The remaining stress is important in shaping the service life and the mechanical performance of components of engineering. Residual stresses, unlike the applied stresses, are not visible in the sense that they are not perceived easily when someone views the material. The tensile residual stresses can enhance the crack initiation and propagation, and the compressive residual stresses can enhance the fatigue resistance and corrosion performance. Other industries that are dependent on the residual stress measurement include aerospace, automotive, power generation, and manufacturing, among others, to optimize the processes and ensure that the processes meet the design requirements. The knowledge of the existing measurement methods can enable engineers to choose suitable methods depending on the type of material, the size, and the level of accuracy needed by the component.
Principle and Methodology
Typically, the residual stress measurement techniques are divided into destructive, semi-destructive, and non-destructive techniques. Destructive methods include the cutting or sectioning of the component and monitoring of deformation due to the release of stress. Semi-destructive techniques eliminate a minor portion of the material and record the local strain variations to determine the residual stress. Non-destructive methods are based on variations in physical characteristics of lattice spacing or wave propagation behavior in the face of stress. The method adopted will depend on whether the component is capable of being changed, the level of depth of stress that is to be measured, and the level of spatial resolution that is needed.
Familiar Residual Stress Measurement Methods
X-ray diffraction. This is a non-destructive technique that is very common and is used to measure the strain and elasticity of a crystal by examining the alterations in the crystal lattice spacing. It can be applied to measure the surface stress of crystalline materials. Neutron diffraction has more penetration and is involved in bulk residual stress analysis, especially in thick parts. A semi-destructive method is hole drilling, entailing the drilling of a small hole and stress relaxation around the hole, measured using strain gauges. The contour method is a destructive methodology that requires the component to be cut and the deformation mapped onto the component to recreate the residual stress distribution.
Industrial Use
Residual stress measurement is widely applied to validate the welding processes and measure the effectiveness of heat treatment and the surface treatments like shot peening and laser peening. It is applicable in the aerospace and automotive industries to predict the fatigue life and prevent failures. Residual stress analysis is a technique in power plants to guarantee the integrity of the pressure vessels and pipelines. In production, the methods are used to reduce distortion and enhance the dimensional stability of high-precision components.
Importance
Residual stress measurement is important to enhance product reliability, safety, and performance. It allows identifying dangerous stress conditions early, which may result in cracking or distortion during service. Correct data on the residual stress enhances the optimal choice of material, the optimal process, and the life cycle simulation. The introduction of residual stress measurement into the quality control programs will enable industries to minimize the risks of failure, improve durability, and achieve long-term cost savings.
