indicate the predominant role of chemisorption in metal removal. Gibbs energy and ∆H° values point at the spontaneous and endothermic character of the sorption. The effect of pH and biosorbent mass on Zn(II) sorption from industrial effluent with an initial Zn(II) concentration of 52.8 mg/L was tested. Maximum removal of zinc ions (85%) was achieved at pH 6.0 by applying a two-step treatment system. Full article

(This article belongs to the Special Issue Environmentally-Friendly Materials in Wastewater Treatment)

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14 pages, 8462 KiB

Open AccessEditor’s ChoiceArticle

The Numerical Analysis of the In-Plane Constraint Influence on the Behavior of the Crack Subjected to Cyclic Loading

by Jaroslaw Galkiewicz and Urszula Janus-Galkiewicz

Materials 2021, 14(7), 1764; https://doi.org/10.3390/ma14071764 - 2 Apr 2021

Cited by 5 | Viewed by 1749

Abstract

The paper presents the influence of in-plane constraints defined by T-stress on the behavior of a crack subjected to cyclic loading. In the analysis, a modified boundary layer model approach was used in which the cohesive model was introduced. In the simulations, the [...] Read more.

The paper presents the influence of in-plane constraints defined by T-stress on the behavior of a crack subjected to cyclic loading. In the analysis, a modified boundary layer model approach was used in which the cohesive model was introduced. In the simulations, the constant maximum value of the stress intensity factor and four levels of T-stress were defined. The model was subjected to ten repeated stress cycles. Based on the results obtained, an analysis of the effect of the in-plane constraint on selected aspects of crack behavior was made. The strong influence of in-plane constraint applied in the model on the crack closure and the fatigue crack growth rate was proven. Since the in-plane constraint described the influence of geometry on the stress field surrounding the fatigue crack tip in real geometry, the results suggested that it is possible to create precise formulae connecting the level of the in-plane constraint with the effective stress intensity factor range and to incorporate the T-stress or Q-stress level in the Paris law. Full article

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

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13 pages, 4138 KiB

Open AccessEditor’s ChoiceArticle

Research on High-Value Utilization of Carbon Derived from Tobacco Waste in Supercapacitors

by Zhenrui Huang, Caiyun Qin, Jun Wang, Lin Cao, Zhuwen Ma, Qinghua Yuan, Zhidan Lin and Peng Zhang

Materials 2021, 14(7), 1714; https://doi.org/10.3390/ma14071714 - 31 Mar 2021

Cited by 38 | Viewed by 3141

Abstract

Large quantities of tobacco stalks residues are generated and discarded as crop waste or combusted directly every year. Thus, we need to find an appropriate way to dispose of this type of waste and recycle it. The conversion of biomass waste into electrode [...] Read more.

Large quantities of tobacco stalks residues are generated and discarded as crop waste or combusted directly every year. Thus, we need to find an appropriate way to dispose of this type of waste and recycle it. The conversion of biomass waste into electrode materials for supercapacitors is entirely in line with the concept of sustainability and green. In this paper, tobacco-stalk-based, porous activated carbon (TC) was successfully synthesized by high-temperature and high-pressure hydrothermal pre-carbonization and KOH activation. The synthesized TC had a high pore volume and a large surface area of 1875.5 m² g⁻¹, in which there were many mesopores and interconnected micro-/macropores. The electrochemical test demonstrated that TC-1 could reach a high specific capacitance of up to 356.4 F g⁻¹ at a current density of 0.5 A g⁻¹, which was carried in 6M KOH. Additionally, a symmetrical supercapacitor device was fabricated by using TC-1 as the electrode, which delivered a high energy density up to 10.4 Wh kg⁻¹ at a power density of 300 W kg⁻¹, and excellent long-term cycling stability (92.8% of the initial capacitance retention rate after 5000 cycles). Therefore, TC-1 is considered to be a promising candidate for high-performance supercapacitor electrode materials and is a good choice for converting tobacco biomass waste into a resource. Full article

(This article belongs to the Special Issue Advances in Mechanical Alloying and Milling)

