Analysis of the effects of strain measurement errors on residual stresses measured by incremental hole-drilling method

摘要

Among the many available methods for measuring residual stresses, the hole-drilling method is surely one of the most popular methods. It is a semidestructive method consisting in drilling a very small hole into the specimen. This produces residual stress relaxation around the hole that causes strains also to change. Strain on the surface can be measured by strain gages or by optical techniques like electronic speckle pattern interferometry. Holes can be drilled at different depths, so that a stress profile can be determined using the stress—strain relationships. However, due to the mathematics of the problem, small measurement errors on the strain can imply big errors in the calculated stress. Accuracy of the final results is strongly dependent on the measurement procedure and on the algorithms adopted to calculate stresses. In this study, the influence of strain measurement errors is evaluated with respect to different measurement procedures. Two kinds of algorithms, namely, integral and power series, are compared also with respect to the use of two different commercial systems both implementing the cited methods. Moreover, the effects of a proper choice of depth increments and also of the number of steps are investigated. Effects of implementation of regularization algorithm are discussed as well as the influence of the drilling depth. Finally, the ability of the analyzed methods in discriminating two different strain signal sources is investigated.