The dynamic behaviour of ballistic soap

Ballistic soap is used as a simulant to observe the effect of a projectile penetrating soft tissue; consequently information on its behaviour at high strain-rates is desirable. The Hugoniot equation-of-state for soap has been determined using the plate-impact technique at impact velocities of 81-967 m/s. The US-uP Hugoniot was linear, taking the form US = 1.99 + 2.04uP (?0 = 1.107 g/cc). In P-uP space the Hugoniot was observed to trend substantially above the predicted hydrodynamic response for Hugoniot stresses greater than 1.2 GPa, indicative of material strengthening. The lateral-stress response of soap was interrogated using embedded lateral manganin stress gauges. Gradients observed behind the shock for ?x > 1 GPa appeared to suggest continuation of the previously observed strengthening mechanism. It is proposed at higher values of ?x, increased compression of hydrocarbon chains acts to increase the materials resistance to shear, a phenomenon known as steric hindrance.