The elastic-plastic deformation of a square plate with a center crack under biaxial stresses was analysed by the finite element method of plane stress. The loading conditions analysed were equi-biaxial, uniaxial and shear. The values of the crack-tip opening displacement and J integral increased as the stress parallel to the crack changed from tension to compression, when compared at the same perpendicular stress. The increment under shear loading was considerably large, while the difference between the equi-biaxial and uniaxial cases was relatively small. The interrelation among the near-tip stress-strain distribution, the crack-tip opening displacement and J integral was confirmed to be characterized by the HRR type singurality field.
A simple method to estimate J integral for a center-cracked plate under biaxial stresses was proposed based on the finite element analysis. The fatigue crack growth data obtained with a cruciform specimen under biaxial cyclic stresses were analysed in terms of J integral range by using the proposed method. The relation between crack growth rate and J integral range was found to be a unique power relation independent of biaxiality and plasticity, although a considerable acceleration was detected under shear loading when the rate was correlated to the stress intensity range.
