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The molecular foundations of epidermal cell wall mechanics are critical for understanding structure-function relationships of primary cell walls in plants and facilitating the design of bioinspired materials. To uncover the molecular mechanisms regulating the high extensibility and strength of the cell wall, the onion epidermal wall is stretched uniaxially to various strains and cell wall structures from mesoscale to atomic scale are characterized. Upon longitudinal stretching to high strain, epidermal walls contract in the transverse direction, resulting in a reduced area. Atomic force microscopy shows that cellulose microfibrils exhibit orientation-dependent rearrangements at high strains: longitudinal microfibrils are straightened out and become highly ordered, while transverse microfibrils curve and kink. Small-angle X-ray scattering detects a 7.4 nm spacing aligned along the stretch direction at high strain, which is attributed to distances between individual cellulose microfibrils. Furthermore, wide-angle X-ray scattering reveals a widening of (004) lattice spacing and contraction of (200) lattice spacing in longitudinally aligned cellulose microfibrils at high strain, which implies longitudinal stretching of the cellulose crystal. These findings provide molecular insights into the ability of the wall to bear additional load after yielding: the aggregation of longitudinal microfibrils impedes sliding and enables further stretching of the cellulose to bear increased loads.

The quantitative relationship between material microstructures, such as grain distributions, and the nonlinear strain-hardening behaviors of polycrystalline metals has not yet been completely understood. This study finds that the grain correlation dimension of polycrystals D is universally equal to the reciprocal of the strain-hardening exponent by experimental research and fractal geometry analysis. From a geometric perspective, the correlation dimension of grains is consistent with that of the equivalent plastic strain field, which represents the correlation dimension of the material manifold. According to the definition of the Hausdorff measure and Ludwik constitutive model, the strain-hardening exponent represents the exponent derived from the Dth root of the measure relationship. This universal law indicates that the strain-hardening behaviors are fractal geometrized and that the strain-hardening exponent represents a geometrical parameter reflecting the multifractal characteristics of grain structures. This conclusion can enhance the comprehension of the relationship between microstructure and mechanical properties of materials and highlights the importance of designing materials with non-uniform grain distributions to achieve desired hardening properties. [ABSTRACT FROM AUTHOR]

A novel precipitate-strengthened Co–Cr–Ni medium-entropy alloy with a pure “FCC + L12” dual-phase structure is developed by adding a high concentration (6 at.%) of Al and Ti elements. After aging heat treatment at 700 °C for 4 h, the hierarchical L12 phases, composed of primary large-sized L12 phases (∼70 nm) and secondary L12 particles (∼14 nm), are achieved. The designed alloy featuring hierarchical L12 phases exhibits excellent strength-ductility combinations and strain-hardening ability, properties that are much improved over their counterparts with homogeneous dispersed L12 phases (∼13 nm) and without L12 phases. Especially, the yield strength (1320 MPa), ultimate tensile strength (1886 MPa), and average strain-hardening rate (5.15 GPa) are obtained in the alloy with hierarchical L12 precipitates deformed at cryogenic temperature. The Orowan bypass mechanism of the primary L12 phases, along with the shearing mechanism of the secondary L12 phases, collectively contributes to the exceptional strength of the alloy with hierarchical L12 precipitates. The penetration of dislocations and stacking faults (SFs) in the primary L12 phases, combined with hetero-deformation-induced (HDI) hardening attributed to these hierarchical L12 precipitates, may be a key factor in improving strain-hardening properties of the alloy.

Laser powder bed-fused Ti6Al4V alloy has numerous applications in biomedical and aerospace industries due to its high strength-to-weight ratio. The brittle α′-martensite laths confer both the highest yield and ultimate tensile strengths; however, they result in low elongation. Several post-process heat treatments must be considered to improve both the ductility behavior and the work-hardening of as-built Ti6Al4V alloy, especially for aerospace applications. The present paper aims to evaluate the work-hardening behavior and the ductility of laser powder bed-fused Ti6Al4V alloy heat-treated below (704 and 740 °C) and above (1050 °C) the β-transus temperature. Microstructural analysis was carried out using an optical microscope, while the work-hardening investigations were based on the fundamentals of mechanical metallurgy. The work-hardening rate of annealed Ti6Al4V samples is higher than that observed in the solution-heat-treated alloy. The recrystallized microstructure indeed shows higher work-hardening capacity and lower dynamic recovery. The Considère criterion demonstrates that all analyzed samples reached necking instability conditions, and uniform elongations (>7.8%) increased with heat-treatment temperatures. [ABSTRACT FROM AUTHOR]

Experimental investigations have revealed that the crushing response of axially loaded tubular metallic members changes significantly depending on the strain-hardening capacity of the material. In this paper, the post-yield response of axially loaded stainless-steel and mild-steel tubes are examined under quasi-static loading from the perspective of deformation-controlled and force-controlled collapse mechanisms. The rotational instability of the plastic hinges developed along the tubes is traced numerically by considering an isolated plastic hinge model selected at the critical length of the tubes' shell. The characteristics of the hinges are probed using the moment-rotation diagrams. The stress profiles in the critical region of the tubes at various loading states are investigated. It is observed that the tubes' stability and energy absorption capacity are significantly dependent on the strain-hardening capacity of the material exploited during the formation of the plastic hinges. [ABSTRACT FROM AUTHOR]

