A continuous damage accumulation scenario for elastomeric frictional wear

Abstract: Understanding how materials wear off following frictional sliding is a long-standing question in tribology. In this respect, the particular case of the wear of soft rubbery elastomeric materials stands apart: tire wear produces several million tonnes of abraded materials per year, bearing immense industrial and environmental impact, while the soft nature of elastomers and their inability to accommodate plastic deformation before failure renders their wear mechanisms almost intractable. Here, we harness mechanochemical approaches on model elastomeric materials, to reveal that mild elastomeric wear does not proceed from crack propagation processes, but rather from the continuous accumulation of diffuse damage by chain scission, extending well below the surface of the material. Damage accumulates in a discontinuous manner through micro-slippage events at the rough contacting asperities, with in-depth damage extension set by the characteristic asperity size. Surprisingly, damage grows through a slow logarithmic-like process over successive cycles, which we interpret as the occurrence of stress-activated scission events in a broad strand elastic energy landscape. These observations point to the probabilistic nature of this fatigue-like damage accumulation mechanism and allow us to formulate the wear rate as an integral of the damage cumulated over successive asperity sliding. Finally, by tuning the molecular architecture of our materials, we evidence an antagonistic relation between fracture resistance and wear resilience, set by the sensitivity of the material to stress fluctuations. Revealing the role of previously invisible subsurface damage in elastomeric wear, our approach should stimulate further physical-based approaches allowing for the development of sustainable and wear-resilient materials.