Damage Tolerance Assessment of Welded Joints Subjected to Fatigue Crack Growth

摘要

The present paper suggests a probabilistic damage tolerance supplement to the design S-N curves for welded joints. The reliability levels are derived from extensive testing with fillet welded joints (F-class detail) for which the entire crack growth history is measured, not only the final fatigue life. The statistics in time to reach given crack depths are determined. A Markov model is fitted to the data base and scaled to in-service conditions. Results for some frequent cases occurring in practice for offshore structures are readily derived and presented. The scope is to provide the practising engineer with simple graphical aids that predict the reliability against fatigue fracture during service life. The impact of chosen fatigue design factors and uncertainty in applied stresses is revealed. The effect of an in-service inspection program is also predicted. The graphical tools are suggested for use in support of decision-making at the design stage, without any advanced fracture mechanics modelling and stochastic simulation.