Modelling of compaction processes of friction material mixes

摘要

In the production of brake disc pads, powder mixes containing, metal chips, filling agents, and abrasive materials, as well as phenolic resins are processed and molded to a back plate by way of pressure and temperature. These molded disc pads reach their final strength through additional thermal treatment such that the phenolic resins approach "full cure." This production process leads to anisotropic, viscoelastic, and to a certain extent heterogeneous materials which are - like the brake system - increasingly subject to even greater demands. E.g. apart from tribological characteristics, more and more focus is placed on structure-mechanical properties to improve the braking comfort. Within the scope of this investigation report, a method is presented explaining two basic influencing factors on the structure-mechanical disc pad characteristics: - the composite-dependent compression behavior of the disc pad mix; - the contour-dependent material structure of the finished disc pads. In the first part of the report the compression behavior of friction material mixes is analyzed by means of a specially developed testing tool. Then, it is demonstrated that the measured compressing properties can be superposed by the behavior of individual materials, considering the mixing relations in each case. In the second part of the report, a simulation method based on finite elements analysis is presented, providing a way of calculating the material behavior during compression in both axial (compression) as well as in radial (friction) direction. Apart from classic flow modelling assuming volume consistency, here different finite element types are superposed. The new elements consider the volume modification during the compression process. For the simulation of the production process the compression curves identified by way of the special testing tools as well as the processing data measured with the production tools can be used. The simulation results demonstrate that because of the pressing process irregular compression distribution can occur. The investigation ends with a recapitulation.