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.
Grinding thermal damages, also known as grinding burns, will shorten the fatigue life and can cause severe failures in dynamically loaded, critical components.
Combined with dimensional inspection, hardness tests and periodic metallographic analysis, the Barkhausen noise analysis method can help close the loop on insuring product quality.
Barkhausen noise gives information from the surface and very close area beneath the surface. Compressive stresses will decrease the intensity of Barkhausen noise while tensile stresses increase it. This fact can be exploited so that by measuring the intensity of Barkhausen noise the amount of residual stress can be determined.
Barkhausen Noise Analysis (BNA) is based on a concept of inductive measurement of a noise-like signal, generated when a magnetic field is applied to a ferromagnet.
Advanced stress testing technology for shot peened surfaces. Interview with Dominik Dapprich, Managing Director of Stresstech GmbH MFN international Vol. 18, July Issue, Year 2017
Shot peening produces compressive stresses to the surface of the workpiece, thus making it more durable. A common technique for measuring residual stresses of shot-peened workpieces is X-ray diffraction. The Xstress Robot system uses an industrial robot as a goniometer, thus bringing more flexibility and automation to measurement processes.