A Novel Approach to Residual Stress Measurement

Residual stress is a topic of ever increasing concern in many industries and aspects of engineering. Existing methodologies for quantifying residual stresses have been proven effective, all with their respective drawbacks. This thesis provides an authentication of a novel strain measurement and residual stress calculation method. This method is heavily rooted in the fields of optical strain measurement and elementary solid mechanics. The types of measurements discussed involve using two specialty optical strain gages to measure strain and compute residual stress in several engineering materials. These gages provide a unique approach to accurately quantify residual stress. The experiments performed provide a validation of the strain measurement techniques and a computational method for determining residual stresses using those strains. A square strain gage is compared to both a traditional strain measurement technique and an accepted closed form solution for beam bending. A circular strain gage is evaluated to quantify strain under linear-elastic deformation, local plastic deformation, and fully plastic deformation of a material by means of mapping the strain fields about a hole for these deformation scenarios. The computational method for quantifying residual stress is substantiated by comparing values obtained experimentally from both a center hole drilling analysis using circular strain gages and the accepted method of cut compliance. The interpretation of residual stresses using both the square and circular gages proved to be very accurate when compared to theory. Also, the comparison between the center hole drilling method and cut compliance experimental data displayed minimal error. The results of these experiments are presented to highlight the accuracy of the measurements performed. Additional research is required for these novel methods to ascertain the precision of existing residual stress measurement techniques. However, this novel approach provides a unique solution to an issue that affects a vast majority of engineered parts and materials