DYNAMIC FRACTURE-TOUGHNESS MEASUREMENTS ON SMALL CHARPY SPECIMENS - APRELIMINARY-STUDY

A technique for measuring dynamic fracture toughness on small specimen s is described and preliminary data are presented. Dynamic crack tip o pening displacements (CTODs) are measured with laser interferometry ov er times as short as 10 mu s. The measured displacement is converted t o stress intensity values via the equations of linear elastic fracture mechanics and the peak value obtained is taken as the dynamic fractur e toughness. Two materials were tested at two different loading rates; a brittle plastic at 10(3) and 10(4) MPa-m(1/2)/s and a ceramic 5 x 1 0(4) and 10(6) MPa-m(1/2)/s. The results from this new technique were compared with simultaneous results from an instrumented Charpy hammer and, in some cases, from foil gages on the specimens. At the slower ra tes, the agreement among the results is acceptable. At the higher rate s, the instrumented hammer technique is no longer valid. The technique is potentially useful on small, brittle specimens at room and high te mperatures.