In light of the effort for decarbonization of the energy sector, it is believed that common geopolymer binding materials such as fly ash may eventually become scarce and new geological aluminosilicate materials should be explored as alternative binders in geopolymer concrete. A novel, tension-hardening geopolymer concrete (THGC) that incorporates high amounts of semi-reactive quarry wastes (metagabbro) as a precursor, and coarse quarry sand (granite) was developed in this study using geopolymer formulations. The material was optimized based on the particle packing theory and was characterized in terms of mechanical, physical, and durability properties (that is, compressive, tensile, and flexural resistance; Young's modulus; Poisson's ratio; absorption; drying shrinkage; abrasion; coefficient of thermal expansion; and chloride-ion penetration, sulfate, and salt-scaling resistance). The developed THGC, with an air-dry density of 1940 kg/m³ (121 lb/ft³), incorporates short steel fibers at a volume ratio of 2%, and is highly ductile in both uniaxial tension and compression (uniaxial tensile strain capacity of 0.6% at an 80% post-peak residual tensile strength). Using digital image correlation (DIC), multiple crack formation was observed in the strain-hardening phase of the tension response. In compression, the material maintained its integrity beyond the peak load, having attained 1.8% compressive strain at 80% post-peak residual strength, whereas upon further reduction to 50% residual strength, the sustained axial and lateral strains were 2.5% and 3.5%, respectively. The material exhibited low permeability to chloride ions and significant abrasion resistance due to the high contents of metagabbro powder and granite sand. The enhanced properties of the material, combined with the complete elimination of ordinary portland cement from the mixture, hold promise for the development of sustainable and resilient structural materials with low CO2 emissions, while also enabling the innovative disposal of wastes as active binding components. [ABSTRACT FROM AUTHOR]

Metallic materials are commonly characterized through tensile tests. For ductile metals, a consistent part of the test occurs after the necking onset. A first estimate of the post-necking behavior could be obtained by extrapolating the mathematical model that fits the pre-necking law. However, as well known, the accuracy of the predictions would not be guaranteed. Therefore, over the past decades many efforts have been devoted to dealing with the necking phenomenon. The most popular correction formula proposed by Bridgman is an analytical method based on the neck geometry. Despite being widely used, it may not be accurate at large strains due to the assumption of uniform distribution of the equivalent stress and equivalent strain in the specimen minimum cross-section. Starting from Bridgman's idea and in order to overcome its limitations, the present paper develops an efficient method to calibrate the hardening law of isotropic metallic materials at large strains. The proposed method requires to record the outer contour of the necking zone during the test and to build a dataset of necking deformed shapes. Experimental quasi-static tensile tests were analyzed with the proposed approach, which appears promising when critically compared with other methods. [ABSTRACT FROM AUTHOR]

Traditional steel-based reinforcements face corrosion issues that compromise the durability of concrete structures. Large concrete covers are recommended to mitigate corrosion of steel reinforcements, resulting in thicker, heavier structures with increased material consumption and costs, making them less sustainable. Textile reinforced concrete (TRC), with its corrosion resistance, high tensile strength, drapeability, formability, and lightweight nature, offers a sustainable alternative. It necessitates less concrete cover, thereby reducing costs and material consumption, making it suitable for lightweight and durable structural components. Various combinations of textile structures achieved through selective adjustments to fibre, yarn, and fabric geometry present significant potential for developing customized TRC elements. This issue of Textile Progress delves into the environmental impact of construction materials, TRC composition and manufacturing, mechanical testing techniques, and the influence of textile (yarn, braided fabric, woven fabric, knitted fabric, 3-D spacer fabric, nonwoven fabric) structural parameters on TRC behaviour. Additionally, the effects of textile coatings, filler incorporation, and discrete fibre integration on TRC properties are also explored. Overall, textile reinforcement in concrete enhances properties such as tensile strength, ductility, strain hardening behaviour, flexural strength, impact resistance, toughness, multiple cracking behaviour, and reduced crack width and spacing, whilst also bolstering resistance to environmental factors. [ABSTRACT FROM AUTHOR]

Adopting the novel proposed unified strain‐hardening and strain‐softening (UHS) model and finite difference method, an efficient semi‐analytical solution is proposed to study the influence of the nonlinear behavior of rock on ground reaction. The proposed solution eliminates stress vibrations of the classical method that occurred in the strain‐hardening zone, because it judges the elastic or plastic state of the calculation nodes before calculating the ground reaction; compared with the iterative solution, the proposed solution avoids iteratively solving for the plastic internal variables at each calculated node, resulting in that its computational efficiency is improved by more than 10 times. The proposed solution was verified by comparing it with the iterative solution, and numerical solution. Moreover, the effects of initial yield strength, peak strength, residual strength, and supporting pressure on ground reaction after tunnel excavation are studied. The results show that increasing the initial yield strength and residual strength will obviously decrease the plastic zone (PZ) and sub‐zones. The peak strength of rock has limited influence on the radius of PZ, which mainly adjusts the ratio of each sub‐zone in PZ. In addition, increasing the support pressure is an effective means to control the radius of PZ and sub‐zones in deep buried tunnels. [ABSTRACT FROM AUTHOR]

