Materials

19 pages, 4986 KiB

Open AccessArticle

Relationship Between Schmidt Hammer Rebound Hardness Test and Concrete Strength Tests for Limestone Aggregate Concrete Based on Experimental and Statistical Study

by Esra Tugrul Tunc

Materials 2025, 18(6), 1388; https://doi.org/10.3390/ma18061388 - 20 Mar 2025

Viewed by 357

Abstract

This study investigated the mechanical properties of concrete specimens produced with a limestone aggregate through laboratory testing. Destructive tests, specifically concrete compressive strength and splitting tensile strength tests, were conducted. Additionally, the Schmidt hammer rebound hardness test, a non-destructive method, was performed on [...] Read more.

This study investigated the mechanical properties of concrete specimens produced with a limestone aggregate through laboratory testing. Destructive tests, specifically concrete compressive strength and splitting tensile strength tests, were conducted. Additionally, the Schmidt hammer rebound hardness test, a non-destructive method, was performed on the same specimens. The experimental results, obtained from varying water-to-cement and limestone aggregate-to-cement ratios, yielded the following ranges: compressive strength from 23.6 to 42.6 MPa, splitting tensile strength from 3.2 to 5.1 MPa, and Schmidt hammer rebound values from 18 to 43 N. The correlation between the non-destructive and destructive test results was analyzed experimentally and statistically. Utilizing the experimental data, statistical models were developed, resulting in equations with a high determination coefficient (R² > 0.95) for accurately predicting concrete compressive and splitting tensile strengths. This approach offers the potential for significant labor and time savings in the production of sustainable conventional concrete that meets relevant standards. Furthermore, it aims to facilitate the estimation of concrete strength in existing structures. Full article

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

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13 pages, 5246 KiB

Open AccessArticle

Study on the Microstructure and Properties of AISI 304 Stainless Steel Corrugated Pipes by Aging and Solution Treatments

by Xiang Zhao, Anheng Wang, Jianbin Wang, Chuanwen Ling and Xiaolong Gui

Materials 2025, 18(6), 1387; https://doi.org/10.3390/ma18061387 - 20 Mar 2025

Viewed by 242

Abstract

This article focuses on the microstructural evolution and mechanical property changes of AISI 304 austenitic stainless steel corrugated pipes after aging treatment and solution treatment. The influence of different heat treatment processes on the microstructural evolution, second phase precipitation behavior, mechanical properties, and [...] Read more.

This article focuses on the microstructural evolution and mechanical property changes of AISI 304 austenitic stainless steel corrugated pipes after aging treatment and solution treatment. The influence of different heat treatment processes on the microstructural evolution, second phase precipitation behavior, mechanical properties, and corrosion resistance of corrugated pipes was analyzed through metallographic microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), fatigue testing, hardness testing, and corrosion resistance experiments. The results showed that after aging treatment at 600 °C, carbides precipitated at the grain boundaries and twin boundaries of the corrugated tube, leading to corrosion behavior. The average microhardness value was 266.08 HV, and the work hardening problem of the corrugated tube was not improved. After solution treatment at 1050 °C, a single-phase austenite structure was obtained in the corrugated tube, and the carbides at the grain boundaries were completely dissolved. The average microhardness value was 66.02 HV, significantly improving the work hardening problem of the corrugated tube. Simultaneously, excellent comprehensive fatigue performance and intergranular corrosion resistance were exhibited. The solid solution treatment process is more suitable for the manufacturing of corrugated pipes that require high formability and corrosion resistance, while the aging treatment requires strict temperature control to avoid the sensitization temperature zone. This study provides a theoretical basis for optimizing the heat treatment process of AISI 304 austenitic stainless steel corrugated pipes. Full article

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35 pages, 15625 KiB

Open AccessArticle

Influence of Optimization Algorithms and Computational Complexity on Concrete Compressive Strength Prediction Machine Learning Models for Concrete Mix Design

by Patryk Ziolkowski

Materials 2025, 18(6), 1386; https://doi.org/10.3390/ma18061386 - 20 Mar 2025

Viewed by 294

Abstract

The proper design of concrete mixtures is a critical task in concrete technology, where optimal strength, eco-friendliness, and production efficiency are increasingly demanded. While traditional analytical methods, such as the Three Equations Method, offer foundational approaches to mix design, they often fall short [...] Read more.

The proper design of concrete mixtures is a critical task in concrete technology, where optimal strength, eco-friendliness, and production efficiency are increasingly demanded. While traditional analytical methods, such as the Three Equations Method, offer foundational approaches to mix design, they often fall short in handling the complexity of modern concrete technology. Machine learning-based models have demonstrated notable efficacy in predicting concrete compressive strength, addressing the limitations of conventional methods. This study builds on previous research by investigating not only the impact of computational complexity on the predictive performance of machine learning models but also the influence of different optimization algorithms. The study evaluates the effectiveness of three optimization techniques: the Quasi-Newton Method (QNM), the Adaptive Moment Estimation (ADAM) algorithm, and Stochastic Gradient Descent (SGD). A total of forty-five deep neural network models of varying computational complexity were trained and tested using a comprehensive database of concrete mix designs and their corresponding compressive strength test results. The findings reveal a significant interaction between optimization algorithms and model complexity in enhancing prediction accuracy. Models utilizing the QNM algorithm outperformed those using the ADAM and SGD in terms of error reduction (SSE, MSE, RMSE, NSE, and ME) and increased coefficient of determination (R²). These insights contribute to the development of more accurate and efficient AI-driven methods in concrete mix design, promoting the advancement of concrete technology and the potential for future research in this domain. Full article

(This article belongs to the Collection Concrete and Building Materials)

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25 pages, 8563 KiB

Open AccessArticle

Numerical Analysis of Inertia Forces in the Connecting Rod and Their Impact on Stress Formation

by Andrzej Chmielowiec, Weronika Woś and Jan Czyżewski

Materials 2025, 18(6), 1385; https://doi.org/10.3390/ma18061385 - 20 Mar 2025

Viewed by 263

Abstract

This paper presents a comprehensive model for the inertia force field acting on a moving connecting rod. The derived formulas enable the accurate calculation of resultant inertia forces and their distribution on individual components for finite element analysis (FEA). The method applies to [...] Read more.

This paper presents a comprehensive model for the inertia force field acting on a moving connecting rod. The derived formulas enable the accurate calculation of resultant inertia forces and their distribution on individual components for finite element analysis (FEA). The method applies to symmetrical and complex-shaped connecting rods, addressing challenges in modeling forces for asymmetrical designs. This work advances the precision of stress and vibration modeling in connecting rods, crucial for tribology and reliability studies. By improving the understanding of wear and failure mechanisms in reciprocating systems, it supports design optimization. The article presents the application of the proposed computational methods using three materials typically used for connecting rod construction: 42CrMo4, aluminum 2618, and Ti6Al4V. The presented results demonstrate how the material selection influences the total inertia force and the resulting stresses within the material. The numerical results are presented based on simulations conducted for two connecting rods of different sizes, operating at extremely different rotational speeds. The conducted analyses show that in the examined cases, rotational speed is the key factor influencing inertia stresses. The implementation, based on Open Source tools, allows a numerical analysis of inertia forces and stresses, with all the methods and models available in an open repository. Full article

(This article belongs to the Section Mechanics of Materials)

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19 pages, 8444 KiB

Open AccessArticle

Machine Learning-Assisted Multi-Property Prediction and Sintering Mechanism Exploration of Mullite–Corundum Ceramics

by Qingyue Chen, Weijin Zhang, Xiaocheng Liang, Hao Feng, Weibin Xu, Pengrui Wang, Jian Pan and Benjun Cheng

Materials 2025, 18(6), 1384; https://doi.org/10.3390/ma18061384 - 20 Mar 2025

Viewed by 410

Abstract

Mullite–corundum ceramics are pivotal in heat transfer pipelines and thermal energy storage systems due to their excellent mechanical properties, thermal stability, and chemical resistance. Establishing relationships and mechanisms through traditional experiments is time-consuming and labor-intensive. In this study, gradient boosting regression (GBR), random [...] Read more.

