Limitations on the Size of Ejecta Craters.
Final rept. 1 Apr-31 Jul 75,
APPLIED THEORY INC LOS ANGELES CALIF
Pagination or Media Count:
A simple model has been developed to compute the shapes of ejecta craters, and to set upper bounds on their sizes, using only data from spherically-symmetric fields of motion. The model was constructed in stepwise fashion to account for 1 relief of direct-induced stresses near the ground surface, with ensuing upward ground motion, 2 downward migration of the center of pressure in the ground as shock-vaporized material expands upward, 3 downward acceleration of a continuous ground medium by overpressure, and 4 downward acceleration of a fragmented ground medium by overpressure. Step 4 is not yet complete at its conclusion, the combined effects of overpressure and direct-induced stresses - effects that do not follow the rules of simple scaling - will be included in the model. The principal result obtained so far is that with the coupled-energy fractions presently accepted for nuclear surface bursts in the megaton range, even the coarse upper bound of the present model limits ejecta craters to radii of 990, 1060, 1220 and 1230 ft, respectively, for the four half-space materials. Deformation of the ground in which material elements experience inelastic shear strains but remain part of a solid continuum plastic flow, forms a second major crater-producing mechanism.