A wear model based on cumulative cyclic plastic straining

Given the specific micro-structure of some steel grades, under tribological conditions the sub-surface material or sub-layers of sliding bodies are prone to cumulative cyclic plastic deformation, leading to the formation and emission of wear debris. In the present paper, a new wear model based on a cyclic ratchetting-type plastic deformation of sub-surface material is proposed. It is considered that the debris is formed and the wear-loss occurs when the accumulated plastic deformation at sub-surface exceeds “a critical strain” or “rupture limit”. The model takes into account the number of cycles or test duration, a characteristic thickness of the sub-layer dependent on tribological conditions and material properties, the shear rupture ductility and an average plastic strain increment. The average plastic strain increment is estimated by numerical simulation of pin-on-disc friction. A very close correlation is found between the predicted and experimental wear heights versus time and/or versus the number of cycles. The wear investigations were carried out on a high-temperature pin-on-disc tribometer under dry friction conditions. Experiments were performed under constant load, speed and disc temperature for different durations. The steel grade involved was a tempered martensitic tool steel X38CrMoV5 (AISI H11). Wear mechanisms were investigated by Scanning Electron Microscopy (SEM) observations in surface and cross-section.