FORMULA 62 Resonant Vibration Method for reducing Residual Stresses in Welded or Machined Fabrications
What Are Residual Stresses and Where Do They Come From?
For many people involved in the metalworking trades, the subject of stress relief is something they are not well versed in. As a result, stress relief is a subject they would just as soon like to avoid. With a little technical assistance, the average layman can get a basic understanding of residual stresses and how to deal with them. With this knowledge, he will be better prepared to evaluate shop problems and find a solution that is effective. The following information is designed to answer some of the most frequently asked questions about stress relieving.
Residual stresses, by definition, are those stresses in an elastic body that is free from external force or restraint and temperature gradients. An incompatibility of regions in the metal created by non-homogenous plastic deformation is the principal cause of these internal stress systems, whether they are in an individual part or in an assembly of parts. This mismatch or misfit between adjacent regions of the same part distorts the neighboring regions. This condition can be either extremely damaging or very beneficial to the part depending on the magnitude and direction. Compressive stresses created by shot peening can be good while tensile stresses created during welding can be bad.
Residual stresses are hard to visualise, difficult to measure and extremely difficult to calculate or predict, yet they are just as important in the function of a part as are externally applied forces that are more easily measured and calculated.
Residual stresses are fundamentally introduced into the material in one or more of the following ways: thermal, metallurgical, mechanical and chemical. Since these are the processes that make up our metalworking trades, it is only right to assume that, at some point in time, a stress relief treatment may be required.