Constitutive relations for copper under shock wave loading: Twinning activation

The simulation of shock-loading sequences in numerical hydrocodes includes the representation of shock fronts as continuous transitions in which the equations of mechanics are solved just as in the rest of the structure. Nonetheless, the elasto-plastic transformations are specific and, for some materials, the elasto-plastic models usually used in dynamic problems do not apply within these fronts. A constitutive law is developed in this study for copper, for dynamic problems to be used both inside and outside shock fronts. The Zerilli and Armstrong formulation is modified to take into account twinning activation under such conditions: twinning and dislocation glide are treated as two competing plastic deformation mechanisms, each having its own flow stress. The mechanical characterization of samples recovered after various shock tests and the numerical simulation of these tests are used to identify coefficients for this plasticity model.