Development and comparison of residual stress measurement on welds by various methods

Abstract

Residual stress constitutes an integral part of the total stress acting on any component in service.It is imperative to determine residual stress to estimate the life of critical engineering components, especially those that are welded. The stresses caused by non-uniform temperature distribution due to welding and the effect of these multiaxial stresses upon service performance are discussed. A controlled thermal severity test (CTS) was performed on mild steel plates bolted together, with anchor welds deposited on opposite sides. After cooling, bithermal and trithermal test welds were deposited one after the other. Varying welding stresses were deliberately introduced by using different thicknesses of both plates to change the thermal severity numbers (TSN). The main experimental technique used here to determine the magnitude and nature of residual stress is based on X-ray diffraction (XRD). It was utilised to develop and standardise other techniques. The XRD method is based on the peak shift in the diffraction pro le due to the presence of stress using a sin 2 y method. The peak shift is determined by orienting the sample at different angles ¡y to the incident X-ray beam. The semidestructive technique of hole drilling and use of a strain gauge was also employed to determine residual stress in CTS specimens. The magnitude, nature, and direction of principal stresses were determined by relieving stresses through incremental blind hole drilling and measuring strain values at each step. The surface displacements arising due to hole drilling can also be determined by laser holography. A sandwich holography technique was developed to avoid unwanted rigid body motions of samples due to hole drilling when relieving stresses. Stress values were obtained by measuring fringe displacement between two exposures of a sandwich hologram, due to hole drilling. Results on the change in residual stress values with TSN are discussed. The residual stress values determined by XRD and sandwich holography were found to be comparable, and stress values obtained by hole drilling/strain gauge measurement were higher than these values. The reasons are discussed.MST/5352

A strain-pattern-based spherical indentation method for simultaneous uniaxial tensile residual stress and flow property determination

“…errors in proportional limit calculation) and the difficulties in the determination of the residual stress even with previous sophisticated (or destructive) methods (e.g. hole drilling) 34 into account, the accuracy in the residual stress calculation is believed to be acceptable in engineering applications. For further verification of the potential of the new proposed method on real metals, whose stress-strain curve may not exactly obey the pre-assumed Holloman constitutive equation, FE-SITs were also performed on six metals used in engineering applications (with stressstrain curves shown in Figure 2).…”

Metal forming beyond shaping: Predicting and setting product properties

“…Thermography [75,79] X X X Ultrasonic [21,28] X X X Radiographic inspections [67] X X X Vibrometry [110,226] X X X Acoustic emission [108] X X X Eddy current techniques [233] X X X Magnetic leakage-flux [210,216] X X X Observation of micro-sections [126] X X Density measurement [209] X X Residual stresses X-ray diffraction [16,185] X X X X Hole drilling [16] X X X Neutron diffraction [16] X X Focused acoustic waves [185] X X applicable measurement principles and categorizes them according their capability into in-situ or offline as well as destructive (DT) or nondestructive (NDT) specimen testing. A measurement principle is categorized as in-situ if process control is feasible without specimen sampling and if the evaluation time is shorter than the time during which process parameters change significantly.…”

Limitations and Recommendations for the Measurement of Residual Stresses in Welded Joints

“…Several techniques are applicable to determine residual stresses in welds [3,4]. Mechanical techniques like the hole drilling use a locally restricted access to the material in order to determine the initial residual stresses while destructive sectioning techniques like the contour method allow the determination of the initial residual stresses in the entire cross section with preference to the longitudinal residual stress component.…”