Critical P2T Value Computation for Explosives Using the Shear Band Initiation Model.

Abstract : Recent computer calculations by Walker at BRL to model antifraticide shield functioning for artillery rounds has indicated a wide applicability of the critical P2T (or critical energy) values for predicting explosive initiation. While previous investigators have sought to give a theoretical explanation of the P2T criterion in explosive initiation, none has proposed a way to compute critical values of P2T from the mechanical and thermodynamic properties of explosives. Frey at BRL has recently proposed a shear band mechanism as a source of hot spots in explosives subjected to rapid shearing. If the shear band mechanism is generally applicable, it must be possible to relate it to the critical values of P2T for different explosives. This would allow one to calculate this important sensitivity criterion from the mechanical and thermodynamic properties of explosives. Gibbons at BRL has observed shear banding in shocked explosives; however, the Frey model for the shear velocity across a band generated by shock loading, and for the density and dimensions of the shear bands. Using the thermodynamic properties of the explosive, this initial heating can be followed to full detonation. Similarly, by making the shock pressure a function of time to model stress relief waves in the shocked explosive, one can compute the conditions for failure to detonate. Thus, we obtain a complete model of shock initiated detonation based on more fundamental physical properties of explosives. This capability should make the control of sensitivity in explosives a more exact procedure.