The carbon-doped Fe50Mn30Co10Cr10 HEAs with excellent cryogenic mechanical properties were prepared by powder metallurgy, and their tensile deformation behavior and strain-hardening mechanism were investigated. The yield strength of the HEAs at 77 K improved from 489.7 to 1087.0 MPa as the carbon content increased from 0 to 3 at. %, which mainly stems from the increased lattice friction caused by the addition of carbon and the cryogenic environment; the ultimate tensile strength of the HEAs doped with 2 and 3 at. % carbon reached 1.2 and 1.4 GPa, respectively, while the elongation to fracture reached 31.6 % and 16.8 %, respectively, which is mainly attributed to the joint activation of microbands, twinning, and HCP phase. The deformation mechanism gradually changed from deformation-induced phase transformation to microbands and twinning with increasing carbon content under cryogenic conditions. This study provides a meaningful reference for the design and development of powder metallurgy HEAs with excellent performance in cryogenic applications.

The quantitative relationship between material microstructures, such as grain distributions, and the nonlinear strain-hardening behaviors of polycrystalline metals has not yet been completely understood. This study finds that the grain correlation dimension of polycrystals D is universally equal to the reciprocal of the strain-hardening exponent by experimental research and fractal geometry analysis. From a geometric perspective, the correlation dimension of grains is consistent with that of the equivalent plastic strain field, which represents the correlation dimension of the material manifold. According to the definition of the Hausdorff measure and Ludwik constitutive model, the strain-hardening exponent represents the exponent derived from the Dth root of the measure relationship. This universal law indicates that the strain-hardening behaviors are fractal geometrized and that the strain-hardening exponent represents a geometrical parameter reflecting the multifractal characteristics of grain structures. This conclusion can enhance the comprehension of the relationship between microstructure and mechanical properties of materials and highlights the importance of designing materials with non-uniform grain distributions to achieve desired hardening properties.

To analyze various types of cold formability in TRIP-aided polygonal ferrite (TPF), annealed martensite (TAM), and bainitic ferrite (TBF) steels, the effects of the mean normal stress on the strain-hardening, strain-induced martensite transformation, and void-formation behaviors were investigated. The strain-hardening behavior was influenced by positive mean normal stress and was hardly influenced by zero and negative mean normal stresses in all steels. Positive mean normal stress promoted the strain-induced martensitic transformation behavior, especially in TBF steel due to the high mechanical stability of the retained austenite. The void-formation behavior was also promoted by positive mean normal stress, especially in TPF steel. These behaviors were also related to the microstructural properties, such as the matrix structure, retained austenite characteristics, and second phase. [ABSTRACT FROM AUTHOR]

Laser powder bed-fused Ti6Al4V alloy has numerous applications in biomedical and aerospace industries due to its high strength-to-weight ratio. The brittle α′-martensite laths confer both the highest yield and ultimate tensile strengths; however, they result in low elongation. Several post-process heat treatments must be considered to improve both the ductility behavior and the work-hardening of as-built Ti6Al4V alloy, especially for aerospace applications. The present paper aims to evaluate the work-hardening behavior and the ductility of laser powder bed-fused Ti6Al4V alloy heat-treated below (704 and 740 °C) and above (1050 °C) the β-transus temperature. Microstructural analysis was carried out using an optical microscope, while the work-hardening investigations were based on the fundamentals of mechanical metallurgy. The work-hardening rate of annealed Ti6Al4V samples is higher than that observed in the solution-heat-treated alloy. The recrystallized microstructure indeed shows higher work-hardening capacity and lower dynamic recovery. The Considère criterion demonstrates that all analyzed samples reached necking instability conditions, and uniform elongations (>7.8%) increased with heat-treatment temperatures.

Metallic materials are commonly characterized through tensile tests. For ductile metals, a consistent part of the test occurs after the necking onset. A first estimate of the post-necking behavior could be obtained by extrapolating the mathematical model that fits the pre-necking law. However, as well known, the accuracy of the predictions would not be guaranteed. Therefore, over the past decades many efforts have been devoted to dealing with the necking phenomenon. The most popular correction formula proposed by Bridgman is an analytical method based on the neck geometry. Despite being widely used, it may not be accurate at large strains due to the assumption of uniform distribution of the equivalent stress and equivalent strain in the specimen minimum cross-section. Starting from Bridgman’s idea and in order to overcome its limitations, the present paper develops an efficient method to calibrate the hardening law of isotropic metallic materials at large strains. The proposed method requires to record the outer contour of the necking zone during the test and to build a dataset of necking deformed shapes. Experimental quasi-static tensile tests were analyzed with the proposed approach, which appears promising when critically compared with other methods.

