INVESTIGATION INTO LOAD ORDER EFFECTS ON THE TREATMENT OF COMBINED PRIMARY AND SECONDARY STRESSES WITHIN R6

摘要

A range of methods are available within the R6 defect assessment procedure to describe how primary and secondary stresses combine. Each of these methods has different levels of associated conservatism depending on the level of elastic follow-up assumed, or inherently modelled, when deriving these methods. Approaches that include an elastic follow-up factor, Z, have recently been investigated by Ainsworth and James and included in the latest amendment to R6. However, one additional factor that has not yet been fully considered is the effect that load order has on this interaction. This work considers finite element analyses of a circumferentially cracked cylinder with two thermal distributions and two crack sizes combined with an axial primary load. These conditions were controlled to manipulate the level of Z. The analyses were performed with either the secondary or primary load applied first to consider load order effects. The work found: 1) The effect of load order has been shown to be linked to the formation of the initial plastic zone by its extent and shape. 2) The recently published approach by Ainsworth generally allowed a very good fit to the results. However, it was not able to conservatively predict the interaction for the case with the greatest Z. 3) The approach derived by James provided a means to capture the peak interaction for all cases. However, the approach was not capable of capturing the entire curve if primary loads were applied first. 4) The Ainsworth and James approaches can be combined to capture any load order effect.