The strong demand for light-weight structures, which is typical for space transportation systems, leads to a close-to-the-limit design of all involved components – including the rocket engines. The combined thermally and mechanically induced Low Cycle Fatigue and creep failure of hot gas walls is one of the strongest limiting factors of the life time of key rocket engine components like combustion chambers and expansion nozzles. The development and flight qualification of such components includes on top of many other actions CFD, structural and life time analyses of the key components and full scale tests of the whole rocket engine. Thermo-Mechanical Fatigue (TMF)-tests can provide essential validation data for these numerical analyses and reduce the need for full scale tests. Therefore, TMF-tests have the potential of both, avoiding failure due to non-validated design analyses as well as saving full scale testing cost.
During a TMF test, only a small section of the hot gas wall of the real engine (the so called TMF panel) is tested. For this TMF panel, realistic cooling conditions like in the full scale rocket engine are chosen.
In Europe, the concept of TMF-panel testing has been first very successfully applied to rocket thrust chamber structures in the frame of the Ariane 5 Flight Recovery Programme in 2003 and 2004. During this programme, TMF tests were performed by EADS Astrium Space Transportation in cooperation with Volvo Aero Corporation, Snecma Safran and Fraunhofer Institute Dresden to demonstrate the life margin of dump-cooled nozzle structures under relevant thermo-mechanical loading conditions.
These encouraging results have motivated the partners DLR Lampoldshausen and EADS Astrium to jointly investigate again the TMF test concept with special focus on meeting relevant requirements for future liquid propulsion needs.
The key component of a TMF test facility is a heating device for the hot gas side of the tested wall component. For the TMF test facility at DLR Lampoldshausen, a diode Laser with a wave length of 940 nm was chosen. This Laser was especially designed by the diode laser producer DILAS in order to obtain an optical output of 11 kW. In combination with a built in modular optics system, this results in an energy density of up to 8 MW per square meter at the focal plane (18 mm x 50 mm). The presentation at the IAA 2008 will show details of the TMF test facility such as the Laser, the TMF panel housing, the fluid system, the MCC system as well as numerical analyses for an experimental TMF panel.