International Journal of Plasticity最新文献

Strain gradient plasticity theory addresses the plastic strain gradient induced hardening by considering the internal stress and Taylor hardening associated with the geometrically necessary dislocations (GNDs). However, the continuum description of internal stress associated with GNDs is inaccurate due to the coarsening of discrete dislocations. Corrections are thus derived as the difference between the stresses produced by the continuous configuration and the discrete configuration. We further demonstrate the capability of this correction in effectively capturing the internal stress induced strengthening effect associated with GNDs, and elucidate that its role in strengthening is to homogenize the deformation and extend the influence of grain boundaries into the interior of grains within polycrystals. This capability to capture intragranular slip distribution is validated through the simulation of a polycrystalline tensile experiment. This work explains the limitations of classical crystal plasticity theory under high strain gradients and offers a straightforward yet robust slip discreteness correction to crystal plasticity with transparent input from dislocation theory, opening a new perspective for the connections between continuum crystal plasticity theory and dislocation theory.

A comprehensive approach addressing the flow behavior and the critical strain for the initiation of serrations in Al-Mg alloys is developed in the present work. The basic premise of the approach is that the solute atmosphere influences the friction as well as the strain hardening component of the flow stress. The friction effect of the solute cloud is modeled by considering the interplay between the characteristic solute migration time and the dislocation waiting time according to the cross-core diffusion mechanism. The impact on strain hardening is modeled by considering the apparent strengthening of the forest dislocations because of formation of solute aggregates near the vicinity of dislocation junctions. The apparent forest strengthening effect scales as the square root of the ratio of solute concentration in vicinity of the dislocation junctions and the bulk solute concentration. The modified constitutive model is validated against experimental flow curves obtained for strain rates varying over several orders of magnitude. It was observed that the modified constitutive model outperforms the standard constitutive model (considers only the friction effect of solute atmosphere) in predicting the flow curves in the dynamic strain aging domain. Furthermore, the modified constitutive model also accurately predicts the critical strain for the initiation of the jerky flow in both the normal and inverse regimes of the critical strain versus strain rate curve. Additional validation of the modified constitutive model is provided by dislocation character and density measurements via X-ray diffractograms, dislocation structure investigation via transmission electron microscopy along with fracture surface analysis.

The equiatomic Cr-Co-Fe-Ni medium-entropy alloy has the face-centered cubic structure. Single crystals of this alloy were tested by in-situ micropillar compression along different loading axes under scanning electron microscope. The transmission electron microscopy characterization and molecular dynamics simulation were incorporated for quantitative analysis of the effects of different crystal orientations on the deformation mechanisms. The <001>-oriented pillar not only exhibited extensive deformation-induced nano twinning, but also has been identified for the first time to undergo the FCCHCP phase transformation at room temperature. The strain localization tendency of <011>-oriented samples was confirmed through uniaxial tests to interpret the significant serration on stress-strain curves. The prominent strain hardening of <111>-oriented pillars was attributed to intense intersection between slip planes as evidenced by the extra density of Lomer-Cottrell locks. Such a high hardening rate has caused subsequent kinking of pillars. Functional division of different regions of kink band was conducted based on Orowan model. In principle, multi-principal element alloys can theoretically be designed and developed to combine a variety of excellent properties, which is an important class of candidate structural materials for advanced engineering systems. These findings provide promising guidance for understanding the mechanical anisotropy and application of these alloys.

The present research focuses on analyzing the deformation mechanisms associated with tensile loading of the Fe₅₀Mn₃₀Co₁₀Cr₁₀ high entropy alloy (HEA) using synchrotron x-ray diffraction (SXRD). This novel material is comprised by two major phases: γ-FCC and ε-HCP, where transformation induced plasticity (TRIP) effectively transforms the first into the latter, upon the application of an external stress. However, the presence of thermally stable ε-HCP prior to loading will also influence the deformation mechanism of the material during mechanical solicitation. As such, here we investigate the activation of different strain accommodation mechanisms and the consequent microstructural evolution. Four stages were identified in the mechanical response of this novel HEA, where the TRIP and the twinning induced plasticity (TWIP) deformation modes are the main events granting this HEA its outstanding properties. Such sequence of events allows to evidence the effectiveness of the collaboration between the transformative capability of the γ-FCC phase and the work hardening potential of the ε-HCP phase. This analysis is performed via quantitative and qualitative analysis of the SXRD data, allowing also to investigate the response behavior of specific crystallographic planes to the increasing stress throughout the experiment.

In this work, the mechanical response and fracture characteristics of (Ti_37.31Zr_22.75Be_26.39Al_4.55Cu₉)₉₄Co₆ high-entropy bulk metallic glass (HE-BMG) were investigated in detail over a wide range of strain rates (10⁻⁴–10⁵ s⁻¹). The HE-BMG exhibited a negative strain rate sensitivity under uniaxial compression, with the strength showing more significant rate dependence under dynamic conditions. The shear band behavior translated from the dominance of multiple shear bands propagations under quasi-static compression to the rapid propagation of a single shear band to form cracks under dynamic compression. Under dynamic loading, the shearing velocity increased along an arc-shaped displacement path, and the local stress state on the shear fracture surface shifted from compressive-shear to tensile-shear, accompanied by changes in fracture morphologies. The spall strength of HE-BMG decreased as flyer impact speed increased, while the long-term dependence of spall strength on strain rate may be positive. With the increase of impact speed, the main microstructural features of the spalling surface translated from flat regions accompanied by dimples to cup-cone structures. Furthermore, the complete parameters of the Johnson–Holmquist II (JH-2) model for HE-BMG were obtained based on experimental data. Numerical simulations of planar impact, penetration, and hypervelocity impact are in good agreement with experimental results, demonstrating the validity of the JH-2 model parameters. The current work has important guiding value for the application of HE-BMG in space debris protection.

