Classic Split-Hopkinson Pressure Bar Testing

A dislocation-based constitutive law for pure Zr including temperature effects

Bulk nanostructured (ns)/ultrafine-grained (UFG) metallic materials possess very high strength, making them attractive for high strength, lightweight and energy efficient applications. The most effective approach to produce bulk ns/UFG metallic materials is severe plastic deformation (SPD). In the last 30 years, significant research efforts have been made to explore SPD processing of materials, SPD-induced microstructural evolutions, and the resulting mechanical properties. There have been a few comprehensive reviews focusing mainly on SPD processing and the mechanical properties of the resulting materials. Yet no such a review on SPD-induced microstructural evolutions is available. This paper aims to provide a comprehensive review on important microstructural evolutions and major microstructural features induced by SPD processing in single-phase metallic materials with face-centered cubic structures, body-centered cubic structures, and hexagonal close-packed structures, as well as in multi-phase alloys. The corresponding deformation mechanisms and structural evolutions during SPD processing are discussed, including dislocation slip, deformation twinning, phase transformation, grain refinement, grain growth, and the evolution of dislocation density. A brief review on the mechanical properties of SPD-processed materials is also provided to correlate the structure with mechanical properties of SPD-processed materials, which is important for guiding structural design for optimum mechanical properties of materials.

Structural evolutions of metallic materials processed by severe plastic deformation

A comparative study on Johnson Cook, modified Zerilli–Armstrong and Arrhenius-type constitutive models to predict elevated temperature flow behaviour in modified 9Cr–1Mo steel

The role of heterogeneous deformation on damage nucleation at grain boundaries in single phase metals

The effects of strain rate, temperature, and tungsten alloying on the yield stress and the strainhardening behavior of tantalum were investigated The yield and flow stresses of unalloyed Ta and tantalum-tungsten alloys were found to exhibit very high rate sensitivities, while the hardening rates in Ta and Ta-W alloys were found to be insensitive to strain rate and temperature at lower temperatures or at higher strain rates This behavior is consistent with the observation that overcoming the intrinsic Peierls stress is shown to be the rate-controlling mechanism in these materials at low temperatures The dependence of yield stress on temperature and strain rate was found to decrease, while the strain-hardening rate increased with tungsten alloying content The mechanical threshold stress (MTS) model was adopted to model the stress-strain behavior of unalloyed Ta and the Ta-W alloys Parameters for the constitutive relations for Ta and the Ta-W alloys were derived for the MTS model, the Johnson—Cook (JC), and the Zerilli-Armstrong (ZA) models The results of this study substantiate the applicability of these models for describing the high strain-rate deformation of Ta and Ta-W alloys The JC and ZA models, however, due to their use of a power strain-hardening law, were found to yield constitutive relations for Ta and Ta-W alloys that are strongly dependent on the range of strains for which the models were optimized

/pdf/constitutive-behavior-of-tantalum-and-tantalum-tungsten-3iwcor3ht1.pdf

Constitutive behavior of tantalum and tantalum-tungsten alloys

Modeling mechanical response and texture evolution of α-uranium as a function of strain rate and temperature using polycrystal plasticity

The influence of grain size on the constitutive behavior (strain-rate and temperature dependence of the yield stress and strain hardening) and substructure evolution of MONEL 400 was investigated. Increasing the grain size from 9.5 to 202 µm was seen to reduce the quasi-static yield strength from 290 to 115 MPa, while having a minimal effect on the work-hardening response. Increasing the strain rate from quasi-static to dynamic strain rates (3000 s−1) was seen to increase the yield and overall flow-stress levels, but has no effect on the strong grain-size dependency exhibited by this alloy. The persistent influence of grain size to large strains is inconsistent with previous d
 −1/2 pileup grain-size modeling in the literature, which predicts convergence at large strains. Substructure evolution differences between the grain interiors and adjacent to grain boundaries supports differential defect storage processes which are consistent with previously published work-hardening d
 −1 modeling arguments for grain size-dependent strengthening in polycrystals. The integration of grain-size dependency into constitutive modeling using the mechanical threshold stress (MTS) model is discussed. The MTS model is shown to provide a robust constitutive description capturing yielding, large-strain work hardening, and grain-size effects simultaneously. The MTS model is, additionally, shown to satisfactorily address the experimentally observed transients due to strain-rate or temperature-path dependency.

Influence of grain size on the constitutive response and substructure evolution of MONEL 400

The present paper focuses on the development of a fully implicit, incrementally objective integration algorithm for a hypoelastic formulation of $$J_{2}$$
 -viscoplasticity, which employs the mechanical threshold strength model to compute the material’s flow stress, taking into account its dependence on strain rate and temperature. Heat generation due to high-rate viscoplastic deformation is accounted for, assuming adiabatic conditions. The implementation of the algorithm is discussed, and its performance is assessed in the contexts of implicit and explicit dynamic finite element analysis, with the aid of example problems involving a wide range of loading rates. Computational results are compared to experimental data, showing very good agreement.

Incrementally objective implicit integration of hypoelastic–viscoplastic constitutive equations based on the mechanical threshold strength model

The stress-strain response of Zr due to twinning is distinctly different from that due to slip as a function of temperature and strain rate When the applied stress is lower than the transition stress, dislocation slip is the dominant deformation mechanism The traditional MTS model is shown to adequately represent the constitutive behavior of Zr Above the transition stress twinning becomes the dominant deformation mechanism where the flow stress increases linearly with strain In this regime the rate-dependent strain hardening can be described by equations based on thermal activation theory that are very similar to the formula used in the MTS model

/pdf/influence-of-twinning-on-the-constitutive-reponses-of-zr-2ndrmi39vh.pdf

Shuh Rong Chen

Papers

Constitutive behavior of tantalum and tantalum-tungsten alloys

Modeling mechanical response and texture evolution of α-uranium as a function of strain rate and temperature using polycrystal plasticity

Influence of grain size on the constitutive response and substructure evolution of MONEL 400

Incrementally objective implicit integration of hypoelastic–viscoplastic constitutive equations based on the mechanical threshold strength model

Influence of Twinning on the Constitutive Reponses of Zr : Experirnents and Modeling