Effect of Local Strain on Low Cycle Fatigue using ESPI System

초록

Fatigue cracks in ship structure are developed by weld defects and stress concentration due to geometric shapes of structures. Itis important to consider fatigue strength because low cycle fatigue crack is mainly detected at discontinuous welded locations with high stresses under repeated cyclic static loads due to cargo loading and unloading. Theoretical and analytical methods have been used for evaluation of local stress and strain which have an effect on a prediction of fatigue life but those have dificulties of considering stress concentration at notched location and complicated material behaviour of welded joint or heat affected zone. Electonic specckle pattern interferometry(ESPI) system is nondestructive and non-contact mearurement system which can measure the relatively accurate strain on large field such as welded zone and structural discontinuous location. Therefore, the accuracy of local strain prediction can be improved with this system. And the expremental results are compared with numerical analysis. In this study, local strain was measured on welded cruciform jointby ESPI system and then low cycle fatigue life was examined by the value and distribution of measured local strain using ESPI system. local strain and stress were calculated using Neuber's rule. Moreover expreimental fatigue life was compared with DNV's design S-N curve using measured local strain.