Integrated Thermal and Mechanical Analysis of Composite Plates and Shells

Kurzfassung

Several todays or tomorrows composite aerospace structures are simultaneously loaded by mechanical and thermal loads. As illustrative examples may serve the load-carrying structure of future reusable launch vehicles under aero-thermodynamical loads, orbital structures subjected to cyclic thermal loading, or even composite wings and fuselage of passenger aircraft, which can reach temperatures of more than 100 °C during stay on the ground. In these cases a thermal analysis providing the temperature field must precede the stress analysis, which has to account for thermal as well as additional mechanical loads. Presently, thermal analyses are mostly carried out by finite difference methods or by 3D finite elements. Some finite element codes provide shell elements for 3D heat transfer. However, they are not applicable to thermally anisotropic laminated composites. The stress analysis is usually performed by use of shell elements based on some kind of lamination theory. Thus, the temperature field has to be transferred from a finite difference or 3D finite element model to a shell finite element model. This process needs a lot of handwork and is very time consuming. The paper presents an integrated analysis process which uses a shell finite element model throughout. It starts with micromechanical investigations for providing homogenized thermo-physical properties. Then, Thermal Lamination Theories are discussed and related finite elements are formulated. The thermal analysis part of the paper concludes with an experimental verification of the numerical results. Furthermore, a stress analysis process is shown which uses the shell geometry model from the thermal analysis and delivers the full state of stress inclusive of all transverse stress components. Accounting for the transverse stresses is very important for correctly predicting the failure of composite structures. This is underlined by comparing common 2D-failure criteria with advanced 3D-criteria. The paper ends with a combined thermal and stress analysis of a composite wing box of the future European Megaliner A3XX.