THE CRYSTAL ORIENTATION DEPENDENCE OF THE ELASTIC PRECURSOR SHOCK STRENGTH IN THE PETN MOLECULAR EXPLOSIVE AND THE MODELING OF THE STERIC HINDRANCE TO SHEAR BY MOLECULAR MECHANICS

The elastic precursor shock strengths of pentaerythritol tetranitrate (PETN) explosive crystals were measured for [100], [101], [110], and [ 001] orientations using VISAR instrumentation for samples 3 to 6 mm th ick. Input shock strength was 1.14 GPa. Measured precursor amplitudes were 0.38, 0.58, 0.98, and 1.22 GPa, respectively, for the four orient ations. Molecular mechanics modeling of slip in the ambient crystal wa s performed, analagous to the shock-induced shear for different orient ations. The results show the observed dependence of the precursor ampl itude on crystal orientation for the cases considered and explains why the {110} <1(1) over bar1$> slip system is observed in quasistatic de formation in spite of having the longest Burgers vector. The results c onfirm the importance of steric hindrance to shear in controlling the orientation-dependent strength in some molecular crystals.