Effect of Thermal Cycling on the Mechanical Properties of a Continuous Fibre Composite Used for Car Clutch Facings

In dry clutch systems, the clutch facing is an annular shaped continuous fibre composite with organic matrix (thermo set resins) which transmits the torque from the engine to the wheels. In use it is submitted to thermo-mechanical cycling. Due to the composite fibre organisation, the strain field under thermo-mechanical loading is not homogenous. Full field data is needed to describe the material behaviour. Digital Image Stereo-Correlation (DISC) was used to determine the coefficient of thermal expansion (CTE) of the material. To determine the effect of temperature and cyclic loading on the mechanical properties, the composite was subjected to different thermal cycles. The material properties are modified with increasing temperature and number of cycles. These results were confirmed by dynamic mechanical analysis which showed thermal ageing of the resin. The local information given by the strain fields revealed a non uniform evolution of the material properties with thermal cycling.