Contact and friction in systems with fibre reinforced elastomers

The tribological behaviour (contact and friction) of systems that include fibre reinforced elastomers is studied in this thesis. The elastomer composite is considered to behave as a viscoelastic anisotropic continuum material. In the defined tribo-system, the most influential friction mechanism is adhesion. Therefore the size of the contact area during sliding and the shear stresses in the contact area are studied. A contact model that considered the viscoelasticity of the elastomer and the anisotropy caused by the directionality of the fibres has been developed to describe the size of the contact area in the static case. To obtain the size of the contact area during sliding, sliding experiments were performed and from these results a function that relates the static and dynamic contact area was proposed. Due to sliding interaction the surface of the elastomer is modified, this modification of the surface is called a tribo-generated surface layer. This layer has poor mechanichal properties when compared to the bulk of the elastomer and influences the tribological behaviour of tribo-systems with elastomers. The friction is considered to be caused by shearing this layer. The shear stresses occurring in the tribo-generated surface layer during sliding contact are modelled using a shear stress model which considers viscoelastic behaviour of the interfacial layer. The viscoelastic behaviour was modelled by a Maxwell model of two elements. Properties of the surface layer are obtained from indentation and friction measurements. The friction model corresponds closely with friction experiments for the unreinforced and reinforced EPDM at different sliding velocities. In the case of the reinforced EPDM a lower coefficient of friction was found, this is the result of a decrease on the contact area due to the reinforcement.