Search Results (236)

A crystal plasticity finite element model is developed and implemented to numerically study the deformation behavior of hexagonal close-packed metals using α-titanium as an example. The model takes into account micromechanical deformation mechanisms through dislocation slip along prismatic, basal, and first-order <c+a> pyramidal systems, as well as tensile twinning. Twin initiation follows a two-conditional criterion requiring that both the resolved shear stress in a twin system and the accumulated pyramidal slip simultaneously reach their critical values. Three-dimensional polycrystalline models are generated using the step-by-step packing method. The crystal plasticity constitutive model describing the deformation behavior of grains is integrated into the boundary-value problem of continuum mechanics, including dynamic governing equations. The three-dimensional problem is solved numerically using the finite element method. The micromechanical model is tested for an α-titanium single crystal along the [0001] direction and a polycrystal consisting of 50 grains. The numerical results reveal that twin propagation is controlled by the critical value of accumulated pyramidal slip, emphasizing the need for experimental calibration. The agreement between numerical and experimental results provides the model validation at the meso- and macroscales. Full article

In this paper, the microstructure, mechanical properties, and strengthening mechanisms of hot-extruded Mg-xGd-4Y-1Sm-0.5Zr (x = 4, 7, 10, wt.%) alloys were studied. The results show that the hot extruded alloys exhibit bimodal grain structures, and with Gd content increasing, the fraction of non-dynamic recrystallized grains gradually decreases, with 46.3%, 38.6%, and 9.3%. After aging for 200 °C × 96 h, all three hot-extruded alloys reach peak-aged hardness, and as Gd content increases, the area number density of the β′ phase increases with Gd increasing, being 7.1 × 10¹⁵/m², 9.9 × 10¹⁵/m², and 16.5 × 10¹⁵/m², respectively. And the yield strength (YS) increases from 287 MPa to 345 MPa, the ultimate tensile strength (UTS) increases from 365 MPa to 418 MPa, and elongation (EL) decreases from 8.5% to 4.2%. The tensile failure mechanism is quasi-cleavage fracture. With Gd content increasing, the dimples and tear ridges on fracture surfaces gradually decrease while cleavage facets increase. The peak-aged GWS741 alloy demonstrates optimal comprehensive mechanical properties, with YS, UTS, and EL reaching 332 MPa, 409 MPa, and 7.8%, respectively. During in situ tensile testing, coarse un-DRXed grains undergo prismatic ($\{10\stackrel{\mathrm{-}}{1}0\}⟨11\stackrel{\mathrm{-}}{2}0⟩$) slip, while DRXed grains experience basal ($\left\{0001\right\}⟨11\stackrel{\mathrm{-}}{2}0⟩$) slip and twinning deformation. Even at 6.6% strain, no microcracks are observed, indicating excellent plasticity. During the tensile failure process, the main crack propagates along tortuous paths, showing crack deflection characteristics, where it either penetrates through elongated deformed grains or bypasses un-DRXed grains. Full article

Microstructural analysis of hot-compressed magnesium alloys is crucial for understanding the plastic formability of magnesium alloys during thermo-mechanical processing. Thermal compression tests and finite element simulations were conducted on a low rare-earth (RE) Mg-1.8Nd-0.4Zr-0.3Ca alloy. Multiple microstructural characterization techniques were employed to analyze slip systems, twinning mechanisms, dynamic recrystallization (DRX), and precipitate phases in the hot-compressed alloy. The results demonstrated that the equivalent strain distribution within compressed specimens exhibits heterogeneity, with a larger equivalent strain in the core. After thermal compression, the original microscopic structure formed a necklace-like structure. The primary DRX mechanisms comprise continuous dynamic recrystallization (CDRX), twin-induced dynamic recrystallization (TDRX), and particle-stimulated nucleation (PSN). Pyramidal slip and recrystallization constitute primary contributors to peak texture weakening and tilting. Mg₄₁Nd₅ and α-Zr phases enhanced dislocation density by impeding dislocation motion and promoting cross-slip activation. Hot compression provided the necessary thermal activation energy and stress conditions for solute atom diffusion and clustering, triggering dynamic precipitation of Mg₄₁Nd₅ phases. Full article

