Dr. Conor McCaughey and Dr. Richard Dignall, Institute of Spring Technology (IST)
Most people who work with springs will be aware of the concept of prestressing, or at least the idea of a spring becoming shorter the first time it is used. However, the underlying mechanisms of why this occurs and the benefits beyond stabilizing the dimensions of the spring are probably less well known. Prestressing occurs when a spring is loaded to a point where the stress in the wire is high enough that it undergoes plastic deformation, but in a controlled manner. This plastic deformation causes a change in the spring, which is visible as a reduction in the free length. Note that this is different from shortening due to relaxation, which generally happens over a longer time frame (although this can be relatively quick in processes such as hot setting). However, the processes going on during prestressing, what is plastic deformation and why this is a benefit to the operation of the spring might be less well known.
This article will hopefully illuminate the reader to give them a better understanding of the concept as a whole, and why prestressing springs should always
be a consideration.