Response of steel disks to explosive loading

Abstract

The response of unsupported 4340 steel disks to coaxially aligned, cylindrical Octol charges is studied using hydrocode DYNA2D. Two flow stress representations for the steel are used. One includes linear strain hardening. The other is the Johnson-Cook model, which contains power law strain hardening, logarithmic strain rate hardening, and power law thermal softening.Each problem displays an initial period of large acceleration and plastic bending. The plastic bending decreases with an increase in strain hardening, and can be placed in substantial agreement with radiographs from associated experiments by judicious assignment of the strain hardening parameter in the first flow stress representation. The bending is overestimated by the Johnson-Cook representation using parameter values recommended by its authors. Evidence is given that the logarithmic representation for strain rate hardening is unsuitable at the observed strain rates in excess of 104 sec−1.A steady-state pattern develops, which consists of constant-velocity rigid-body translation and elastic flexural vibrations. The rigid-body velocity is insensitive to flow stress representation and is in reasonable agreement with estimates from radiographs. The amplitude of the vibrations increases and their frequency decreases with increasing strain hardening.