Experimental and Theoretical Work on the Viscoelastic Behavior of Friction Materials 2002-01-2593

In the development phase the suitability of parking brake systems is evaluated in vehicle tests. In these tests a pair of brake pads is first bedded in, then the vehicle is parked on a steep hill with high brake torque at brake disc temperatures of up to 400°C. If the vehicle does not move in the cooling-down phase of the brake disc, the test is considered successful.

This test is appropriate for the evaluation of system properties. However, it does not provide a differentiation of relevant pad characteristics i.e. the temperature-dependent static friction coefficient and the viscoelastic deformation of the friction material. The deformation occurs under extreme pressures and elevated temperatures.

Viscoelastic materials store and dissipate energy in varying degrees during loading and unloading cycles. Constitutive equations for viscoelastic materials include both features of elastic solids and characteristics of viscous fluids. The analysis of viscoelastic behavior of friction material is divided in an experimental and a FEM-simulation part. In the experimental part, different brake pads are tested on a compressibility test stand under constant load and temperature. In connection with these experiments the parameters for constitutive equations have been determined by using the MARQUART-LEVENBERG algorithm. Then, by way of the Finite Element analysis, the effects on the parking brake system are calculated. This method optimises product development processes. The investigation ends evaluating the results.