Scratch-induced deformation modes in rubber compounds

Transitions in tribologically induced deformation and wear are well established for metals and polymers, through scratch-based deformation maps, yet a comparable framework for elastomeric materials is still lacking. In particular, the relationship between frictional response and deformation mode transitions in rubber remains insufficiently established. In this study, single-asperity scratch-based testing was employed to systematically investigate the relationship between friction, penetration depth, and deformation behaviour in four elastomer compounds under dry and lubricated conditions. Four distinct deformation modes, namely elastic deformation, ploughing, tearing, and cutting were identified and linked, not only to visual damage but also to characteristic frictional response signatures under both constant and increasing penetration depth. Scratch-based tests were conducted in dry and lubricated conditions. Elastic deformation is characterised by low friction and a small deviation in the amplitude of the frictional force along a single scratch. For ploughing, higher friction is measured along a slightly higher deviation of the amplitude of the frictional force. The tearing mode shows high friction, though, the amplitude of the frictional force over the scratch length still remains low. The cutting mode exhibits both a high frictional force and large amplitude variations in this signal, primarily due to the stick slip phenomena, as commonly known for rubber materials. Lubricating the samples decreased the coefficient of friction and increased the penetration depth required to generate a transition in deformation mode of the material. A deformation mode map was developed to illustrate the different modes based on the relation between the penetration depth and the interfacial shear strength. This deformation map contributes to a better understanding of rubber deformation under varying tribological circumstances. By capturing the initial deformation behaviour, the deformation map could provide valuable insight into the mechanisms driving wear evolution.