In the present investigation, stress–strain curves and strain hardening rates on samples rolled at ambient temperature with thickness reductions of 0%, 10%, 30%, and 50% were studied. On the processed samples, static tensile tests at ambient temperature were performed. Transformation of the engineering stress–strain curves to true stress–strain curves and their numerical processing by first derivation (θ = dσ/dε) was carried out. Dependencies θ = f(ε_T) characterizing the strain hardening rates were derived. From the curves and the true stress–strain and strain hardening rates, the three stages describing different rates of strain hardening were identified. A rapid increase in true stress and a rapid decrease in the strain hardening rate in Stage I were observed. Quasi-linear dependencies with an increase in true stress but with a slow, gradual decline in the strain hardening rate in Stage II were obtained. Slowly increasing true strains, accompanied by a decrease in strain hardening rates and their transition to softening, led to the formation of plastic instability and necking in Stage III. The endpoints of the strain hardening rate depending on the cold rolling deformations lie in the following intervals: θ_{Stage I} ∈ <1904;3032> MPa, θ_{Stage II} ∈ <906;−873> MPa, θ_{Stage III} ∈ <−144;−11,979> MPa. While in Stage I and Stage II, the plastic deformation mechanism is predominantly dislocation slip, in Stage III, the plastic deformation mechanism is twinning accompanied by dislocation slip. Full article

Wood–plastic composites (WPCs) are polymeric materials, usually thermoplastic, filled with wood flour or fibers. They are relatively durable and stiff and resistant to water. They are also, importantly, relatively cheap compared to materials with similar properties. The WPCs market has grown significantly in recent years, mainly thanks to the increasing construction and automotive markets. Currently, the global WPCs market is forecasted to reach about USD 15 billion by 2030, increasing at an impressive compound annual increase rate of about 12% until 2030. There are some review articles on WPCs written from many different points of view, e.g., the type of materials used (polymers, fillers, auxiliaries), the method of manufacturing and processing, processing properties (thermal and rheological) and functional properties, methods of designing composite products and designing (modeling) forming processes. In this article, we will summarize these different points of view and will present a thorough literature review of rheology and material processing, and more specifically, the modeling of WPCs processing. This work will be presented in relation to state-of-the-art research in the field of modeling the processing of other polymeric materials, i.e., standard (neat) polymers and polymer blends. The WPCs’ processing is significantly different from that of standard plastics due to the differences in thermo-rheological properties, diverse structures, etc. So far, the global WPCs processing models have only been developed for both gravity-fed and starve-fed single-screw extrusion. The models for twin-screw extrusion, both co-rotating and counter-rotating, as well as for injection molding, have still not been developed. WPCs show a yield stress and wall slip when extruding, which must be considered when modeling the process. As the slippage on the screw and barrel grows, the process throughput and pressure diminish, but as the slippage on the die grows, the throughput grows and the pressure diminish. As the yield stress in the screw grows, the process throughput and pressure grow, whereas as the yield stress in the die grows, the throughput diminishes and the pressure grows. Full article

High-Mn steels are commonly fabricated by hot rolling and on-line cooling for cryogenic applications, because there exists an aging embrittlement zone in most high-Mn steels, and this shortcoming makes it difficult to optimize their mechanical properties by heat treatments. Hence, 0.6C-18Mn-0/3/5Al (in wt.%) steels were designed to investigate the effects of Al on their strength and toughness. The addition of 5 wt.% Al can increase yield strength from 357 to 461 MPa and the Charpy impact absorbed energy from 56 to 119 J. Although there is still a cryogenic aging embrittlement zone in each steel, we found that the addition of Al can narrow this brittle zone. Moreover, the absorbed energy is lowered by around 89%, 48%, and 40% for the 0Al, 3Al, and 5Al steels at −196 °C, respectively. Additionally, impact plastic deformation mechanisms were also revealed in the steels with a heat-treating temperature of 600 °C, revealing that the main deformation mechanism shifts from numerous partial dislocation slip to twinning plus strong planar slip as the addition of Al increases. Full article

