Materials and mechanics of rate effects in brittle fracture. Progress report, October 1974--October 1975. [Stress intensity factors for crack propagation

Abstract

The critical stress intensity factors for propagating cracks, K/sub ID/, was experimentally found to decrease with increasing crack velocity. K/sub ID/ was measured using rapidly wedged double cantilevered beam specimens. The crack length versus time was continuously recorded using electro-potential techniques. The specimens were fractured at temperatures well below the brittle to ductile transition temperature. The crack velocity in these specimens varies continuously but is typically in the range of 100 to 200 m/s. The analysis of fully dynamic crack propagation in double torsional beam specimens was solved in closed analytic form. The solutions for rotational rate loading and for constant applied torque, predict constant crack velocity. The crack velocity is given by the applied rate of rotation, the magnitude of the applied torque and specifics about the beam. The maximum crack velocity is the torsional wave speed. The use of the analysis is to deduce K/sub ID/ during crack propagation without measuring the crack velocity directly. The measurements of static, dynamic loading and propagating crack, stress intensity factors establishes that rate is an important variable in specifying the stress intensity factor for fracture. (auth)