Highly-ductile alkali-activated slag-based composites (HD-AASC) are fiber-reinforced cement-free materials possessing pseudo strain-hardening behavior and multiple-cracking phenomena. In this research, the feasibility of developing extremely-ductile alkali-activated slag-based composite (ED-AASC) with a tensile strain capacity over 20% is presented. Specimens with a moderate amount of sand and crumb rubber particles were made by applying new mixing and curing procedures. Then the density, compressive strength, and tension tests were performed. Test results showed that the ED-AASC (R5-S8-M1 mixture) had a tensile strain capacity of 22.3%, compressive strength of 53.6 MPa, and average crack width of 212 μm. By adopting two performance indexes (f c ε t s and f t s ε t s ), the performance of ED-AASC was compared with those of previous high-ductile composites; the tensile strain capacity of the composite was also compared with the minimum extensibility of steel bars for concrete reinforcement, as specified in ASTM and ISO. In addition, the sustainability of ED-AASC was evaluated. [ABSTRACT FROM AUTHOR]

In order to find the ideal process parameters, the friction stir welding (FSW) is assessed with a mathematical optimisation technique in this paper. In terms of optimisation, the objectives are process-related in that they define or represent how the process behaves. Since the FSW is solid-state and does not involve melting, many of the problems of conventional fusing welding techniques may be avoided. In FSW process, two work pieces are submerged in a spinning tool. As a result of friction and plastic dissipation, the temperature rises to the point where the material is sufficiently softened to be mixed together, forming a weld. Involving solid material, heat transmission, thermal softening, recrystallization and the production of residual stresses, the process is multi-physics in nature. [ABSTRACT FROM AUTHOR]

In this research, an upper bound (UB) analysis of channel angular pressing process was carried out considering die geometric characteristics including die angle, thicknesses of the inlet and the outlet channels, radiuses of outer and inner corners, length of the outlet channel, as well as the length of initial billet, friction and strain-hardening of material, under cold conditions and for a billet with a rectangular cross-section. To validate the results of the UB analysis, the result of the analytical equations was compared with that of the numerical simulation and actual process. The results revealed that the total plastic strain and the process force were augmented by reducing the die angle, the outlet channel thickness, and the outer corner radius, as well as by increasing the inlet channel thickness and the inner corner radius. It was also shown that the process force increased with augmenting the initial billet length. A very good agreement was obtained between the results of the analytical method and numerical and experimental methods. [ABSTRACT FROM AUTHOR]

Advanced elastomers are increasingly used in emerging areas, for example, flexible electronics and devices, and these real‐world applications often require elastomers to be stretchable, tough and fire safe. However, to date there are few successes in achieving such a performance portfolio due to their different governing mechanisms. Herein, a stretchable, supertough, and self‐extinguishing polyurethane elastomers by introducing dynamic π–π stacking motifs and phosphorus‐containing moieties are reported. The resultant elastomer shows a large break strain of ≈2260% and a record‐high toughness (ca. 460 MJ m−3), which arises from its dynamic microphase‐separated microstructure resulting in increased entropic elasticity, and strain‐hardening at large strains. The elastomer also exhibits a self‐extinguishing ability thanks to the presence of both phosphorus‐containing units and π–π stacking interactions. Its promising applications as a reliable yet recyclable substrate for strain sensors are demonstrated. The work will help to expedite next‐generation sustainable advanced elastomers for flexible electronics and devices applications. [ABSTRACT FROM AUTHOR]

Rare earth materials containing magnesium alloy AZ91B and AZ31B is finding widespread use in the automotive, aerospace and military industries due to its greater strength-to-weight ratio and formability. Magnesium is typically regarded as difficult to fuse together through material fusion procedures due to flaws found in welding inclusions, porosity and welded junction distortions. Friction stir welding solid state joining procedure is used for Mg joining alloys successfully. The process variables influencing the combined characteristics of weldments include tool pin geometry, downward axial force, tool welding speed (rpm). In the current research, five distinct tool types were used to create friction stir weldment geometries. There were 18 trials overall with 3 components and 8 stages run in accordance with the primary composite design matrix. The information produced by a mathematical model through response surface approach was sufficient for the developed ANOVA was used to verify the model. Large interaction between welding parameters and tensile strength graphs are utilised to depict its behaviour. It was discovered that the cylindrical straight pin has the greatest tensile qualities. The mathematical model is beneficial for adjusting the tensile strength forecast to enhance the weld quality by choosing suitable process parameters for AZ31B and AZ91B welded magnesium alloys. [ABSTRACT FROM AUTHOR]

To analyze various types of cold formability in TRIP-aided polygonal ferrite (TPF), annealed martensite (TAM), and bainitic ferrite (TBF) steels, the effects of the mean normal stress on the strain-hardening, strain-induced martensite transformation, and void-formation behaviors were investigated. The strain-hardening behavior was influenced by positive mean normal stress and was hardly influenced by zero and negative mean normal stresses in all steels. Positive mean normal stress promoted the strain-induced martensitic transformation behavior, especially in TBF steel due to the high mechanical stability of the retained austenite. The void-formation behavior was also promoted by positive mean normal stress, especially in TPF steel. These behaviors were also related to the microstructural properties, such as the matrix structure, retained austenite characteristics, and second phase.

Abstract Advanced elastomers are increasingly used in emerging areas, for example, flexible electronics and devices, and these real‐world applications often require elastomers to be stretchable, tough and fire safe. However, to date there are few successes in achieving such a performance portfolio due to their different governing mechanisms. Herein, a stretchable, supertough, and self‐extinguishing polyurethane elastomers by introducing dynamic π–π stacking motifs and phosphorus‐containing moieties are reported. The resultant elastomer shows a large break strain of ≈2260% and a record‐high toughness (ca. 460 MJ m−3), which arises from its dynamic microphase‐separated microstructure resulting in increased entropic elasticity, and strain‐hardening at large strains. The elastomer also exhibits a self‐extinguishing ability thanks to the presence of both phosphorus‐containing units and π–π stacking interactions. Its promising applications as a reliable yet recyclable substrate for strain sensors are demonstrated. The work will help to expedite next‐generation sustainable advanced elastomers for flexible electronics and devices applications.

