Effect of spatial hardness distribution in rolling contact fatigue performance of bearing contacts

Abstract

In this investigation the effect of various spatial hardness gradients (e.g. linear and nonlinear) on rolling contact fatigue (RCF) life are examined through a Mises-based plasticity framework. The plasticity framework, which utilizes kinematic hardening was embedded into a finite element (FE) model, which utilized continuum damage mechanics (CDM) to facilitate life calculations by simulating material deterioration as a function of cycle. CDM critical parameters – elastic damage law resistance stress (σr), elastic damage rate exponent (m), plastic damage law resistance stress (S0), plastic damage rate exponent (q) – were established from open literature experimental torsion stress-life data. A parametric study was then performed to quantify the relation between RCF life and (1) type of spatial gradient (e.g. linear, polynomial degree 4, polynomial degree 0.25), (2) depth of spatial gradient normalized with respect to half-contact width (e.g. 1b, 2.5b, 5b, 10b), (3) magnitude of residual stress, and (4) contact pressure. Additionally, FE simulations were conducted on non-graded, or uniform hardness microstructures and used to compare to the results from the parametric study. The RCF results indicated that polynomial gradients with degree greater than 1 outperform linear and polynomial gradients with degree less than 1, with differences between gradient types more apparent at shallower gradient depths. RCF resistance is improved with increasing gradient depth and increasing compressive residual stress. Regression analysis of the results from this investigation yielded a fatigue life expression that was formed as a function of the 4 input variables, with life improvement factors comparing well with experimental data from the open literature.