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20 pages, 3920 KiB

Open AccessEditor’s ChoiceArticle

Towards Embedded Computation with Building Materials

by Dawid Przyczyna, Maciej Suchecki, Andrew Adamatzky and Konrad Szaciłowski

Materials 2021, 14(7), 1724; https://doi.org/10.3390/ma14071724 - 31 Mar 2021

Cited by 8 | Viewed by 2678

Abstract

We present results showing the capability of concrete-based information processing substrate in the signal classification task in accordance with in materio computing paradigm. As the Reservoir Computing is a suitable model for describing embedded in materio computation, we propose that this type of [...] Read more.

We present results showing the capability of concrete-based information processing substrate in the signal classification task in accordance with in materio computing paradigm. As the Reservoir Computing is a suitable model for describing embedded in materio computation, we propose that this type of presented basic construction unit can be used as a source for “reservoir of states” necessary for simple tuning of the readout layer. We present an electrical characterization of the set of samples with different additive concentrations followed by a dynamical analysis of selected specimens showing fingerprints of memfractive properties. As part of dynamic analysis, several fractal dimensions and entropy parameters for the output signal were analyzed to explore the richness of the reservoir configuration space. In addition, to investigate the chaotic nature and self-affinity of the signal, Lyapunov exponents and Detrended Fluctuation Analysis exponents were calculated. Moreover, on the basis of obtained parameters, classification of the signal waveform shapes can be performed in scenarios explicitly tuned for a given device terminal. Full article

(This article belongs to the Special Issue Advanced Cement and Concrete Composites)

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14 pages, 5519 KiB

Open AccessEditor’s ChoiceArticle

Numerical Study on the Dependency of Microstructure Morphologies of Pulsed Laser Deposited TiN Thin Films and the Strain Heterogeneities during Mechanical Testing

by Konrad Perzynski, Grzegorz Cios, Grzegorz Szwachta, Piotr Bała and Lukasz Madej

Materials 2021, 14(7), 1705; https://doi.org/10.3390/ma14071705 - 30 Mar 2021

Cited by 3 | Viewed by 2227

Abstract

Numerical study of the influence of pulsed laser deposited TiN thin films’ microstructure morphologies on strain heterogeneities during loading was the goal of this research. The investigation was based on the digital material representation (DMR) concept applied to replicate an investigated thin film’s [...] Read more.

Numerical study of the influence of pulsed laser deposited TiN thin films’ microstructure morphologies on strain heterogeneities during loading was the goal of this research. The investigation was based on the digital material representation (DMR) concept applied to replicate an investigated thin film’s microstructure morphology. The physically based pulsed laser deposited model was implemented to recreate characteristic features of a thin film microstructure. The kinetic Monte Carlo (kMC) approach was the basis of the model in the first part of the work. The developed kMC algorithm was used to generate thin film’s three-dimensional representation with its columnar morphology. Such a digital model was then validated with the experimental data from metallographic analysis of laboratory deposited TiN(100)/Si. In the second part of the research, the kMC generated DMR model of thin film was incorporated into the finite element (FE) simulation. The 3D film’s morphology was discretized with conforming finite element mesh, and then incorporated as a microscale model into the macroscale finite element simulation of nanoindentation test. Such a multiscale model was finally used to evaluate the development of local deformation heterogeneities associated with the underlying microstructure morphology. In this part, the capabilities of the proposed approach were clearly highlighted. Full article

(This article belongs to the Special Issue Computational Modelling and Design of Novel Engineering Materials)

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15 pages, 11275 KiB

Open AccessEditor’s ChoiceArticle

Mitigation of Galvanic Corrosion in Bolted Joint of AZ31B and Carbon Fiber-Reinforced Composite Using Polymer Insulation

by Jiheon Jun, Yong Chae Lim, Yuan Li, Charles David Warren and Zhili Feng

Materials 2021, 14(7), 1670; https://doi.org/10.3390/ma14071670 - 29 Mar 2021

Cited by 11 | Viewed by 3465

Abstract

The use of polymer insulation to mitigate galvanic corrosion was examined for bolted joints of AZ31B Mg alloy and carbon fiber-reinforced composite. To assess the corrosion behaviors of bolted joints with and without polymer insulation, solution immersion and salt spray exposure (ASTM B117) [...] Read more.

