Welding Residual Stress

Welding residual stress refers to the internal stress generated in welded structures due to constrained thermal deformation during the welding process. Particularly, during the melting, solidification, and cooling shrinkage of the weld metal, significant thermal stress is generated due to the constraints, making it the primary component of residual stress. In contrast, the internal stress arising from changes in the metallographic structure during the cooling process is a secondary component of residual stress. The greater the rigidity of the structure and the higher the degree of constraint, the greater the residual stress, and consequently, the more significant its impact on the structural load-bearing capacity. This article mainly discusses the impact of welding residual stress on structures.

Impact of Welding Residual Stress on Structures or Components

Welding residual stress is the initial stress present on the cross-section of a component even before it bears any external load. During the service life of the component, these residual stresses combine with the working stresses caused by external loads, leading to secondary deformation and redistribution of residual stress. This not only reduces the stiffness and stability of the structure but also, under the combined effects of temperature and environment, significantly affects the structure’s fatigue strength, brittle fracture resistance, resistance to stress corrosion cracking, and high-temperature creep cracking.

Impact on Structural Stiffness

When the combined stress from external loads and residual stress in a certain area of the structure reaches the yield point, the material in that area will undergo localized plastic deformation and lose its ability to bear further loads, causing a reduction in the effective cross-sectional area and, consequently, the stiffness of the structure. For instance, in structures with longitudinal and transverse welds (such as the rib plate welds on I-beams), or those that have undergone flame straightening, significant residual tensile stress may be generated in larger cross-sections. Although the distribution range of these stresses along the length of the component may not be extensive, their impact on stiffness can still be substantial. Particularly for welded beams subjected to extensive flame straightening, there may be a noticeable decrease in stiffness during loading and reduced rebound during unloading, which cannot be overlooked for structures with high requirements for dimensional accuracy and stability.

Impact on Static Load Strength

For brittle materials, which cannot undergo plastic deformation, the stress within the component cannot be evenly distributed as the external force increases. The stress peaks will continue to rise until they reach the material’s yield limit, causing localized failure and eventually leading to the fracture of the entire component. The presence of residual stress in brittle materials reduces their load-bearing capacity, leading to fractures. For ductile materials, the existence of triaxial tensile residual stress in low-temperature environments can hinder the occurrence of plastic deformation, thereby significantly reducing the load-bearing capacity of the component.

In conclusion, welding residual stress has a significant impact on the performance of structures. Reasonable design and process control can reduce residual stress, thereby enhancing the reliability and durability of welded structures.