Modeling to Quantify Improved Durability of Superfinish Gear Processing

The objective of the proposed project is to develop physics based models which include the effects of surface condition, i.e. surface roughness in combination with residual stress state, on fatigue life. The final objective is the development of an engineering fatigue model to assess the benefits of various surface treatments on gear fatigue life so that performance of rotorcraft powertrains can be improved. Many efforts have sought to improve helicopter gear performance, but a main obstacle has been the lack of a software tool to accurately predict fatigue life to shorten the necessary endurance testing of transmissions and other critical powertrain assemblies. A quantitative materials engineering approach is proposed, using an internal state variable mechanical model that will capture the complicated mechanical behavior associated with residual stress formation, as well as the cumulative strain hardening/softening associated with cyclic fatigue loading. A set of related micro- and macro- models will be developed to model surface and microstructural interactions that result in cyclic softening or hardening. In addition, the use of simplified coupon geometries to represent complex part geometries and service stress states will be achieved through judicious application of finite element based models and statistical methods such as the response surface.