Reliability Consideration on Acceptance Criteria of CTOD Fracture Toughness Testing

Abstract

This paper presents a method of applying the probabilistic fracture mechanics technique to the selection of better acceptance crieria for CTOD test, primarily in terms of the required fracture toughness and the number of test specimens. Particular reference was given to welded mists of marime structures subjdcted to sea wave induced stresses, such as ships and offshore structures. In carrying out the analysis, sea wave induced stress, crack size in weldments and fracture toughsess of materials were taken as random variables.
It was proposed to decide the required fracture toughness in a probabilistic manner by estimating the distribution of fracture driving parameter which depends on mechanical environmental conditions such as boundary force and crack size and by specifying the risk level of required fracture toughness which corresponds to the importance of structural component to be evaluated.
From the viewpoint of structural safety and reliablility, it is rational that the materials of fracture toughness distribution characteristics with low fracture probability should be given high probability of acceptance in an acceptance criterion. The superiority of acceptance criteria was considered in terms of fracture probability vs. probability of acceptance. The dicussions are made on the numerical results obtained for some specified values of the pamameters inuolved. It is found out that the most excellent acceptance criterion varies with the given conditions, which implies that a single criterion can not be adopted as the universally best one.