Linear Least Square Approach for the Estimation of Crack Tip Fracture Parameters Using Isopachic Data from Thermoelastic Stress Analysis

Abstract

Thermoelastic stress analysis (TSA) is a nondestructive evaluation tool used for obtaining the stress fields in the vicinity of critical region of the structure. In this work, TSA was used to determine the stress fields around discontinuities like hole and crack in metallic structure and the stress results were post-processed to obtain the stress concentration/stress intensity factor. Initially, experiments were conducted on a mild steel specimen with a hole under tensile cyclic loading and an infrared thermography camera was used to capture the temperature distribution on the surface of the specimen. The stress fields around the hole obtained using TSA were then used to evaluate the stress concentration factor (SCF) and compared with analytical and finite element results. Subsequently, experiments were extended to analyze mild steel specimens with straight and inclined cracks to obtain near-crack-tip stress fields using TSA. A linear least square approach was then used to determine the stress intensity factor (SIF) from the TSA stress results. Finite element modeling of the straight and inclined cracks were done to compute the SIFs. The stress intensity factors calculated from TSA results were then compared with analytical and numerical results. The procedure outlined here establishes an experimental approach based on TSA technique for the accurate determination of SCF/SIF.