Compressive failure threshold of brittle materials

Planar impact experiments widely used for determining dynamic strength of hard materials do not provide a possibility to obtain information about the mode, ductile or brittle, of their inelastic response or about thresholds conditions of their compressive failure. Using the controlled sample pre-stressing in the experiments (E. Zaretsky and G. Kanel, APL, 2002, 81, 119) allows one only to conclude whether the response of the studied material at the stress level of elastic limit is brittle or ductile leaving the problem of the material compressive failure threshold still unsolved. The experimental/numerical technique for determination of compression failure threshold of brittle solids is presently suggested. The technique is based on measuring the velocity of the sample/window interface while the sample front surface is struck by curved copper impactor. The divergent stress flow produced by such loading results in the incipient compressive failure of the sample and, respectively, in the appearance of the failure signatures at the measured velocity profile. Reproducing these signatures with aid of AUTODYN 2D commercial computer code including the constitutive and failure description of the studied material yields the values of the principal stress tensor components corresponding to the brittle failure initiation. The locus of these values in the principal stress space is the material compressive failure surface.