A model for shear-band formation and high-explosive initiation in a hydrodynamics code

Abstract

This report describes work in progress to develop a shear band model for MESA-2D. The object of this work is (1) to predict the formation of shear bands and their temperature in high explosive (HE) during a MESA-2D calculation, (2) to then assess whether the HE would initiate, and (3) to allow a detonation wave initiated from a shear band to propagate. This requires developing a model that uses average cell data to estimate the size and temperature of narrow region (generally much narrower than the cell size) that is undergoing shear within the cell. The shear band temperature (rather than the average cell temperature) can be used to calculate the flow stress of the material in the cell or to calculate heat generation from reactive materials. Modifications have been made to MESA-2D to calculate shear band size and temperature, and to initiate HE detonation when conditions warrant. Two models have been used for shear-band size and temperature calculation, one based on an independent estimate of the shear band width and a second based on the temperature distribution around the shear band. Both models have been tested for calculations in which shear band formation occurs in steel. A comparison of the measured and calculated local temperature rise in a shear band has been made. A model for estimating the time to initiation of the HE based on the type of HE and the temperature distribution in a shear band has also been added to MESA-2D. Calculations of conditions needed to initiate HE in projectile-impact tests have been done and compared with experimental data. Further work is d to test the model.