Mullite–corundum ceramics are pivotal in heat transfer pipelines and thermal energy storage systems due to their excellent mechanical properties, thermal stability, and chemical resistance. Establishing relationships and mechanisms through traditional experiments is time-consuming and labor-intensive. In this study, gradient boosting regression (GBR), random forest (RF), and artificial neural network (ANN) models were developed to predict essential properties such as apparent porosity, bulk density, water absorption, and flexural strength of mullite–corundum ceramics. The GBR model (R² 0.91–0.95) outperformed the RF and ANN models (R² 0.83–0.89 and 0.88–0.91, respectively) in accuracy. Feature importance and partial dependence analyses revealed that sintering temperature and K₂O (~0.25%) positively affected bulk density while negatively influencing apparent porosity and water absorption. Additionally, sintering temperature, additives, and Fe₂O₃ (optimal content ~5% and 1%, respectively) were positively related to flexural strength. This approach provided new insight into the relationships between feedstock compositions and sintering process parameters and ceramic properties, and it explored the possible mechanisms involved. Full article

(This article belongs to the Special Issue Advanced Additive Manufacturing Processing of Ceramic Materials)

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13 pages, 5998 KiB

Open AccessArticle

The Microstructure, Crystallization Behavior, and Mechanical Performance Evolutions of Li₂O-Al₂O₃-SiO₂ Glass and Glass–Ceramics with Different Alkaline Earth Oxide Modifications

by Chi Zheng, Danni Li, Mengshuo Guo, Jihong Zhang, Jun Xie and Jianjun Han

Materials 2025, 18(6), 1383; https://doi.org/10.3390/ma18061383 - 20 Mar 2025

Viewed by 375

Abstract

The introduction of alkaline earth oxides into Li₂O-Al₂O₃-SiO₂ glass components can improve the mechanical and optical performances of glass and glass–ceramics for various applications. In this research, microstructures, thermal properties, crystallization behavior, and mechanical performance changes [...] Read more.

The introduction of alkaline earth oxides into Li₂O-Al₂O₃-SiO₂ glass components can improve the mechanical and optical performances of glass and glass–ceramics for various applications. In this research, microstructures, thermal properties, crystallization behavior, and mechanical performance changes in specific Li₂O-Al₂O₃-SiO₂ glass with the introduction of different alkali earth oxides, MgO, CaO, SrO, and BaO, were investigated. From Raman and NMR spectra microstructure analysis, it was confirmed that the addition of MgO could compete with Al as a network former and charge compensator, while increasing the bridging oxygen number with Si and affecting the chemical shift in ²⁹Si. Meanwhile, the glass structures slightly changed due to the introduction of CaO, SrO, and BaO, with larger ionic radii. Meanwhile, the glass transition and first crystallization temperatures increased due to MgO introduction and then decreased with larger-radii alkali earth oxides’ addition, due to different glass network connectivity. After heat treatment, the crystal phases in the glass–ceramics changed with the introduction of alkaline earth oxides. The main crystal phases varied from Li₂Si₂O₅, SiO₂, and LiAlSi₄O₁₀ in glass without alkali earth oxide introduction; to SiO₂, Li_xAl_xSi_3−xO₆, and MgAl₂Si₄O₁₂ in glass with MgO addition; to SiO₂ and Li_xAl_xSi_3−xO₆ with CaO addition; to SiO₂, LiAlSi₄O₁₀, and Li₂SiO₃ for glass with SrO addition; and further to Li₂SiO₅, SiO₂, and LiAlSi₄O₁₀ for glass with BaO addition. Moreover, in the mechanical performance of the glass–ceramics, the Vickers hardness and elastic modulus reached a maximum of 8.61 GPa for glass with MgO and 90.12 GPa for glass with BaO modification, respectively, probably due to different crystal phases. More importantly, the crack resistance values presented a large increase for MgO glass and MgO- or CaO-modified glass–ceramics. Full article

(This article belongs to the Section Advanced and Functional Ceramics and Glasses)

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20 pages, 14845 KiB

Open AccessArticle

The Influence of Ti and Al on the Evolution of Microstructure and Mechanical Properties in Medium-Entropy and High-Entropy Alloys Based on Al_xTi_xCrFe₂Ni₂

by Róbert Kočiško, Patrik Petroušek, Karel Saksl, Ivan Petryshynets, Ondrej Milkovič and Dávid Csík

Materials 2025, 18(6), 1382; https://doi.org/10.3390/ma18061382 - 20 Mar 2025

Viewed by 319

Abstract

This study focuses on the cobalt-free medium-to-high-entropy alloys Al_xCrFe₂Ni₂ and Al_xTi_xCrFe₂Ni₂, investigating the influence of Al_x and Ti_x (where x = 0.2, 0.3, 0.4, 0.5, and 0.6) on [...] Read more.

This study focuses on the cobalt-free medium-to-high-entropy alloys Al_xCrFe₂Ni₂ and Al_xTi_xCrFe₂Ni₂, investigating the influence of Al_x and Ti_x (where x = 0.2, 0.3, 0.4, 0.5, and 0.6) on the development of microstructural and mechanical properties in as-cast and annealed states. Structural changes were examined using optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) measurements, while mechanical properties were evaluated through Vickers hardness testing and compression testing. X-ray diffraction analysis of the Al_xCrFe₂Ni₂ alloys confirmed that increasing the Al content in the as-cast state leads to the formation of a BCC phase, which completely dissolves into the FCC matrix after homogenization annealing. These single-phase alloys exhibit good ductility with relatively high strain hardening, such as the Al_0.6CrFe₂Ni₂ alloy, which achieved a maximum compressive strength of

σ_{m a x} = 1511 M P a

at 50% deformation. A significant strengthening effect of Ti was observed in the Al_xTi_xCrFe₂Ni₂ alloys, the mechanical properties of which are closely linked to the higher BCC phase content in the homogenized structure. The highest compressive strength,

σ_{m a x} = 2239 M P a

, was achieved by the Al_0.5Ti_0.5CrFe₂Ni₂ alloy, which fractured via a transcrystalline brittle fracture at 43% deformation. All alloys investigated offer an excellent balance between strength and ductility, which could meet the requirements of demanding structural applications. Full article

(This article belongs to the Special Issue Research on the Microstructure and Properties of Metal Alloys (2nd Edition))

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18 pages, 9061 KiB

Open AccessArticle

Preparation and Performance Optimization of Lead–Zinc Tailing Sintered Bricks

by Dongliang He, Yanhui Cheng, Rui Li and Hang Lin

Materials 2025, 18(6), 1381; https://doi.org/10.3390/ma18061381 - 20 Mar 2025

Viewed by 317

Abstract

Lead–zinc tailings are waste materials generated from mineral processing and smelting, and their long-term accumulation poses potential threats to the environment and soil. To achieve resource recycling and sustainable development, this study used lead–zinc tailings and clay as raw materials and glass powder [...] Read more.

