The use of strain gauges in the measurement of the B1/B2 phase transformation in shock-loaded potassium chloride

The shock induced phase transformation in potassium chloride (from the NaCl B1 structure to the CsCl B2 structure) has been investigated using constan tan strain gauges. These gauges have been mounted in pressed, polycrystalli ne samples in an orientation that renders them sensitive to the uniaxial st rain that characterizes the plate impact geometry. At the phase transformat ion stress (of similar to 2 GPa), measured strains of similar to -0.1 were observed, slightly higher than the values quoted in the literature. We sugg ested that residual porosity within the microstructure is a possible explan ation. Over impact stresses of 2.5-4.0 GPa, total measured strains agree wi th the work of others at the lower end of our measured range, but are signi ficantly lower at higher stresses. We suggest that this might be due to the nonequilibrium state of the material at the time of measurement. (C) 2000 American Institute of Physics. [S0021-8979(00)02406-3].