Effect of thermomechanical loading on near tip constraint

Two parameter approaches to elastic-plastic fracture mechanics were introduced to remove some of the conservatism inherent in the one parameter approach based on the J integral, ([1]) and to account for constraint effects on fracture toughness. It was shown in [2], [3] and [4] among others that much of the dependence of fracture toughness on specimen geomrtry could be explained by two parameter fracture theories based on Q or T. This paper examines the effect of residual or thermal stress fields on constraint in a mechanically loaded body. Finite element analyses of representative thermal loading which give rise to high and low constraint stress field (high and low T or Q) have been conducted. The structure is then subjected to mecanical loading, both tension and bending dominated to assess the effect on the near tip constraint. It is observed that the two parameter structure of the fields is maintained and values of Q stress have been obtained from the analyses. The thermal loading initially has a strong effect on the Q value but at higher loads when the mechanical loading dominates, this effect is much weaker. The ability of a two parameter approach using the T stress to account for constraint is assessed.