Lead–zinc tailings are waste materials generated from mineral processing and smelting, and their long-term accumulation poses potential threats to the environment and soil. To achieve resource recycling and sustainable development, this study used lead–zinc tailings and clay as raw materials and glass powder as a modifier to prepare modified lead–zinc tailing sintered bricks. Through full-factor experiments and single-factor experiments, the effects of the material proportions, the sintering temperature, and the holding time on the properties of the sintered bricks were investigated. The results show that the addition of glass powder significantly enhanced the compressive strength of the sintered bricks, reduced their water absorption rate, and improved their volume shrinkage rate. The optimal preparation conditions were as follows: 9% glass powder content, 90% lead–zinc tailings content, a sintering temperature of 1060 °C, and a holding time of 60 min. The resulting sintered bricks met the MU30-strength-grade requirements of the national standard for ordinary sintered bricks (GB/T5101-2017). The sintering temperature has a significant impact on brick performance; the compressive strength first increases, and then decreases, the water absorption rate continues to decrease, and volume change shifts from expansion to contraction. The influence of holding time was relatively weaker, but as the holding time increased, the compressive strength and the water absorption rate of the sintered bricks gradually stabilized. XRD and SEM analyses indicated that the minerals in the lead–zinc tailings decomposed and recrystallized during the sintering process. The liquid phase melt from the glass powder filled the pores and enhanced skeletal strength, thereby improving the microstructure and properties of the sintered bricks. The research findings provide a theoretical basis and practical guidance for the efficient utilization and building material application of lead–zinc tailings. Full article

(This article belongs to the Special Issue Advances in Sustainable Construction and Building Materials (3rd Edition))

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15 pages, 8576 KiB

Open AccessArticle

A Study on the Failure Behavior and Force Transmission of Composite Skin-Stringer Structures Under a Compressive Load

by Guoyang Zhao, Jian Shi, Wei Xu, Nan Sun, Jianjiang Zeng, Guang Yang, Kun Song and Jie Zheng

Materials 2025, 18(6), 1380; https://doi.org/10.3390/ma18061380 - 20 Mar 2025

Viewed by 243

Abstract

Carbon fiber-reinforced composite stringers, which support aircraft skins in resisting tensile, compressive, and shear loads, are widely used in aircraft structures. These composite structures play a crucial role in enhancing the performance and safety of the structural integration of aircrafts. To better understand [...] Read more.

Carbon fiber-reinforced composite stringers, which support aircraft skins in resisting tensile, compressive, and shear loads, are widely used in aircraft structures. These composite structures play a crucial role in enhancing the performance and safety of the structural integration of aircrafts. To better understand the load-bearing capacity of composite stringer structures, this study developed a novel model to study the complex failure and load transmission behavior of T800/3900S-2B fiber-reinforced composite skin-stringer structures under compressive loading. Compression strength tests were conducted on a composite stringer/skin structure, and a three-dimensional FEM was developed using Abaqus/Standard 2022. The model incorporated the modified 3D Hashin initiation criteria and Tserpes degradation law through a UMAT subroutine, which can effectively capture the in-plane ply failure and interlaminar damage. The results revealed a high degree of similarity between the load–displacement curves and failure modes (i.e., matrix compressive cracking, fiber compressive failure, and fiber–matrix shear-out failure) obtained from the simulations and those from the experiments. This study provides an efficient and accurate model to simulate the failure and load transfer of composite skin-stringer structures, offering significant advancements in understanding and predicting the behavior of these critical components. Full article

(This article belongs to the Special Issue Advances in Structural Design and Numerical Modelling of Composite Materials)

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10 pages, 5038 KiB

Open AccessCommunication

ITO Meta-Absorber-Loaded Conformal UHF Monopole Antenna with Wide-Angel RCS Reduction

by Pan Lu, Jiuhao Gong, Xiaona Liu, Yuanxi Cao, Anxue Zhang and Sen Yan

Materials 2025, 18(6), 1379; https://doi.org/10.3390/ma18061379 - 20 Mar 2025

Viewed by 270

Abstract

In this paper, a conformal UHF antenna with a wide-angle radar cross section (RCS) reduction capability is proposed. The radiator of the design is a planar monopole antenna. Since the large physical size of the antenna in UHF band can generate a scatter [...] Read more.

In this paper, a conformal UHF antenna with a wide-angle radar cross section (RCS) reduction capability is proposed. The radiator of the design is a planar monopole antenna. Since the large physical size of the antenna in UHF band can generate a scatter beam with a large RCS in the high operating frequency of radars and other sensing applications, i.e., the X band, two types of ITO (Indium Tin Oxide) meta-absorber are proposed and loaded onto the monopole antenna to suppress the scatter. For the incident beam around the direction orthogonal to the radiator plane, the periodical meta-absorber can realize around a 20 dB RCS reduction in the X band. The incident wave around the parallel direction of the radiator is absorbed by the taper meta-absorber, which can greatly suppress the surface and then reduce the RCS in the horizontal plane. The combined effect means the antenna can achieve a wide-angle RCS reduction. It should be noted that the antenna can still produce a high-efficiency omnidirectional beam after the lossy meta-absorber is loaded. In our opinion, the advantages of the proposed antenna design, including good radiation performance in UHF band and high RCS reduction in X band, make it a suitable candidate for airborne and drone applications. Full article

(This article belongs to the Special Issue Advancements in Optical Materials and Photonic Device Technologies)

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15 pages, 5620 KiB

Open AccessArticle

Physical and Mechanical Properties of Cement Mortars with Recycled Polyethylene Terephthalate: Influence of Grain Size and Composition

by Andrea Petrella, Francesco Todaro, Pravendra Yadav, Jennifer Gubitosa and Michele Notarnicola

Materials 2025, 18(6), 1378; https://doi.org/10.3390/ma18061378 - 20 Mar 2025

Viewed by 313

Abstract

Polyethylene terephthalate (PET) with different grain size after grinding (fine and coarse) was recycled and used as aggregate for non-conventional lightweight cement mortars. The physical and mechanical characteristics were compared to conventional sand-based composites. The workability in the fresh state was evaluated. Accordingly, [...] Read more.

