Shock-Induced Damage in Rock and Concrete

Abstract

REPORT DOCUMENTATION PAGE &ik>fcTh. r*M\r r»nnrtino burden tor this collection of informetion is estlmeted to «verso» 1 hour par response. Indui J«h.ÄÄÄ «»",, """. ,", , 2302/CX5f. WORK UNIT NUMBER PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)California Institute DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release J distribution unlimited. PERFORMING ORGANIZATION REPORT NUMBER SPONSOR/MONITOR'S ACRONYMIS) SPONSOR/MONITOR'S REPORT NUMBER(S) SUPPLEMENTARY NOTES14 ABSTRACT We have developed a technique for measuring the depth time history of rigid body penetration into brittle • materials under a deceleration of -10 5 g. A series of 4140 steel projectile penetrations into G-mixture mortar targets has been conducted in the velocity range of 100 to 500 m/s. Based on the experimental results, the target materials are damaged via compacting and brittle radial and lateral crack propagation in front of and surrounding the penetration path. The projectiletarget contact length on the projectile lateral surface is <20% of final penetration depth. This suggests that the effect of lateral friction on the penetration process can be ignored. Final penetration depth is found to be linearly scaled with initial projectile energy per unit cross-section area. Based on the fact that the penetration duration increases slowly with impact velocity, does not approximately depend on projectile. Deduced penetration velocity-time histories suggest that the whole penetration is divided into three stages: an initial stage, a steady penetration stage and a penetration stop stage. The average deceleration m the steady penetration stage for projectiles with the same dimensions is found to be linearly proportional to initial impact velocity. The average resistance pressure during penetration is estimated to be comparable to shock wave pressure. The present data demonstrate that a very strong similarity of penetration depth-time history is described by a relation between normalized penetration depth and normalized penetration time. This similarity can be used to predict penetration depth-time history under different initial projectile conditions.