Arc-Jet Testing of Ultra-High-Temperature-Ceramics

The article deals with arc-jet experiments on different Ultra High Temperature Ceramics models in high enthalpy hypersonic non equilibrium flow. Typical geometries for nose tip or wing leading edges of interest for hypersonic vehicles, as rounded wedge, hemisphere and cone are considered. Temperature measurements have been performed using pyrometers, an IR thermocamera and thermocouples. Spectral emissivity has been evaluated by suitable experimental techniques. The details of the experimental set-up, the tests procedure and the measurements are discussed in the text. The UHTC materials have been tested for several minutes to temperatures up to 2050 K showing a good resistance in extreme conditions. Fundamental differences between the various model shapes have been analysed and discussed. Numerical-experimental correlations have been carried out by a CFD code, resulting in good agreement with proper modelling. The numerical rebuilding also allowed to evaluate the catalytic efficiency and the emissivity of the materials at different temperature

Plasma wind tunnel characterization of plasma-sprayed UHTC coatings

Ceramic coatings are widely used as thermal barrier or as oxidation barrier, in many industrial applications. The use of UHTC is mandatory when dealing with hypersonic vehicles characterized by high thermal flux in oxidizing environment. Since 2000, in the framework of the national aerospace research program (PRORA-SHS) and within various other National and European programs, CIRA has studied, developed, and tested monolithic UHTCs and UHTC coatings on different high temperature structural materials. Small winglets and nose made in UHTC (EXPERT and SHARK project) or UHTC coated (SCRAMSPACE project) were designed, manufactured and installed on rockets or re-entry vehicles for in-flight qualification. Unfortunately, only the SHARK nose tip experienced the flighty environment. Please click Additional Files below to see the full abstract

The AM3aC2A Project: Multiscale approach for modeling CMC and UHTCMC materials for reusable components for aerospace

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Arc-Jet Testing on HfB2-TaSi2 Models: Effect of the Geometry on the Aerothermal Behaviour

Arc-jet experiments in high enthalpy hypersonic (Mach 3) non equilibrium flow were carried out on a HfB2 composite with addition of 15 vol% TaSi2, at temperatures exceeding 2000 K. The aerothermal behaviour was tested considering models having two different geometries, i.e. hemispheric and cone-shaped. The surface temperature and emissivity of the material were evaluated during the tests. Numerical computations of the nozzle flow were carried out in order to identify the flow conditions around the model and to analyze the details of thermal heating. The chemical- physical modifications were analysed after exposures. The surface emissivity changed from 0.85 to 0.5 due to surface oxidation. The maximum temperatures reached on the tip were strongly dependent on the sample geometry, being around 2300 K for the hemisphere and 2800 K for the cone. Post test SEM analyses confirmed an excellent stability for this HfB2-based materia

Plasma wind tunnel testing of UHTC coated components for hypersonic applications

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ON THE DAMAGE TOLERANCE OF C/C-SIC COMPOSITE HOT STRUCTURES

Thanks to their excellent structural performance at high temperature, the Ceramic‐Matrix Composites (CMCs) are good candidates for light‐weight structures in high temperature applications, such as applications to re-entry vehicles. Beyond the well-known high temperature resistance, the CMCs do also show good damage tolerance properties, making them suitable for applications to large primary structures. Unfortunately, the production at the industrial level is currently at an embryonic stage due to the criticalities in the involved manufacturing processes which do not allow to produce defects free components. During the design phase, the presence of these manufacturing related defects are taken into account by introducing knock-down factors reducing the mechanical properties. However, this approach can be highly conservative and can strongly limit the intrinsic advantages of using such materials. Moreover, even if suitable non-destructive techniques (such as tomography) can be adopted to identify the manufacturing defects, still uncertainties exist about these defects evolution and, above all, about their influence on the structural performance (in term of stiffness and strength) of real components. The adoption of suitable material and fracture mechanics numerical models, could help to correctly predict the stiffness and strength characteristics of CMCs at coupon and subcomponent level. Which such advanced numerical models the manufacturing defects and their influence on the structural performance could be taken into account leading to a strong reduction of the currently adopted knockdown factors. The present work aims to investigate the damage tolerance of a C/C-SiC hot structure acting as aerodynamic control surface of a reusable re-entry vehicle. These vehicles are exposed to severe environmental conditions when re-entering Earth atmosphere. Indeed, the highest loaded areas such as nose, leading edges and control surfaces can experience temperatures up to 1650°C. Since the structural integrity of a re-entry vehicle needs to be guaranteed during all the mission phases and for multiple missions, a damage tolerant reliable design is required. Starting from the validation at coupon level of the material and fracture mechanics numerical models, by means of experimental data available in literature, a full parametric Finite Element model has been developed. The proposed parametric model is able to consider any delamination in any planar and thickness location all along the body flap domain. In order to reduce the computational costs, the entire body flap was modelled by means of layered shell elements, while layered solid elements have been used in the delaminated area. Hence, to connect the global coarse model and the local refined model, a global-local approach has been implemented. Finally, a sensitivity analysis has been performed finalised to assess the influence of location (in plane and trough the thickness) and dimension (radius) of a circular delamination on the damage tolerance of the investigated structure