The use of polymer insulation to mitigate galvanic corrosion was examined for bolted joints of AZ31B Mg alloy and carbon fiber-reinforced composite. To assess the corrosion behaviors of bolted joints with and without polymer insulation, solution immersion and salt spray exposure (ASTM B117) tests were conducted, and the corrosion depths and volumes were determined for the joint specimens after the tests. The polymer-insulated bolted joints exhibited much lower corrosion depths and volumes, highlighting the effective mitigation of galvanic corrosion. The reductions of joint strength in the post-corrosion joint specimens were relatively small (up to ~10%) in the polymer-insulated group but greater (up to 90%) in the group with no insulation. Cross-sectional characterization of post-corrosion joints with polymer insulation revealed local pits developed on AZ31B under galvanic influence, indicating that limited galvanic attack (that did not decrease the joining integrity significantly) could still occur during a long salt spray exposure (~1264 h) owing to the permeation of an aqueous corrosive medium. Full article

(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)

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15 pages, 3495 KiB

Open AccessEditor’s ChoiceArticle

Geometric Specification of Non-Circular Pulleys Made with Various Additive Manufacturing Techniques

by Piotr Krawiec, Dorota Czarnecka-Komorowska, Łukasz Warguła and Szymon Wojciechowski

Materials 2021, 14(7), 1682; https://doi.org/10.3390/ma14071682 - 29 Mar 2021

Cited by 18 | Viewed by 3285

Abstract

The paper presents the procedure of generating geometrical features on the contours of non-circular pulleys through the selection of materials and technological parameters for easy and efficient production of these parts. Based on the models designed in the computer aided design (CAD) system, [...] Read more.

The paper presents the procedure of generating geometrical features on the contours of non-circular pulleys through the selection of materials and technological parameters for easy and efficient production of these parts. Based on the models designed in the computer aided design (CAD) system, several prototype non-standard pulleys were made, which were assessed for functional characteristics and correct operation of non-linear gears. The effect of additive technology on the geometric specification of non-circular pulleys was also assessed. The results showed that thanks to the use of additive methods, the need for costly manufacturing of such wheels with subtractive methods was eliminated. Additionally, it is not necessary to design specialized cutting tools or to use conventional or numerically controlled machine tools to manufacture these wheels. The test results showed that in case of selective laser sintering (SLS) the highest accuracy of mapping (0.01 mm) of geometrical features of the surface was obtained. This result is confirmed by the assessment of the morphology of the surface of the teeth of gears made with this technique, characterized by a uniform structure of the working surface of the wheel while maintaining a high tolerance of the outer profile of gear for selective laser sintering at the level of ±0.03 mm. Research has shown that most of the additive methods used to manufacture non-circular pulleys meet the required geometrical features and due to the short production time of these pulleys, these methods also facilitate quick verification of the designed pulley geometry. Full article

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

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16 pages, 3715 KiB

Open AccessEditor’s ChoiceArticle

Abrasive Waterjet (AWJ) Forces—Indicator of Cutting System Malfunction

by Libor M. Hlaváč, Damian Bańkowski, Daniel Krajcarz, Adam Štefek, Martin Tyč and Piotr Młynarczyk

Materials 2021, 14(7), 1683; https://doi.org/10.3390/ma14071683 - 29 Mar 2021

Cited by 11 | Viewed by 2758

Abstract

Measurements enabling the online monitoring of the abrasive waterjet (AWJ) cutting process are still under development. This paper presents an experimental method which can be applicable for the evaluation of the AWJ cutting quality through the measurement of forces during the cutting process. [...] Read more.

