Within the European space program, a new upper stage engine (Vinci) for the Ariane 5 launcher is being developed, and the Volvo Aero Corporation (VAC) is contributing with turbines for the fuel turbo pumps.
This study investigates the possibility of designing the Turbine Exhaust Duct (TED) of the Vinciengine in a carbon fibre composite material with adhesively attached titanium flanges. The focus of the project has been on stress analyses of the adhesive joints using Finite Element Methods (FEM), more specifically by using a cohesive zone material (CZM) to model the adhesive layer. Analysing adhesive joints is complex and an important part of the work has been to develop and concretise analysis methods for future use within VAC.
To obtain the specialised material parameters needed for a CZM analysis, FE-models of tensile test specimens were analysed and the results compared to those of equivalent experimental tensile tests. These parameters were then used when analysing the TED geometry with load cases specified to simulate the actual operation conditions of the Vinci engine. Both two-dimensional axisymmetric and fully three-dimensional models were analyzed and, addition-ally, a study was performed to evaluate the effect of cryogenic temperatures on the strength of the joint.
The results show that the applied thermal and structural loading causes local stress concentrations on the adhesive surface, but the stresses are not high enough to cause damage to the joint if a suitable joint design is used. Cryogenic temperatures (-150 °C) caused a significant strength reduction in the tensile specimens, partially through altered adhesive properties, but no such severe effects were seen in the temperature-dependent FE-analyses of the TED.
It should be pointed out however, that some uncertainties about the material parameters exist, since these were obtained in a rather unconventional way. There are also several other important questions, beside the strength of the adhesive joint, that need to be answered before a metal-composite TED can be realized.
Source: Linköping University
Author: Fors, Fredrik