Probability fracture mechanics analysis of plates with surface cracks

Background: The uncertainties of input parameters in an deterministic structural integrity assessment of pressure vessels may affect the assessment results. This can be improved by performing probability fracture mechanics (PFM) analysis. Purpose: This work investigates the effect of uncertainties of load, defect size, fracture toughness and failure criteria on the failure probability of semi-elliptical surface cracks in plates under combined tension and bending. Methods: The correction factor method provided by EPRI is used to estimate the stress intensity factor (SIF). The J-integral values at the deepest point of the surface crack tip are evaluated using the reference stress method and the globe limit load solution developed by Goodall and Webster and Lei. PFM analysis is performed with considering the uncertainty of crack size, yield strength and fracture toughness and Monte-Carlo (MC) simulation is used to calculate the failure probability. Results: Failure probability increases with increase of load level, L_r, for all load ratio values considered in this work for a given failure criterion. However, the failure probability based on the elastic-plastic fracture criterion is higher than that based on the linear elastic fracture criterion for a given load lever, L_r. Conclusions: The load level and the failure criteria have significant effect on the failure probability. However, the load ratio makes a little contribution to the failure probability for a given failure criterion. (authors)