Limited tensile ductility usually restricts the practical applications of new classes of high-strength materials in many industrial fields. Therefore, in-depth understanding of the work hardening behavior and its underlying plastic deformation mechanism are critical for the newly developed high-entropy alloys (HEAs). In this work, a geometric atomistic model of face-centered cubic (FCC)/ordered body-centered cubic (BCC (B2)) interfaces and the evolution of dislocation substructures have been investigated to explore the microstructural origins of work hardening responses for two additively manufactured AlCoCrFeNi_2.1 eutectic high-entropy alloys (EHEAs) with the respective lamellar and cellular microstructures. Unlike the lamellar interphase interfaces with the most classical Kurdjumov-Sachs (KS) FCC-BCC relationship of ${\left\{111\right\}}_{\text{FCC}}\parallel {\left\{110\right\}}_{B2}{〈011〉}_{\text{FCC}}\parallel {〈111〉}_{B2}$, the Nishiyama-Wassermann (NW) relationship, namely ${\left\{111\right\}}_{\text{FCC}}\parallel {\left\{110\right\}}_{B2}{〈011〉}_{\text{FCC}}\parallel {〈001〉}_{B2}$, is observed to be dominant on the cellular interphase interfaces. Furthermore, our intermittent high-resolution transmission electron microscopy (HR-TEM) results directly show that the deformation of lamellar AlCoCrFeNi_2.1 alloy first proceeds with massive stacking faults (SFs) and then dislocation walls developed across phases interfaces, due to the effective dislocation transfer capability of lamellar boundaries. The large uniform elongation of the cellular AlCoCrFeNi_2.1 alloy is attributed to the stable and progressive strain-hardening mechanism that is stemmed from the activated multiple slip systems, deformation-induced SF networks, and the associated Lomer-Cottrell locks in the middle and later stages of plastic deformation. Moreover, the nano-bridging of FCC cells in the 3D-printed microstructure provides unique channels for dislocation movement, which offsets the “blocking effect” of cellular boundaries and thus suppresses the pre-mature fracture.

TSV-Cu is widely used for chip interconnects, where high testing costs and complex crystal plasticity finite element (CPFE) limit the research of its deep microplastic evolution process. Considering the stored energy density (SED) based on dislocation density and plastic work as a fatigue indicator factor (FIP), this paper proposes for the first time a physics-informed neural network (PINN) framework based on SED, which aims to achieve the solution of SED distributions quickly and efficiently to save computational time and cost. The grain orientation, geometrical compatibility factor, back stress, and effective plastic strain are taken into account as inputs to the PINN model. The total dislocation density is used as an indirect solution variable to construct the associated loss boundary terms, which results in the solution of the SED. The results of the two real EBSD tests show that the PINN model is able to accurately and sensitively predict the SED concentration distribution for different thermal cycle loadings, and maintains a high degree of agreement with the CPFE calculation results. Moreover, The superiority of PINN over other machine learning algorithms in terms of physical model interpretation and prediction accuracy is verified. These make it a reality for PINN to solve for the FIP distribution for the first time, and to accurately and quickly predict the location of crack initiation.

This study investigates the effect of shear band evolution on the nucleation of Goss {110}<001> texture during the primary recrystallization of 3.24 wt% Si grain-oriented electrical steel. Nucleation at the early stage of primary recrystallization of the steel is explored both experimentally and numerically. The experimental approach involves cold rolling the steel specimens to obtain a thickness reduction ratio of 76 % and then applying heat treatment to them at 600 °C for less than 1 min. The numerical simulation employes crystal plasticity (CP) finite element model (FEM) to simulate the plastic deformation induced by the dislocation slips on predefined slip systems and non-crystallographic shear bands during cold rolling. Based on the CPFEM results, the generalized strain energy release maximization (GSERM) model is used to predict the preferential orientation probability of recrystallized nuclei for the steel by considering shear band formation. Subsequently, the microstructure evolution during the early stage of primary recrystallization of the steel is simulated using the phase field model (PFM). The developed CP model successfully predicted shear band activation and evolution in the γ-fibers centered on the {111}<112> texture component. The model also demonstrated that shear bands would be the preferred nucleation sites at the early stage of primary recrystallization because of their high stored energy. Moreover, by coupling with the GSERM model, the PFM could reproduce the nucleation of Goss grains at the beginning of primary recrystallization in shear bands.

This research couples a Lode-dependent anisotropic-asymmetric (LAA) frame (Lou and Yoon, 2023. International Journal of Plasticity, 166, 103,647) with a stress-invariant-based coupled quadratic-non-quadratic (CQN) anisotropic hardening function to analytically characterize the anisotropic-asymmetric hardening of sheet metals under uniaxial tension and uniaxial compression. Experiments are conducted for AA2A12-O under uniaxial tension, uniaxial compression, equibiaxial tension, plane strain tension and shear. Anisotropy is investigated by conducting the experiments along different loading directions from the rolling. The flow curves are obtained from these experimental data at distinct stress states and loading directions. The plastic hardening is represented by the CQN-coupled LAA function to verify its accuracy. The CQN-coupled LAA model is also utilized to represent the plastic flow of DP980 under uniaxial tension, uniaxial compression, shear and plane strain tension along different loading directions as well as equibiaxial tension. The application to AA2A12-O and DP980 demonstrates that the CQN-coupled LAA function is capable of modeling plastic hardening behaviors under uniaxial tension, uniaxial compression, equibiaxial tension and equibiaxial compression and dramatically improving the prediction accuracy of flow curves under plane strain tension.