Hole drilling residual stress measurement using three-dimensional-digital speckle pattern interferometry

This dissertation work presents a residual stress measurement system using three-dimensional digital speckle pattern interferometry (3d-DSPI) and hole drilling mechanism. Traditionally speckle interferometry is used in various applications in the field of mechanics and the advancements in digital techniques significantly impacted the speckle interferometric applications. In the proposed method, deformations produced by the hole drilling operation are measured in the three-dimensional field. Using 3D-DSPI, which is a full field non-contact optical technique unlike the traditional techniques where only point information is obtained and only in-plane deformations are measured. Although there are many other optical techniques that are used for the measurement of residual stresses using hole-drilling mechanism based on either in-plane or out-of plane deformation data, in the proposed method the both the in-plane and out-of-plane deformations are used for the accurate calculation of the residual stresses. Residual stress measurements using 3D-DSPI and hole drilling mechanism have been classified into three main categories: (i) through hole drilling in thin parts; (ii) blind hole drilling to measure residual stresses in thick parts where it is not possible to drill a through hole and (iii) incremental hole drilling has been proposed to measure the residual stresses which vary as a function of depth. A portable system for the measurement of residual stresses has been developed using 3D-DSPI based on the measurement of released deformation during the hole drilling process. Simulation of the hole drilling process had been performed using finite element analysis to determine the calibration coefficients; these coefficients are used to calculate the residual stresses based on the established governing equations. A customized software application has been developed to make the calculation procedure in a shorter amount of time and some of these results have been published in scholarly journals.