Mismatch effect on plastic yield loads in idealised weldments: I. Weld centre cracks

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The accuracy of the defect assessment methods for strength mismatched structures is directly related to the accurate estimate of the (mismatch) yield load of the defective component of interest. This paper provides accurate closed form solutions of mismatch yield loads for two representative cracked plates, a middle crack tensile plate and a single edge cracked plate in pure bending. The weld configurations are idealised as a simple strip model, and the crack is assumed to be located in the centre of the weld metal. Solutions are given for two limiting out-of-plane constraint conditions, plane strain and plane stress. Comparisons with the results from detailed finite element limit analyses show excellent agreement, for almost all values of strength mismatch levels, ligament-to-weld width ratios, and crack lengths. Another important outcome is that, based on the proposed solutions, useful guidelines are given for assessing cracked structures with weldments, in the form of windows where the plastic yield load solutions of mismatched components can be obtained assuming the component can be wholly characterised by either base material or weld material properties. Such guidelines could be very useful when complex components with weldments are to be assessed, for which the plastic yield load solutions are not available or difficult to find.