Recent Thermo-Mechanical Test Series and Innovative Test Procedures

Kurzfassung

Development of thermally protected load-carrying structures of reusable launch vehicles capable to withstand the environment and manoeuvre loads during re-entry needs ground test facilities simulating at least the thermal input and mechanical loads under ambient atmospheric conditions. By this means, the predicted structural behaviour can be confirmed. As a consequence, the DLR-Institute of Structural Mechanics developed the THERMEX test facilities and still improves the test procedures. Within the first part of the presentation the recent challenging test series on European contributions to the X-38 re-entry vehicle will be highlighted. Testing the rudder model surface temperatures up to 1175 °C have been achieved by enforcing infrared lamp radiation. A strongly curved panel, the so-called nose skirt, was heated by accommodation of the heater arrays to the geometry of the test article. Because the nose skirt panel was manufactured from C/SiC very small deformations were measured by high-resolution displacement transducers. Within the preceding FESTIP activities cryogenic tank wall panels with an outer high-temperature insulation were tested simultaneously by an outside heating up to 950 °C and an inside cryogenic cooling by liquid nitrogen. Within the second part new developments for forthcoming tests will be illustrated. Such as testing of structures with complicated shapes under combined hot and cryogenic temperature loading will be considered. The concept of modular assemblage of facility components will allow a variety of applications, e.g. ablation exclusively caused by heat irradiation and even brazing of stringers to a titanium panel by fast infrared heating. Another attempt of improvement will be the feasibility to study kinematics of hot structures such as flaps or rudders. Again, the hot gas test facility, part of the THERMEX assembly, will be used to simulate in addition to the thermal loading aerodynamic pressure and flow as well as acoustic excitation. Measurement and data recording will be refined by new amplifiers allowing also the use of type S thermo-couples. For temperature determination even the application of colour coating and infrared camera recording will be studied. The presentation will close with considerations on realisation of successful test procedures. The most important aspect is pre-testing on dummy structures to optimise thermal input and temperature distribution within the tested structure, to adapt the ranges of measurement, and to determine the control parameters of thermal and mechanical loading, especially in the case of kinematics.