The response of metals to high-strain-rate deformation is successfully described by physically-based mechanisms which incorporate dislocation dynamics, twinning, displacive (martensitic) phase transformations, grain-size, stacking fault, and solution hardening effects. Several constitutive equations for slip have emerged, the most notable being the Zerilli-Armstrong and MTS. They are based on Becker's and Seeger's concepts of dislocations overcoming obstacles through thermal activation. This approach is illustrated for tantalum and it is shown that this highly ductile metal can exhibit shear localization under low temperature and high-strain-rate deformation, as predicted from the Zerilli-Armstrong equation. A constitutive equation is also developed for deformation twinning. The temperature and strain-rate sensitivity for twinning are lower than for slip; on the other hand, its Hall-Petch slope is higher. Thus, the strain rate affects the dominating deformation mechanisms in a significant manner, which can be quantitatively described. Through this constitutive equation it is possible to define a twinning domain in the WeertmanAshby plot; this is illustrated for titanium. A constitutive description developed earlier and incorporating the grain-size dependence of yield stress is summarized and its extension to the nanocrystalline range is implemented. Computational simulations enable the prediction of work hardening as a function of grain size; the response of polycrystals is successfully modeled for the 50 nm-100 m range. The results of shock compression experiments at pulse durations of 3 -10 ns (this is two-three orders less than gas-gun experiments) are presented. They prove that the defect structure is generated at the shock front; the substructures observed are similar to the ones at much larger durations. A mechanism for dislocation generation is presented, providing a constitutive description of plastic deformation. The dislocation densities are calculated which are in agreement with observations. The threshold stress for deformation twinning in shock compression is calculated from the constitutive equations for slip, twinning, and the Swegle-Grady relationship.
We present numerical simulations of bulge formation at the trailing edge of an inclined surface and its inhibitory effect on particle removal during surface cleaning. We investigate the spatial variations in liquid films near the trailing edge and find that the Weber number can be used as a dominant parameter to determine bulge occurrence over the trailing edge. We divide the film region near the trailing edge at which the bulge occurs into two: the region where the surface linearly grows and the surface tension is negligible, and the region where the surface tension force becomes dominant and the film surface is curved. In the investigated cases in which the Reynolds number is $O(10)$ or greater, the viscous forces is negligible, which allows for the derivation of the scaling laws for the length of the two regions according to the condition that the bulge height scales with the capillary length.In the resulting scaling law, the length scales depend on the Froude number and the inclination angle. The proposed scaling law allows for the prediction of the bulge shape and the prediction agrees with the simulation results, particularly at low Weber numbers (i.e, We < 0.5$). Moreover, we construct a particle removability map to assess the removal of particles of different sizes at specific locations on the substrate. The map reveals the reduced of the removability for small-size particles or particles located in the bulge.
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