Polyethylene terephthalate (PET) with different grain size after grinding (fine and coarse) was recycled and used as aggregate for non-conventional lightweight cement mortars. The physical and mechanical characteristics were compared to conventional sand-based composites. The workability in the fresh state was evaluated. Accordingly, the composites showed decreases in fluidity with increases in PET percentage weight. Higher thermal insulation and lower mechanical strengths were observed with the increase in plastic dosage due to a density decrease and porosity increase in the composites. Finer grain size PET samples were more resistant (~12–24 MPa) than the coarse-grain samples (~3–23 MPa) due to the higher density and specific surface area of the aggregate. Conversely, higher thermal insulation was obtained with coarse PET addition (~0.6–0.2 W/mK vs. ~0.7–0.35 W/mK). A ductile behavior with discrete cracks after failure was observed after plastic addition to the mixture. Low wettability was observed in PET samples which, although more porous than the sand specimens, showed a hydrophobic behavior which contributed to water repellency. The reported physical, mechanical, thermal, wettability and microstructural features suggest the potential of these composites for both inside and outside applications of non-structural objects. Full article

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58 pages, 23645 KiB

Open AccessReview

Reviewing Additive Manufacturing Techniques: Material Trends and Weight Optimization Possibilities Through Innovative Printing Patterns

by Arturo Ramos, Virginia G. Angel, Miriam Siqueiros, Thaily Sahagun, Luis Gonzalez and Rogelio Ballesteros

Materials 2025, 18(6), 1377; https://doi.org/10.3390/ma18061377 - 20 Mar 2025

Viewed by 732

Abstract

Additive manufacturing is transforming modern industries by enabling the production of lightweight, complex structures while minimizing material waste and energy consumption. This review explores its evolution, covering historical developments, key technologies, and emerging trends. It highlights advancements in material innovations, including metals, polymers, [...] Read more.

Additive manufacturing is transforming modern industries by enabling the production of lightweight, complex structures while minimizing material waste and energy consumption. This review explores its evolution, covering historical developments, key technologies, and emerging trends. It highlights advancements in material innovations, including metals, polymers, composites, and ceramics, tailored to enhance mechanical properties and expand functional applications. Special emphasis is given to bioinspired designs and their contribution to enhancing structural efficiency. Additionally, the potential of these techniques for sustainable manufacturing and industrial scalability is discussed. The findings contribute to a broader understanding of Additive Manufacturing’s impact on design optimization and material performance, offering insights into future research and industrial applications. Full article

(This article belongs to the Special Issue Advances and Applications of 3D Printing and Additive Manufacturing)

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16 pages, 13439 KiB

Open AccessArticle

Three-Dimensional-Printed Biomimetic Structural Ceramics with Excellent Tribological Properties

by Zhaozhi Wang, Yajie Liu, Biao Jiang, Zhiheng Xin and Zhibin Jiao

Materials 2025, 18(6), 1376; https://doi.org/10.3390/ma18061376 - 20 Mar 2025

Viewed by 318

Abstract

Inspired by the ventral scale structure of the oriental sand boa, this study successfully fabricated multiscale bioinspired alumina (Al₂O₃) ceramics by combining the excellent mechanical properties, high-temperature resistance, and high hardness of ceramic composites with direct ink writing (DIW) [...] Read more.

Inspired by the ventral scale structure of the oriental sand boa, this study successfully fabricated multiscale bioinspired alumina (Al₂O₃) ceramics by combining the excellent mechanical properties, high-temperature resistance, and high hardness of ceramic composites with direct ink writing (DIW) 3D printing technology and femtosecond laser processing. A MoS₂ thin film was then deposited on the ceramic surface via radio frequency magnetron sputtering (PVD) to systematically investigate the impact of bioinspired structures on the tribological properties of ceramic composites under both dry and lubricated conditions. Experimental results demonstrated that bioinspired structures at different scales exhibited significant friction-reducing and wear-resistant characteristics compared to blank structures. Specifically, under room-temperature conditions, the friction coefficients of bioinspired ceramic composites with solid lubricants and oil lubrication were 0.3 and 0.148, respectively, indicating excellent tribological performance. These findings confirm the synergistic lubrication effect between bioinspired structures, two-dimensional solid lubricants, and lubricating oil, which significantly enhanced the friction-reducing and wear-resistant properties of ceramic components. Therefore, the synergistic design of multiscale bioinspired structures and solid lubricants provides an innovative strategy for the advanced application of ceramic components. Full article

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13 pages, 3791 KiB

Open AccessArticle

Thermoelectric Properties of Tetrahedrites Produced from Mixtures of Natural and Synthetic Materials

by Beatriz A. Santos, Luís Esperto, Isabel Figueira, João Mascarenhas, Elsa B. Lopes, Rute Salgueiro, Teresa P. Silva, José B. Correia, Daniel de Oliveira, António P. Gonçalves and Filipe Neves

Materials 2025, 18(6), 1375; https://doi.org/10.3390/ma18061375 - 20 Mar 2025

Viewed by 269

Abstract

Thermoelectric materials have considerable potential in the mitigation of the global energy crisis, through their ability to convert heat into electricity. This study aims to valorize natural resources, and potentially reduce production costs, by incorporating tetrahedrite–tennantite (td) ores from the Portuguese Iberian Pyrite [...] Read more.

Thermoelectric materials have considerable potential in the mitigation of the global energy crisis, through their ability to convert heat into electricity. This study aims to valorize natural resources, and potentially reduce production costs, by incorporating tetrahedrite–tennantite (td) ores from the Portuguese Iberian Pyrite Belt into synthetic samples. The ore samples were collected in a mine waste at Barrigão and as “dirty-copper” pockets of ore from the Neves Corvo mine. Subsequently, high-energy ball milling and hot pressing were employed in the production of thermoelectric materials. These are characterized by XRD, SEM/EDS, and thermoelectrical properties. The complete dissolution of the dump material sulfides with the synthetic tetrahedrite constituents led to an increase in the amount of the tetrahedrite–tennantite phase, which was made up of a tetrahedrite–tennantite–(Fe) solid solution. The thermoelectric characterization of these materials is provided, revealing that most of the combined synthetic ore samples displayed better results than the pristine tetrahedrite, mostly due to higher Seebeck coefficient values. Furthermore, the best thermoelectric performance is achieved with 10% of ore, where a power factor of 268 µW.K⁻².m⁻¹ is reached at room temperature. Full article

(This article belongs to the Section Energy Materials)

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17 pages, 4489 KiB

Open AccessArticle

Research on Dynamic Mechanical Properties of Silicon Carbide-Modified Concrete

by Tao Chen, Qingwei Chen, Yang Yu, Erlei Bai, Li Wang, Yanqin Guo and Ang Li

Materials 2025, 18(6), 1374; https://doi.org/10.3390/ma18061374 - 20 Mar 2025

Viewed by 246

Abstract

This research investigates the dynamic mechanical properties of silicon carbide-modified concrete using a ∅ 100 mm large-diameter split Hopkinson pressure bar (SHPB). The effects of silicon carbide content, particle size, and strain rate on dynamic compressive strength, deformation, and energy dissipation characteristics were [...] Read more.

This research investigates the dynamic mechanical properties of silicon carbide-modified concrete using a ∅ 100 mm large-diameter split Hopkinson pressure bar (SHPB). The effects of silicon carbide content, particle size, and strain rate on dynamic compressive strength, deformation, and energy dissipation characteristics were examined. The results indicate that both ordinary concrete and silicon carbide-modified concrete exhibit significant strain rate effects, with peak stress, impact toughness, and fracture degree progressively increasing as strain rate rises. The peak strain and ultimate strain of ordinary concrete decreased with increasing strain rate, while those of silicon carbide-modified concrete decreased initially before increasing again. At a strain rate of 180 s⁻¹, the concrete fracture morphology showed almost no occurrence of cement paste connecting adjacent aggregates. The addition of silicon carbide directly increased the strength of aggregates at the micron scale, thereby enhancing the concrete’s load-bearing ability under high-velocity impact loads. Therefore, the modifying effect of coarse-fineness high-strength silicon carbide particles on the strength and deformation characteristics of concrete was more evident under high strain rate conditions. Full article

(This article belongs to the Special Issue Numerical Modeling and Mechanical Properties of Fiber-Reinforced Cementitious Composites)

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16 pages, 5538 KiB

Open AccessArticle

A New Strategy for the High-Value Utilization of Cobalt Slag: A Solid-State Reaction for the Preparation of Microwave-Absorbing Composite Materials with Excellent Properties

by Xuanzhao Shu, Zeying Wang, Rifan Chen and Yangyang Fan

Materials 2025, 18(6), 1373; https://doi.org/10.3390/ma18061373 - 20 Mar 2025

Viewed by 237

Abstract

Abundant valuable metals such as manganese and cobalt are present in cobalt-rich slags from the hydrometallurgical zinc industry. However, due to the high cost of traditional hydrometallurgical separation methods, these metals cannot be effectively recovered. In this paper, a novel recycling strategy based [...] Read more.