This article presents the effects of thermal annealing at elevated temperatures (> glass transition temperature Tg) on the performance of polymer parts via material extrusion 3D printing. Both semi-crystalline and amorphous filaments were used. As-printed parts were designed to be amorphous and then annealed at 60, 110 and 150 °C for different durations ranging from 50 to 6400 s. The flexural strength and Young’s modulus increased by a maximum of approximately 10%. The increase was ascribed to crystallisation development during annealing, as confirmed by thermal and morphology characterisations. Hence, this effect was only observed with semi-crystalline materials. On the other hand, all the annealed parts expanded in the thickness direction and shrank in the perpendicular plane. The maximum linear strain reached 20%, while the volume strain was negligible. These morphology changes after annealing reversed the strain-hardening of the strand and led to inferior strand performance against local tensile deformation. The degradation can outweigh the benefits of crystallinity development. For amorphous parts, the degradation reached approximately 25% in both the flexural strength and the modulus.

The strain-hardening behavior of soils and rocks under compression is critical for evaluating the construction stability in geological and mining engineering. Numerical simulation is an effective approach and widely used in the stability analysis of constructions. To ensure the accuracy of the simulation results, it is necessary to select appropriate constitutive models and determine the correct model parameters. The double-yield model, built in FLAC3D, is often used to describe the strain-hardening behavior of geotechnical materials. On the assumption that there is only volume yielding in the material, a relationship between the cap pressure, plastic strain in the double-yield model, and the axial stress–strain in the compression test with axial loading and four lateral-face constraints was established. Then, the cap pressure and plastic strain could be calculated directly by a series of known axial stress–strain data. With this calculation method, the double-yield model parameters can be determined quickly and accurately. This method was derived based on the constitutive equation of the double-yield model and could quickly determine the model parameters by reverse calculation according to the expected results, so it was more efficient and credible than the more widely used trial-and-error method. Based on comparisons between the calculation and trial-and-error methods, some case studies also proved its efficiency and effectiveness. Moreover, there are no requirements for the source of known stress–strain data. Therefore, this method can be applied to the model parameter assignment based on the stress–strain data from experimental tests, theoretical analyses, empirical formulas, and other numerical simulations. Highlights: A relationship between the double-yield model parameters and the axial stress-strain in a uniaxial loading test with lateral constraints was established. An approach for accurate numerical modeling of strain-hardening materials using a double-yield model was developed. Some contrastive analyses with similar studies were conducted to verify the accuracy and efficiency of the approach in this paper. [ABSTRACT FROM AUTHOR]

Material transfer on the active surfaces of tools during parts' machining and rolling processes can significantly affect product quality. This transfer can be deposited on the edges and cutting surfaces of the tools, which will cause poor production (poorly machined parts), and by a simple manufacturing control, these parts will be rejected. For evaluating the adverse effects of this transfer, the example of bi-punching was chosen, which covers the process of stamping and rolling. This work investigates the different surface transformations following material transfer from a sheet or steel of XES grade to an HSS tool. It consists of examining the effect of the transfer on the surface condition and the friction behavior of the crushed sheet on the faces of the two upper and lower punches that grip the sheet. The results help to avoid scrap and to improve the tool's life. In addition, we studied the different transformations at the surface level following the transfer of material from a steel sheet of an SXE grade to an HSS tool. Optical observations by SEM, XRD, and XRF were carried out to see more closely the effect of the transfer on the surface state and the friction behavior of the crushed sheet on the faces of the two upper and lower punches that grip the sheet. The objective is to avoid waste and consider the tools' longevity. [ABSTRACT FROM AUTHOR]

With the increasing demand for high-performance alloys in extreme environments, there has been an active development of new materials. High-entropy alloys (HEAs) are considered a promising choice due to their exceptional properties. Even though HEAs exhibit remarkable mechanical properties, only a limited number of studies have explored the mechanical properties and microstructures of additively manufactured HEAs under extreme conditions. In this work, the dynamic mechanical properties at high strain rates and different temperatures (i.e., 293 K and 77 K), as well as quasi-static mechanical properties for the CoCrFeMnNi HEAs fabricated by selective laser melting (SLM) are investigated. Microstructure observations have demonstrated that the as-printed sample displays a single face-centered cubic (FCC) phase with a columnar dendrite feature. Within dendrites, a large number of dislocations and substructures appear due to the applied high cooling rates during the SLM process. The as-printed sample exhibits a significant strain rate dependence from quasi-static to dynamic loading during deformation. Compared to the quasi-static mechanical properties, the as-printed HEA reveals higher dynamic yield strength (e.g., ∼1081 MPa and ∼1020 MPa along the build and scanning directions under 2800 s−1, respectively), more pronounced strain-hardening behavior, and larger remarkable plasticity under dynamic loading at cryogenic temperatures. When subjected to increasing strain rates ranging from 0.001 s−1 to 3500 s−1 at 293 K, the yield strength of the as-printed HEAs exhibits a notable enhancement, increasing from ∼517 MPa to ∼723 MPa along the BD direction, and from ∼545 MPa to ∼667 MPa along the SD direction. The corresponding variation in the strength of the BD samples is more pronounced than that of the SD samples. The enhancement in strength should be attributed to the differences in the features of grain orientation and dislocation distribution along different build directions, as well as the strain rate dependence. During plastic deformation, the dominant mechanisms of dislocation slips and deformation twins (DTs) are transformed into multi-stage-twin-controlled ones at cryogenic temperatures, which is beneficial to improve the strain hardening rate and plasticity. The present studies provide a deep understanding of the deformation mechanism of HEAs under extreme conditions and help promote the application of HEAs in the future. [ABSTRACT FROM AUTHOR]

