The influence of welding residual stress on welded structures

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The last edit to this post was made by huanghong on 2020-12-30 at 09:49. 1. The effect of welding residual stresses on the static load strength of structures: For smooth components, as long as the material has sufficient plasticity, plastic deformation can help uniformize the stresses within the cross-section; therefore, the presence of residual stresses does not affect the load-bearing capacity of the component, that is, it has no impact on its static load strength； If the material is in a brittle state, has been heat-treated, or is under triaxial stress, it is unable to undergo plastic deformation; as a result, the stresses within the cross-section of the component cannot be evenly distributed. The residual tensile stresses combine with the applied stresses, leading to localized failure of the structure and ultimately the fracture of the entire component. In components with notches, high tensile internal stresses may exist simultaneously due to severe stress concentration. When a component is subjected to large tensile forces for some reason (such as a drop in temperature, an increase in deformation rate, or a thick-walled cross-section), the combined effect of these tensile stresses and severe stress concentrations reduces the structural strength under static loads, causing it to suffer brittle fracture at stress levels well below its yield point. 2. Effect of welding residual stress on fatigue strength: Compressive residual stress in the specimen, especially on its surface, can improve fatigue strength. Therefore, to improve the fatigue strength of welded structures, it is necessary not only to reduce residual tensile stress but also to minimize factors that cause stress concentration at the joints, such as excessive burr height and overly protruding fillet welds. Furthermore, introducing compressive residual stress into the components through methods such as shot peening, spot heating, and overloading can improve the fatigue resistance of welded structures. 3. The effect of welding residual stresses on machining accuracy and dimensional stability: If there are welding residual stresses in a workpiece, mechanical cutting processes remove not only the material but also the residual stresses present in that material. This disrupts the stress balance within the workpiece, causing it to deform and thereby affecting its machining accuracy. Furthermore, the residual stress in welded components gradually changes and redistributes over time, resulting in stress relaxation. At the same time, the dimensions of the welded parts also change accordingly, affecting the precision and dimensional stability of the components. Low-carbon steels and austenitic steels with stable microstructures exhibit weak stress relaxation at room temperature; as a result, internal stresses change little over time, and the dimensions of the welded parts remain relatively stable ； Certain superalloy structural steels and high-strength aluminum alloys experience significant changes in internal stress due to the transformation of their unstable microstructures over time. The most thorough way to ensure machining accuracy is to first eliminate welding residual stresses and then carry out machining. 4. The effect of welding residual stress on the stability of compressed members: When a member is under compression, the compressive residual stress in its cross-section combines with the stress induced by external loads. As a result, the compressive stress zone in the member reaches its yield limit first; the stress in this zone no longer increases, which means that this zone loses its ability to bear additional external loads. This is equivalent to reducing the effective cross-sectional area of the member, thereby lowering its critical stress and having an adverse effect on the stability of the compressed member. The effect of internal stress in the compression rod on stability is related to the cross-sectional shape of the rod and the distribution of residual stresses; improving the stability can be achieved by moving the effective cross-section away from the rod’s neutral axis. 5. The influence of welding residual stress on stress corrosion cracking: Stress corrosion cracking is a phenomenon in which cracks occur as a result of the combined action of tensile stress and a corrosive environment. The superposition of residual stresses and service stresses after welding leads to rapid stress corrosion cracking near the weld. Therefore, for corroded structures, taking appropriate measures to eliminate residual stress is beneficial for improving their corrosion resistance. 6. Effect of welding residual stress on structural stiffness: After welding, tensile stresses are generated in the weld area and its vicinity, while compressive stresses occur in areas far from the weld; these tensile stresses can reach the material’s yield limit. Therefore, when the member is under tension, this area is unable to bear load, which is equivalent to a reduction in the effective load-bearing area and results in a decrease in stiffness. For beams prone to bending deformation, the stiffness also decreases for similar reasons; the extent of this decrease depends on the size and location of the plastic deformation zone, with welds located near the neutral axis having a lesser impact on stiffness.