Yield Stress Anisotropy Research Articles

A generalized, computationally versatile plasticity model framework - Part II: Theory and verification focusing on shear anisotropy

Shear-dominated deformation (SHDD) is pivotal in sheet metal forming; however, comprehensive modeling of plastic anisotropy in SHDD, specifically shear anisotropy considering both yield stress and plastic flow, has been inadequately addressed in existing literature. In this work, a generalized constitutive framework is introduced on the basis of stress triaxiality-dependent state variable to accurately emulate plastic anisotropy and the physics-based shear constraint in SHDD. The framework is capable to seamlessly integrate with existing yield criteria, preserving computational efficiency and versatility. Notably, the yield function, anisotropic parameters, and their optimization or analytical determination for the non-shear deformation state remain unaltered. When integrated with the Hill48 yield function, featuring either one or two anisotropic parameters within the generalized constitutive framework, precise characterization of yield strength and plastic flow in SHDD is achieved. The applicability of the framework extends to various anisotropic yield functions such as the widely employed Yld2k-2d and the sixth-order polynomial (Poly6) function as a class of associated flow rule-based yield functions, and one non-quadratic yield function for non-associated flow rule scenarios. Experimental validation with two engineering sheet metals, high-strength dual-phase steel DP980 and high-strength aluminum alloy AA7075-T6, was conducted. Comparative analyses with several recently proposed yield criteria, especially Poly6-18p, highlighted the efficiency of the proposed constitutive framework. Furthermore, this study explores intrinsic shear constraints, particularly the absence of through-thickness strains under in-plane shear stress. Additionally, it offers an enhanced description of plastic anisotropy in shear yield stress within the general framework, providing valuable insights into the complexities of SHDD.

Development of Low Anisotropic Commercially Pure Titanium Foils by Asymmetric Rolling and Annealing

This work studies the evolution of microstructure, texture, and anisotropy of pure titanium foils by symmetric rolling (SR) and asymmetric rolling (ASR) and subsequent annealing. The as‐received material shows equiaxed alpha grains and strong transverse texture (S‐T texture), which leads to severe anisotropy. The index of plane anisotropy (IPA) of yield stress (YS) and ultimate tensile stress (UTS) of the as‐received material is 15.2% and 7.5%, respectively. With the increase of deformation, the S‐T texture is mainly transformed into a mixed texture of transverse texture (T texture) and rolling direction texture (R texture), which balances the start‐up of the slip system when loading in the rolling direction (RD) and transverse direction (TD), so that the mechanical stress along RD and TD are close to each other and the anisotropy is improved. Especially for the samples prepared by ASR and annealing, the appearance of more R texture or basal texture (B texture) at the same deformation makes them show lower anisotropy. Therefore, after the same annealing treatment, the IPA of titanium foil with a thickness of 0.2 mm prepared by ASR is the smallest, which is 6.6% and 0.03%, respectively, while the IPA prepared by SR is 10.5% and 2.5%.

Plastic anisotropy in yield stress of drawn pearlitic steels

Plastic anisotropy in the yield stress of pearlitic steels evolved by drawing was studied. The tension and compression tests were performed in parallel and perpendicular directions to the drawing direction. The yield stress in the parallel tension and vertical compression tests increased with the increase in drawing strain. On the other hand, in the parallel compression, the yield stress decreased significantly at the small drawing strain and then increased at the larger strain. The difference between the yield stress at the tension and at the compression did not change largely after the start of the drawing. The observation of microstructure indicated no significant heterogeneity of the deformation microstructure and texture at the different locations in the radial direction of the drawn samples, meaning that the plastic anisotropy was brought by reasons other than the non-uniformity of the deformation condition. The measurement of the distribution of the local misorientation in ferrite suggested the large plastic deformation even at smaller strain by drawing. This result indicates that the residual stress in plastically deformed ferrite brings back stress, which can be the source of the plastic anisotropy.

