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The Portevin-Le Chatelier (PLC) effect manifests itself as an unstable plastic flow during tensile tests of some dilute alloys under certain regimes of strain rate and temperature. The plastic strain becomes localized in the form of bands which move along a specimen gauge in various ways as the PLC effect occurs. Because the localization of strain causes degradation of the inherent structural properties and surface quality of materials, understanding the effect is crucial for the effective use of alloys. The characteristic behaviors of localized strain bands and techniques commonly used to study the PLC effect are summarized in this review. A brief overview of experimental findings, the effect of material properties and test parameters on the PLC effect, and some discussion on the mechanisms of the effect are included. Tests for predicting the early failure of structural materials due to embrittlement induced by the PLC effect are also discussed.

The plastic flow characteristics of the metal material in mechanical scratching is determined on the important parameters of the negative rake angle, the material deformation amount, the scratching force, the groove quality, and the tool wear. However, the chip flow angle and the plastic flow direction of the metal material in the cutting or mechanical scratching are often derived from the approximate solution according to the metal cutting theory and assumptions. Meanwhile, there is no theoretical model of the plastic flow characteristics suitable for the mechanical scratching the metal material with diamond wedge scratching tool (irregular triangular pyramid tool). Therefore, the unit plastic flow vector (PFV), the working negative rake angle, and the chip flow angle (CFA) theoretical model are established in this paper. And the evolution law of plastic flow angle of the unit PFV and CFA under the influence of the multi-scratching factors was also studied. It can be known that the PFA is related to the elevation angle of the scratching tool, but independent on the speed and material, while the CFA is related to the above multi-scratching factors. Meanwhile, the evolution law of theoretical PFA is consistent with the experimental value, and the maximum deviation is 6.687°, which verifies the theoretical model. In addition, compared with the CFA, the PFV can directly reflect the material plastic flow direction on the contact surface.

The single-peak overload test based on DIC technology was carried out in this study, and U71MnG steel was used to explore the influence of dislocation motion on crack propagation during overload. The changes in the shape and size of the plastic zone during the overload fatigue cycle are tracked and recorded, and the trends in the stress intensity factors of the Christopher–James–Patterson (CJP) and dislocation correction models are compared. The degree of influence of the dislocation motion on the variation in the stress intensity factors is evaluated, and the variation pattern of the plastic flow factor is derived (the amount of crack tip blunting, ρ ). The results showed that the dislocation correction model increased the accuracy of the solution of the coefficient set, and the predicted size of the plastic zone of the correction model was more consistent with the experimental data. A better match with the crack tip was observed in the experimental plastic zone, the dislocation correction model error with the theoretical plastic zone fluctuates within 10%, whereas the CJP model can reach a maximum of 36.75%, demonstrating the insensitivity of the dislocation correction model. The plastic flow factor ρ follows the same pattern as that of the plastic zone area and stress intensity factor amplitude, ρ increases slowly with the increase of crack length before overload, ρ increases significantly after overload and then decreases sharply, and it recovers to be stable with the disappearance of the overload hysteresis effect of crack propagation.

Experimental flow stress–strain data under different stress states are often used to calibrate the plastic constitutive model of anisotropic metal materials or identify the appropriate model that is able to reproduce their plastic deformation behavior. Since the experimental stress–strain data are discrete, they need to be mathematically returned to a continuous function to be used to describe an equivalent hardening increment. However, the regression results obtained using existing regression models are not always accurate, especially for stress–strain curves under biaxial stress loading conditions. Therefore, a new regression model is proposed in this paper. The highest-order term in the recommended form of the new model is quadratic, so the functional relationships between stress–strain components can be organized into explicit expressions. All the experimental data of the uniform deformation stage can be substituted into the new model to reasonably reproduce the biaxial experimental stress–strain data. The regression results of experimental data show that the regression accuracy of the new model is greatly improved, and the residual square sum SSE of the regression curves of the new model reduced to less than 50% of the existing three models. The regression results of stress–strain curves show significant differences in describing the yield and plastic flow characteristics of anisotropic metal materials, indicating that accurate regression results are crucial for accurately describing the anisotropic yielding and plastic flow behaviors of anisotropic metal materials.

Localized deformation is the failure precursor of quasi-brittle rocks. The objective herein is to propose an enhanced constitutive model incorporating the evolution of localized damage in quasi-brittle rocks. The plastic and damage behaviors are assumed inside the localization zone, and elastic deformation is considered outside the zone. As a consequence, the macroscopic responses are obtained by using a volume average procedure incorporating the evolution of the volume fraction of the localization zone. The plastic and damage behaviors inside the localization zone are, respectively, described by a nonlinear yield criterion and an exponential damage criterion. The onset of localized failure is defined by introducing a critical value of localized damage parameter. For application, a semi-implicit return mapping algorithm is developed to deal with the numerical implementation at the material level. Finally, the validity of the model and the robustness of the algorithm are assessed by the consistent comparison between simulation results and the triaxial compression test of three typical quasi-brittle rocks. The post-peak snapback and brittle-ductile transition behaviors are captured by adjusting the evolution rates of localization zone and localized damage, respectively. This model has two main innovative features: (1) the simulated peak strength of the model only depends on the strength parameters and is not affected by the damage and localization parameters, and (2) the proposed approach can effectively overcome the overestimation of plastic deformation by the traditional associated plastic flow rule and accurately describe the post-peak mechanical behaviors of quasi-brittle rocks.

