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A critical damage degree model was established for spall fracture in high-purity ductile polycrystalline metals. Three critical characteristic damage degrees (i.e., nucleation, complete plasticity, and fracture damage) were used to divide the dynamics of damage evolution into four stages: void nucleation, elastoplastic growth, plastic growth, and coalescence. For each stage, a physical model was established based on the damage evolution regularities and mechanism. Simulated results of the proposed model coincided well with the experimental ones in terms of serious spall experiments for oxygen-free copper. Finally, the association between the characteristics of the pullback signal in the spall experiment and the dynamic properties of damage evolution is discussed, indicating that the three critical damage degrees in the model had definite physical meanings.

A dislocation-based constitutive model is applied to revisit the anomalous thermal hardening behavior of fcc metals under shock loading. Two scale-dependent dislocation motion mechanisms are found to dominate the thermal hardening behavior of fcc metals under shock loading. In particular, because of the shear stress decay with the propagation of the shock wave, the relativistic effect of dislocation motion is only significant near the impact surface, whereas the phonon drag mechanism dominates dislocation motion in a macroscopic fcc metal. Furthermore, we provide a detailed picture of the thermal hardening behavior on the continuum scale, in which the role of the newly generated stress wave from plastic deformation in the dynamic deformation process is highlighted. We show that the mechanical response at the elastic precursor is mainly controlled by the stress wave emanating from the plastic front.

A novel explanation of the quasielastic release phenomenon in shock compressed aluminum is presented. A dislocation-based model, taking into account dislocation substructures and evolution, is applied to simulate the elastic plastic response of both single crystal and poly crystalline aluminum. The calculated results are in good agreement with experimental results from not only the velocity profiles but also the shear strength and dislocation density, which demonstrates the accuracy of our simulations. Simulated results indicate that dislocation immobilization during dynamic deformation results in a smooth increase of yield stress, which leads to the quasi-elastic release, while the generation of dislocations caused by the plastic release wave results in the appearance of a transition point between the quasielastic release and the plastic release in the profile., 13 pages and 12 figures