EFFECT OF THERMOMECHANICAL LOADING ON NEAR-TIP CONSTRAINT

Two parameter approaches to elastic-plastic fracture mechanics were in troduced to remove some of the conservatism inherent in the one parame ter approach based on the J integral, ([1]) and to account for constra int effects on fracture toughness. It was shown in [2], [3] and [4] am ong others that much of the dependence of fracture toughness on specim en geometry could be explained by two parameter fracture theories base d on Q or T. This paper examines the effect of residual or thermal str ess fields on constraint in a mechanically loaded body. Finite element analyses of representative thermal loadings which give rise to high a nd low constraint stress fields (high and low Tor Q) have been conduct ed. The structure is then subjected to mechanical loading, both tensio n and bending dominated to assess the effect on the near tip constrain t. It is observed that the two parameter structure of the fields is ma intained and values of Q stress have been obtained from the analyses. The thermal loading initially has a strong effect on the Q value but a t higher loads when the mechanical loading dominates, this effect is m uch weaker. The ability of a two parameter approach using the T stress to account for constraint is assessed.