CRACK PROPAGATION LIFE PREDICTION UNDER CREEP-FATIGUE CONDITIONS

Several aircraft structural components operate under cyclic elastic plastic (fatigue) and time dependant (cyclic creep) deformations. Proper estimation of life for these components subjected to such deformation histories is certainely needed for safe operation following safe life philosophy. In addition many of these components are considered defect-free parts and life is estimated based on damage accumulation concepts. However a more rigorous analysis based on fracture mechanics predicts life of such components by crack growth calculations around the preexisted flaws. Following such design technique, tremendous cost savings could be realized if a procedure was developed to provide accurate assessment of inspection and fracture mechan-ics life prediction techniques. In this paper cyclic elastic plastic creep fracture mechanics model is developed to predict crack growth in structural components subjected to creep-fatigue conditions typically exists in aircraft structural elements. Based on this model estimates of residual life could be predicted. Such analysis could certainely provide the necessary information neededf or establishing preventive maintenance programmes. Results based on the present model and exprimental results found in the literature are in close agreement.