Concentration of constraints

Stress concentration is a problem often encountered in the mechanical design of a component or mechanical part. It is a phenomenon of local stress increase in a zone involving a geometric modification of the part. It occurs, for example, in a discontinuity in the part or structure, with the presence of a notch after machining. The stress concentration zone is often the site of fatigue crack initiation, but can also be the origin of a sudden fracture in the case of a brittle material.

Why, for example, does the end of the glass bulb always break at the point of the kerf, however small? The reduction in cross-section is negligible and, what's more, as the end is conical, the cross-section near the kerf is certainly smaller. The explanation is simple: at the bottom of the very small notch thus created, there is a stress concentration phenomenon that causes the breaking limit to be exceeded.

In addition to static failure problems, fatigue stress concentration is an important factor in structural lightweighting. Fatigue is the cause of most failures of components containing stress concentrations. An analysis is therefore needed to show how to deal with this type of problem in the context of structural FEA.

In this article, we use specific examples to illustrate the physical phenomenon, define the terminology and provide a methodology for dealing with case studies, gradually increasing the difficulty. One of our aims is also to integrate new calculation methods. Finally, we provide information to facilitate the use of existing documentation.