Anisotropy of Consolidation Yield Stress and Comparison with Anisotropy of Elastic Wave Velocity and Tensile Strength in Sedimentary Soft Rocks

Anisotropy of Consolidation Yield Stress and Comparison with Anisotropy of Elastic Wave Velocity and Tensile Strength in Sedimentary Soft Rocks

A generalized, computationally versatile plasticity model framework - Part I: Theory and verification focusing on tension‒compression asymmetry

Microstructural characteristics and complex loading conditions in the deformation of metallic materials lead to complexity in mechanical responses. In this study, we propose a generalized constitutive framework that reproduces the plastic anisotropy and asymmetry under various loading conditions. Particularly, the developed model can accurately capture distinctive flow stress, plastic flow and strain hardening between tensile and compressive dominant loadings under a wide range of stress states. The model is based on the stress triaxiality dependence of state variable (or weighting factor) newly incorporated in the existing plasticity theory to keep the computational efficiency and versatility. For example, the new generalized framework can be applied to widely employed Hill48, Yld2k-2d, and Poly6 as a class of associated flow rule-based yield functions, as well as Stoughton-Yoon2009 and Min2016 yield functions for the non-associated flow rule. Also, the model is adaptable when selecting the yield function under tension or compression, which efficiently controls the degree of accuracy in anisotropic modeling under tension and compression. The generalized plasticity framework is validated comprehensively by demonstrating the predictive capability for anisotropy in yield stress and plastic flow of metallic materials with different crystal structures. Moreover, the model can efficiently capture the continuous evolution of asymmetric yield surfaces as functions of strain, temperature, and strain rate. Finally, the identification procedure of the model is discussed by demonstrating the analytical determination of model parameters utilizing the experimental or generic material data obtained from various loading conditions such as tension, compression, plane strain loading, and pure shear.

The effect of temperature on detwinning and mechanical properties of face-centered cubic deformation twins

Inverse temperature dependences of the detwinning stress of face-centered cubic deformation twins were discovered by studying the effect of elevated temperatures on plastic deformation properties of multilayer twin/matrix structure of the Cu-8at.%Al alloy. The critical stress of detwinning was found to increase remarkably with temperature when plastic yielding of the twin/matrix structure occurred by the π detwinning mode. However, when the alternative π/3 mode of detwinning was involved, a decrease of the detwinning stress with an increase of temperature was observed, instead. Thus, the twin/matrix structure behaved in two opposite ways, showing anneal hardening (the case of π mode) or anneal softening (the case of π/3 mode) upon temperature increase. As concluded, the dual effect of temperature on the detwinning stress resulted from irreversible reduction of internal stresses pre-existing within the deformation twins. The complete reduction of the internal stresses at about 530 °C led to the equivalence of the critical stresses of different detwinning modes and a large decrease of the yield stress anisotropy of the twin/matrix structure. It was postulated that temperature induced annihilation of the internal stresses resulted from constriction of extended cube dislocations pre-existing within deformation twins. The temperature limit of about 540 °C, beyond which the twin/matrix structure became unstable due to recrystallization, was also established. Moreover, transfer of plastic shear throughout the twin/matrix structure was found to be predominantly controlled by internal dislocation substructure of deformation twins, not by the twin/matrix interfaces.

Effect of variation of cold-rolling strain-paths on the microstructure, texture and mechanical properties of alloy Ni-16Cr-8Fe

In this work, the effect of variation of cold-rolling strain-paths (one-directional (U), two-stage cross (T), and multi-stage cross (M) rolling) on the evolution of microstructure as well as texture and their correlation with mechanical properties of alloy Ni-16Cr-8Fe has been studied. The overall texture strengthens while increasing rolling reductions from 30-to-50 and 50-to-90 % in all the strain-paths. In U strain-path, two of the standard rolling components—copper and brass—are strengthened significantly, while in T and M strain-paths only brass component strengthens. The overall texture has strong relationship with the brass-component of β-fibre irrespective of the strain-paths used during cold-rolling. The strain-path plays an important role in the changeover of texture from metal- to alloy-type, unlike what was previously thought that lowering of alloy’s stacking fault energy is the only reason. The yield (σYS) and tensile (σUTS) strength of 90 % rolled samples are significantly higher in U as compared to T and M strain-paths. The flow curves of 90 % rolled alloy follow Ludwigson-relationship with negative deviation in all the strain-paths. Regardless of the strain-paths, the area of yield locus ellipse increases as the rolling reductions are increased from 30-to-50 and 50-to-90 % and bear a good relationship with the overall texture. The average in-plane anisotropy in yield stress is observed to be highest in U strain-path. The theory of relative resolved shear stress of fcc slip systems in presence of highest intensity texture component well explains the variation in the values of in-plane anisotropies.

