Assessment of Residual Stresses in a Carbon Steel Weld Pad Using Critically Refracted Longitudinal (LCR) Waves

The knowledge of residual stresses in engineering structures is important for ensuring their reliable performance, structural integrity and life assessment and extension. Welded components are of major concern as it is well known that welding processes generate considerable residual stresses that are detrimental to the performance of the components. Several destructive, semi destructive and non destructive techniques are in use for the quantitative assessment of residual stresses in welded joints. Ultrasonic non destructive techniques are useful for the assessment of surface, subsurface and bulk residual stresses. In the present work, application of critically refracted longitudinal (LCR) waves for the estimation of surface/sub-surface residual stresses in a 20 mm thick single " V" butt joint fabricated from carbon steel plates is explored. Transit time measurements were made at different locations across the weld, for the L_CR waves propagating along the weld direction (longitudinal direction) representing the longitudinal stresses in the weld joints, using 2MHz L_CR wave probe assembly. Repeatability in the transit time measurements is found to be within 2 ns. For accurate measurement of the transit time, cross-correlation technique was implemented in Lab VIEW. The measurements carried out across the carbon steel weld joint clearly establish the capability of the L_CR wave based technique and the reliability of the inhouse designed and developed transducer assembly for residual stress measurements, after establishing the acoustoelastic constant for L_CR waves.