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A numerical study of the dynamic steady-state antiplane shear (Mode III) crack growth process is described. The study is based on continuum mechanics, and the material is modeled as being elastic-viscoplastic. Using the small-scale yielding concept of fracture mechanics and allowing only for steady-state crack growth, but including the effects of material inertia explicitly, a full-field solution for the deformations is obtained by means of an iteration procedure involving the finite-element method. Numerical results for the strain distribution in the active plastic zone are presented. The fracture criterion for materials which fail in a locally ductile manner proposed by McClintock and Irwin ,3 which stipulates that crack growth will proceed such that a critical strain level is maintained at a characteristic distance ahead of the crack tip, is adopted. This criterion is coupled with the results of numerical calculations to develop theoretical dynamic fracture toughness versus crack tip speed relationships for two levels of critical strain. For rate-dependent materials a range of toughness-versus-speed relations is manifested, ranging from that similar to rate-independent materials for low rate sensitivity to a relationship which rises dramatically for even a small increase in crack speed at low crack speeds, but which levels off for higher speeds for extremely rate-sensitive materials.
fracture (materials), elastic-plastic crack propagation, dynamic crack propagation, crack propagation, small scale yielding, finite element method, elasticplastic fracture
Professor, Division of Engineering, Brown University, Providence, R.I.
Assistant professor, Johns Hopkins University, Baltimore, Md.