Measurements enabling the online monitoring of the abrasive waterjet (AWJ) cutting process are still under development. This paper presents an experimental method which can be applicable for the evaluation of the AWJ cutting quality through the measurement of forces during the cutting process. The force measuring device developed and patented by our team has been used for measurement on several metal materials. The results show the dependence of the cutting to deformation force ratio on the relative traverse speed. Thus, the force data may help with a better understanding the interaction between the abrasive jet and the material, simultaneously impacting the improvement of both the theoretical and empirical models. The advanced models could substantially improve the selection of suitable parameters for AWJ cutting, milling or turning with the desired quality of product at the end of the process. Nevertheless, it is also presented that force measurements may detect some undesired effects, e.g., not fully penetrated material and/or some product distortions. In the case of a proper designing of the measuring device, the force measurement can be applied in the online monitoring of the cutting process and its continuous control. Full article

(This article belongs to the Special Issue Advanced Technology of Material Processing: Abrasive Water Jet Machining)

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32 pages, 11073 KiB

Open AccessEditor’s ChoiceArticle

Model-Based Adaptive Machine Learning Approach in Concrete Mix Design

by Patryk Ziolkowski, Maciej Niedostatkiewicz and Shao-Bo Kang

Materials 2021, 14(7), 1661; https://doi.org/10.3390/ma14071661 - 28 Mar 2021

Cited by 28 | Viewed by 5748

Abstract

Concrete mix design is one of the most critical issues in concrete technology. This process aims to create a concrete mix which helps deliver concrete with desired features and quality. Contemporary requirements for concrete concern not only its structural properties, but also increasingly [...] Read more.

Concrete mix design is one of the most critical issues in concrete technology. This process aims to create a concrete mix which helps deliver concrete with desired features and quality. Contemporary requirements for concrete concern not only its structural properties, but also increasingly its production process and environmental friendliness, forcing concrete producers to use both chemically and technologically complex concrete mixtures. The concrete mix design methods currently used in engineering practice are joint analytical and laboratory procedures derived from the Three Equation Method and do not perform well enough for the needs of modern concrete technology. This often causes difficulties in predicting the final properties of the designed mix and leads to precautionary oversizing of concrete properties for fear of not providing the required parameters. A new approach that would make it possible to predict the newly designed concrete mix properties is highly desirable. The answer to this challenge can be methods based on machine learning, which have been intensively developed in recent years, especially in predicting concrete compressive strength. Machine learning-based methods have been more or less successful in predicting concrete compressive strength, but they do not reflect well the variability that characterises the currently used concrete mixes. A new adaptive solution that allows estimating concrete compressive strength on the basis of the concrete mix main ingredient composition by including two observations for a given batch of concrete is proposed herein. In presented study, a machine learning model was built with a deep neural network architecture, trained on an extensive database of concrete recipes, and translated into a mathematical formula. Testing on four concrete mix recipes was performed, which were calculated according to contemporary design methods (Bolomey and Fuller method), and a comparative analysis was conducted. It was found out that the new algorithm performs significantly better than that without adaptive features trained on the same dataset. The presented algorithm can be used as a concrete strength checking tool for the concrete mix design process. Full article

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

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12 pages, 1956 KiB

Open AccessEditor’s ChoiceArticle

Green Microwave-Assisted Synthesis of CoFeRu-Based Electrocatalyst for the Oxygen Reduction Reaction

by Antonia Sandoval, Edgar Borja, Lorena Magallón and Javier Su

Materials 2021, 14(7), 1662; https://doi.org/10.3390/ma14071662 - 28 Mar 2021

Cited by 1 | Viewed by 2438

Abstract

A simple and rapid synthesis of a CoFeRu-based electrocatalyst by a microwave-assisted method (using water as the microwave absorbing solvent) is reported in this work. Agglomerates with different sizes and shapes are observed by scanning electron microscopy technique. The energy dispersive X-ray spectroscopy [...] Read more.

