Investigation in biaxial-stress effect on mode I fracture resistance of brittle materials by FEM simulation and K-G-J-δ relationship

Difference in the stress distribution and failure initiation for brittle materials between uniaxial and biaxial loads was confirmed by FEM simulation. To explain the influence of biaxial stress on fracture, the relationship among the stress intensity factor K, the energy release rate G, the crack opening displacement and J-integral is investigated. It is demonstrated that the crack opening displacement and the strain energy release rate are biaxiality-dependent because they are related to strain that is affected by biaxial stress, whereas K and J are biaxiality-independent. Thus, the conventional concept on the equivalent relation among the four parameters is found to be invalid for brittle materials under biaxial stress, and the influence of biaxial stress on fracture resistance is attributed to the strain-depending failure.