Direct measurements of strain in a shock-loaded, lead filled glass

Commercial strain gauges have been used to measure the plate impact behavio r of type D, extra dense flint, a high density, lead filled glass. Impact s tresses were in the range 2.0-4.6 GPa, just above the materials quoted Hugo niot elastic limit of 4.3 +/- 0.2 GPa. This glass (and similar materials) h as been shown to display a reduction in shear strength across a slowly movi ng front (the failure wave) behind the main shock wave. At stresses below w hich this glass displays this feature, measured strains agree well with val ues calculated from the elastic relations. Above this stress, the failure w ave leads to an increase in compressive strain, which has been correlated w ith measurements using other techniques. In this case, we show that the cal culated values of strain agree only with the measured values behind the fai lure wave. (C) 2000 American Institute of Physics. [S0021-8979(00)03012-7].