Evaluation of Residual Stresses in Carbon Steel Weld Joints by Ultrasonic L$_\mathrm{{cr}}$ Wave Technique

Abstract

Ultrasonic based residual stress measurements are nondestructive and offer quantitative estimation of surface/sub-surface and bulk residual stresses. The underlying principle of the ultrasonic techniques is the ‘acoustoelasticity’ i.e. the stress dependence of ultrasonic velocity. Three pairs of 20 mm thick low carbon steel weld joints were fabricated using manual metal arc welding process with three marginally different heat inputs (optimum, marginally below optimum and above optimum) and used in the study. Critically refracted longitudinal (L$_\mathrm{{cr}}$) ultrasonic wave technique was employed for this study. This paper gives the details of development of ultrasonic L$_\mathrm{{cr}}$ wave based technique for residual stress measurements and the quantitative estimation of surface/sub-surface residual stresses in carbon steel weld joints. The study indicates lower value of tensile residual stress in weld joints made using marginally below optimum heat input when compared to the residual stress values in weld joints made using optimum and marginally above optimum heat inputs. The developed ultrasonic L$_\mathrm{{cr}}$ wave technique is found to be very sensitive even to the small variations in the residual stress profiles across the weld joints induced by marginally different heat inputs employed during welding.