A Study on J-Integral as a Fracture Criterion (2nd Report)

Abstract

In the previous paper, an improved method to evaluate J-value from single load-displacement record has been proposed.In this paper, the effects of material properties on J-value for 3-point bend specimens with different notch ratios are investigated by elasto-plastic FEM calculations using 8-noded isoparametric quadrilaterals. It is concluded that yield stress (σY) and strain hardening rate (H') have less effect on the relationship between non-dimensional J-value (EJ/aσ2Y) (E : Young's modulus, a : notch length) and stress ratio (σN/σY) (σN : nominal skin stress in the notched section), or non-dimensional deflection (Eu/dσY) (u : deflection at load point, d : depth of specimen).Several practical methods to evaluate J-value from single load-displacement record, that is, Rice's method, the more convenient method using total displacement and the authors' method proposed in the previous paper are compared one another, and it is shown that the authors' method gives the best approximation out of the three methods compared, but it still gives overestimation especially for shallow notched specimen in highly load range.On the basis of numerical results with varied conditions, a more simple and accurate J evaluation method for 3-point bend specimen is newly proposed and is expressed by Eq. (17) and Eq. (18). Using this proposed method, J-value can be estimated from crack opening at edge or applied load which is easily measured in fracture testings.