Calculation of screw assemblies

In this article and the next, we present the two main analytical models that can be used to calculate real assemblies with a single fastener (screw or bolt).

In this article, we present the model proposed by the VDI 2230 recommendations, which is the oldest and probably still the most widely used model. We shall see that it should be used with caution and reserved for the static dimensioning of assemblies whose bending deformations remain very low under the imposed load.

In article BM 5 563v2, we present the so-called "bending beam" model, well suited to assemblies of parts for which bending deformations cannot be neglected: i.e. those whose thickness is small compared to other dimensions, and in particular compared to the loading eccentricity.

After analyzing and comparing these two models, we describe a new approach for extending the field of application of the "flexed beam" model, and then demonstrate the relevance of this modeling approach using a few significant examples. A generalization of the model is also proposed, enabling it to be rapidly applied to most real-life situations.

Finally, after demonstrating the importance of installed prestressing in the behavior of an assembly subjected to fatigue loading, we develop a procedure for optimizing assemblies, taking into account prestressing conditions.