Short Fibre Reinforced CMC Materials for High Performance Brakes

Carbon fibre reinforced Ceramic Matrix Composites (CMC) on the basis of woven fabrics are well known from the development of highly complex and thin walled structures for heat shields of reusable spacecrafts. Since 1988, DLR has developed so called C/C-SiC materials via a three step manufacturing route based on the infiltration of liquid silicon into porous carbon/carbon. Especially for automotive brake disks, the costs of the carbon fabrics and of the common processing techniques for the CFRP preform, like resin transfer moulding or autoclave technique, are too high for a serial production. The most promising way to reduce the costs for the brake disks and to simplify the CFRP manufacture is using a short fibre reinforcement and applying hot pressing techniques. In different tribological test campaigns the performance and the excellent wear resistance of brake disks with short fibre reinforcement were proven. Due to their high thermal stability and their low weight, a great leap in brake technology could be achieved, combining non-fading characteristics with better driving dynamics. This paper describes the manufacture of different short fibre reinforced C/C-SiC materials as well as patented processing techniques, especially for ventilated brake disks. Also, principal material properties and some specific problems in measuring mechanical strength values are reported.