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

研究目的是确定高性能球轴承中与滚动接触疲劳（RCF）相关的塑性梯度表面（PGS）的单调和循环应力-应变特性。在循环疲劳过程中，表层经历循环微塑性、残余应力积累和接触疲劳损伤，最终导致疲劳裂纹。我们提出了一个协调的实验和建模方法，明智地结合微观和宏观压痕调查与三维弹塑性有限元分析，以确定本构响应的PGS。通过在实际条件下进行受控RCF测试和探测局部塑性区，我们提取循环本构响应作为RCF循环的函数，从而提供了一种定量评估局部材料损伤演化的方法。上述方法适用于任何工程材料，而不管塑性特性的梯度性质如何。 先进的军事和空间推进系统的挑战性要求，导致了混合轴承的发展与塑性梯度渗碳表面。然而，轴承系统的可靠性仍然是一个主要问题，因为当前用于轴承疲劳寿命估计的方法很大程度上基于本质上是经验的概率方法，并且不直接考虑RCF载荷下材料的本构行为。所提出的方法允许强大的寿命估算方法的发展，汇集了许多跨学科的想法，从制造，材料科学，摩擦学，疲劳，固体力学和实验力学。这种方法将有利于梯度层的表面工程以及滚动体轴承中RCF寿命的定量描述的发展，从而提高性能、耐用性和可靠性。该项目还将有助于美国制造业研究人员的教育和培训，并增加代表性不足的群体的参与。

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.