Fracture Mechanics Approach to Small Fatigue Crack Growth and Coalescence under Low Cycle Fatigue

Under low cycle fatigue condition, small cracks initiate on the specimen surface, and then they grow and coalesce with each other. The coalescence of small cracks is an important factor in evaluating fatigue life based on the fracture mechanics approach. However, surface observation of the coalescence is not sufficient in order to understand the mechanism and the influence on the fatigue life. Present study performed numerical simulations of the crack coalescence using the S-FEM based on the linear elastic fracture mechanics. The results revealed that the fatigue life was reduced when the main crack coalesces with a crack of comparative size, while the effect of fatigue life reduction was small when the main crack coalesces with a crack of less than half size. Experimental results were compared with the simulated results.