Abundant valuable metals such as manganese and cobalt are present in cobalt-rich slags from the hydrometallurgical zinc industry. However, due to the high cost of traditional hydrometallurgical separation methods, these metals cannot be effectively recovered. In this paper, a novel recycling strategy based on mineral phase recovery was proposed, utilizing cobalt-rich slags as raw materials to fabricate microwave-absorbing composite materials. A feasible solid-phase thermochemical method has been developed to recover the mineral phase from cobalt-rich slags, with calcination temperature 800 °C and duration 90 min, yielding MnCo₂O₄ spinel. The results demonstrated that under the conditions of a ball-to-material ratio of 20:1 and ball milling time of 4 h, the MnCo₂O₄ powder and graphene materials, after being ball-milled and compounded, exhibited appropriate electromagnetic parameters and impedance matching. At 5.2 GHz, the minimum reflection loss of the composite material reached −40 dB. This study provides a new approach for the value-added utilization of valuable metal resources in cobalt-rich slags. Full article

(This article belongs to the Special Issue Advances in Efficient Utilization of Metallurgical Solid Waste)

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16 pages, 9709 KiB

Open AccessArticle

Al Doping Effect on Enhancement of Nonlinear Optical Absorption in Amorphous Bi₂Te₃ Thin Films

by Tengfei Zhang, Shenjin Wei, Shubo Zhang, Menghan Li, Jiawei Wang, Jingze Liu, Junhua Wang, Ertao Hu and Jing Li

Materials 2025, 18(6), 1372; https://doi.org/10.3390/ma18061372 - 20 Mar 2025

Viewed by 248

Abstract

Bismuth telluride (Bi₂Te₃) has attracted significant attention due to its broadband ultrafast optical response and strong nonlinearity at high laser fluence in the field of optoelectronic materials. The objective of this work is to study the effect of Al [...] Read more.

Bismuth telluride (Bi₂Te₃) has attracted significant attention due to its broadband ultrafast optical response and strong nonlinearity at high laser fluence in the field of optoelectronic materials. The objective of this work is to study the effect of Al doping on the structure, linear optical properties, and nonlinear optical absorption behavior of Bi₂Te₃ thin films. The amorphous Al-doped Bi₂Te₃ thin films with varying Al doping concentrations were prepared using magnetron co-sputtering. The structure and linear optical properties were characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry, and UV/Vis/NIR spectrophotometry. The third-order nonlinear optical absorption properties of Al: Bi₂Te₃ thin films were investigated using the open-aperture Z-scan system with a 100 fs laser pulse width at a wavelength of 800 nm and a repetition rate of 1 kHz. The results indicate that Al dopant reduces both the refractive index and extinction coefficient and induces a redshift in the optical bandgap. The optical properties of the films can be effectively modulated by varying the Al doping concentration. Compared with undoped Bi₂Te₃ thin films, Al-doped Bi₂Te₃ thin films exhibit larger nonlinear optical absorption coefficients and higher damage thresholds and maintaining high transmittance. These findings provide experimental evidence and a reliable approach for the further optimization and design of ultrafast nonlinear optical devices. Full article

(This article belongs to the Special Issue Advances in Phase Change Materials: Characterization, Design and Applications)

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16 pages, 19319 KiB

Open AccessArticle

Aging Effect on Push-Out Bond Strength of Six Resin Cements: An In Vitro Study

by Eugenia Baena, Nuria Escribano, Victoria Fuentes, Isabel Reche and Laura Ceballos

Materials 2025, 18(6), 1371; https://doi.org/10.3390/ma18061371 - 20 Mar 2025

Viewed by 975

Abstract

The number of resin cements marketed for fiber post cementation has increased significantly. This study compared the push-out bond strength (PBS) of self-adhesive and universal resin cements used to lute fiber posts at 24 h and after 6 months of aging in artificial [...] Read more.

The number of resin cements marketed for fiber post cementation has increased significantly. This study compared the push-out bond strength (PBS) of self-adhesive and universal resin cements used to lute fiber posts at 24 h and after 6 months of aging in artificial saliva. Fiber posts were luted to eighty human roots endodontically treated with four self-adhesive/one-step resin cements, with one of them also used in combination with its appropriate tooth primer; one universal resin cement, applied as one-step or together with its corresponding universal adhesive (multi-step); and one adhesive/multi-step resin cement, as a control. After storage (24 h or 6 months), the interfaces were subjected to PBS tests and the data were analyzed by two-way ANOVA and Tukey and Student’s t-tests (p < 0.05 defined as statistical significance). The results showed that Scotchbond Universal Plus + RelyX Universal attained statistically higher values at 24 h and 6 months. At 24 h, all resin cements yielded similar PBS to root dentin, while at 6 months, NormoCem obtained the lowest PBS. Storage for 6 months significantly decreased PBS for NormoCem and Multilink Automix. Root section did not influence PBS regardless of storage time. It was concluded that PBS is resin cement dependent. The universal resin cement, RelyX Universal, applied in combination with Scotchbond Universal Plus adhesive, obtained a higher and more stable PBS than the other resin cements tested. Full article

(This article belongs to the Special Issue Advances in New Alloys, Polymers and Composites for Biomedical Applications)

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11 pages, 2994 KiB

Open AccessFeature PaperArticle

How the Pretreatment Temperature of Zeolitic Catalysts Can Affect the Reaction Temperature of Methanol to Olefins and Gasoline Processes

by Simón Yunes, Abel Gaspar Rosas and Antonio Gil

Materials 2025, 18(6), 1370; https://doi.org/10.3390/ma18061370 - 20 Mar 2025

Viewed by 310

Abstract

The dehydration of methanol to produce light olefins and gasoline, known as MTO (methanol-to-olefins) process requires acidic catalysts that maintain their acidity at reaction temperatures. Zeolites, such as SAPOs and ZSM-5, are commonly used for this purpose due to their acidic centers. The [...] Read more.

