4. Multiaxial loading

The majority of fatigue tests carried out on specimens to determine the characteristics of a material are performed under simple loading: tension-compression, bending or torsion. In reality, parts or structural elements are often subjected to several loading sources, independent or otherwise. If the critical point of these elements is subjected to a state of stress with several components, the condition is multiaxial. Examples include a drive shaft subjected to coupled torsional and rotary bending stress, a sheet metal part subjected to tensile stress in two directions, a tube in tension with a pressurized fluid inside, etc.

For all these cases, fatigue design can be carried out using multiaxial criteria, the aim of which is to calculate an equivalent uniaxial stress in terms of fatigue strength in the multiaxial state. Among the best known are Gough and Pollard...