Fracture Analysis Consultants, Inc. — Department of Defense SBIR Phase II: N06-126

Description

The US Navy is concerned with fretting fatigue as a controlling factor in aircraft component life, such as the dovetail contact of blade/disk assemblies and spline gears in helicopter transmissions. To model fretting fatigue crack nucleation and subsequent fatigue crack growth, the FRANC3D software was modified to include fretting nucleation models. These models, combined with finite element results predict fretting nucleation life and crack nucleation sites. Discrete crack insertion and growth is then simulated to predict total life. FRANC3D has been used to successfully simulate fretting fatigue in: dog-bone specimens, small scale dovetail specimens, a blade/disk assembly, helicopter transmission gear teeth, and a wind turbine shaft/bearing assembly. These simulations highlighted the need for additional fretting experiments, as fretting nucleation models require material dependent parameters. The Army Research Lab will conduct a suite of experiments on bare- and coated-steel dog-bone specimens with titanium fretting pins. This data will verify and validate the fretting nucleation models, and the FRANC3D simulations will provide benchmarks for simulating fretting fatigue in more complex components. Enhancements to the software will allow a straightforward transition from fretting nucleation to fatigue crack growth, thereby providing total life predictions for critical aircraft components.