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:
Some of the platforms Proto has worked on include C-141, B-2, Space Shuttle, Joint Strike Fighter, Boeing 777, and Dash 7. Aerospace problems that can be addressed using Proto systems and services include the following:
Residual stress can be used for controlling production quality on the factory floor by detecting abusive machining, verifying effects of surface enhancements, and evaluating the effectiveness of heat treating.
XRD can be used to determine that heat treatment processes have been applied correctly. Post heat treatment XRD residual stress measurement of components can ensure that residual stresses are being managed correctly, thereby reducing issues such as distortion during machining or cooling strains.
Turbine components often have complicated geometries that are enhanced by shot peening and other processes. XRD residual stress measurements can be used to verify that these locations have been enhanced to the specified residual stress level. A residual stress value, once established, can be specified on the engineering and processing documents and will attach an engineering value in stress rather than an Almen strip number designation.
Machining can cause significant variations in the final residual stress state of a machined turbine component. XRD can be used to determine if any machined areas were subjected to abuse due to excessive tool wear, intermittent lack of cooling, or aggressive machining practices. Abusive machining can create regions of tensile stress that could then become a potential source of crack initiation.
Prevent over-peening of disks during overhaul. Some in-service disks are shot peened during overhaul maintenance in an attempt to rejuvenate them. However, the residual stress level before the treatment is usually unknown, and this could unknowingly have a deleterious effect on individual disks, especially if the disk is over-peened. The ability to measure residual stress enables maintenance staff to exercise better control and rework disks on a selective basis.
Proto iXRD measuring an aerospace part
Characterizing stress corrosion cracking (SCC) susceptibility on an aircraft frame using a Proto iXRD portable residual stress measurement system
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.
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.