Experimental and numerical study of laser induced spallation into aluminum and copper targets

Laser driven shocks can lead to the dynamic failure, called spallation, of materials which undergo a dynamic tension at the crossing of two rarefaction waves. We present here a numerical and experimental study of ductile material scabbing with the particular laser shock conditions (very short durations and very high induced pressure levels). A cumulative damage criterion is implemented into both numerical codes shylac and radioss■. Experiments have been carried out by laser irradiation of thin foils of pure aluminum, copper, and iron by laser pulses with the three durations at medium height 0.6, 2.5, and 27 ns, generating an incident flux ranging from 5×1011 to 5×1012 W/cm2. The validity of the cumulative damage criterion is asserted by the consistency of numerical and experimental results for aluminum whose criterion parameters are known. The unknown constants for copper are determined by fitting the numerical simulations to the experimental data. The material influence on the scab thickness and on the spallation threshold is analyzed. Experimental laser induced spallation data given by irradiation of a rear stepped target have been validated experimentally and numerically.