High Temperature Monitoring by means of Electrical Properties of CMC Materials under Tensile Stress

Abstract

Damage to thermal protection systems (TPS) during atmospheric re-entry is a severe safety issue, especially when considering re-usability of space transportation systems. There is a need for structural health monitoring systems and non-destructive inspection methods. However, damages are hard to detect. When ceramic matrix composites, in this case carbon fibre reinforced silicon carbide (C/C-SiC), are used as a TPS, the electrical properties of the present semiconductor material can be used for health monitoring, since the resistivity changes with damage, strain and temperature. In this work the electrical resistivity as a function of the material temperature and tensile stress is analysed. A sensor network is applied for locally and time resolved monitoring of the 300 mm x 120 mm x 3 mm panel shaped samples. Since the material is used for atmospheric re-entry it needs to be characterised for a wide range of temperatures up to 2000 �°C. Therefore, experiments in an inductively heated test bench were conducted. Behaviour of electrical resistance under heat load as well as tensile stress is analysed and discussed and a formula to calculate the specific electric resistance is established.