A simple and rapid synthesis of a CoFeRu-based electrocatalyst by a microwave-assisted method (using water as the microwave absorbing solvent) is reported in this work. Agglomerates with different sizes and shapes are observed by scanning electron microscopy technique. The energy dispersive X-ray spectroscopy shows a low atomic percentage of Co and similar atomic percentage of Fe and Ru. However, the X-ray diffraction exhibits only the presence of metallic Ru and Fe₂O₃ (hematite) phases. The oxygen reduction without and with 2 mol L⁻¹ methanol is studied using the rotating disk electrode technique. The electrochemical kinetic parameters obtained are compared to a similar electrocatalyst reported in the literature, which was synthesized using a mixture of an organic solvent with DI water as the microwave absorbing solvent. An improvement on the activity of the electrocatalyst synthesized is observed, where high Tafel slopes are not observed. The electrocatalyst also showed tolerance to the presence of methanol during the oxygen reduction reaction. Full article

(This article belongs to the Special Issue Microwave Processing of Materials and Applications)

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28 pages, 12086 KiB

Open AccessEditor’s ChoiceArticle

Experimental Investigations on Interface between Ordinary and Lightweight Aggregate Concretes Cast at Different Times

by Michał Gołdyn and Tadeusz Urban

Materials 2021, 14(7), 1664; https://doi.org/10.3390/ma14071664 - 28 Mar 2021

Cited by 8 | Viewed by 2518

Abstract

Experimental investigations on 12 push-off specimens with dimensions of 600 × 300 × 180 mm (200 × 180 mm shear plane) were presented. Models reflected the connection between ordinary concrete (NWC) substrate and lightweight aggregate concrete (LWAC) overlay. The main purpose of the [...] Read more.

Experimental investigations on 12 push-off specimens with dimensions of 600 × 300 × 180 mm (200 × 180 mm shear plane) were presented. Models reflected the connection between ordinary concrete (NWC) substrate and lightweight aggregate concrete (LWAC) overlay. The main purpose of the study was to investigate behaviour of the interface between concretes cast at different times. Two different interface conditions were considered: Smooth and rough (obtained by graining). In the selected elements, additional reinforcement consisting of one ∅8 bar was injected. The elements were tested under load control. The failure of the specimens without interface reinforcement was violent and resulted from breaking of the adhesive bond. Specimens with shear reinforcement failed in a ductile manner, however, due to the low reinforcement area, the residual load capacity was much lower than the load recorded just before cracking. It was found that mechanical roughening of the surface can lead to degradation of the concrete structure. As a result, the load-carrying capacities of elements with smooth interface proved to be higher than the ultimate loads of elements with deliberately roughened contacts. Comparative analysis showed that the existing design procedures ACI 318-19, Eurocode 2, Model Code 2010, and AASHTO can lead to safe but conservative estimation of the actual resistance of the concrete interface. Full article

(This article belongs to the Special Issue Masonry Structures and Reinforced Concrete Structures)

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23 pages, 1320 KiB

Open AccessEditor’s ChoiceArticle

Topological Classification of Correlations in 2D Electron Systems in Magnetic or Berry Fields

by Janusz E. Jacak

Materials 2021, 14(7), 1650; https://doi.org/10.3390/ma14071650 - 27 Mar 2021

Cited by 1 | Viewed by 2015

Abstract

Recent topology classification of 2D electron states induced by different homotopy classes of mappings of the planar Brillouin zone into Bloch space can be supplemented by a homotopy classification of various phases of multi-electron homotopy patterns induced by Coulomb interaction between electrons. The [...] Read more.

Recent topology classification of 2D electron states induced by different homotopy classes of mappings of the planar Brillouin zone into Bloch space can be supplemented by a homotopy classification of various phases of multi-electron homotopy patterns induced by Coulomb interaction between electrons. The general classification of such type is presented. It explains the topologically protected correlations responsible for integer and fractional Hall effects in 2D multi-electron systems in the presence of perpendicular quantizing magnetic field or Berry field, the latter in topological Chern insulators. The long-range quantum entanglement is essential for homotopy correlated phases in contrast to local binary entanglement for conventional phases with local order parameters. The classification of homotopy long-range correlated phases induced by the Coulomb interaction of electrons has been derived in terms of homotopy invariants and illustrated by experimental observations in GaAs 2DES, graphene monolayer, and bilayer and in Chern topological insulators. The homotopy phases are demonstrated to be topologically protected and immune to the local crystal field, local disorder, and variation of the electron interaction strength. The nonzero interaction between electrons is shown, however, to be essential for the definition of the homotopy invariants, which disappear in gaseous systems. Full article