The predictive capability of an anisotropic yield function highly relies upon the number of the model parameters and its calibration type. Conventional calibration of a plane stress anisotropic yield function considers material behavior in uniaxial and equi-biaxial stress states, whereas it violates shear and plane strain loading conditions. In this study, the direction of the plastic flow in both loading regions was corrected by including shear and plane strain constraint terms to the conventional calibration of the Yld2000 function, and its effect on the sheet metal forming simulations, namely cup drawing and hole expansion tests, was investigated. Two highly anisotropic sheet materials (AA2090-T3 and low-carbon steel) were selected for the investigation, and the anisotropy coefficients were determined. Stress anisotropy was accurately predicted by the conventional method, whereas any decrease in the prediction of the deformation anisotropy could not occur by the applying of the constrained methods. Significant increases in the predicted cup height and differences in the number of the ears were observed by shear constraint identification in the cup drawing. The maximum thinning location in the hole expansion test could be accurately predicted by plane strain constraint identification.

This paper presents research on the influence of material anisotropy caused by the technological process of its manufacturing on the plastic properties of the material. In the experimental study, samples cut from an AISI 304L rolled sheet in the rolling direction, transverse, and at a 45° angle to the rolling direction were predeformed by axial deformation at 18 and 30%. The principal specimens extracted from the pre-deformed plates, cut in the longitudinal, transverse, and 45° angle directions, were subjected to tensile loading until failure. The data thus obtained allowed for the analysis of the plastic flow mechanism using the author’s calculation procedure. The CR coefficient analysis provided information on the state of plastic anisotropy caused by the pre-deformation. For the specimens predeformed in the rolling direction, plastic flow isotropy was observed at a strain of 35%. For the specimens predeformed in the transverse direction—the plastic anisotropy is completely removed at a strain of 33%. For the specimens predeformed at 45 degrees to the rolling direction, it was found that the strain completely removed the plastic anisotropy induced by rolling. The calculations provided information that due to an abrupt change in the strain path, a strong reconfiguration of the plastic flow mechanism occurs, causing the removal of anisotropy generated by rolling.

Metallic materials are frequently exposed to high strain rates and complex stress conditions. Research on dynamic mechanical behaviors of these materials is essential for engineering design and industrial applications. In this paper, the dynamic plastic and flow behaviors of TC17 alloy under compression/tension-torsion were studied. The initial yield behaviors of TC17 alloy under quasi-static and dynamic loadings were researched, and a dynamic asymmetric yield criterion (DAYC) proposed by Yang, Guo, and Li was used to characterize the initial yield behavior. According to the hardening properties under different stress states, a modified dynamic hardening law (MDHL) was proposed to fit the loading surface. The plastic flow directions under quasi-static and dynamic loadings of TC17 alloy were investigated. Results showed that the plastic potential function may conform with the associated flow rule (AFR). The yield properties, strain hardening law, and plastic flow rule of TC17 alloy were systematically investigated and successfully characterized by DAYC and MDHL.

The plastic potential surface and yield surface need to be established separately due to the difference between the plastic flow direction and loading direction in the soil modeling in traditional plasticity mechanics. However, the difference between the plastic flow direction and loading direction can be described by choosing one of the plastic potential surface and yield surface by introducing the fractional calculus. For that, the new modeling approach by using the fractional derivative of Riemann–Liouville is adopted in this study. First, a plane model for peak stress ratio considering the initial void ratio and confining pressure is proposed, and a dilatancy equation considering particle breakage for rockfill material is employed to derive a plastic potential function. Then, the fractional derivative direction and first derivative direction of the plastic potential function are deduced and developed as the loading direction and plastic potential direction, respectively. On this basis, a non-associated fractional-order plastic model without yield function is developed for rockfill material. Finally, a number of drained triaxial test results of rockfill materials are simulated to verify the capability of the proposed model. Good agreement between test data and model simulations indicates that the proposed fractional-order plasticity model can accurately capture the stress–strain behaviors of rockfill materials.

For the adiabatic shear behavior of metal materials at high strain rates, a compression test of the FV520B martensitic precipitation-hardened stainless steel was conducted in a wide range of strain rates (1.0 × 10 −3  s −1 -8 × 10 3  s −1 ), temperatures (20-800 °C), and hardness values (HRC32-HRC40). The effects of strain rate, temperature, and hardness on the plastic flow behavior of the materials and microstructural characteristics of the dynamic compression materials were analyzed. The mechanism of adiabatic shear damage (ASD) dissipation on the plastic flow stress (PFS) was revealed. The stress gradient change factor was proposed, and an analytical equation for the non-uniform gradient change in the PFS with respect to temperature and hardness was established. Therefore, based on the adiabatic shear microvoid evolution mechanism, strain equivalence principle, high-temperature softening effect, and hardness hardening effect, a novel dynamic constitutive model considering ASD and non-uniform gradient stress changes was established. The results showed that ASD caused a loss of PFS under high strain rate loading and even the phenomenon of strain rate inverse strengthening. ASD gradually became significant with the increase in hardness and disappeared when the temperature exceeded 600 °C. The PFS of the FV520B steel was characterized by a significant non-uniform gradient decrease with increasing temperature. The prediction error of the PFS in the dynamic constitutive model was reduced from 5-74.8 to 1.1-7.3%. The application of novel dynamic constitutive model in high-speed machining is further discussed.