Aero-thermo-dynamic characterization of large-scale near-zero ablation thermal protection systems in ultra-high-temperature ceramic matrix composites

This paper presents an extensive experimental campaign carried out, in the framework of the Horizon2020 project C³HARME, for the characterization of a new class of Ultra-High-Temperature Ceramic Matrix Composite (UHTCMC) materials for Thermal Protection Systems (TPS) of hypersonic vehicles. Eight different material formulations, all based on an Ultra-High-Temperature Ceramic (UHTC) matrix and carbon fiber reinforcement, but with slightly different compositions, fiber architectures and densification techniques, were tested in the arc-jet wind tunnel L3K at DLR in Cologne (Germany), in different configurations, according to an upscaling logic. First, flat button-shaped samples, with a diameter of 50 mm, were tested in a stagnation point configuration, reproducing conditions typical of atmospheric re-entry. These tests were divided into three phases to match different aerothermodynamic requirements extracted by a reference re-entry mission: 1) tests at nominal heat flux (around 2 MW/m²) and pressure below specification; 2) tests at nominal pressure (around 70 kPa) and heat flux above specification; 3) reusability tests at nominal heat flux. The most promising materials were then upscaled in order to manufacture and test a complete TPS assembly, with a large UHTCMC tile (240x190x4 mm³) and UHTCMC integration elements. The assemblies survived repeated tests without damage nor relevant erosion, thus achieving the objective Technology Readiness Level of 5.