Residual stress is defined as the stress present in a material in the absence of externally applied loading. Residual stresses often form during manufacturing and are typically an unintentional byproduct of a manufacturing process. They can be caused by plastic deformations, temperature cycles, or phase transformations.
Residual stresses are important because they can negatively or positively affect a product’s performance. Often structures are designed with considerable safety factors and the effects of residual stresses can be ignored. But as we push for higher performing structures that operate closer to the cutting-edge of technology, factors like residual stress can be the difference between successful performance and structural failure.
Residual stresses can be classified by their sign. Positive values of residual stress are referred to tensile, which means that the material is being pulled or stretched. Negative values of residual stress are referred to as compressive. Overall, the residual stress over a plane must be in equilibrium, but there can be local regions with tensile or compressive residual stress.
Unintended tensile residual stresses can cause undesirable results including cracking and failure. If tensile residual stresses induced by the manufacturing process of a product are not taken into effect, these can lead to premature failure.
On the other hand, compressive residual stresses can improve material performance. Processes like shot peening and laser shock peening intentionally introduce compressive residual stress at the material surface in select locations to make products perform better. For instance, introducing compressive stress can toughen brittle materials such as toughened glass in smartphone screens, and pre-stressed concrete in buildings and city infrastructure.
At Hill Engineering, we work with our customers to decide which tests will give them the data they’re looking for.