Relation between Compressibility and Viscoelastic Material Properties of a Brake Pad

Nowadays an important factor for the selection and development of friction materials is the compressibility value defined by the customer. This critical to quality aspect of a brake pad may be influenced both by the production process as well as the chemical pad formulation. Modifications to reach a target compressibility value during a development process of a brake pad come at a cost. While interfering with the production process and/or the pad formulation not only the compressibility value may change; most certainly the whole behavior of the brake pad will be subject to change.

The compressibility value is a measure for pad deformation due to a standardized load collective. The total pad deformation after a compressibility test is a combination of elastic and plastic deformation as well as a creep portion depending on the viscosity of the material. Thus the compressibility value is always a combined physical effect and it does not separate the different mechanical behaviors of the material.

The paper will suggest an optimized approach in measuring the physical components elasticity, viscoelasticity and plasticity of a friction material. This is supported by modeling the behavior of the friction material based on existing theories. The model then will be adapted to and verified by the results of the optimized measurement technology. The model introduced will be used for the simulation of a standard compressibility load cycle. The results of this simulation will be discussed in comparison to real brake pad compressibility measurements.