Steel–ultra-high-performance concrete (UHPC) composite beams with small-rib-height perfobond strip connectors (SRHPBLs) exhibited advantages of light weight and high bearing capacity, demonstrating the potential for applications of UHPC in bridge engineering. During service stages, the composite beams were usually under combined tension–shear loads, rather than pure shear loads. Nevertheless, there were research gaps in the static behavior of SRHPBLs embedded in UHPC under combined tension–shear loads, which limited their applications in practice. To address this issue, systematic experimental and theoretical analyses were conducted in the present study, considering the test variables of tension–shear ratio, row number, and strip number. It was demonstrated that the tension–shear ratio had less effect on ultimate shear strength, initial shear stiffness, and ultimate slip of SRHPBLs. When the tension–shear ratio was increased from 0 to 0.42, the shear capacity, initial shear stiffness, and slip at peak load of SRHPBLs decreased by 24.31%,19.02%, and 22.00%, respectively. However, increasing the row number and strip number significantly improved the shear performance of SRHPBLs. Compared to the single-row specimens, the shear capacity and initial shear stiffness of the three-row specimens increased by an average of 92.82% and 48.77%, respectively. The shear capacity and initial shear stiffness of the twin-strip specimens increased by an average of 103.84% and 87.80%, respectively, compared to the single-strip specimens. Finally, more accurate models were proposed to predict the shear–tension relationship and ultimate shear capacity of SRHPBLs embedded in UHPC under combined tension–shear loads. Full article

The advent of additive manufacturing (AM), also known as 3D printing, has revolutionized the production of titanium alloys, offering significant advantages in fabricating complex geometries with enhanced mechanical properties. This study investigates the variant-specific deformation mechanisms in HIP-treated TA15 (Ti-6.5Al-2Zr-1Mo-1V) titanium alloy, fabricated via selective electron beam melting (SEBM). The alloy exhibits a dual-phase (α+β) microstructure, where six distinct α variants are formed through the β→α phase transformation following the Burgers orientation relationship. Variant selection during AM leads to a non-uniform distribution of these α variants, with α6 (22.3%) dominating due to preferential growth. Analysis of the prismatic slip Schmid factor reveals that α4–α6 variants, with higher Schmid factors (>0.45), primarily undergo prismatic slip, while α1–α3 variants, with lower Schmid factors (<0.3), rely on basal or pyramidal slip and twinning for plastic deformation. In-grain misorientation axis (IGMA) analysis further reveals strain-dependent slip transitions: pyramidal slip is activated in α1–α3 variants at lower strains, while prismatic slip becomes the dominant deformation mechanism in α4–α6 variants at higher strains. Additionally, deformation twins, primarily {10–12}<1–101> extension twins (7.1%), contribute to the plasticity of hard-oriented α variants. These findings significantly enhance the understanding of the orientation-dependent deformation mechanisms in HIPed TA15 alloy and provide a crucial basis for optimizing the performance of additively-manufactured titanium alloys. Full article

