Assessment of the Influence of Plasticity and Constraint on Measured Residual Stresses Using the Contour Method Available to Purchase

The contour method is a relatively new relaxation method for residual stress measurement and may be seen as an evolution of established methods such as hole drilling. The general procedure when applying the contour method is cutting, measurement and calculation of residual stress normal to the cut plane using Bueckner’s principle of elastic superposition. That is the residual stresses are determined from the measured profile of a cut surface. While the contour method is simple in concept there are certain underlying issues relating to the cutting process that may lead to uncertainties in the measured results. Principally the issues are that of constraint and plasticity during cutting and the influence they have on the measured residual stresses. In this paper both issues are investigated in detail by simulating the entire contour method process using finite element techniques for two welded specimens. Constraint has been a recognised concern for the contour method with the general requirement being to hold the specimen as rigidly as possible. Both clamping and fixing bolts are routinely used however in reality these methods do not provide a fully rigid constraint. In this work a range of constraints have been examined to determine the influence on the measured residual stresses. Plasticity, as a consequence of the cutting process, has also been recognised as a factor which may affect the measured residual stresses. In this work the extent of plasticity is predicted by simulation of the cutting process. With a known initial residual stress field the effects of plasticity are directly quantifiable. This work therefore provides an extremely useful insight into some of the key issues that affect the measurement performance of the contour method.