This study demonstrated the feasibility of utilizing calcined clay (metakaolin) as a silica source for the development of polyethylene (PE) fiber-reinforced strain-hardening magnesium-silicate-hydrate composite (SHMSHC). The study also discussed the effects of variation in the Mg/Si ratio of the mixture when pure silica source (silica fume with SiO 2 content >90 %) is replaced with metakaolin (SiO 2 content ⁓ 51 %) on the mechanical performance of SHMSHC. A comprehensive mechanical characterization of SHMSHC at composite scale and fiber-matrix interaction effects was conducted. The damage characterization was carried out using residual crack width and spacing analysis. The chemical characterization of the MSH matrix (SHMSHC without fibers) was performed using XRD, TGA, and FTIR, and the microstructural investigation was done using FE-SEM. The MgO-metakaolin paste based SHMSHC showed compressive strength of 51.9 MPa, tensile strength of 5.0 MPa, and tensile strain capacity of 4.7 %, demonstrating the feasibility of calcined clay utilization in SHMSHC. The tensile strain capacity was reduced after the addition of aggregates in SHMSHC. The study demonstrated that the variation in the Mg/Si ratio significantly affects the toughness of the MSH matrix and fiber-matrix interaction characteristics, influencing the strain-hardening potential of SHMSHC. [ABSTRACT FROM AUTHOR]

The objective of the present study is to fundamentally explore the evolution of deformed structures of CrCoNiSi 0.3 medium entropy alloy subjected to high-speed compression deformation with true strains of 0.16, 0.33, and 0.46 (via split Hopkinson pressure bar system, strain rate of ∼6 × 103 s−1, denoted as HSR deformation), and quasi-static compression deformation with true strains of 0.20, 0.30 and 0.50 (via MTS compression system, strain rate of ∼10−3 s−1, denoted as LSR deformation). From the comparison between the results of HSR and LSR samples, it clearly indicates that the formation of deformation nanotwins is promoted under the HSR deformation and enhances the work hardening effect in the early stage of deformation; as the HSR deformation proceeds, the nanotwins effectively provide the dynamic Hall–Petch effect, leading to an increase in flow stress beyond the stress required for HCP phase transformation. The HCP phase also induces a stronger work hardening capacity at the late stage of deformation. Profuse deformation nanotwins and HCP phase promoted by HSR deformation result in a strong work hardening effect. Furthermore, the flow stress of the HSR deformed sample with a true strain of 0.46 is 1536 MPa, which is about 36% higher than that of the LSR deformed sample with the same true strain, 1102 MPa. It is clear that under the HSR deformation, the defect structures including deformation nanotwins and ultra-thin HCP platelets are much more favorably generated, greatly improving the working capacity. [Display omitted] • The evolution of defect structures at High/Low Strain Rates (HSR∼6 × 103 s-1 /LSR∼10-3 s-1) was observed in CrCoNiSi 0.3 alloy. • The flow stress of HSR sample (1536 MPa) is 36% higher than LSR sample (1102 MPa) at an identical true strain of ∼0.46. • The deformation nanotwins were observed at a lower strain in HSR sample (ε T ∼0.16) than in LSR sample (ε T ∼0.30). • Sub-micron HCP bundles were found in HSR sample at ε T ∼0.46, while only HCP nanolayers were found in LSR sample at ε T ∼0.50. [ABSTRACT FROM AUTHOR]

The mechanical behavior of the single phase (fcc) CrMnFeCoNi high-entropy alloy (HEA) is examined in the dynamic regime. A series of experiments by dynamic-loading hat-shaped specimens using stopper rings to control the displacement are performed, and the alloy resists adiabatic shear-band formation up to a very large imposed shear strain of ∼7. It is proposed that the combination of the excellent strain-hardening ability and moderate thermal-softening effect retard shear localization. Recrystallized ultrafine-grained grains (diameters of 100–300 nm) with twins are revealed inside the shear band. Their formation is explained by the rotational dynamic recrystallization mechanism. The stability of the structure at high strain rates strongly suggests a high ballistic resistance for this class of alloys.

