Fatigue lifespan of compliant planetary roller screws: multiscale modelling and stiffness measurements

Planetary roller screw mechanisms are rotation-translation converters able to support high axial loads making them appealing for aerospace applications. Alternate loads but also rotation under constant load put a cyclic strain on the mechanism. In this context, fatigue failures may occur. A fatigue design strategy is proposed considering mechanism compliance. The fatigue design is a modelling sequence that (i) analyses mechanism thread contact geometry, (ii) finds the non-uniform load distribution at thread contacts along the mechanism axis, (iii) determines bulk and surface stress fields, (iv) computes the Dang-Van’s criterion for creek initiation. The modelling of mechanism compliance is made minimal for fatigue design applications. This modelling is validated with stiffness experiments on an inverted PRMS. Finally, the fatigue analysis of the considered PRSM shows that the mechanism compliance reduces the loading limits for infinite lifespan.