Third body layer—experimental results and a model describing its influence on the traction coefficient

•We found a Third Body Layer (3BL) in Twin Disc tests run under dry conditions.•The properties of said 3BL influence the traction characteristic.•We created a model that accounts for the properties of said 3BL.•This physical model fits the test data better with a 3BL than without 3BL.•This model will lead to a better prediction and understanding of traction.

When adding substances to the wheel–rail contact, they mix with wear particles and form a Third Body Layer (3BL). This layer influences the initial gradient of the traction characteristic.During twin-disc tests presented in this paper, a granular layer consisting of iron and iron oxides with a thickness of up to 50μm was found. In addition, a creepforce model is presented that uses non-linear properties of the 3BL to describe its influence on the traction characteristic. The results of the model were compared to the results of the experiment. A qualitative and quantitative agreement was achieved. This will improve, e.g., the quality of vehicle dynamics simulations, optimizations of control devices for traction and braking, and predictions of wear and damage on wheel and rail.