Effect of Welding Residual Stresses on Fracture Toughness Testing : Part 2: Crack Tip Opening Displacements in the Residual Stress Field of Multipass Weldments of Thick Plates(Mechanics, Strength & Structure Design)

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There are several methods of allowing for residual stresses in Elastic-Plastic Fracture Mechanics, but all of the approaches imply such simplifying assumptions that could contribute to the observed scattering in test results. This paper examines the prediction and incorporation of residual stresses in fracture toughness test data evaluation. Part 1 dealt with the Finite Element analysis of Crack Tip Opening Displacement specimens of thick plates, paying special attention to the peculiarities in behavior of deep and shallow cracks. Calculations of stress and strain fields, together with the shape and size of the plastic zones ahead of crack tips, were presented for several loads and crack lengths. Opening displacements in the crack tip, values of rotation factors under bending and J integrals were obtained in order to characterize the different behaviors, when residual stresses were absent from the models. For Part 2, residual stresses were computed using thermal elastic plastic Finite Element analysis and crack tip opening displacements recalculated to assess any variation with respect to the ideal unstressed specimen. Results point to substantial dissimilarity in behavior for both specimens-with and without residual stresses- and, in addition, such differences are found to be linked to the failure loads. Hence, as the model suggests, actual toughness values could be smeared by the residual stress state in the CTOD test specimens.
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