Some possible criteria for incipient scabbing of Be

Incipient scabbing experiments on beryllium were analyzed using a one-dimensional, uniaxial strain, finite difference computer code which integrates the equations of motion using an elasto-plastic constitutive relations for the metal. It is shown that because of the marked difference between the elastic and plastic wave velocities in beryllium, due to its abnormally low Poisson's ratio, the peak tension is only about two-thirds of the peak compressive stress behind the plastic shock wave, and that the tension--time history at the plane that scabs is more triangular than square. The calculations are used to examine various possible criteria for incipient scabbing, including critical values for the integrals of various functions of the tension with time. Several possible criteria fit the experimental results, but the criteria that fit depend on the assumptions made for the constitutive relation of Be in the calculations. (U.S.)