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.
Peening effectiveness is normally characterized via the Almen intensity and the % coverage. It should be noted that many potentially different residual stress gradients can result from what may appear to be the same deflection of the Almen strip and observed % coverage. The % coverage is an optical assessment of the as-peened surface and is generally thought of as a measure of the uniformity of peening on the component surface.
3D printing is increasingly being used as an alternative method of manufacturing components. In particular, replacement parts that were manufactured via traditional methods such as casting are now being made using additive manufacturing processes. While a printer can produce a dimensionally identical part, the process may not produce the same residual stress distribution in the part.
The weight of the concrete and the steel superstructure in a bridge, and thus the resultant dead load in each of the critical members, are well known when the bridge is initially constructed, assuming all goes to plan. However, major maintenance, repair, or any significant damage to the structure can cause the loads to redistribute and thus change the dead loads and the load path.
Residual stress plays an important role in many of the issues found in pipelines, such as stress corrosion cracking (SCC), hydrogen induced cracking (HIC), fatigue cracking, welding stresses, heat treatment effectiveness, surface enhancements due to cold work, ending due to seismic activity, and installation stresses. The significant effect that residual stress has on the performance and life of a component makes it extremely important to characterize these stresses.
Residual stresses created during the manufacturing process can lead to stress corrosion cracking, distortion, fatigue cracking, premature part failure, and instances of over design. The nondestructive nature of the x-ray diffraction (XRD) technique has made the residual stress characterization of power generation components a useful tool for process optimization, design improvements, and failure analysis.
Residual stresses play a key role in the life of aerospace structures. Proto provides both measurement services and x-ray diffraction residual stress measurement instruments, enabling our customers to obtain residual stress measurements in the lab or in the field on various aerospace components.