Research On Welding Residual Stress Measurement Technology Of Thick Multipass Joint

Multi-pass welding is an important way to fabricate structures with large thickness.For the thick welded components,the weld and the adjacent materials undergo repeated thermal cycles,which resulted the high amplitude and complex distribution of internal welding residual stress,and seriously affected the service performance of the structural parts.Welded components are usually repaired during post-welding or in-service after removal of defects or degraded material.Repair welds can significantly influence the distribution and magnitude of welding residual stress.Therefore,it is of great theoretical significance and engineering practical value to study the magnitude and distribution of internal as-welded residual stress and its variation after local repair of the thick parts.In this paper,the original internal stress distribution in a SA738 Gr.B specimen with a thickness of 47.6mm is measured by two kinds of improved contour method and a composite stress measurement method.Meanwhile,the transverse stress distribution and magnitude obtained by the proposed methods are compared and analyzed.The original internal stress of 50 mm thick Q345 D specimen before and after partial repair welding is tested by using the contour method with three cuts.Besides,the influence of partial repair on residual stress of the thick welded joint and the release degree of welding stress after transverse cutting are analyzed.The longitudinal stress distribution on the cut plane is constructed by the eigenstrain method based on part of the internal stress data measured by the contour method,and the surface stress error is corrected by the eigenstrain method;the effect of the order of basis function for constructing eigenstrain distribution on the constructed stress is also investigated.The internal stress of SA738 Gr.B specimen can be obtained by the contour method with two orthogonal cuts and the improved contour method(one-cut contour method + slice method +XRD method),and the results of transverse stress obtained by the two improved contour methods are in good agreement.As the specimen surface is treated by the ultrasonic impact,the transverse and longitudinal surface stress in the impact area are compressive stress,and the compressive stress layer can reach up to 2~4mm.The internal stress distribution of the 50 mm thick Q345 D specimen with partial repair weld is achieved by using the contour method with three cuts.Investigated results show that the full maps of the welding longitudinal and transverse stress distributions can be obtained by the mutiple-cut contour method;the peak longitudinal stress within the repair weld increases by 30% as compared with that in the initial weld;due to the heat effect exerted by the multipass welding of the repair weld,the peak longitudinal stress in the region above the partial repair weld decreases by 60% in relation to the peak stress in the initial weld;the extent of stress release caused by the transverse cut changes with the location from the cut edge,the stress within the region with a distance from the cut adge over twice times the thickness is almost unaffected by the cut.The longitudinal stress on the cut plane constructed by eigenstrain method agrees well with that by the contour method.In addition,the stress error on the surfaces can be corrected to some extent by the eigenstrain method;the longitudinal stress on the cut plane can be constructed with the eigenstrain basis function with the order of 16 in the y direction and 10 in the z direction along the cutting surface.