Theory 13/Tribology & Wear /Wear mechanics/3 min
The Debris Sets the Wear Rate
Two surfaces are blamed for wear. The abrasion may be done by what is stuck between them.
Wear rate is controlled by the size and hardness of third-body debris trapped in the contact rather than by the properties of the two sliding surfaces, so identical material pairs can wear at very different rates depending on what particles are present.
01The evidence
- Third-body wear has been shown to change wear-particle generation substantially, with particles trapped in the contact altering the wear rate rather than merely resulting from it.BioMed Research International
- The surface roughness evolution of wear particles and wear components has been measured under lubricated conditions, showing that particles participate in the contact rather than being passive products.Wear
02The tension
Wear is modelled as a property of the material pair: hardness ratio, toughness, and a wear coefficient. That model works in clean laboratory conditions and fails in service, where the contact is full of debris, and the failure is absorbed into a service factor.
03The theory
In a real contact, debris is trapped and acts as an abrasive layer between the surfaces. The size of the particles determines whether they indent, roll or plough, and the hardness relative to the surfaces determines how much damage each pass does.
If the third body controls wear, then the wear rate should correlate with debris size and hardness better than with the properties of the surfaces, and filtering debris should reduce wear even when the surfaces are unchanged.
The prediction is that introducing controlled debris should change the wear rate in a predictable way, and that the transition from mild to severe wear should coincide with a debris size threshold rather than a load threshold.
The practical consequence is that lubrication and filtration are wear-control measures of the first order, and that material selection alone cannot guarantee a wear rate in a dirty environment.
04What this is not
Material-pair models treat wear as a property of the surfaces. This treats it as a property of the debris, which explains rate differences between identical pairs in different environments.
05Predictions
- P1Wear rate should correlate with debris size and hardness better than with surface properties.
- P2Filtering debris should reduce wear at unchanged surfaces and load.
- P3The mild-to-severe transition should coincide with a debris size threshold.
06What would refute it
Wear rate tracking material pair at controlled debris would leave the third body as a byproduct.
07What it would change
It would elevate filtration and lubrication to primary wear control.
08Evidence base
- PMMA third-body wear decuples wear-particle generation in vitrohttps://onlinelibrary.wiley.com/doi/full/10.1155/2015/575849
- Surface roughness evolution of wear particles under lubricated wear — Wearhttps://www.sciencedirect.com/science/article/abs/pii/S0043164804004223