This study employs synchrotron polychromatic X-ray microdiffraction (micro-XRD) to resolve the dynamic interplay between deformation mechanisms and stress redistribution in a commercial Mg-3Al-1Zn (AZ31) alloy under uniaxial tension. Submicron-resolution mapping across 13 incremental load steps (12–73 MPa) reveals sequential activation of deformation modes: basal slip initiates at 46 MPa, followed by tensile twinning at 64 MPa, and non-basal slip accommodation during twin propagation at 68 MPa. Key findings include accelerated parent grain rotation (up to 0.275° basal plane tilt) between 43–46 MPa, stress relaxation in parent grains coinciding with twin nucleation, and a ~35 MPa stress reversal within twins. The critical resolved shear stress (CRSS) ratio of twinning to basal slip is experimentally determined as 1.8, with orientation-dependent variations attributed to parent grain crystallography. These results provide unprecedented insights into microscale deformation pathways, critical for optimizing magnesium alloy formability and performance in lightweight applications. Full article

The Charpy impact toughness of single-phase austenitic Fe-32Mn-0.6C steel was systematically investigated across a wide temperature spectrum from 25 °C to −196 °C using Charpy V-notch impact tests. The material exhibited a remarkable temperature dependence of impact energy, decreasing dramatically from 120 J at ambient temperature (25 °C) to 13 J under cryogenic conditions (−196 °C). Notably, a steep transition in impact energy occurred within the critical temperature window of −100 °C to −150 °C. Microstructural analysis revealed that synergistic effects of high strain rates and low temperatures significantly restrict dislocation slip and multiplication mechanisms, while also suppressing deformation twinning activation. This restricted plasticity accommodation mechanism fundamentally differs from the deformation characteristics reported in conventional low-carbon high-manganese steels and other face-centered cubic (FCC) alloy systems. Full article

This study addresses critical challenges in manufacturing GRCop-42 Cu alloy (Cu-4Cr-2Nb) components via laser-directed energy deposition (LDED). We systematically establish process–microstructure–property correlation for this alloy, demonstrating that laser power critically governs defect formation and mechanical performance. The alloy exhibited optimal microstructure and properties at a laser power of 2000 W, with a room temperature tensile strength of 319 ± 6.5 MPa and an elongation of 25.42 ± 1.9%. The tensile strength in the high-temperature tensile test at 600 °C was measured at 98 ± 3.1 MPa, with an elongation of 15.83 ± 1.5%. The comprehensive performance reaches the optimal value of the processing window. Through cross-scale characterization techniques, the differences in fracture mechanisms at different temperatures are clarified for the first time: at room temperature, a microporous aggregation-type ductile fracture is observed, with plastic deformation primarily dominated by dislocation slip; in a high-temperature environment, due to the weakening of grain boundary strength, the fracture mode shifts to intergranular fracture, and the deformation mechanism evolves into a synergistic effect of dislocation slip and twinning. The findings of this study not only provide valuable insights into optimizing the LDED process parameters for the GRCop-42 alloy but also shed light on the relationship between its microstructure and mechanical properties under different temperature conditions, offering a solid foundation for the further application of this alloy in complex aerospace components. Full article

Autonomous navigation in mining environments is challenged by complex wheel–terrain interaction, traction losses caused by slip dynamics, and sensor limitations. This paper investigates the effectiveness of Deep Reinforcement Learning (DRL) techniques for the trajectory tracking control of skid-steer mobile robots operating under terra-mechanical constraints. Four state-of-the-art DRL algorithms, i.e., Proximal Policy Optimization (PPO), Deep Deterministic Policy Gradient (DDPG), Twin Delayed DDPG (TD3), and Soft Actor–Critic (SAC), are selected to evaluate their ability to generate stable and adaptive control policies under varying environmental conditions. To address the inherent partial observability in real-world navigation, this study presents an original approach that integrates Long Short-Term Memory (LSTM) networks into DRL-based controllers. This allows control agents to retain and leverage temporal dependencies to infer unobservable system states. The developed agents were trained and tested in simulations and then assessed in field experiments under uneven terrain and dynamic model parameter changes that lead to traction losses in mining environments, targeting various trajectory tracking tasks, including lemniscate and squared-type reference trajectories. This contribution strengthens the robustness and adaptability of DRL agents by enabling better generalization of learned policies compared with their baseline counterparts, while also significantly improving trajectory tracking performance. In particular, LSTM-based controllers achieved reductions in tracking errors of 10%, 74%, 21%, and 37% for DDPG-LSTM, PPO-LSTM, TD3-LSTM, and SAC-LSTM, respectively, compared with their non-recurrent counterparts. Furthermore, DDPG-LSTM and TD3-LSTM reduced their control effort through the total variation in control input by 15% and 20% compared with their respective baseline controllers, respectively. Findings from this work provide valuable insights into the role of memory-augmented reinforcement learning for robust motion control in unstructured and high-uncertainty environments. Full article