Evaluation of anisotropy of yield stress using surface in-plane displacements around an indentation residual imprint

This study proposed a practical method to evaluate the anisotropy of yield stress using spherical indentation with in-plane surface radial displacements around residual imprint measured by the digital image correlation method for metallic material without indentation curve. The relation between the ratio of yield stresses and the in-plane displacements developed on the surface was analyzed using finite element method (FEM) simulations for the materials with various mechanical properties. The development of radial displacements depends on the anisotropy of the yield stresses, and the ratio between radial displacement values on principal directions has a strong relation with the anisotropy of the yield stresses. An analytical solution for predicting the ratio of yield stresses was developed and it was verified using experimental data with anisotropic materials. The results for various metallic materials showed the feasibility of the proposed model with good accuracy.

A novel multiscale computational methodology for numerical material testing based on finite element polycrystal model

In this paper, a novel computational procedure for numerical material testing method based on a strain rate-independent crystal plasticity model and an optimization scheme is presented. In order to simulate deformation of materials that exhibit mechanical anisotropy with high accuracy, it is necessary to apply material models that include many material parameters. Therefore, if difficult-to-perform material tests such as biaxial tests can be replaced by numerical material tests, the cost and time required for experiments can be significantly reduced. The proposed method was developed using a crystal plasticity-based finite element model, known as finite element polycrystal model (FEPM), and an optimization scheme based on a genetic algorithm (GA) for microscopic parameters. FEPM is a model that performs analysis while determining the activity of all slip systems without using the strain rate-dependent constitutive law that is commonly used and is suitable for numerical material testing because it has less physical ambiguity. In the optimization process, deformation anisotropy is related to the grain orientation expressed by the Euler angle, and yield stress anisotropy is related to the work-hardening coefficients of the slip system. In addition, by generating pseudo-anisotropic crystal orientation by numerical rolling, the need for crystal orientation observation is eliminated. In this paper, after giving a description of the proposed method, experimental verifications on aluminum alloys to prove the effectiveness of the proposed method are presented. Data will be available on reasonable request.

Material Extrusion Additive Manufacturing of Poly(Lactic Acid): Influence of infill orientation angle

The effect that the infill orientation angle has on the strain-rate dependence of the yield stress for material extrusion additive manufactured (ME-AM) PolyLactic Acid (PLA) material was investigated. Symmetric angle-ply stacking sequences were used to produce ME-AM tensile test samples. Measured yield stresses were compensated for the voided structure, typical of ME-AM components. Furthermore, molecular orientation and stretch was macroscopically assessed by a thermal shrinkage procedure. Additionally, hot-press compression molded ( CM ) samples were manufactured and mechanically characterized in uniaxial tensile and compression in order to determine the material’s isotropic bulk properties. Initial model parameters for the Ree–Eyring modification of the Eyring flow rule were determined using CM data. According to SEM fractography, all samples showed microscopically brittle fracture behavior. Notwithstanding, contrary to CM samples, ME-AM specimens showed macroscopically ductile stress–strain behavior and a transition from a regime with only a primary α -deformation process, at low strain rates, to a regime with 2 deformation processes ( α + β ), at high strain rates. These effects are an influence of the processing step and are attributed to the molecular orientation and stretch of the polymer chains, provoking anisotropic mechanical properties. As a consequence, a deformation-induced change of the Eyring rate constants is needed to adequately describe the strain-rate dependence of the ME-AM yield stress behavior, leaving the initial activation volumes unchanged. Taking this deformation-dependence of the rate constants into account, yield stresses as a function of infill orientation angle can be appropriately predicted. • ME-AM samples with different symmetric angle-ply stacking sequences were produced. • PLA shows anisotropy in yield stress and strain-rate dependent behavior. • ME-AM samples show ductile stress–strain behavior, due to molecular orientation. • ME-AM samples show transition in strain-rate dependence, due to molecular orientation. • PLA demonstrates deformation-dependent Eyring rate constants.

Anisotropic ductile fracture: experiments, modeling, and numerical simulations

The continuous hot rolling process induces anisotropy in the plastic yield and flow and results in an anisotropic ductile fracture. In this study, experiments, including uniaxial in-plane tension tests and shear tests of butterfly specimens along different material orientations, were performed, and microscopic observations were used to determine the differences in damage mechanisms. The Yld91 anisotropic yield stress was introduced into the extended isotropic Gurson-Tvergaard-Needleman (GTN) model, and the associated flow rule (AFR) and non-associated flow rule (NAFR) were adopted to formulate two anisotropic GTN models. Anisotropic GTN models were implemented in finite element software via user subroutines, and were used to predict the fracture initiation of Al2024-T351. For different plastic flow rules, the anisotropic parameters were calibrated using the anisotropic stress and Lankford coefficients. An inverse analysis with a two-stage optimization algorithm was adopted to calibrate the damage-related parameters. Moreover, an extended isotropic GTN model was adopted for comparison. The prediction accuracy of the proposed anisotropic GTN models was evaluated by analyzing the load responses and displacements at fracture for various specimens and material orientations. The good conformation between the experimental results and numerical predictions verifies the predictive ability of the proposed models to a certain degree. In addition, some suggestions and conclusions are provided for the formulation of an advanced anisotropic GTN model with enhanced accuracy.

