The structural reliability of advanced fiber composite materials is greatly dependent upon the knowledge of fatigue and fracture behavior of the composite materials.
For assessment of the reliability of composite materials, it is necessary to predict the growth of damages inherent in fiber composites due to fabrication procedures or produced in service.
An experimental investigation was conducted to study the fatigue damage growth and the applicability of linear fracture mechanics parameter, e.g., stress intensity factor, by means of equivalent crack length concept and x-ray nondestuctive evaluation (NDE) technique, using a notched graphite/epoxy $[90˚/45˚/0˚/-45˚]_4s $laminate.
It was observed that the equivalent crack length due to fatigue damage increased slightly during the period of fatigue test and there did not exist definite relationship between the equivalent crack length growth rate and the stress intensity factor. The critical stress intensity factor concept based on the equivalent crack length can be applied to the fracture initiation of the tested laminate.
Limited results obtained by the x-ray NED method indicate that matrix cracking appears to precede delamination between plies.
