Anisotropy is a typical property of friction materials, which can be influenced by temperature gradients, depending on the geometry and the production process, as well as by the components itself present in the mixture like fibres and its orientation. Although orthotropic descriptions from continuum mechanics, as a special case of anisotropy, give good results in simulations of the average brake pad's behaviour using the Finite Element Method (FEM), they don't allow a "mixture simulation" of the friction material and its corresponding components to predict physical properties like stiffness and strength in the mesoscopic range.
This work is a first approach to describe exemplary in a mesoscopic scale the interaction of different components present in a friction material, in particular the influence of temperature gradients on the reaction of binding materials (like resins) and how, together with the orientation of fibres, the local mechanical properties are generated in the brake pad. The simulation explains simple mesoscopic effects in a mixture, responsible for the creation of internal forces, resulting in the macroscopic properties like material stiffness and strength.
A numerical method based on the Discrete Element Method (DEM) and Molecular Dynamics (MD) is used to create a Mesoscopic Particle System (MPS), in which a penalty force definition describes the interaction between different particles, a potential definition is used for the particles correspondent to the fibres material and a newly temperature dependent cross-linking radius is introduced to simulate the corresponding material reaction and its binding properties to other particles. The temperature gradient of the selected brake pad section for the investigation is extrapolated from a thermal simulation during the pressing process using FEM.
Wegmann, Enrique*, Stenkamp, Axel - TMD Friction GmbH Ostermeyer, Georg-Peter - Technische Universität Braunschweig