Predicting the fatigue cycles on aluminum panels

A finite element method was developed and used to predict fatigue crack growth in thin, middle-cracked panels. Fatigue cycles were calculated from predicted fracture toughness, a predicted R-curve point, and the dissipated plastic energy under a fatigue load. Experimental fracture and fatigue parameters were not required. The method worked best when crack closure did not occur. A plot of the dissipated plastic energy versus crack growth showed which fatigue cases had partial closure and which would provide good results. Smooth fatigue energy curves resulted in predicted fatigue cycles within 10% of the number of experimental cycles.