Phase transition in medium entropy alloy CoCrNi under quasi-isentropic compression

Under high strain-rate loading, prominent increases in pressure usually triggers phase transition (PT), but the concomitant temperature rise may also cause melting. Quasi-isentropic (QI) compression provides a strategy to explore solid-state phase transition by reducing the temperature rise while retaining high pressure. Using large-scale molecular dynamics simulations, we investigate PTs in single crystal CoCrNi medium entropy alloys (MEAs) under QI compression. With the applied strain rates ranging from 108 s−1 to 1011 s−1, the strain-rate dependence and anisotropy of yield stress and solid-state PT path are revealed by comparing the mechanical responses along three compressed crystallographic orientations ([100], [11¯0], and [111]). Positive strain-rate sensitiveness is found in the yield stress along the [11¯0] and [111] directions, while insensitiveness along the [100] direction. Various PTs occur alongside massive plastic deformation in the post-yield regime. As the strain rate rises, face-centered-cubic (FCC) to body-centered-cubic (BCC) PT overrides the stacking fault-induced hexagonal-close-packed (HCP) phase formation and dominates the plasticity for the [100] loading. By contrast, crystalline PTs give way to amorphization for [11¯0] and [111] loading at high strain rates. Chemical short-range order hinders dislocation slip and promotes dislocation interactions, which further facilitate early formation of the BCC phase, suggesting a potential strategy to tailor polymorphism in MEAs.

Temperature dependent anisotropic mechanical behavior of TiAl based alloys

γ-based titanium aluminides exhibit remarkable mechanical properties at high temperatures and are deployed in jet engines. The microstructure of these alloys, consisting of alternating plates of the γ (TiAl) and α2 (Ti3Al) phases, exhibits highly anisotropic mechanical behavior. However, deep understanding of the associated micromechanics is lacking. The effect of differential strength of the slip/twin systems, structural length scales and temperature in determining the homogeneity of deformation at the intercolony and intracolony level has not been well understood. Hence, we establish structure–property relationships, under uniaxial compression and uniaxial tension, by crystal plasticity finite element techniques. The deviation from Hall–Petch behavior and the temperature-dependent yield stress anomaly are rationalized and included in the model. Our results reveal a complex interplay between lamellar orientation, structural length scale, temperature, and stress state. Key findings include: (1) Basal slip in the α2 phase can be activated by differential strengthening of slip systems at lamellar interfaces. Basal slip increases the propensity for crack nucleation due to coarse slip bands. (2) There is preferential activation of twinning in the γ phase under tension. These twins can improve ductility by increasing strain hardening. However, they can also promote crack nucleation. (3) Smaller lamellar widths at higher temperatures can improve strain homogeneity between the γ and α2 phases. (4) Yield stress anisotropy exhibited a non-monotonic variation with lamellar size and temperature. (5) Increasing the strength of slip/twin systems through solid solution or precipitation strengthening can improve intracolony deformation homogeneity, reducing crack nucleation. We suggest strategies for alloy and microstructure design to improve damage tolerance in these alloys.

