Characterization of carbon-fiber reinforced ultra-high-temperature ceramic matrix composites in arc-jet environment

In the framework of the Horizon 2020 project C3HARME, an experimental campaign has been carried out to characterize a new class of Ultra-High-Temperature Ceramic Matrix Composites for near-zero ablation Aerospace Thermal Protection Systems. Small sized specimens, with ZrB2-based matrix and different carbon fiber architectures, were exposed to a supersonic flow of simulated air generated by an arc-jet wind tunnel, achieving specific total enthalpies up to 20 MJ/kg, in an aero-thermo-chemical environment representative of atmospheric re-entry. Ablation rates were estimated by means of mass and thickness measurements before and after testing, demonstrating a good performance of the analyzed samples, although with some mechanical resistance issues. Surface temperatures were monitored by means of infrared pyrometers and a thermo-camera, and during most of the tests a spontaneous temperature jump was observed, with temperatures that reached values over 2800 K at the steady state. Computational Fluid Dynamics simulations allowed for the rebuilding of the thermo-fluid-dynamic and chemical flow field. Moreover, it was possible to propose a correlation of the temperature jump with an increased catalytic activity and a dramatic reduction of the thermal conductivity of the oxide layers forming on the exposed part of the sample, which anyway had a key role in preserving the unoxidized bulk materials at reasonable temperatures