Article by James Thomas and Stephen Kendrish. Featured in Gear Solutions magazine, January 15, 2019
Modern industry has many requirements like cost efficiency, durability, lightness of manufactured parts and eco-friendliness to name a few. With these requirements in mind it’s crucial to have deep understanding of the manufacturing process and how it affects the finished part. Residual stress is one physical property that is becoming more crucial as the requirements and quality of manufacturing process grow.
Cold working causes plastic deformation that creates residual stresses. The degree and sign of the residual stress depend on degree and type of the working process. Shot peening is a cold working process in which the surface of a component is peened with small spherical balls called shots.
Residual stresses are spontaneously in equilibrium as tensile residual stresses (detrimental) and compressive residual stresses (beneficial). For example, a surface formed in tensile stresses will comprise compressive residual stresses, and a surface formed in compressive stresses will contain tensile residual stresses.
There are many methods to measure residual stresses. The methods are commonly grouped as non-destructive, semi-destructive and destructive or diffraction based, strain relaxation based and other methods.
Residual stress measurement is one essential way to find out if the component can withstand the demanding load and stress conditions in its service life. The possibility of distortion of the component during storage or in service life can also be checked by measuring the residual stresses. In fact, measurement is the only way to find the sign and magnitude of residual stresses. Measurement of residual stresses is also useful for quality control purposes and verification of processes such as surface hardening, heat treatment, machining...
Thermal and mechanical treatments are available to relieve the residual stresses.
Distortion is the unexpected, uneven change in size or shape caused by dissimilarities in manufacturing and heat treatment processes. Distortion is affected by material properties, part geometry, the size of the component and the most importantly the residual stress state of the component.
Residual stresses are induced during the machining due to mechanical, thermal or chemical factors. They may lead to lower fatigue life hence they should be analyzed and controlled.
Independent of external loads, there are internal stresses inside structures and materials. These stresses are called residual stresses. Even though “stress” is an abstract term, the plural form “residual stresses” is often used. Residual stresses / Residual Stress terms were first mentioned in literature already in 1841. Since then, the importance of residual stress has become a well-known fact.
Grinding is a chip-forming process which requires high energy to remove material to specified dimensions.
Stresstech is a world leader in developing and manufacturing non-destructive inspection equipment for grinding burn detection and residual stress measurement.