Finite-strain thermoelasticity based on multiplicative decomposition of deformation gradient

The constitutive formulation of the finite-strain thermoelasticity is revisited within the thermodynamic framework and the multiplicative decomposition of the deformation gradient into its elastic and thermal parts. An appealing structure of the Helmholtz free energy is proposed. The corresponding stress response and the entropy expressions are derived. The results are specified in the case of quadratic dependence of the elastic strain energy on the finite elastic strain. The specific and latent heats are discussed, and the comparison with the results of the classical thermoelasticity are given.

Laser shock compression of copper monocrystals: Mechanisms for dislocation and void generation

Copper with two orientations ([001] and [134]) was subjected to high intensity laser (energy levels of 40-300 J; energy densities of 15-70 MJ/m$^2$ and durations below 10 ns). The defects created are characterized by transmission electron microscopy. An orientation-dependent threshold stress for twinning is observed. The results are rationalized in terms of a criterion in which slip and twinning are considered as competing mechanisms. A constitutive description is applied to the two orientations, incorporating both slip and twinning. The predictions are in agreement with experiments. The threshold stress for twinning in the [001] orientation is 20-40 GPa, whereas the one for the [134] orientation is 40-60 GPa. The threshold stress is calculated, considering the effect of shock heating. The constitutive description provides a rationale for the experimental results; the calculated thresholds are 18 GPa for [001] and 25 GPa for [134]. A mechanism for void generation and growth based on the emission of geometrically necessary dislocations is proposed and analytically formulated