A STUDY ON THE PREDICTION TECHNIQUE OF REMAINING FATIGUE LIFE USING FATIGUE INDICATOR

초록

It is difficult to predict the accurate fatigue life of marine structures in the seagoing state because of the uncertainty of wave loads and structural forces. Fatigue indication sensor (FIS) that is able to estimate the remaining fatigue-life of marine structures can be an efficient method to predict the fatigue strength of marine structures. FIS is a small fatigue specimen that is designed so that fatigue crack can be generated in the indicator earlier than in the real structure when it is attached on the surface of the structural member. If fatigue crack is produced in the FIS sufficiently earlier to the fatigue crack in the structural member, the fatigue life of the structural member can be expected and the remaining fatigue life can be estimated. Present study suggests a series of FIS which is attached on the structural member by using adhesive bond. Geometric properties of the FIS are determined according to the usages, such as short life, medium life, and long life expectation of crack initiation. The FIS is attached on the structural member, namely mother specimen, and the fatigue test is carried according to the type of FIS. Stress distribution and SCF (stress concentration factor) for several shapes of pre-notch in the indicators are investigated by finite element analysis(FEA) in order to determine the geometric properties. The geometric shapes of FIS are designed through the SCF and the stress distribution. Thereafter, the mother specimen which has the same SCF to the indicator is designed. Fatigue indicators are attached on the mother specimen using metal epoxy adhesive bond. Prior to the HCF (high cycle fatigue) test, the load transfer rate test is conducted for several stress level. Loading procedure of HCF test is calculated by equivalent stress considering the various loading condition in the seagoing state. Through the evaluation of test, prediction of remaining fatigue life is proposed using the relationship between S-N curve of mother specim