Using TSA to Identify Regions Having Developed Plastic Strain during Welding

Abstract

Residual stress can be related to plastic strain experienced by a component; therefore the measurement of plastic strain presents the potential for residual stress to be investigated. Previous work has shown that Thermoelastic Stress Analysis (TSA) can identify regions that have undergone plastic strain. To do this, it was necessary to manufacture a test specimen of identical geometry containing zero plastic strain known as a reference specimen. Identifying the regions that have undergone plastic strain is then a simple matter of subtracting two data sets. This approach assumes there is always a reference specimen available, which in an industrial context is not the case. To make the work applicable to in-service components it is necessary to create a simulated reference specimen. The paper presents a means of establishing the simulated TSA reference specimen using Finite Element (FE) modelling through building a linear, elastic model and then including effects of nonlinear plasticity. To validate the idea a welded mock-up is used that contains a known level of plastic strain alongside a strain free specimen of identical material and geometry to the mock-up that has been manufactured to shape using water jet cutting. The work in the paper describes the outcome of using both the experimental and simulated reference specimens and considers the effect of varying material properties.