(This article belongs to the Special Issue Topological Approaches to 2D Multielectron Correlated States)

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22 pages, 34796 KiB

Open AccessEditor’s ChoiceArticle

Cutting Forces and Tool Wear Investigation during Turning of Sintered Nickel-Cobalt Alloy with CBN Tools

by Wojciech Zębala, Grzegorz Struzikiewicz and Ksenia Rumian

Materials 2021, 14(7), 1623; https://doi.org/10.3390/ma14071623 - 26 Mar 2021

Cited by 13 | Viewed by 2309

Abstract

This article describes issues related to the machining of parts made of sintered nickel-cobalt alloy. Longitudinal turning with a CBN (cubic boron nitride) tool was analyzed. The results of experiments showed the influence of cutting parameters in the field of finishing machining on [...] Read more.

This article describes issues related to the machining of parts made of sintered nickel-cobalt alloy. Longitudinal turning with a CBN (cubic boron nitride) tool was analyzed. The results of experiments showed the influence of cutting parameters in the field of finishing machining on the values of cutting forces and specific cutting force, taking into account the wear of the cutting edge. Measurements and analysis of the topography and roughness parameters of the machined surface, as well as the cutting tool wear, were presented. The microscopic examination showed that the average grain size of the sintered nickel-cobalt alloy was 3.22 ± 0.1 (μm). The presence of the hardening state variability of the material during machining, as well as the value of the cutting force fluctuation as a function of the tool wear VB, were stated. The specific cutting force values increased to a small degree for the tool wear in the range of VB = 0–0.2 mm, and reached similar values in the range k_c = 5500–7500 N/mm². The specific cutting force values increased significantly for wear VB > 0.2 mm and were characterized by a large variability. The occurring phenomena were analyzed and several explanations were proposed. A recommendation was developed for the machining of parts made of sintered nickel-cobalt alloy. The Taguchi method was used in the experiment methodology. Full article

(This article belongs to the Special Issue Research on Additive Manufacturing of Novel Alloy Materials)

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21 pages, 7451 KiB

Open AccessEditor’s ChoiceArticle

Machine-Learning-Based Atomistic Model Analysis on High-Temperature Compressive Creep Properties of Amorphous Silicon Carbide

by Atsushi Kubo and Yoshitaka Umeno

Materials 2021, 14(7), 1597; https://doi.org/10.3390/ma14071597 - 25 Mar 2021

Cited by 7 | Viewed by 3637

Abstract

Ceramic matrix composites (CMCs) based on silicon carbide (SiC) are used for high-temperature applications such as the hot section in turbines. For such applications, the mechanical properties at a high temperature are essential for lifetime prediction and reliability design of SiC-based CMC components. [...] Read more.

Ceramic matrix composites (CMCs) based on silicon carbide (SiC) are used for high-temperature applications such as the hot section in turbines. For such applications, the mechanical properties at a high temperature are essential for lifetime prediction and reliability design of SiC-based CMC components. We developed an interatomic potential function based on the artificial neural network (ANN) model for silicon-carbon systems aiming at investigation of high-temperature mechanical properties of SiC materials. We confirmed that the developed ANN potential function reproduces typical material properties of the single crystals of SiC, Si, and C consistent with first-principles calculations. We also validated applicability of the developed ANN potential to a simulation of an amorphous SiC through the analysis of the radial distribution function. The developed ANN potential was applied to a series of creep test for an amorphous SiC model, focusing on the amorphous phase, which is expected to be formed in the SiC-based composites. As a result, we observed two types of creep behavior due to different atomistic mechanisms depending on the strain rate. The evaluated activation energies are lower than the experimental values in literature. This result indicates that an amorphous region can play an important role in the creep process in SiC composites. Full article

(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)

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13 pages, 3319 KiB

Open AccessEditor’s ChoiceArticle

A Pressure Swing Approach to Selective CO₂ Sequestration Using Functionalized Hypercrosslinked Polymers

by Alex M. James, Jake Reynolds, Daniel G. Reed, Peter Styring and Robert Dawson

Materials 2021, 14(7), 1605; https://doi.org/10.3390/ma14071605 - 25 Mar 2021

Cited by 9 | Viewed by 3636

Abstract

Functionalized hypercrosslinked polymers (HCPs) with surface areas between 213 and 1124 m²/g based on a range of monomers containing different chemical moieties were evaluated for CO₂ capture using a pressure swing adsorption (PSA) methodology under humid conditions and elevated temperatures. [...] Read more.

