It is found that the energy release rate derived by assuming built-in conditions at the crack tip can be used to calculate the fracture (surface) energy more accurately and conveniently than Berry's scheme [2] even in cases where the built-in assumption is apparently invalid. The analyses suggest that it is possible to infer from detailed macroscopic measurements of the deformations of the beam prior to and during crack growth the approximate characteristics of the complete (uniaxial ) material stress-strain behavior of the cohesive interlayer including loading and strain-softening. 21. This paper is a shortened version of reference 1.

This study investigates the effect of nonlinear cohesive forces on crack growth with the special problem of craze mechanics in mind. The work is presented in two parts. In the first and present one, we develop a numerical method for determining the equilibrium shape of a craze in an infinite elastic plane whose fibrils exhibit very general nonlinear force-displacement (P-V) behavior, including strain softening characteristics. The second part of this study deals with the numerical simulation of craze and crack growth (Ungsuwarungsri and Knauss, 1986).1 The problem formulation is based on the superposition of the relevant elasticity Green’s function and the solution for the resulting nonlinear problem is effected by using Picard’s successive approximation scheme. Both field equilibrium and the Barenblatt condition for vanishing stress and strain singularities are satisfied simultaneously, rendering the craze tip profile cusp-like. The formulation allows the stress distribution profile and the corresponding P-V relation to be computed from experimentally measured craze/crack displacement contours; it also allows the computation of the craze or crack/craze profile if the P-V relation, far-field load, and craze or crack size are specified. Numerical investigations indicate that only certain classes of the fibril P-V relations are consistent with measured craze profiles. In addition, it is found that for a given P-V relation, nontrivial solutions exist only for certain ranges of craze lengths.

In this study we investigate the effects of nonlinear fibril behavior on the mechanics of craze and crack growth. The effect of strain-softening cohesive material on crack stability is of particular interest and is examined via a craze and crack model developed in the first part of this work where the formulation and solution of the problem are discussed.1 In this second part, quasi-static growth of a craze with a central crack is analyzed for different nonlinear force-displacement (p-v) relations for the craze fibrils. A “critical crack tip opening displacement” (CTOD), or more precisely, “critical fibril extension” is employed as the criterion for fracture. The p-v relation is further assumed to be invariant with respect to the craze and crack lengths. The results are compared with the Dugdale model; the craze zone size and the energy dissipation rate approach asymptotic values in the limit of long cracks. The problem of craze growth from a precut crack under increasing far-field loading is then studied. In the case where the p-v relation is monotonically softening, the crack can start to grow in an unstable manner before the crack tip opening displacement reaches its critical value.