Thermoelastic assessment of plastic deformation

Thermoelastic stress analysis (TSA) is used to assess the effect of plastic deformation in small-diameter stainless steel pipework that has been subjected to multiple deformation cycles. In theory the residual stress resulting from the plastic deformation cannot be detected as the thermoelastic response is only a function of the stress change. However, it has been shown that plastic deformation may modify the thermoelastic constant in steel and aluminium. This change can be used to estimate the level of plastic strain that a component has experienced and has potential for TSA to be used as the basis for non-contact non-destructive full-field residual stress assessment. In this paper it is shown that strain hardening during the deformation process plays an important role in modifying the thermoelastic constant. X-ray computed tomography is used on the pipework to verify the estimates of geometry change that are used in determining the applied stress and estimating the residual stress levels. It is shown that TSA is not sensitive to residual stress; however, some interesting anomalies appear in the experimental results that provide a basis for discussion and open avenues of further work. Finally the non-adiabatic thermoelastic response is used to assess whether any damage has occurred in the pipework