J an Weichert

In industrial practice, bolted joints are widely used connecting elements that are often subjected to cyclic loading and are therefore prone to fatigue. In most cases, bolts are loaded by a cyclic combination of axial and bending loading typically as a result of eccentric loading, such as in flange connections. The cyclic loading is superimposed by a preload.
Another example is, in the case of wheel bolts, that high bending stresses occur in addition to the axial preload due to displacement of the wheel relative to the brake disk pot during sharp braking.

Typical characteristics of bolts are sharp radii in the thread notch and the head-shaft transition from which cracks may initiate during cyclic loading. The combined global axial and bending loading leads to locally stress concentrations in these highly stressed regions. The objective of the study is to investigate experimentally and numerically the local effects caused by the occurring bending stresses such as the supporting effect due to the stress gradient and the multiaxial stress condition. These variables are of crucial importance for the fatigue strength assessment.

This paper presents a reliable fatigue strength assessment approach based on the strain-life approach. Material mechanical effects of high mean stresses and mean stress sensitivity are considered by various damage parameters such as P_B and P_J according to Bergmann resp. Vormwald.
Finally, recommendations are given as to how bending loading can be considered in a fatigue strength assessment.

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