The dehydration of methanol to produce light olefins and gasoline, known as MTO (methanol-to-olefins) process requires acidic catalysts that maintain their acidity at reaction temperatures. Zeolites, such as SAPOs and ZSM-5, are commonly used for this purpose due to their acidic centers. The initial step in these experiments involves the activation or pretreatment of these solids to remove physically adsorbed water from their pores. Inadequate pretreatment can lead to the destruction of the existing Brönsted sites through the dihydroxylation of surface -OH groups. Therefore, it is crucial to pretreat the zeolites properly to preserve the Brönsted sites. One method is to subject the fresh catalyst to programmed dehydration, which involves desorption at a controlled temperature while monitoring the appearance of water that results from Brönsted site dihydroxylation. The temperature at which the dehydration peak appears determines the optimal reaction temperature. The results presented in this work will demonstrate the progressive deactivation of the catalysts when the reaction temperature exceeds 400 °C. Full article

(This article belongs to the Special Issue Research on Zeolites and Zeolite-Like Materials: Synthesis, Structure, Properties and Application)

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21 pages, 5421 KiB

Open AccessArticle

Prediction Models for Radiological Characterization of Natural Aggregates Based on Chemical Composition and Mineralogy

by Andrés Caño, María del Mar Alonso, Alicia Pachón-Montaño, Queralt Marzal, Guillermo Hernáiz, Luís Sousa and José Antonio Suárez-Navarro

Materials 2025, 18(6), 1369; https://doi.org/10.3390/ma18061369 - 20 Mar 2025

Viewed by 269

Abstract

The radiological characterization of aggregates used in construction materials is essential to determine their suitability from a radiological protection perspective and to ensure their safety for health and the environment. While the activity concentrations of radionuclides present in construction materials are typically determined [...] Read more.

The radiological characterization of aggregates used in construction materials is essential to determine their suitability from a radiological protection perspective and to ensure their safety for health and the environment. While the activity concentrations of radionuclides present in construction materials are typically determined using gamma spectrometry, an alternative approach involves the development of statistical methods and predictive models derived from the chemical composition of the material. A total of 39 aggregates used in construction of various types (siliceous, carbonatic, volcanic, and granitic) have been analyzed, correlating their chemical compositions obtained through X-ray fluorescence (XRF) with the activity concentrations of natural radionuclides measured via gamma spectrometry using principal component analysis (PCA). The results obtained allowed for the observation of an inversely proportional relationship between the chemical composition of the grouping of siliceous and carbonatic aggregates and the content of radionuclides. However, the set of granitic aggregates showed a strong correlation with the natural radioactive series of uranium, thorium, and ⁴⁰K. Conversely, the radionuclide content of volcanic aggregates was independent of their chemical composition. The results obtained from the PCA facilitated the development of different models using multiple regression analysis. The chemical parameters obtained in the proposed models were related to the typical mineralogy in each grouping, ranging from primary minerals such as feldspars to accessory minerals such as anatase, apatite, and pyrolusite. Finally, the models were validated using independent samples from those used to determine the models, achieving RSD (%) values ≤ 30% in 50% of the activity concentrations of ²²⁶Ra, ²³²Th(²¹²Pb), and ⁴⁰K, as well as the estimated ACI. Full article

(This article belongs to the Special Issue Characterization and Optimization of Cement-Based Materials)

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20 pages, 9364 KiB

Open AccessArticle

Analysis of Residual Compressive Strength in 3D Four-Directional Braided Composites After Hygrothermal Aging

by Yongxin Niu, Lingze Bu, Shi Yan, Songming Cai and Zixiang Meng

Materials 2025, 18(6), 1368; https://doi.org/10.3390/ma18061368 - 20 Mar 2025

Viewed by 283

Abstract

This study investigates the effect of hygrothermal environments on the compressive properties of three-dimensional four-directional braided composites through experiments and finite element simulations, revealing the degradation behavior under various hygrothermal conditions. The results indicate that the moisture absorption behavior of the material conforms [...] Read more.

This study investigates the effect of hygrothermal environments on the compressive properties of three-dimensional four-directional braided composites through experiments and finite element simulations, revealing the degradation behavior under various hygrothermal conditions. The results indicate that the moisture absorption behavior of the material conforms to Fick’s law. The longer the hygrothermal aging duration and the higher the temperature, the more significant the reduction in compressive performance, as evidenced by the continuous decline in ultimate stress. The hygrothermal environment primarily affects material performance through moisture absorption and thermal expansion characteristics of the epoxy resin, while the carbon fibers exhibit high stability in such conditions, maintaining the integrity of the three-dimensional four-directional structure. Microscopic observations reveal that hygrothermal aging exacerbates damage at the resin–fiber interface, leading to more pronounced stress concentration. Finite element simulations further quantify the internal stress distribution under hygrothermal conditions, demonstrating that moisture-induced expansion stress is more significant than thermal expansion stress, providing theoretical support and design guidance for improving the performance of composites in extreme environments. Full article

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15 pages, 400 KiB

Open AccessArticle

Magnetic, Phonon, and Optical Properties of Pure and Doped Ba₂FeReO₆ and Sr₂CrReO₆—Bulk Materials and Nanoparticles

by Angel T. Apostolov, Iliana N. Apostolova and Julia M. Wesselinowa

Materials 2025, 18(6), 1367; https://doi.org/10.3390/ma18061367 - 19 Mar 2025

Viewed by 324

Abstract

On the basis of a microscopic model and employing Green’s function technique, the effects of temperature, size, and ion doping on the magnetization and phonon energy of the A_1g mode in double perovskites Ba₂FeReO₆ and Sr₂CrReO [...] Read more.

On the basis of a microscopic model and employing Green’s function technique, the effects of temperature, size, and ion doping on the magnetization and phonon energy of the A_1g mode in double perovskites Ba₂FeReO₆ and Sr₂CrReO₆—both in bulk and nanoscale samples—are investigated for the first time. The Curie temperature T_C and magnetization M decrease as nanoparticle size is reduced. Doping with rare-earth ions such as Sm, Nd, or La at the Ba or Sr sites further reduces M. This behavior originates from the compressive strain induced by the smaller ionic radii of the dopant ions compared to the host ions. As a result, the antiferromagnetic superexchange interaction between Fe or Cr and Re ions is enhanced, along with an increase in the magnetic moment of the Re ion. The dependence of the band gap energy of Sr₂CrReO₆ on temperature, size, and doping is also studied. Near the magnetic-phase-transition temperature T_C, anomalies in phonon energy and damping indicate strong spin–phonon coupling. The theoretical calculations show good qualitative agreement with experimental data. Full article

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14 pages, 4862 KiB

Open AccessArticle

Solid-State Synthesis and Thermoelectric Properties of CuFeSe₂–CuFeS₂ Solid Solutions

by Soon-Man Jang and Il-Ho Kim

Materials 2025, 18(6), 1366; https://doi.org/10.3390/ma18061366 - 19 Mar 2025

Viewed by 337

Abstract

Thermoelectric technology, which converts heat and electricity into each other, has been attracting attention from the perspective of efficient energy utilization. Recently, eco-friendly and cost-effective Cu-based thermoelectric materials have been actively studied. In particular, efforts have been made to improve thermoelectric properties and [...] Read more.

