| Popis: |
A model to predict material damage and spall fracture is applied to low-angle oblique plate-impact experiments. In this configuration, impact of parallel plates occurs along a direction inclined relative to the flyer velocity direction, resulting in normal and transverse deformations in both plates. The model uses the Perzyna viscoplastic constitutive theory that contains a scalar field variable description of the material damage, which is taken as the void volume fraction of the polycrystalline material. Incorporation of the damage parameter permits description of rate-dependent, compressible, inelastic deformation and ductile fracture. The model for microvoid growth is based upon a random distribution of microvoids idealized as spherical holes of arbitrary size, which, as an approximation, are assumed to remain spherical under the high mean stresses and moderate shear stresses that occur when the angle of inclination of the impact is small. A local spall fracture criterion based on critical microvoid volume is utilized. The constitutive equations are specialized for deformation associated with propagating plane waves of combined pressure and shear. Normal and transverse rear surface velocities are computed for oblique impact of 6061-T6 aluminum and compared to measured velocity histories. Numerical predictions are extended to conditions resulting in spallation under combined pressure-shear waves, using OFHC copper as the plate material. The void volume distribution resulting from the tensile mean stress in the target plate is computed to predict material damage. Computations are performed to illustrate the effect of damage on both the normal and transverse rear surface velocities. |
