Prestressing of compression springs

03 May 2022

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 stabilising 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

What happens during prestressing?

When a relatively low stress (compared to the tensile strength of the material) is applied to most metals/alloys, they act by obeying Hooke’s Law. The deflection experienced by a material (strain) under a load is directly proportional to the stress on it. This is known as the elastic region, and any material stressed in this way will return to its original dimensions after the stress is removed. This relationship holds to a certain stress, known as the yield stress or elastic limit. After this point, the relationship between the stress and strain is not directly proportional. This can be seen in a tensile test, shown in Figure 1. This is known as the plastic region. Material stressed beyond the yield stress, into the plastic region, will not return to its original shape after the stress is removed.

Read the full article in the May issue of DPA