Computer aided analysis for residual stress measurement using ultrasonic techniques

Abstract

Critically refracted longitudinal (Lcr) waves have been investigated with a computerized data acquisition and analysis technique to evaluate residual stresses present in a residual stress reference standard. This measurement system has an ability to detect travel-times with a precision of 0. l nanoseconds and an accuracy of less than 2.5 nanoseconds. A residual stress reference standard developed for previous research was used as the sample to measure travel-times. The sample was designed and developed so as to create large areas of uniaxial compressive and tensile stresses. Travel-time measurements were made across the breadth of the sample on both sides in increments of 0. 127 m (0.5 inches). This provided data for mapping travel-time variations across both sides of the sample. The zero stress travel-time was determined by averaging the travel-times across the sample. From the travel-time data, stress changes and strain across the sample were also mapped. Strain gage data from a previous study on the same sample was used to compare the residual stress patterns with the ones obtained with the Lcr travel-time data. The strain gage data were found to generally support the Lcr travel-time mapping. However, in addition the Lcr travel-time data indicated bending in the sample. The results showed that Lcr technique presented travel-time data accurately and precisely and represented the true state existing in the sample.