Crack Stability of Fracture Specimens used to Test Unidirectional Fiber Reinforced Material

The traditional compliance-based criterion of the crack stability in fracture mechanics states that the stability of the crack propagation in the different specimens under different fracture modes is determined by the derivative of the energy release rate with respect to the crack length. In this work the compliance-based criterion is verified by experiments performed on fracture mechanical systems. The large number of experiments carried out on different (mode-I, mode-II, mixed-mode I/II and mixed-mode II/III) specimens shows that the stability of the crack propagation depends on the derivative of the critical displacement (the displacement at the point of fracture initiation) with respect to the crack length. The experimentally established limits of crack stability were compared to the limits of the traditional criterion and it is shown that in each case they lead to approximately the same restriction considering the stable zone of crack propagation.