Achieving a balance between strength and room-temperature ductility remains an urgent need and a significant challenge for body-centered cubic (BCC) structure materials. In this paper, a good combination of strength and ductility in single-phase BCC-structured Ti₃VNbAl_0.5Zr_x (x = 0, 0.1, 0.5, and 1) lightweight high-entropy alloys (LHEAs) was designed by reducing the valence-electron concentration in combination with the d-electron theory. The influences of Zr on the microstructures and mechanical properties of the alloys were systematically studied. The yield strengths of Zr0, Zr0.1, Zr0.5, and Zr1 alloys were 644 MPa, 703 MPa, 827 MPa, and 904 Mpa, respectively. The tensile strains of Zr0, Zr0.1, Zr0.5, and Zr1 alloys were 29%, 30%, 20%, and 16%, respectively. The deformation mechanism was studied using transmission electron microscopy (TEM). The results demonstrate that the alloys could still maintain single-phase BCC structure after deformation, and neither phase transformation nor twinning was detected during the deformation process. The main deformation mechanism of the Zr1 alloy is dislocation slip. The current work has great significance for developing high-strength, ductile, and low-density structural materials. Full article

The generalized planar fault energies of 1/2<110] and 1/6<112] slip directions on {111} planes in $\gamma$-TiAl at temperatures up to 1500 K were predicted through first-principles calculations and quasi-harmonic approximation. The obtained unstable stacking and twinning fault (USF and UTF) energies, as well as superlattice intrinsic and extrinsic stacking fault (SISF and SESF) energies, are consistent with existing theoretical data. Results show that the USF, UTF, SISF, and SESF energies for both slip directions decrease overall as temperature increases. The effect of temperature on the 1/2<110] ordinary dislocation and 1/6<112] order twinning in $\gamma$-TiAl is further analyzed generalized planar fault energies. It is demonstrated that the nucleation of ordinary dislocation and twinning dislocations becomes more favorable with increasing temperature. Furthermore, it is shown that order twinning in $\gamma$-TiAl is more likely to occur at crack tips or grain boundaries, and its twinnability is enhanced at elevated temperatures. Full article

The generalized stacking fault energy (GSFE) and shear modulus (G) are critical parameters in determining the strength and ductility balance of Fe-based alloys, playing a significant role in alloy design and performance optimization. This study focuses on FeNiAl alloys and proposes a composition optimization method based on molecular dynamics simulations. The results reveal that Fe₉₀Ni₉Al alloy exhibits the best synergy between strength and ductility, achieving a yield strength of up to 16.33 GPa and a yield strain of 10.4%. During tensile deformation, this alloy demonstrates a complex microstructural evolution, including dislocation slip, phase transformations, and deformation twinning. These mechanisms collectively contribute to the significant enhancement of its mechanical properties. This study not only elucidates the profound influence of GSFE and G on the micro-deformation mechanisms and macroscopic mechanical properties of FeNiAl alloys but also establishes an efficient composition design and screening system. This system provides theoretical support and practical guidance for the rapid development of novel alloy materials with balanced strength and ductility. The proposed method is broadly applicable to the design and optimization of high-performance structural materials, offering critical insights for advancing the application of lightweight and high-strength metallic materials in aerospace, automotive manufacturing, and other fields. Full article