The roller profile appears to be the key element to attain a longer rating life for both cylindrical and tapered roller bearings. A genuine elastic analysis is able to optimize the roller profile to obtain a stress distribution in the contact zones that provides enhanced operational reliability and greater insensitivity to misalignment. For traditional cylindrical-crowned roller profile design class I discontinuities exist at the intersection points of roller profile with the crowning radius as well as at the end chamfer. In an elastic analysis these discontinuities generate very sharp increases in pressure distribution diminishing the rating life of the bearing. In fact, these local increases in pressure distribution are able to overcome, locally, the yield limit and to induce both plastic deformations and residual stresses. After a certain number of cycles the material will shakedown elastically to a slightly modified roller profile and a stable state of compressive residual stresses. If were taken place, these changes have to be considered in the life evaluation.
An analysis model has been developed to simulate the nonlinear strain rate dependent deformation of rolling bearing steel stressed in the elastic-plastic domain.
The model is developed in the frame of the incremental theory of plasticity by using the von Mises yield criterion and Prandtl-Reuss equations. By considering an isotropic and non-linear kinematic hardening laws the model accounts for the cyclic hardening phenomena. For each new load increment new increments for the components of stress and strain tensors, but also increments of residual stresses, are computed for each point of the 3D mesh. Both the new contact geometry and residual stresses distributions, are further considered as initial values for the next loading cycle, the incremental technique being reiterated. The cyclic evaluation process of both the plastic strains and residual stresses is performed until the material shakedowns. For the case of cylindrical roller bearings with cylindrical-crowned roller profile, the role played by the crowning geometry on pressure distribution is pointed out for both the elastic analysis and elastic-plastic analysis. Further, the modified rating lives are evaluated using the methodology given in ISO 16281-2008.
