No abstract

This paper presents a theoretical model for anisotropic wave attenuation in composites. The model has been implemented in a software called FIBREWAVE in order to predict dispersion and attenuation of A0 Lamb wave modes. The required input data are the complex stiffness matrix coefficients of the unidirectional plies of the composites, which have been measured by an immersion technique. Good agreement has been observed between predicted and experimental group velocities and wave attenuations.

This study assesses the bird strike resistance of the satellite communication (SatCom) radome of a medium altitude, long endurance (MALE) remotely piloted aircraft system (RPAS), which is designed as a lightweight sandwich structure with thin quartz fibre composite skins and a cellular honeycomb core. In order to perform accurate, predictive numerical bird strike simulations, the building block approach was applied, involving extensive experimental characterisation and model validation of the materials and structures from simple coupon level up to full-scale radome level. Coupon tests of the quartz fibre composite skin material under high-rate dynamic loading revealed significant strain rate effects, which needed to be taken into account in the simulation model in order to predict the structural response under high-velocity bird strike loading. In summary, this work presents a systematic and detailed approach for obtaining validated modelling methods for high-velocity impact analyses, which could be used efficiently for various design and parameter studies during the development of the SatCom radome.

KurzfassungIm Rahmen dieser Arbeit werden numerische und experimentelle Untersuchungen zur Wellenausbreitung infolge eines Impacts durchgeführt mit dem Ziel der zerstörungsfreien Kennwertermittlung an FKV und der Untersuchung des Einflusses der Wellenausbreitung auf das sukzessive Bruchgeschehen an Faserverbundwerkstoffen nach einem Impact. Darüber hinaus ist das Verständnis der Wellenausbreitung Grundvoraussetzung zur Entwicklung eines Systems zur Detektierung und Lokalisierung der Impactstelle und Abschätzung der Impactenergie und des Stoßkraftverlaufs. Dazu werden mit Hilfe spannungsoptischer Oberflächenschichtverfahren und der holografischen Interferometrie experimentell die Dehnungszustände nach einem Impact quasi-kontinuierlich bis zum Abklingen der hervorgerufenen Dehnungswellen erfasst und ausgewertet. Begleitend zu den experimentellen Arbeiten wird mittels der Finite-Elemente-Methode die Wellenausbreitung simuliert.

An approach is presented to determine the design that minimizes the weight in consideration of the postbuckling behavior of stiffened composite panels. Since, due to computational expense, for optimization purposes a nonlinear finite element approach is not appropriate, a semianalytical approach is implemented in the EADS MAS software LAGRANGE. A gradient-based optimization scheme is employed to determine the ply thicknesses and fiber orientation of the composite skins and the cross-sectional areas of the stiffeners. Strength and stability constraints are used. Based on two examples of different complexity, weight savings are shown to be due to the fact, that skin buckling is allowed above a certain load level.