GOALI: Monotonic and Cyclic Response of Plastically Graded Surfaces Subject to Rolling Contact Fatigue

University Of Florida, Gainesville FL

Investigators

Abstract

The research objective is to determine the monotonic and cyclic stress-strain properties of plastically graded surfaces (PGSs) relevant to rolling contact fatigue (RCF) in high-performance ball bearings. During RCF, the surface layer experiences cyclic micro plasticity, buildup of residual stress, and contact fatigue damage, eventually leading to fatigue spallation. We propose a coordinated experimental and modeling approach that judiciously combines micro- and macro-indentation investigations with 3D elastic-plastic finite element analysis to determine the constitutive response of PGSs. By performing controlled RCF testing under realistic conditions and probing the localized plastic zones, we extract the cyclic constitutive response as a function of RCF cycles, thereby providing a means for quantitative evaluation of localized material damage evolution. The above approach is applicable to any engineering material irrespective of the nature of gradients in the plastic properties. The challenging requirements of advanced military and space propulsion systems have led to the development of hybrid bearings with plastically graded case carburized surfaces. However, reliability of bearing systems continues to be a major concern because the current methods used in bearing fatigue life estimation are largely based on probabilistic approaches that are empirical in nature, and do not directly consider the constitutive behavior of materials under RCF loading. The proposed approach allows for development of robust life-estimation methodology by bringing together many cross-disciplinary ideas from manufacturing, materials science, tribology, fatigue, solid mechanics, and experimental mechanics. This approach will facilitate surface engineering of graded layers as well as development of a quantitative description of RCF life in rolling element bearings leading to improved performance, durability and reliability. The project will also contribute to the education and training of the manufacturing research workforce in the US and lead to increased participation by under-represented groups.