Application of Diffraction Methods for the Residual Stress Determination in Welded Joints

The paper gives an overview about the most important diffraction methods for the determination of residual stresses in welded joints. The basic principles and the particular advantages and limitations of the methods are shown as well as the applicability for lab size samples and welded components.</jats:p

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

Effects of residual stresses and compressive mean stresses on the fatigue strength of longitudinal fillet welded gussets

AbstractResults from fatigue testing of small-scale specimens are widely used to study residual stress effects on fatigue of welded structures. It was observed from a literature that welding distortion may cover residual stress effects due to high-bending stresses from clamping. Here, presented are fatigue test results and results from residual stress measurements from welded longitudinal stiffeners in different residual stress conditions. The axial welding distortion was corrected for all samples by straightening reducing effects from clamping and making residual stress effects visible. It was found that the fatigue strength depends strongly on the stabilized residual stresses, especially at high numbers of load cycles. It could be shown that residual stresses at the weld toe either were far below the yield strength or were degraded mainly at the first load cycle but still have major effects. This was investigated at two stress ratios of R = −1 and R = −3.</jats:p