Modelling of Launcher’s Combustion Chamber (Material & Computation)
- Paper number
IAC-07-E2.2.08
- Author
Mr. Wissam Bouajila, LISMMA – SUPMECA, France
- Year
2007
- Abstract
The increasing request of the cryogenic engines reliability and performances associated to the continuous need to reduce the exploitation costs and production costs lead the space industry to develop Reusable Launch Vehicles (RVL). Fifty cycles or more is the typically wanted CC life used for such vehicles (i.e. quite higher than the current combustion chamber life). The combustion chamber, which is a critical launcher component, is designed to resist to the combustion effects between hydrogen and oxygen at very high temperature. The very high temperature induced by the combustion reactions, associated to the combustion chamber regenerative cooling, lead to a great heat gradient through the whole combustion chamber wall thinness. The heat gradient induces very important thermal strains. Consequently, inelastic strains appear generating material damages. Those damages can have three different origins: low cycle fatigue (cyclic load), creep (during the work at constant high temperature) and environment effects such blanching and hydrogen embrittlement. This context defines the thesis framework. The main work objective is the combustion chamber life increase for the RLV development. Reaching this objective leads to, (I) search for a material which presents the wanted physical and mechanical properties, (II) understand the physical phenomena which occur during the combustion and (III) model the material behaviour and material damage. The severe working conditions define the material properties such, very low hydrogen embrittlement, very high thermal conductivity, very high purity, very high LCF, high creep strength and low development and machining costs. Current research works are focused on a new promising copper alloy based on Cu-4, Cr-2 and Nb. Indeed, this material presents excellent mechanical properties at high temperature, high creep strength and high LCF combined with a very good conductivity and thermal stability. So this material may be used instead of the currently used copper alloy based on Cu-3, Ag-0.5 and Zr. In modelling, it is important to define well the nature of the applied load on the material and to determine the physics of the three damage mechanisms, separately or jointly, under conditions same to the CC work ones, with thinner wall in other words. The material mechanical behaviour is modelled using an elasto-viscoplastic model like “Chaboche” (or more complex), which is particularly adapted to the cyclic behaviour description. The test samples have been machining by VPS (Vacuum Plasma Spraying). The material viscoelastic properties are provided by a non-destructive, precise and not expensive dynamic method: the Eigen frequencies method. Moreover, this test, using the bandwidth of the Eigen modes, allows determining the material damping with the variable (tan Φ). This result provides information about the material quality. The material inelastic properties are obtained using an experimental method developed in SUPMECA: the disc test. This test uses disc sample with constant thinness equal to the combustion chamber wall thinness. It allows being close to the real material working conditions. The material hydrogen embrittlement can be taken into account with the nature of the using gas (inert He or embrettling H2). Moreover, this test offers a wide strain rates range (from 10-6 s-1 to 1 s-1) and a wide temperatures range (from RT to 1100K). The creep damage and low fatigue cycles damage are provided using conventional tests. A numerical method of the experimental data processing has been developed and validated within the thesis framework. The material parameters values used in the behaviour law are optimized using the nonlinear least squares minimization method. The numerical method is supplemented by finite elements model of the disc test. This approach allows using a comparative method to determine the relevance of the obtained coefficients values.
- Abstract document
- Manuscript document
IAC-07-E2.2.08.pdf (🔒 authorized access only).
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