Manipulating deformation mechanisms with Y alloying of Mg

The effect of Y concentration on the slip and twinning mechanisms in binary Mg–Y alloys are investigated using transmission electron microscopy, electron backscattered diffraction, and visco-plastic self-consistent polycrystal constitutive modeling. Four concentrations of Y are studied in hot-rolled and recrystallized sheet material. The materials were deformed in tension and compression in the rolling direction and compression in the normal direction in order to invoke distinct proportions of slip and twin mechanisms with each test. Within the single crystal hardening model used in polycrystal modeling, a slip-twin interaction law is introduced to account for dislocation density reductions due to dislocation absorption during twin boundary migration. We show that increasing Y concentration reduces the intensities of both the initial and deformation textures. During deformation, the plastic anisotropy in yield stress, the tension-compression asymmetry, and amount of 101‾2⟨1‾011⟩ twinning is shown to decrease with increasing Y. For each alloy, the model identifies a single set of material parameters that successfully reproduced all measured stress-strain curves and achieved agreement with measured deformation textures and twin area fractions. Transcending texture effects, the model interpretation of the flow responses suggests that increased concentrations of Y increase the critical resolved shear stress for basal slip but have negligible effects on the other slip modes. The reduced plastic anisotropy with increases in Y is explained by a concomitant decrease in the prismatic-to-pyramidal slip critical resolved shear stress ratio. The model suggests that their nearly equivalent critical resolved shear stress values lead to the enhanced non-basal activity of Mg–Y alloys, which was confirmed by transmission electron microscopy. The calculations suggest that beyond any texture differences, this reduction in twinning can be attributed to a slightly increased resistance for 101‾2⟨1‾011⟩ twin propagation, particularly in the binary with the highest Y content.

Effect of uniaxial loading direction on mechanical responses and texture evolution in cold pilgered Zircaloy-4 tube: Experiments and modeling

Mechanical responses of cold pilgered Zircaloy-4 (Zr-4) tubes are measured under different uniaxial (tension/compression) loading directions. Tensile tests were carried out along three directions: rolling direction (RD), transverse direction (TD) and 45° to the rolling direction (45RD) at quasi static strain rate. Compression test was also performed in the RD. Texture was characterized at intermediate strains with electron backscattered diffraction method. For different uniaxial loading conditions, anisotropic yield stress and strain hardening behavior can be observed. Such complex mechanical behavior is well explained with the variations in activation of deformation mechanisms predicted by the Schmid factor distribution and visco-plastic self-consistent (VPSC) model. In order to calibrate the VPSC model’s parameters more accurately, both mechanical responses and texture changes for four different directional tests are compared with VPSC simulations. The calculated Lankford coefficients are also calibrated with anisotropic tensile results. Furthermore, a deepening understanding of the texture evolution under different loading directions were disclosed based on VPSC method. The results indicate that the activity of deformation mechanisms changes significantly with different uniaxial loading directions. Non-prismatic slips with higher critical resolved shear stress, e.g. basal and pyramidal slip, make larger contributions to the yield and strengthening stress resulting in the highest stress in TD compared with RD and 45RD. Compression test along RD prefers the activation for tensile twinning (TTW). Meanwhile, TTW can be detected in 45RD and TD tension owing to the spread distribution of initial texture towards TD.

Influence of Texture on Deformation Mechanism of Hot Extruded Oxide Dispersion Strengthened 18Cr Ferritic Steel

This paper focuses on studying the influence of texture on the deformation mechanism of oxide dispersion strengthened (ODS) 18Cr ferritic steel subjected to high-temperature tensile testing after consolidation by hot extrusion. The initial microstructure of the hot extruded steel showed preferential (1 1 0) planes alignment in perpendicular and parallel direction to extruded (ED) and transverse (TD), respectively. Two types of anisotropy have been highlighted: (1) A strong anisotropy of elongation properties with a transverse ductility is lower as compared to the axial ductility; (2) yield stress anisotropy (mechanical strength anisotropy) which is found to be temperature dependent. The material flow in 〈1 1 1〉 direction is observed during the application of load along extruded direction during the tensile test; however, (1 1 0) slip plane normal is parallel to the direction of loading for transverse direction and brings the Schmid factor to a lower level which makes slip activation unlikely. Deformation band is found to be aligned with the loading direction in the ED specimen and covering across a number of neighboring ferrite grains could be noticed irrespective of material flow. However, the areas near the grain boundaries in the microstructure are found to be the strain gradient regions. Further, it shows a preferential accommodation of strain in proximity to the boundary network for TD specimen. High temperature (973 K) tensile test in ED is found to promote grain-subdivision of elongated bands by dynamic recrystallization, and inverse pole figure distribution reveals a preferential increase in the intensity of clustering toward (1 1 1) plane parallel to the loading direction.

