Experimental and Computational Investigation of Fretting Wear
Fretting occurs wherever short amplitude reciprocating sliding between contacting surfaces is sustained for a large number of cycles. It results in two forms of damage: surface wear and deterioration of fatigue life. The extent of wear and surface damage is much greater than suggested by the magnitude of sliding distance. Reciprocating movement as small as 0.1 microns in amplitude can cause severe failure if the motion is maintained for a million cycles.
Since microscopic displacements and contact mechanics influence the fretting wear behavior more than the gross sliding, an experimental and computational investigation of contact behavior is necessary to understand and prevent fretting wear.
Fig. 1. A schematic representation of contact stresses during fretting wear
The purpose of this research is to experimentally investigate the fretting wear resistance of different materials and to computationally simulate the fretting wear process. To achieve this, a fretting wear test rig was built to study different contact geometries under varying loads and amplitudes. The FWTR also enables fretting wear tests at elevated temperatures and in the presence of lubricants. The wear scars are studied and the wear volume is recorded using a Surface Profilometer. Furthermore, wear coefficients are evaluated and the fretting wear maps are generated to quantify and compare fretting wear resistance of different materials and coatings. Contact variables like Energy ratio, Coefficient of friction, friction force, Energy dissipated are also recorded.
Fig. 2. Fretting Wear profile
Fig 3. Fretting Loops obtained from FWTR
Fig 4. A typical Fretting wear map
In parallel, a computational fretting wear model is being developed which could be integrated with the commercial FEA package, Abaqus. This model would incorporate the experimentally observed fretting behavior under different loads, amplitudes, temperatures and lubrication condition. Contact parameters like the Hertzian contact pressure and the contact shear stress are being accurately modeled in Abaqus to obtain theoretical values of the parameters and definite slip & stick zones. This data would be further processed using a user subroutine which would enable adaptive meshing of wear surfaces.