Summary of numerical analyses of the effect of W/A in earth penetration
Wagner, Mark H.
Miscellaneous PaperAbstract: A series of three finite-difference WAVE-L code solutions of projectile penetration has been conducted to assess the effect of projectile sectional pressure (W/A) on penetration dynamics. The analysis of the third case is presented in this report, using comparisons with the results of the first two cases, which were analyzed in a previous program. The program results are being used in an investigation of penetration scaling relations under way at the U.S. Army Engineer Waterways Experiment Station. The penetrator problems consisted of the normal impacts of rigid-body projectiles into sand targets at a velocity of 200 ft/sec. The projectiles for Cases 1 and 2 were 6 in. in diameter with a 6-in.-long ogive nose (CRH = 1.25). The Case 3 projectile was scaled up in size by √3, giving a 10.392-in.- by 10.392-in.-diameter nose. Two penetrator weights were selected, 141.4 lb (Case 1) and 424.1 lb (Cases 2 and 3), to give projectile sectional pressures of 5 psi for Cases 1 and 3 and 15 psi for Case 2. The solutions of each penetrator problem were run from initial impact to a penetration depth of 1-1/3 nose lengths. The computed penetration dynamics indicated that the comparative penetrator decelerations were related to the sectional pressure by aα(W/A)⁻¹, in agreement with conventional (rate-independent) scaling rules. During the later stages of the penetrations, the relative decelerations tended to depart from this rule. These deviations are believed to be due principally to the effects of the nonequivalent projectile velocities that developed during the penetrations, resulting from the different deceleration levels or event durations associated with each case. Since there is some experimental evidence suggesting that penetrator decelerations of this type are related by aα(W/A)⁻½, there is the possibility that rate-dependent behavior, such as viscoplasticity, may be occurring in the media that should be accounted for in the material models. Detailed results of the numerical analyses, including time histories of the penetration dynamics variables, force loading distributions, and field plots of the target response, are presented.
Soils and Pavements Laboratory (U.S.)Engineer Research and Development Center (U.S.)
Computer analysis; Computer programs; WAVE-L; Projectile penetration; Finite difference method; Soil penetration; Numerical analysis; Numerical models; Mathematical analysis; Mathematical models; Penetration
Miscellaneous Paper S-78-15
Miscellaneous Paper (U.S. Army Engineer Waterways Experiment Station) ; S-78-15
Approved for public release; distribution is unlimited.