Functionalized hypercrosslinked polymers (HCPs) with surface areas between 213 and 1124 m²/g based on a range of monomers containing different chemical moieties were evaluated for CO₂ capture using a pressure swing adsorption (PSA) methodology under humid conditions and elevated temperatures. The networks demonstrated rapid CO₂ uptake reaching maximum uptakes in under 60 s. The most promising networks demonstrating the best selectivity and highest uptakes were applied to a pressure swing setup using simulated flue gas streams. The carbazole, triphenylmethanol and triphenylamine networks were found to be capable of converting a dilute CO₂ stream (>20%) into a concentrated stream (>85%) after only two pressure swing cycles from 20 bar (adsorption) to 1 bar (desorption). This work demonstrates the ease with which readily synthesized functional porous materials can be successfully applied to a pressure swing methodology and used to separate CO₂ from N₂ from industrially applicable simulated gas streams under more realistic conditions. Full article

(This article belongs to the Special Issue Advanced Porous Polymers: Synthesis, Characterisations and Applications)

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13 pages, 4921 KiB

Open AccessEditor’s ChoiceArticle

High-Performance Complementary Electrochromic Device Based on Iridium Oxide as a Counter Electrode

by Tien-Fu Ko, Po-Wen Chen, Kuan-Ming Li, Hong-Tsu Young, Chen-Te Chang and Sheng-Chuan Hsu

Materials 2021, 14(7), 1591; https://doi.org/10.3390/ma14071591 - 24 Mar 2021

Cited by 15 | Viewed by 2785

Abstract

In complementary electrochromic devices (ECDs), nickel oxide (NiO) is generally used as a counter electrode material for enhancing the coloration efficiency. However, an NiO film as a counter electrode in ECDs is susceptible to degradation upon prolonged electrochemical cycling, which leads to an [...] Read more.

In complementary electrochromic devices (ECDs), nickel oxide (NiO) is generally used as a counter electrode material for enhancing the coloration efficiency. However, an NiO film as a counter electrode in ECDs is susceptible to degradation upon prolonged electrochemical cycling, which leads to an insufficient device lifetime. In this study, a type of counter electrode iridium oxide (IrO₂) layer was fabricated using vacuum cathodic arc plasma (CAP). We focused on the comparison of IrO₂ and NiO deposited on a 5 × 5 cm² indium tin oxide (ITO) glass substrate with various Ar/O₂ gas-flow ratios (1/2, 1/2.5, and 1/3) in series. The optical performance of IrO₂-ECD (glass/ITO/WO₃/liquid electrolyte/IrO₂/ITO/glass) was determined by optical transmittance modulation; ∆T = 50% (from T_bleaching (75%) to T_coloring (25%)) at 633 nm was higher than that of NiO-ECD (ITO/NiO/liquid electrolyte/WO₃/ITO) (∆T = 32%). Apart from this, the ECD device demonstrated a fast coloring time of 4.8 s, a bleaching time of 1.5 s, and good cycling durability, which remained at 50% transmittance modulation even after 1000 cycles. The fast time was associated with the IrO₂ electrode and provided higher diffusion coefficients and a filamentary shape as an interface that facilitated the transfer of the Li ions into/out of the interface electrodes and the electrolyte. In our result of IrO₂-ECD analyses, the higher optical transmittance modulation was useful for promoting electrochromic application to a cycle durability test as an alternative to NiO-ECD. Full article

(This article belongs to the Section Thin Films and Interfaces)

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