Welded mechanical parts - Fatigue design of welded joints and harmfulness of flaws

A large proportion of mechanical parts, including those whose function is to transmit motion, are subjected to variable stresses during operation, which exposes welded assemblies to a mode of failure involving progressive fatigue cracking.

The dimensioning of a welded assembly under variable load is therefore the final stage in the design of a mechanical part. This verification, which is often neglected or even ignored, is frequently the cause of premature failure in service, with serious consequences for the companies that manufacture and use the damaged equipment.

This article discusses the justification for the design of welded assemblies subjected to variable loads during the design phase of a structure, as well as the verification of the suitability for use of this same structure in service, on which non-destructive testing reveals welded assemblies with progressive defects that are then identified and characterized.

It is essential to note that the article cannot replace a dimensioning code. Its main objective is to specify the methodologies that can be used for analyses relating to fatigue on the one hand, and the harmful effects of defects on the other, in the context of the construction of welded structures for mechanical use.

At the end of the article, readers will find a table of abbreviations and symbols used.