For the assessment of the retardation of fatigue crack propagation behavior by overload, the retardation model of fatigue crack propagation based on the finite element analysis considering the redistribution of compressive residual stress near crack tip was proposed in this paper. The compressive residual stress distribution near crack tip was evaluated by elasto-plastic analysis. The amount of residual stress redistribution was assessed by subsequent elasto-plastic analysis. In the analysis of the retardation in fatigue crack propagation, the applied Stress Intensity factor (SIF) range was evaluated by equations in ASTM E647, and the effect of residual stresses on crack propagation was considered using the effective SIF concept. The test results of the retardation in fatigue crack propagation were compared with the predicted data obtained by the analysis.
Recently, the ship structure becomes larger in size and lighter in weight and the bigger load is applied in the parts of stress concentration such as welded joints. In order to apply damage-tolerance design (DTD) which is one of recent fatigue design methods, the effect of ship structure due to propagated crack has to be assessed during design life. Practically, because fluctuating environmental loads act on ship structure, the effect of fluctuating environmental loads on fatigue crack propagation needs to be precisely assessed. Especially, the retardation of fatigue crack propagation due to overload should be evaluated. Elber(1971) considered the crack closure which is induced by compressible residual stress in the fatigue crack surface. He proposed effective stress intensity factor. Wheeler(1972) suggested the retardation model of crack propagation that considered the size of plastic zone near crack tip induced by overload. Kim et.al. (2003) measured the size of plastic zone using ESPI system. ESPI system which uses optical equipment can measure the large field strain distribution on the surface of structure which has a complex shape.
