Residual stresses created during the welding process can lead to stress corrosion cracking, distortion, fatigue cracking, premature failures in components, and instances of over design. The nondestructive nature of the x-ray diffraction technique has made the residual stress characterization of welds a useful tool for process optimization and failure analysis, particularly since components can be measured before welding, after welding, and after post-welding processes have been applied.
Numerous techniques such as heat treating and shot peening are available to help manage potentially harmful residual stresses created during the welding process. Knowledge of the residual stress state is required to ensure that these post-welding processes have been correctly applied.
The residual stress state in weld toes and undercuts are critical when stress concentration geometries exist that can magnify the effects of applied loads. When issues of fatigue cracking are considered, potentially harmful tensile residual stresses, alone or in combination with stress concentrations, can lead to fatigue crack initiation and propagation.
Heat treatment processes are also commonly applied to welds to lower or reduce the residual stresses present in the weld and heat-affected zone (HAZ). Residual stress measurement can be used to ensure that such processes have been correctly applied and that any harmful residual stresses have been reduced to an acceptable level.
Aggressive or abusive post-welding machining can create regions of tensile stress that can make the weld area susceptible to crack initiation and increase the rate of crack propagation.
An effective way to manage the residual stresses in welds is to cold work the weld using a process such as shot peening. Residual stress measurements can be performed to ensure that tensile residual stresses have been reduced and beneficial compressive residual stresses have been introduced.
Much time and effort is spent modeling the residual stress state of welds. Residual stress measurement can be used to verify that these models are correct or improve models that have deficiencies.
Utilizing a “Design to RS, produce to RS, and manage to RS” philosophy helps to achieve reduced component weight, improve life expectancy, and lower manufacturing and maintenance costs.