Thermoelectric technology, which converts heat and electricity into each other, has been attracting attention from the perspective of efficient energy utilization. Recently, eco-friendly and cost-effective Cu-based thermoelectric materials have been actively studied. In particular, efforts have been made to improve thermoelectric properties and enhance performance through the formation of solid solutions. This study examines the formation and thermoelectric properties of Cu-chalcogenide solid solutions between eskebornite (tetragonal CuFeSe₂) and chalcopyrite (tetragonal CuFeS₂), synthesized as CuFeSe_2−yS_y (y = 0–2) using solid-state synthesis. These compounds share similar crystal structures, which enable the formation of solid solutions that enhance phonon scattering and may potentially improve thermoelectric performance. As the S content (y) increased, the lattice parameters a and c decreased, attributed to the smaller ionic radius of S²⁻ compared to Se²⁻, as X-ray diffraction analysis identified single-phase regions for 0 ≤ y ≤ 0.4 and 1.6 ≤ y ≤ 2, respectively. However, for 0.8 ≤ y ≤ 1.2, a composite phase of eskebornite and chalcopyrite formed, indicating incomplete solid solution behavior in the intermediate range. Thermoelectric measurements showed a sharp increase in electrical conductivity with increasing S content, alongside a transition in the Seebeck coefficient from positive (p-type) to negative (n-type), attributed to the intrinsic semiconducting nature of the end-member compounds. Eskebornite behaves as a p-type semiconductor, whereas chalcopyrite is n-type, and their combination affects the carrier type and concentration. Despite these changes, the power factor did not show significant improvement due to the inverse relationship between electrical conductivity and the Seebeck coefficient. The thermal conductivity decreased significantly with solid solution formation, with CuFeSe_0.4S_1.6 exhibiting the lowest value of 0.97 Wm⁻¹K⁻¹ at 623 K, a result of enhanced phonon scattering at lattice imperfections and the mass fluctuation effect. This value is lower than the thermal conductivity values of single-phase eskebornite or chalcopyrite. However, the reduction in thermal conductivity was insufficient to compensate for the modest power factor, resulting in no substantial enhancement in the thermoelectric figure of merit. Full article

(This article belongs to the Special Issue Research Progress of Thermoelectric Materials, Modules and Applications)

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15 pages, 2803 KiB

Open AccessArticle

Superplastic Deformation Behavior and Microstructural Evolution of Electroformed Nickel Foils Determined by Thermomechanical Analysis

by Minsu Lee, Hohyeong Kim and Jinho Ahn

Materials 2025, 18(6), 1365; https://doi.org/10.3390/ma18061365 - 19 Mar 2025

Viewed by 197

Abstract

Superplastic deformation, which occurs when fine-grained metals exhibit high ductility (often exceeding 300%) under specific conditions at approximately half of their melting temperature, allows the creation of complex shapes required by the aerospace and electronic material industries. Typically, superplastic characteristics are evaluated using [...] Read more.

Superplastic deformation, which occurs when fine-grained metals exhibit high ductility (often exceeding 300%) under specific conditions at approximately half of their melting temperature, allows the creation of complex shapes required by the aerospace and electronic material industries. Typically, superplastic characteristics are evaluated using universal testing machines (UTMs). However, nickel (Ni) and its alloys, which are applied as electrodeposits in the fabrication of electronic materials, are nanocrystalline in nature and exhibit superplasticity under specific temperatures and deformation conditions. Electrodeposited foils are very thin, making traditional UTM testing challenging; therefore, a new approach is required. In this study, we used a thermomechanical analyzer (TMA) to analyze the superplastic properties of electrodeposited nickel foils simply and precisely. TMAs are particularly appropriate when evaluating thin foils because they yield detailed thermal deformation data, whereas UTMs do not. A TMA reveals thermal deformation of electrodeposited nickel foils across various temperatures, as well as microstructures and grain growth. We performed superplastic analysis at 400 °C, 500 °C, and 600 °C at a strain rate of 1 × 10⁻³ s⁻¹, and microstructural data were obtained through X-ray diffraction and electron backscatter diffraction. Superplastic deformation was apparent at 400 °C. The data obtained through our systematic analysis using a TMA will guide future studies on the application of superplastic properties of electrodeposited nanocrystalline nickel foils. Full article

(This article belongs to the Special Issue Quality, Microstructure and Properties of Metal Alloys (Second Volume))

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27 pages, 19915 KiB

Open AccessArticle

The Effect of Incorporating Lüders Plateau into a Plasticity Model in Predicting the Ballistic Impact Responses of 40CrNiMoA Steel Projectiles and Plates

by Yahui Shi, Xinke Xiao, Bin Jia, Yuge Wang and Jicheng Li

Materials 2025, 18(6), 1364; https://doi.org/10.3390/ma18061364 - 19 Mar 2025

Viewed by 355

Abstract

Lüders plateau, a frequently observed phenomenon in uniaxial tensile tests of 40CrNiMoA high-strength steel, significantly influences material fracture behavior but is often neglected in characterizing metal plasticity and fracture properties. This study aims to develop a modified Johnson–Cook-2 (MJC-2) plasticity model incorporating Lüders [...] Read more.

Lüders plateau, a frequently observed phenomenon in uniaxial tensile tests of 40CrNiMoA high-strength steel, significantly influences material fracture behavior but is often neglected in characterizing metal plasticity and fracture properties. This study aims to develop a modified Johnson–Cook-2 (MJC-2) plasticity model incorporating Lüders plateau effects and evaluate its predictive capability for impact response. A series of mechanical tests were conducted and the plasticity model was calibrated through an experimental–numerical approach. Taylor impact and ballistic impact tests were conducted using a single-stage gas gun, with corresponding numerical simulations performed in finite element (FE) software. The results demonstrate that the MJC-2 model provides superior accuracy in predicting the fracture behavior of both targets and Taylor rods, as well as ballistic limit velocities (BLVs). Compared to models neglecting Lüders plateau, MJC-2 significantly enhances prediction precision. Full article

(This article belongs to the Section Metals and Alloys)

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14 pages, 4804 KiB

Open AccessArticle

Enhancement of Fracture Toughness of Inner Liner Material for Type IV Hydrogen Storage Cylinders Based on Molecular Dynamics Method

by Bingyu Yang, Jinqi Luo, Yuan Wu, Zhenhan Yang and Jianping Zhao

Materials 2025, 18(6), 1363; https://doi.org/10.3390/ma18061363 - 19 Mar 2025

Viewed by 277

Abstract

To develop liner materials with improved toughness, this study combines molecular dynamics simulations and experimental testing to investigate the effect of different mass ratios (10/0, 7/3, 6/4, 4/6, 3/7, and 0/10) of high-density polyethylene (HDPE)/polyamide 6 (PA6) on their fracture toughness of the [...] Read more.

To develop liner materials with improved toughness, this study combines molecular dynamics simulations and experimental testing to investigate the effect of different mass ratios (10/0, 7/3, 6/4, 4/6, 3/7, and 0/10) of high-density polyethylene (HDPE)/polyamide 6 (PA6) on their fracture toughness of the composites. The fracture toughness was quantitatively assessed using the J-integral method, while the material’s behavior in terms of crack propagation during tensile deformation was examined at the molecular level. The results reveal that as the HDPE mass ratio increases, the fracture toughness of the composites also gradually improves. Furthermore, the fracture toughness of four materials (PA6, 4HDPE/6PA6, 7HDPE/3PA6, and HDPE) was tested using the essential work of the fracture method. The trend observed in the simulation results was in agreement with the experimental results, validating the reliability of the molecular dynamics simulation. Full article

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15 pages, 3613 KiB

Open AccessArticle

Dynamic Response of Buried Pressurized Pipelines When Subjected to Transverse Impact Loading: Experimental Study

by Ruobing Wu, Kai Zhuang, Yuchao Yang, Zhijie Wu and Feng Liu

Materials 2025, 18(6), 1362; https://doi.org/10.3390/ma18061362 - 19 Mar 2025

Viewed by 204

Abstract

This study investigated the dynamic behavior of pressurized pipelines under impact loads in various burial environments. A total of 60 tests were conducted using a drop-weight impact testing apparatus, with high-speed cameras and sensors used to collect data throughout the experiments. This approach [...] Read more.

