Response of aluminium-infiltrated boron carbide cermets to shock wave loading
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Shock-recovery and shock-spallation experiments were performed on two compositions of aluminium-infiltrated B4C cermets as a function of shock pressure. Sixty-five per cent volume B4C-Al cermets were recovered largely intact after shock loading up to pressures of ca. 12 GPa which permitted a critical study of the microstructural changes produced by the shock. Significantly, shock loading to between 12 and 13 GPa produced a combination of dislocation debris, stacking faults and deformation twins in a small fraction of the B4C grains. Fragmentation of shock-loaded 80% B4C-Al samples prevented meaningful microstructural investigation. Spall-strength testing also provided indirect evidence for the Hugoniot elastic limits (HEL) of these composites. Spall-strength calculations based on an elastic equation of state for 65% B4C-Al indicated that the elastic regime extended up to shock pressures of ca. 10 GPa, or approximately 65% of the HEL of polycrystalline B4C. A complete loss of spall strength was then observed at the transition to a plastic equation of state at a pressure of 12 GPa which coincided with observations of plasticity within the B4C-substructure. This study demonstrated that composites containing a highly ductile phase combined with a high compressive strength ceramic phase could support high dynamic tensile stresses by resisting the propagation of catastrophic cracks through the brittle ceramic substructure.
KeywordsShock Wave Compressive Strength Boron Carbide Deformation Twin Shock Pressure
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