5. Fatigue tests

5.1 Material strength under dynamic loads

Usual tests carried out at slow speeds provide interesting characteristics, but are insufficient to inform the designer about the material's resistance to dynamic stresses. In fact, it has been observed that parts subjected to variable loads break after a certain period of operation. Although the dimensions of the parts have been calculated so that the constituent material works below the conventional elasticity limit, failure occurs suddenly without any prior deformation being visible. The part is said to have failed by fatigue.

To avoid this drawback, special fatigue tests are carried out to determine the characteristics of parts subjected to variable stresses. These tests enable us to study the behavior of materials...