Improved Spatial Resolution Within Deep-Hole Drilling Residual Stress Measurements

The deep-hole drilling method provides a very effective technique for measuring residual stress profiles through the thickness of large metallic specimens ranging in size up to several hundred mm. This capability is challenging to achieve by any other method. The method involves drilling a small diameter pilot hole through the specimen and then measuring the change in the internal diameter caused by a subsequent overcoring of the material around the hole. Classical Kirsch equations are used to calculate the residual stresses from the measured diameter changes at the various depths within the pilot hole. In this calculation, it is typically assumed that the response of the material at each depth depends only on the material at that depth, without any influence from the adjacent material. This approach works satisfactorily when the residual stresses vary smoothly with depth. However, it gives rather poor spatial resolution when detailed features are present. The present work considers the interactions between the material at each hole depth and the adjacent material and presents a practical computational method for accounting for those interactions. Example calculations demonstrate a much-enhanced ability to resolve local residual stress details.