Stability and Relaxation of Welding Residual Stresses

Residual stress relaxation of butt-welded small scale steel specimens under static and cyclic mechanical loading was investigated. The experiments were carried out on different types of steel with yield strengths between 300 and 1200MPa. The x-ray and neutron diffraction techniques were applied for the residual stresses analysis. The maximum values of initial residual stresses were measured at the weld bead centerline and were not as frequently assumed as high as the yield strength of the material. From fatigue point of view the internal stresses at the weld toe are of importance. It was observed that only a fraction of maximum residual stress accommodated in the weld bead centerline, is available at the weld toe. Under static tensile and compressive loading by increasing the load level the residual stress field relaxes continuously. The relaxation sets in with delay under compression since the tensile residual stresses should be first overcome. Under cyclic loading, once the first relaxation takes place further cyclic relaxation is either not considerable or continues moderately depending on loading conditions. In high cycle fatigue the residual stresses are stable until 2x106 cycles. In low cycle fatigue however the variation of the residual stresses continues until failure. This variation is partly related to crack initiation and propagation. The von Misses failure criterion with the local yield strength as material resistance against plastic deformation was able to describe the relaxation of surface welding residual stresses in low cycle fatigue.</jats:p

Stress measurement at loaded aluminium welds using diffraction methods

Aluminium alloys welded with arc welding and electron beam welding processes were investigated to analyse the local deformation behaviour under static loads. Therefore strain measurements were carried out. These investigations were combined with X-ray diffraction experiments which should provide information about the residual stress condition and additionally about load-induced changes of the hardening condition. Additionally diffraction experiments using synchrotron and neutron radiation where carried out to analyse the deformation behaviour of particular welds under varying static loads.</jats:p

Welding Residual Stress Behavior in Tubular steel Joints under Multiaxial Loading Schwei eigenspannungsverhalten in Stahlrohrverbindungen unter mehrachsiger Beanspruchung

AbstractThe lack of insight into the initial welding residual stress field and its behavior during the different phases of the fatigue damage namely crack initiation and propagation has led to conservative assumptions in fatigue design codes of welds. Since a significant amount of fatigue failures in welded joints are caused by torsion or combined tension-torsion in machinery components, estimating the potential threat of the inevitable residual stresses to structural integrity seems to be mandatory for the design of the future tubular lightweight welded components and structures. In this paper the residual stresses in cylindrical specimens with bead on tube welds out of S355J2H were determined experimentally by means of X-ray and neutron diffraction. Welding residual stresses as high as almost the yield strength of the base metal were observed in the weld bead. At the weld toes which are potentially fatigue crack initiation sites, however compressive residual stresses were present. After discussing briefly the sources and origins of the residual stress field, its behavior under pure torsional and combined tension-torsion loading will be presented.</jats:p