Crater Volume-Relative Contributions of Flow, Compaction and Elastic Transport~30Jun 88-18 Sep 95

摘要

As now modeled, near surface (and contained) bursts make room for craters(cavities) mainly by missile ejection, flow of otherwise elastic material, and compaction. An exact solution discovered here for locking solid admits elasticity, plasticity and compaction: For spherical bursts, a cavity radius dependent pressure Pc on the wall then forces nearby material to flow (and compact) until, at radii >rep, falling shock stress precludes shear failure. Flow ends; material freezes compressive hoop stress out to rep, beyond rep, a compressive elastic wave moves ever outward. Exactly that field develops in a half space whose hemispherical crater bears pressure Pc, while the (flat) balance of its surface bears the spherical field's hoop stress. Such ground loading is no surface burst replica, but is compressive and decays as it spreads and so drives a surface burst related cratering field. After freezing occurs, stiffness is more apt than rigidity within radius rep. An elastic wave due to overpressure's fall to zero at the ground surface, thus adds in to produce our terminal field. Out to rep, part of the compacted out volume then reverts to elastic compression; the crater's volume becomes a sum of volumes due to compaction and elastic compression out to rep, plus volume trapped in the elastic wave moving outward from rep. For six media whose elastic moduli reflect tests of Pacific coral, the fraction of crater volume in that wave ran from 1/6 to 1/3.