This paper employs PVA, PE, steel fibers, as well as the hybrids of two of the three fibers to reinforce alkali-activated slag (AAS) material, aiming to prepare strain-hardening and clinker-free composites. The flexural strength, compressive strength, uniaxial tensile performance of the composites and bond behavior between fibers and the matrix were tested to clarify the reinforcement effects of different fibers on the matrix. Strain-hardening AAS materials are obtained with compressive strengths of 116 MPa − 137 MPa (with fibers contributions of 17%−38%) and strain capacities over 0.8% at 60 d. The results indicate that there are several kinds of reinforcement effects of fibers on the matrix, namely bridging effect, lapping effect (for steel fibers), synergetic effect (for hybrid fibers) and static effect (for flexible fibers). Deterioration of PVA and PE fibers are found, indicating that these two fibers have poor adaptability in AAS material with a high alkalinity. This paper specially distinguishes the difference of the crack numbers during the strain-hardening stage only with the ones during the whole period including the following strain-softening stage. A new relationship is established between the crack numbers and the strain-stress curves, which provides a more reasonable way to characterize the strain-hardening property of fiber-reinforced composites.

Cement-based materials are the most widely used construction materials in the world for infrastructure works. Unfortunately, they come with a high environmental burden due to carbon dioxide emissions and the need for regular maintenance and repairs. Without these, the service life can decrease. By using a self-healing approach, the service life can be extended, as well as the durability and sustainability of the building material. As the ability to self-heal depends on the age of the material, so will the potential influence of added materials to promote this healing. However, the effects of reduced healing beyond one year are not ubiquitous in the literature. In this study, specimens were studied after a decade of maturation under different storage conditions to conclude on the self-healing capabilities of the old samples. Cracks can still be partially healed after ten years, mainly due to the formation of calcium carbonate crystals, related to the observed regain in mechanical properties measured by repeated four-point bending tests. The initial addition of superabsorbent polymers to the mixture results in greater healing compared to the reference samples, making it a sustainable option for the future of cement-based composites. [ABSTRACT FROM AUTHOR]

Indentation size effect (ISE) is a critical feature for investigating the local properties of materials using the indentation test method. Although there are numerous works on the indentation response, there is a lack of data in the literature on the association between nanoindentation and uniaxial compression. Herein this study, uniaxial compression tests combined with Digital Image Correlation Technique are conducted on Ti6Al4V alloy with a focus on investigating the elastic–plastic properties and obtaining the accurately constitutive relation. Then, an ISE model of Ti6Al4V is established based on this constitutive relation and strain gradient theory. Indentation hardness, predicted by this proposed model, agrees well with the measurement by nanoindentation experimental techniques. This model can be used to bridge the gap between the uniaxial stress–strain and the depth‐dependent hardness, and clarifies the effect of the strain hardening on indentation hardness. The significance of this model is that it provides a direct and reasonable theory foundation to investigate ISE by uniaxial compression, and promotes the potential application of nanoindentation. [ABSTRACT FROM AUTHOR]

Continuous drive friction welding (CDW) is a state-of-the-art solid-state welding technology for joining metallic components used in aerospace, oil and gas, and power generation industries. This study summarizes the results of mechanical and microstructural investigations on a modified AISI-8630 steel subjected to CDW. The effects of welding process parameters, including rotational speed, friction, and forge forces, during CDW were explored to determine an optimum welding condition. The mechanical properties of the weld, and microstructural characteristics across different regions of the weld were measured and examined. The microstructure characterization results suggest that the weld zone (WZ) experiences temperatures above the Ac3 and the thermo-mechanically affected zone (TMAZ) experiences temperatures between Ac1 and Ac3 of the material. Investigations with electron backscatter diffraction (EBSD) demonstrated the occurrence of strain-induced dynamic recrystallization in the weld. The weld demonstrated higher yield and ultimate tensile strengths at the expense of ductility and hardening capacity compared to the base metal (BM). The strain-hardening profiles of the welds exhibited a dual-slope characteristic, an indication of different levels of plastic deformation experienced by the constituent phases (i.e., martensite, bainite and ferrite) present in the microstructure. The maximum strength-to-ductility combination and static toughness values were obtained for the weld produced under the highest rotational speed, maximum friction force and an intermediate forge force of 1200-1400 rpm, 375-425 kN, and 600-650 kN, respectively. [ABSTRACT FROM AUTHOR]

The present paper considers the wire drawing process through a conical die and provides an approximate solution for the drawing force, assuming an arbitrary hardening law. The solution is based on the upper bound theorem. However, this theorem does not apply to the stationary flow of strain-hardening materials. Therefore, an adopted engineering approach is to replace the original material model with a non-homogeneous, perfectly plastic model. The kinematically admissible velocity field is derived from an exact semi-analytical solution for the flow through an infinite channel, which increases the accuracy of the solution. The solution for the homogeneous perfectly plastic material compares with an available solution. The general solution is valid for any die angle. The numerical example focuses on the range of angles used in wire drawing. Since the material model is pressure-independent, it is straightforward to adopt the solution for calculating the force in extrusion. [ABSTRACT FROM AUTHOR]

