Residual Stress & Retained Austenite

Application Note


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:

  • Skins
  • Wings
  • Frames
  • Landing gear
  • Engine supports
  • Engine casings
  • Engine cowlings

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:

  • Distortion
  • Fatigue life
  • SCC potential
  • Total stress (residual + applied)
  • Weld residual stress maps
  • Holes - effectiveness of cold work
  • Fastener thread stress characterization
  • Localized stress distribution characterization around fasteners
  • Oil canning stress distribution due to machining practices
  • Detecting abusive machining
  • Evaluating shot peening, LSP, and LPB effectiveness

Production Quality: Nondestructive and Quantitative

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.

Evaluate 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.

Verify Surface Enhancement Processes

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.

Identify Abusive Machining

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.

Maintenance Improvements

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

Additional Applications:

Residual Stress & Retained Austenite