A study on crystal plasticity of face-centered cubic structures induced by deformation twinning

The effect of deformation twinning on the accessible slip and twin shear systems of a dislocated face-centered cubic structure and their critical stresses is studied. In particular, the plastic shear modes of critical matrix structure – single glide oriented Cu-8at.%Al alloy crystals deformed by room temperature tension up to the onset of deformation twinning - and the plastic shear modes of bimodal twin/matrix layered structure – subsequently twinned Cu-8at.%Al crystals – were examined. It was found that all twin and slip systems of the matrix structure may operate independently and their critical stresses are dispersed by about fifteen percent around the mean value. However, not all of the accessible slip and twin systems of the twin/matrix structure may operate independently and their critical stresses may differ by a factor of well over four. This large discrepancy of the critical stresses is responsible for giant yield stress anisotropy of the twin/matrix layered structure; the maximal and minimal yield stresses may differ even by one order of a magnitude. The twin/matrix layered structure reveals also very strong asymmetry of the tension/compression yield stress. It is suggested, that the giant anisotropy and very strong asymmetry of the yield stress have the same physical origin, i.e. the internal stress field associated with extended configurations of cube dislocations located within a twin lamellae - the deformation twinning induced effect of cube dislocation stress. It is concluded, that the cube dislocation stress effect seems greatly responsible for plasticity and strengthening of mechanically twinned face-centered cubic structures.

Strain-Rate Sensitivity, Tension-Compression Asymmetry, r-Ratio, Twinning, and Texture Evolution of a Rolled Magnesium Alloy Mg-1.3Zn-0.4Ca-0.4Mn

In this work, the deformation response, texture evolution, and twinning development of a magnesium (Mg) alloy, Mg-1.3Zn-0.4Ca-0.4Mn, for biocompatible applications are investigated. Further, the alloy’s formability, by examining the instantaneous r-ratio and strain-rate sensitivity (SRS) as a function of strain and loading direction, is investigated. It is found that after rolling and peak aging, the alloy has a rolled texture of moderate intensity with the basal planes contained in the rolling plane and with a bimodal, fine-grained microstructure. The alloy shows both high room-temperature tensile strength (300 MPa) and ductility (25 pct) in the rolling direction (RD) and, remarkably, r-ratios saturating close to unity in all three in-plane testing directions. It is also found that the SRS is relatively high and uniform, with averages ranging from 0.015 to 0.025, depending on the in-plane testing directions. These are outstanding properties compared to pure Mg and most of its biocompatible alloys. Typical of Mg alloys, this alloy has a propensity for twinning by multiple twin modes, which leads to rapid texture evolution, anisotropy, and tension-compression (T-C) asymmetry in yield stress, with compression having the weaker response. These mechanical characteristics along with their microstructural origins are presented and discussed in this article.

Anisotropic features of natural Teguline clay

In general, due to their geological formation by deposition, natural stiff clays exhibit anisotropic thermo-hydro-mechanical behaviour. This behaviour is important to be considered in geological and geo-environmental engineering. In this study, natural stiff Teguline clay was extracted at different depths and the thermal conductivity, compressibility and hydraulic conductivity were determined on samples along various orientations with respect to the bedding plane. Significant thermal and hydraulic conductivity anisotropies were evidenced with higher values along the bedding plane, indicating that both heat and water transfers preferentially occurred along the direction parallel to the bedding plane. Moreover, the compression index in the horizontal direction were found lower than in the vertical direction, while opposite phenomenon was observed for the yield stress. The degrees of thermal conductivity anisotropy ηΤ, compression index anisotropy ηCc1, yield stress anisotropy ησ'y and hydraulic conductivity anisotropy ηk1 were found comparable, indicating that bedding is a good indicator of the inherent thermo-hydro-mechanical anisotropy for natural stiff clays. Upon loading in oedometer after the yield stress, the inherent anisotropy changed: for the vertical sample (loading direction normal to the bedding plane), loading led to more and more anisotropy, while for the horizontal sample (loading direction parallel to the bedding plane), the inherent anisotropy disappeared first; then, the induced anisotropy was developed. These findings provided useful information for analyzing the thermo-hydro-mechanical anisotropy of natural soils in geotechnical and geo-environmental engineering.

Enhancement of plastic anisotropy and drastic increase in yield stress of Mg-Li single crystals by Al-addition followed by quenching

Strong orientation dependence of yield stress was found in a body-centered cubic (bcc)-structured Mg-Li alloy single crystal by adding 5 at.% of Al combined with rapid quenching, which was negligible in Mg-Li binary single crystals.Furthermore, the addition of 5 at.% of Al combined with rapid quenching caused an extreme increase in yield stress up to ~470 MPa; this compares to ~50 MPa in a Mg-Li binary crystal. Increased valence-electron to atom ratio and development of chemical modulation in the alloy by Al-addition are probable causes of the enhancement of plastic anisotropy and the drastic increase in yield stress, respectively.