Thermostructural Design of a Flying Winglet Experimental Structure for the EXPERT Re-entry Test

Abstract

Within the framework of the European Experimental Re-entry Test Bed (EXPERT) Program, aimed at improving the understanding of physical phenomena occurring during the return of space vehicles from space to earth, the design of a flying winged experimental payload has been performed in order to assess the thermomechanical behavior and resistance of ultrahigh temperature ceramics (UHTC) in real flight aerothermal environment. The EXPERT flying winglet article is intended to reproduce such conditions. Particular interest covers the design of the interfaces between the UHTC winglet and the EXPERT capsule thermal protection systems since thermal stresses arise during the re-entry phase. The fixation of the winglet to the capsule is achieved by means of dedicated bolts that must tolerate mechanical loads occurring at the first stages of the flight, that is, lift-off, ascent, and separation stages. The thermostructural design is performed by employing ANSYS/Workbench finite element commercial code; simulations take into account transient thermostructural loading conditions, the elastic-fragile behavior of the ceramic materials, and the temperature dependent elastic-plastic behavior of the capsule thermal protection systems. In the postprocessing phase, UHTC critical areas have been identified by following two different approaches. The first approach is deterministic and consists in applying a maximum stress criterion, the stress at a node is compared with the temperature dependent strength at that node. The second approach, which is commonly employed for elastic-fragile materials, is probabilistic and consists in applying a Weibull-like failure criterion. Thermal and structural analyses simulating the re-entry phase have demonstrated that the maximum stresses and temperatures evaluated do not exceed their corresponding limits. Then, a configuration respecting all the requirements of the design has been identified, and its thermal and mechanical performances are discussed in detail.