Abstract
Since all residual stress measurement methods have inherent limitations, it is normally impractical to completely characterise a three-dimensional residual stress field by experimental means. This lack of complete information makes it difficult to incorporate measured residual stress data into the analysis of elastic–plastic fracture without resorting to simplified methods such as the Failure Assessment Diagram (FAD) approach. We propose a technique in which the complete residual stress field is reconstructed from measurements and used in finite element analysis of the fracture process. Residual elastic strains and stresses in three-point bend fracture specimens were measured using neutron diffraction and an iterative method was used to generate a self-consistent estimate of the complete residual stress field. This enabled calculation of the J contour integral for a specimen acted on by both residual stress and an externally-applied load, allowing the interaction between residual and applied stress to be observed in detail.
Highlights
Residual and thermal stresses can influence both brittle fracture and elastic–plastic fracture
In structural integrity assessment procedures such as R6 Rev. 4 maintained by EDF Energy and others [3, 4], and the British standard BS 7910:2013 [5], combinations of residual and applied loading can be accounted for using an interaction factor to adjust the apparent contribution of residual stress loading to the stress intensity factor at a given crack
In this work we have demonstrated a method for incorporating measured residual elastic strain or stress data into a finite element simulation of elastic–plastic fracture
Summary
Residual and thermal stresses can influence both brittle fracture and elastic–plastic fracture. The effects of thermal or residual stresses combine with the action of externally-applied loads in a non-linear manner [2] This complicates the prediction of fracture initiation and crack growth. In structural integrity assessment procedures such as R6 Rev. 4 maintained by EDF Energy and others [3, 4], and the British standard BS 7910:2013 [5], combinations of residual and applied loading can be accounted for using an interaction factor (denoted V) to adjust the apparent contribution of residual stress loading to the stress intensity factor at a given crack During an assessment, this factor is applied to the stress intensity factor calculated for secondary (i.e. self-equilibrating) stresses before it is combined with the corresponding stress intensity factor for primary (i.e. externally-applied) loading. At higher primary load levels, pre-existing residual stresses tend to be partly relaxed by plastic deformation prior to fracture and the formulation of V within R6 reflects this
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