Contact with wear

Philipp Farah, Alexander Popp and Michael W. Gee

"Fretting fatigue", a serious damage mechanism which can happen for example in joints of aircraft engines, comes along with wear. Wear appears together with frictional contact and can lead to a surface degeneration due to material removal. This material removal is often specified by Archard's law of wear, a simple but widely used model.

The above described, wear-induced change of surface geometry can change the distribution of contact stresses in the contact zone. It is known from literature that capturing this redistribution of contact stresses is essential for "fatigue models" to predict fatigue life. From this, realistic contact simulations with wear implying a high quality of contact stresses are a fundamental contribution to this.

At our institute, the modeling of wear is embedded in the contact dynamics framework. It is realized with basically two methods: Both contain the evaluation of the amount of wear, whereas the first one simply modifies the gap between the contacting bodies. The second one models the material removal with an arbitrary Lagrangian-Eulerian approach (ALE) in a staggered scheme.

The picture on the right exemplifies the change of contact stress distribution due to wear. The famous Hertz example is loaded with a vertical and a subsequent oscillating horizontal displacement (above). Contact stress distribution truncates for gross sliding (middle) and increases for partial slip in the center (below).