This paper first presents a new type of path independent integral expressing the energy release rate for the crack growth in nonlinear materials. It is path independent even for the non-straight crack and gives the energy release rate without any limiting process; the J-integral is path independent only for the straight crack.
It also generalizes the well-known expression derived by Rice, which may be evaluated from the load versus load-point-displacement curves for slightly different crack sizes. Then, as an application of the new expression, a simplified formula under multiaxial loadings, which may be evaluated only from a single loads-displacements curve, is derived in the similar way as Rice et al. developed under uniaxial loadings.
Finally, the difference between the J-integral and the new expression, when they are applied to elastic-plastic materials, is examined in some detail.