This study investigated the dynamic behavior of pressurized pipelines under impact loads in various burial environments. A total of 60 tests were conducted using a drop-weight impact testing apparatus, with high-speed cameras and sensors used to collect data throughout the experiments. This approach enabled a thorough investigation of the effects of the soil type, burial depth, and internal pressure on pipeline behavior. The results show that pipeline deformation decreases as burial depth and soil stiffness increase. Under similar conditions, unpressurized pipelines exhibit significantly greater plastic deformation than pressurized pipelines, indicating superior energy absorption. The application of internal pressure leads to a marked increase in the peak impact force compared to scenarios without internal pressure. Fluctuations in internal volume cause pressure variations, affecting the response of the pipeline. Additionally, higher soil stiffness results in increased peak impact force, particularly in loess environments, suggesting that stiffer soils improve pipeline impact resistance. It is important to note that deeper burial does not always lead to reduced impact forces. In stiff soil conditions, greater burial depth may even amplify the impact force. These effects are closely associated with stress concentration under impact loads, changes in soil support capacity, and the influence of internal pressure. The test data and analysis provided in this paper will contribute to optimizing pipeline design and protective strategies, thereby enhancing their safety and reliability. Full article

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8 pages, 2927 KiB

Open AccessCommunication

Preparation of an Fe₈₀P₁₄B₆ Bulk Nanocrystalline Alloy via Solidification from a Molten Alloy at Deep Undercooling

by Xiaoming Chen, Tuo Wang, Zhe Zhang, Yuluo Li, Mingming Wang, Kuang Lv, Guigen Wu, Xiaoli Wang, Zhangyin Li and Xidong Hui

Materials 2025, 18(6), 1361; https://doi.org/10.3390/ma18061361 - 19 Mar 2025

Viewed by 214

Abstract

Using fluxing technology, molten Fe₈₀P₁₄B₆ alloy achieved significant undercooling (ΔT). Experimental results demonstrate that the solidified morphologies of the Fe₈₀P₁₄B₆ alloy vary considerably with ΔT. At ΔT = [...] Read more.

Using fluxing technology, molten Fe₈₀P₁₄B₆ alloy achieved significant undercooling (ΔT). Experimental results demonstrate that the solidified morphologies of the Fe₈₀P₁₄B₆ alloy vary considerably with ΔT. At ΔT = 100 K, the microstructure is dendritic. At ΔT = 250 K, a variety of eutectic morphologies are observed, including a network-like structure near the solidification center, attributed to liquid spinodal decomposition. At ΔT = 350 K, the microstructure exhibits a uniform, random network-like morphology with approximately 50 nm. The mechanical property of the specimens solidified at different ΔT was checked by microhardness test, indicating that the hardness of the specimens increases with the increase in ΔT, reaching a maximum value of 1151 HV_0.2. Full article

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21 pages, 4891 KiB

Open AccessArticle

Description of the Lubricant Behavior Based on the Theory of Elasto-Viscoplastic

by Yuriy O. Nosov, Anna A. Kamenskikh and Anastasia P. Bogdanova

Materials 2025, 18(6), 1360; https://doi.org/10.3390/ma18061360 - 19 Mar 2025

Viewed by 219

Abstract

The aim of the work is to provide a mathematical description of the lubricant’s behavior model used in sliding bearings of bridge structures. It was previously established that the Maxwell model does not correctly describe the lubricant’s behavior in a wide range of [...] Read more.

The aim of the work is to provide a mathematical description of the lubricant’s behavior model used in sliding bearings of bridge structures. It was previously established that the Maxwell model does not correctly describe the lubricant’s behavior in a wide range of temperatures and deformation rates. The lubricant model should take into account not only viscosity but also plasticity. The Anand model, which was adapted by introducing temperature dependencies for a number of material parameters, was chosen to describe the lubricant behavior. The functionality of the previously created procedure for identifying material properties was also expanded on the modified Anand model. This made it possible to obtain a lubricant mathematical model with an error of less than 5% in the operating temperature range from −40 to +80 °C. The study included a description of the behavior model for two lubricants: CIATIM-221 and CIATIM-221F. CIATIM-221F differs from CIATIM-221 by including superfine particles of polytetrafluoroethylene (PTFE) to improve properties. The study confirmed that the modified Anand model allows describing the material behavior more accurately than the Maxwell model. It was found that the samples behave as a solid over the entire temperature range (from −40 to +80 °C). A comparative analysis of the thermal behavior of CIATIM-221 and CIATIM-221F was performed. Full article

(This article belongs to the Special Issue Reliability Modeling of Complex Systems in Materials and Devices)

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18 pages, 8268 KiB

Open AccessArticle

Comparative Study of the Corrosive Behaviors of Rust Layers on Bronze Ware in Different Corrosive Environments

by Bingbing Li, Qixing Xia and Wenqiang Dong

Materials 2025, 18(6), 1359; https://doi.org/10.3390/ma18061359 - 19 Mar 2025

Viewed by 313

Abstract

It is of great significance to clarify the corrosion mechanism of rust layers on bronze ware for appropriate conservation measures. In this study, the corrosion behavior of Cu-Sn bronze alloys in a 3.5 wt.% NaCl solution and a simulated archaeological soil solution was [...] Read more.

It is of great significance to clarify the corrosion mechanism of rust layers on bronze ware for appropriate conservation measures. In this study, the corrosion behavior of Cu-Sn bronze alloys in a 3.5 wt.% NaCl solution and a simulated archaeological soil solution was studied and compared using electrochemical measurements, microscopic observations, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results showed that the presence of Cl⁻ was the key factor leading to the formation of harmful rust such as Cu₂(OH)Cl₃. In the NaCl solution, the rapid accumulation of Cl-containing corrosion products provided a certain degree of protection to Cu-Sn alloys, but the products easily fell off, thus increasing the continuous corrosion reactions again. This resulted in a significant increase in the corrosion rate of the alloy (i_corr from 4.845 μA·cm⁻² to 27.21 μA·cm⁻²) and a decrease in polarization resistance (R_p from 5.17 kΩ·cm² to 3.27 kΩ·cm²). In contrast, the corrosion reactions of the Cu-Sn alloy were dominated by complex ions other than Cl⁻ in archaeological soil environments, and the corrosion products tended to form stable and dense rust layers (i_corr was always lower than 1.6 μA·cm⁻², and R_p was maintained above 24 kΩ·cm²), which improved corrosion resistance by two orders of magnitude compared to the unstable rust layer that formed in NaCl solution. In addition, Cl-containing corrosion products boosted the wettability of rust layers, thereby facilitating penetration of corrosive media that strengthened corrosion reactions. This study deepens our understanding of the degradation mechanisms of bronze artifacts and provides a scientific basis for developing bronze conservation strategies. Full article

(This article belongs to the Special Issue Corrosion Electrochemistry and Protection of Metallic Materials)

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Materials, Volume 18, Issue 6 (March-2 2025) – 201 articles

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