A.L. Mohd Tobi and colleagues at the University of Nottingham published an article describing how to model fretting wear of materials protected by a diamond-like-carbon coating.  They used Abaqus to perform their analysis as well as experimental tests for validation.Diamond-Like-Carbon coatings or DLC coatings are made from carbon.  They are referred to as diamond-like because of their extreme hardness.  They are frequently reinforced with a metal or metal carbide such as tungsten or titanium; in this case the coating was reinforced with tungsten.  DLC coatings frequently fail due to cracking, delamination, spallation, and coating buckling.  They experience abrasive and adhesive wear, but they generally experience failure at the coating-substrate interface before they have completely worn through.There are aspects to this wear modeling approach which will be of interest to anyone trying to perform similar analyses using Abaqus:

• The Archard wear law was used in this study
• The “umeshmotion” subroutine was used to implement wear
• Adaptive meshing was used but only for the coating.  The authors did not want to change the coating-substrate interface.
• The cylinder was the master surface while the flat was the slave surface.
• The finite sliding contact pair algorithm was selected.
• Coulomb friction was implemented using Lagrange multipliers.

Using the model the authors developed an equation for estimating the wear life of a coating and came up with some general guidelines for coatings:  

• A coating is less likely to fracture (tensile stress) or buckle (compressive stress) as the wear scar becomes deeper because the tangential stresses in it decrease.  However, the coating is more likely to delaminate (shear stress at the coating-substrate interface).
• In general thicker  coatings are more resistant to all modes of failure (fracture, buckling, and delamination).
• A higher coefficient of friction increases the probability of all failure modes occuring.
• Assuming a catastrophic failure of the coating does not occur, W-DLC coatings should last between 0.4 and 2 million cycles under unlubricated conditions.

This paper was published by the research group at Nottingham University which is one of the top groups in finite element modeling of fretting wear and fretting fatigue.

• Mohd Tobi, A.L., Ding, J., Pearson, S., Leen, S.B., Shipway, P.H., 2010, “The Effect of Gross Sliding Fretting Wear on Stress Distributions in Thin W-DLC Coating Systems,” Tribology International, Vol. 43, pp. 1917-1932.