Nonlocal fracture criteria. Finite fracture criterion

Abstract

The paper considers some specific features of application of nonlocal criterion, based on the concept of finite fracture mechanics, in the strength problem of a solid body containing a stress raiser under tension or compression. The criterion is pertained to energy-based methods. The approach of finite fracture mechanics consists in modification of the traditional energy balance as used in linear elastic fracture mechanics (LEFM). The modification involves the using of a finite amount of crack extension instead of an infinitesimal extension when calculating the energy release rate in LEFM. This makes LEFM to be suitable for predictions in situations of blunt notches in which it is normally invalid. Advantages and restrictions of the using of the finite fracture criterion are shown. The expressions for the failure stress in the problems of tension or compression of the plate with a circumferential hole are obtained. The reductions in strength of the plates with a circumferential hole predicted by the finite fracture criterion are compared with known experimental data on composite plates in tension, and own experimental data on gypsum plates in compression. In reference to some materials, the finite fracture criterion similar to other non-local criteria (the criteria of average stress, point stress, and fictitious crack) can be successfully applied to describe the hole-size effect on tensile fracture initiation and assess the critical size of the flaw under compression. However, its application to other materials allows us to obtain only a qualitative assessment of the failure stress.