Incoprea Theory
Volume VI · 2026

Theory 14/Tribology & Wear /Contact mechanics/3 min

Wear Is a Scale Effect

A wear test uses a small specimen. The machine uses a large one. The ranking may not survive the change.

The claim

Abrasive wear rates depend on the ratio of particle size to contact size rather than on absolute particle size, so the same abrasive produces different wear in a small and a large contact, and laboratory tests on small specimens systematically mis-rank materials.

01The evidence

  • Wear mechanisms and scale effects in two-body abrasion have been examined directly, with the wear rate changing as the scale of the contact changes relative to the abrasive.Wear

02The tension

Wear testing is standardised on small specimens, and the resulting coefficients are used to predict component life. The prediction is then adjusted by experience factors, which is a way of hiding a scale dependence rather than modelling it.

03The theory

An abrasive particle damages a surface if it can indent and plough. Whether it does depends on how many particles are in contact and how the load is distributed, which changes with the size of the contact relative to the particle.

If the ratio matters, then the same abrasive will produce different wear in geometrically similar contacts of different size, and material rankings can invert. That makes scale a first-class variable rather than a correction.

The prediction is that wear rate should collapse onto a single curve when plotted against the size ratio, and that rankings which invert between scales should do so in the order predicted by the curve.

The practical consequence is that laboratory wear tests should be designed at the service scale ratio, or the results should be rescaled before use.

04What this is not

Scale-free wear coefficients

Standard models treat the wear coefficient as a material constant. This treats it as a function of the size ratio, which predicts ranking inversions between test and service.

05Predictions

  • P1Wear rate should collapse onto a curve when plotted against the size ratio.
  • P2Material rankings should invert between scales in a predicted order.
  • P3Tests matched on size ratio should predict service wear better than standard tests.

06What would refute it

Wear coefficients constant across size ratios would restore the scale-free model.

07What it would change

It would change wear-test standards and how material selection is validated.

08Evidence base

  1. Wear mechanisms and scale effects in two-body abrasion — Wearhttps://www.sciencedirect.com/science/article/abs/pii/S0043164808002809