DYNAMIC STEADY CRACK-GROWTH IN ELASTIC-PLASTIC SOLIDS - PROPAGATION OF STRONG DISCONTINUITIES

The near-tip field of a mode I crack growing steadily under plane stra in conditions is studied. A key issue is whether strong discontinuitie s can propagate under dynamic conditions. Theories which impose rather restrictive assumptions on the structure of an admissible deformation path through a dynamically propagating discontinuity have been propos ed recently. Asymptotic solutions for dynamic crack growth, based on s uch theories, do not contain any discontinuities. In the present work a broader family of deformation paths is considered and we show that a discontinuity can propagate dynamically without violating any of the mechanical constitutive relations of the material. The proposed theory for the propagation of strong discontinuities is corroborated by Very detailed finite element calculations. The latter shows a plane of str ong discontinuity emanating from the crack tip (with its normal pointi ng in the direction of crack advance) and moving with the tip. Elastic unloading ahead of and/or behind the plane of discontinuity and behin d the crack tip have also been observed. The numerical investigation i s performed within the framework of a boundary layer formulation where by the remote loading is fully specified by the first two terms in the asymptotic solution of the elasto-dynamic crack tip field, characteri zed by K-I and T. It is shown that the family of near-tip fields, asso ciated with a given crack speed, can be arranged into a one-parameter field based on a characteristic length, L(g), which scales with the sm allest dimension of the plastic zone. This extends a previous result f or quasi-static crack growth.