A New Approach Towards Life Prediction of Case Hardened Bearing Steels Subjected to Rolling Contact Fatigue

Effect of plasticity on the dynamic capacity of modern bearing steels

Abstract: Dynamic capacity, defined as the load under which rolling element bearing raceways will survive for 1 million revolutions with 90% probability of survival, is commonly used in bearing life-rating standards. This term was introduced by Lundberg and Palmgren to simplify life prediction equations, and was derived using the elastic Hertzian-theory of contact mechanics for earlier, relatively impure bearing materials. Modern ultra-clean steels with fewer impurities can survive for multi-millions of contact stress cycles, even under elastic-plastic loading conditions. Under such conditions, elastic-plastic stresses are significantly different from the elastic Hertz contact stresses. Current experimental and finite-element study, shows accounting for plastic deformation of the material necessitates significant correction in the material parameters used in the expressions for dynamic capacity calculations.

Influence of axial and torsional cyclic loading on the fatigue behavior of 304LN stainless steel using solid and hollow specimens

Abstract: Effect of loading path and geometry on fatigue behavior was evaluated for 304LN stainless steel using solid and thin walled hollow specimens. Hollow specimens were subjected to both axial and shear loading under strain control. Solid specimens were used only for strain controlled axial loading. Fatigue life was highest for shear loading despite the higher stress response and the least for the axial loading for hollow specimens. The cyclic deformation behavior marked by Masing behavior, cyclic stress strain curves and probability density function analysis was found to be remarkably different for shear loading. All disparities in the cyclic deformation behavior due to difference in loading path has been accounted by the dislocation dynamics and martensitic transformation investigated through TEM.

A 3D Finite Element Model of Rolling Contact Fatigue for Evolved Material Response and Residual Stress Estimation

Abstract: Rolling bearing elements develop structural changes during rolling contact fatigue (RCF) along with the non-proportional stress histories, evolved residual stresses and extensive work hardening. Considerable work has been reported in the past few decades to model bearing material hardening response under RCF; however, they are mainly based on torsion testing or uniaxial compression testing data. An effort has been made here to model the RCF loading on a standard AISI 52100 bearing steel with the help of a 3D Finite Element Model (FEM) which employs a semi-empirical approach to mimic the material hardening response evolved during cyclic loadings. Standard bearing balls were tested in a rotary tribometer where pure rolling cycles were simulated in a 4-ball configuration. The localised material properties were derived from post-experimental subsurface analysis with the help of nanoindentation in conjunction with the expanding cavity model. These constitutive properties were used as input cyclic hardening parameters for FEM. Simulation results have revealed that the simplistic power-law hardening model based on monotonic compression test underpredicts the residual generation, whereas the semi-empirical approach employed in current study corroborated well with the experimental findings from current research work as well as literature cited. The presence of high compressive residual stresses, evolved over millions of RCF cycles, showed a significant reduction of maximum Mises stress, predicting significant improvement in fatigue life. Moreover, the predicted evolved flow stresses are comparable with the progression of subsurface structural changes and be extended to develop numerical models for microstructural alterations.

Steels for bearings

Abstract: A casual metallurgist might be forgiven in believing that there are but a few basic types of steels used in the manufacture of some of the most technologically important engineering components, the rolling bearings. First the famous 1C–1.5Cr steel from which the majority of bearings are made. Its structure is apparently well-understood and the focus is on purity in order to avoid inclusions which initiate fatigue during rolling contact. Then there is the M50 steel and its variants, from which bearings which serve at slightly higher temperatures in aeroengines are manufactured, based on secondary-hardened martensite. The casual metallurgist would be wrong; there is a richness in the subject which inspires deep study. There are phenomena which are little understood, apparently incommensurate observations, some significant developments and other areas where convincing conclusions are difficult to reach. The subject seemed ready for a critical assessment; hence, this review. The structure and properties of bearing steels prior to the point of service are first assessed and described in the context of steelmaking, manufacturing and engineering requirements. This is followed by a thorough critique of the damage mechanisms that operate during service and in accelerated tests.

The hardness of solids

Abstract: This review is concerned with the basic physical meaning of hardness. It is shown that indentation hardness of ductile materials is essentially a measure of their plastic properties. With brittle solids the high hydrostatic pressures around the deformed region are often sufficient to inhibit brittle fracture. Under these conditions both indentation and scratch hardness are essentially a measure of the plastic rather than the brittle properties of the solid. This provides a simple physical basis for the Mohs scratch hardness scale