Identification of Inhomogeneous Material Strength near Weld Joint by Three-Dimensional Digital Image Correlation Technique

Abstract

It has been shown that susceptibility and growth rate of stress corrosion cracking depend on the material strength such as yield strength. However, the material strength is not uniform near weld joint, where the stress corrosion cracking has been found in nuclear power plants. In this study, the digital image correlation (DIC) technique was applied for identifying the inhomogeneous material strength distribution near weld joint of a pipe. A specimen was taken from a butt welded joint and subjected to tensile test. The DIC technique enabled to measure the displacement field on the specimen surface during the tensile test. The local stress-strain curves were successfully measured and the inhomogeneous distribution of 0.2% proof strength was identified. It was confirmed that the stress triaxiality caused by inhomogeneous deformation had little influence on the identification of the proof strengths and local stress-strain curves. Furthermore, it was shown that the change in cross-sectional area of the specimen during the tensile test could be measured by the DIC technique, and then, the local stress (true stress) considering the change in the cross-sectional area was estimated.