Parameter Identification of a Copper-Base Alloy Using Digital Image Correlation and Application to a Liquid Rocket Engine Combustion Chamber Wall

Abstract

In recent years the cost aspect of the development, production and operation of liquid rocket engines became more and more important with respect to the competitiveness on the commercial satellite launch market. Therefore, one aspect of the development is focused on novel inexpensive hot gas wall materials for inner liners of rocket combustion chambers that can withstand the extreme operational conditions. The copper-base alloy consisting of copper, chromium and zirconium is such an inexpensive material that has the potential to be used as an inner liner material for future rocket combustion chambers. To predict the damage behavior caused by tensile rupture, a viscoplastic model coupled with ductile isotropic damage, crack-closure effect and thermal ageing is defined and implemented as a user-material routine in the commercial finite element package ANSYS. Uniaxial displacement-controlled tensile tests at temperatures up to 1000 K are performed. In contrary to traditional extensometer based measurements, an optical stereo camera system based on digital image correlation is used to determine the local strain distribution in the necking area of an hourglass-shaped test sample. The material model's parameters are then least squares fitted and applied to a two-dimensional thermomechanical finite element analysis of a half-channel model representing a rocket engine combustion chamber wall with a simplified geometry and a representative heat flux, pressure level and maximum temperature. This paper shows that digital image correlation can be used to capture the local strain distribution in the necking area of highly ductile copper materials at elevated temperatures. Indeed, the numerical analysis with tensile test based material parameters results in an estimated life time of 13 cycles but thinning and bulging of the hot gas wall could not be reproduced.