Ultrafine-grained dual-phase ferrite/martensite steel produced through intercritical annealing at 765, 775 and 795 °C. The microstructures at all temperatures consisted of ultrafine ferrite, martensite and carbides. Carbides were found in two different morphologies, alloy carbides and V(C, N). The grain size of ferrite was decreased to 0.83 ± 0.3 μm when the intercritical temperature was increased to 795 °C. Higher kinetics of phase transition from ferrite to austenite and ferrite grains growth restriction by alloy carbides and V(C, N) carbides reduced the ferrite size. The maximum yield strength of 1710 ± 15 MPa with total elongation of 11.5 ± 0.3% was achieved at 795 °C. The larger volume fraction of martensite, smaller ferrite grain size and smaller (FeMnCr)3C particles improved the yield strength. Despite the higher ferrite grain size and higher carbon content in martensite, the maximum strain hardening rate was attained at 765 °C. Higher amount of carbides increased the strain hardening rate at 765 °C. The strengthening mechanism of dual-phase steels at each intercritical temperature was studied and strength contribution from each strengthening factor was calculated. The calculated results at each temperature were agreed well with the experimental results. [ABSTRACT FROM AUTHOR]

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The dislocation density in strain-hardened Alloy 690 was analyzed using scanning transmission electron microscopy (STEM) to study the relationship between the local plastic strain and susceptibility to primary water stress corrosion cracking (PWSCC) in nuclear power plants. The test material was cold-rolled at various thickness reduction ratios from 10% to 40% to simulate the strain-hardening condition of plant components. The dislocation densities were measured at grain boundaries (GB) and in grain interiors of strain-hardened specimens from STEM images. The dislocation density in the grain interior monotonically increased as the strain-hardening proceeded, while the dislocation density at the GB increased with strain-hardening up to 20% but slightly decreases upon further deformation to 40%. The decreased dislocation density at the GB was attributed to the formation of deformation twins. After the PWSCC growth test of strain-hardened Alloy 690, the fraction of intergranular (IG) fracture was obtained from fractography. In contrast to the change in the dislocation density with strain-hardening, the fraction of IG fracture increased remarkably when strain-hardened over 20%. From the results, it was suggested that the PWSCC growth behavior of strain-hardened Alloy 690 not only depends on the dislocation density, but also on the microstructural defects at the GB.

The role of stress-induced β → α″ martensitic transformation in contributing to the exceptional strain-hardening behavior of a Ti-11Mo (wt. %) model alloy was studied. The results reveal that the α″-martensite plates, undergoing relatively high transformation strains upon formation, act as effective barriers against dislocation motion. As deformation proceeds, the progressive generation of these plates dynamically reduces the dislocation mean free path (dynamic Hall-Petch effect), while simultaneously encouraging the accumulation of dislocations. These dual effects substantially enhance the flow stress with increasing strain, thereby resulting in remarkable strain-hardenability, a crucial factor for maintaining excellent ductility. This study presents innovative experimental evidence elucidating the mechanism of the transformation-induced plasticity effect in metastable β-titanium alloys, while also offering insights for designing novel alloys with superior strain-hardenability and ductility. [Display omitted] [ABSTRACT FROM AUTHOR]

• Mechanical interaction of a tilting suture anchor and bone was modeled. • Geometrical parameters affected the anchor's fixation mechanism and stiffness. • A decreased distal width improved the anchor's tilting action during implantation. • Larger distal width and fillet radius improved the fixation stiffness of anchor. • Fixation stiffness of anchor was substantially larger in higher bone densities. The mechanical interaction of a tilting anchor and cancellous bones of various densities was simulated using finite element modeling. The model enjoyed a sophisticated representation of the bone, as an elasto-plastic material with large deformation capability. The anchor's tilting action during implantation phase, as well as its fixation stiffness during pull-out test, were predicted by the model and a parametric study was performed to investigate the effects of the anchor's distal width and corner fillet radius, on these measures. The model predictions were validated against the results of an experimental test on ovine humerus specimens. The model could reasonably reproduce the tilting action of the anchor during the implantation phase. Comparison of the model predictions with the experimental results revealed similar trends during both the implantation and the pull-out phases, but smaller displacement magnitudes (end points: 1.4 vs. 2.1 mm and 4.6 vs. 5.2 mm, respectively). The results of the parametric study indicated substantial increase in the fixation stiffness with increasing bone density. Reducing the distal width and increasing the fillet radius improved the anchor's implantation configuration and fixation stiffness in low-density bones. For high-density bone applications, however, a larger distal width was favored for improving the fixation stiffness. [ABSTRACT FROM AUTHOR]

A series of Mg-RE composites were fabricated through the sintering process involving a Mg-Gd-Zn-Zr alloy and externally introduced TC4 particle powder, follow-up subsequent hot extrusion. The addition of TC4 manifested a discernible influence on the weakening of the texture and refinement of the grain size. The TC4/GZ151K composite evinced an excellent mechanical property with 305 MPa, 361 MPa, and 10.5 % for yield strength, ultimate tensile strength, and elongation. Microstructural characterization shows that the activation of {10–12} twinning has been restrained in TC4/GZ151K composite undergoing tension, leading to a later strain-hardening rate and higher yield strength. The prominent yield plateau and the extended work-hardening stage of the TC4/GZ151K composite can be attributed to dislocation multiplication, e.g., basal slip and prismatic slip, and the interaction between the mobile dislocations and the TC4 reinforcements. The misorientation distribution analysis demonstrated that deformable Ti metal particles exhibit co-deformation with the matrix, positively influencing the plasticity of the composite. This study extended the feasibility of fabricating Mg-RE composites reinforced with deformable metal particles, providing a deeper exploration for achieving the strength-ductility trade-off for Mg composites. [ABSTRACT FROM AUTHOR]