Boehmite nanoparticles show great potential in improving mechanical properties of fiber reinforced polymers. In order to predict the properties of nanocomposites, knowledge about the material parameters of the constituent phases, including the boehmite particles, is crucial. In this study, the mechanical behavior of boehmite is investigated using Atomic Force Microscopy (AFM) experiments and Molecular Dynamic Finite Element Method (MDFEM) simulations. Young’s modulus of the perfect crystalline boehmite nanoparticles is derived from numerical AFM simulations. Results of AFM experiments on boehmite nanoparticles deviate significantly. Possible causes are identified by experiments on complementary types of boehmite, that is, geological and hydrothermally synthesized samples, and further simulations of imperfect crystals and combined boehmite/epoxy models. Under certain circumstances, the mechanical behavior of boehmite was found to be dominated by inelastic effects that are discussed in detail in the present work. The studies are substantiated with accompanying X-ray diffraction and Raman experiments.

Static and fatigue analyses are presented for a new blended wing body (BWB) fuselage concept considering laminar flow control (LFC) by boundary layer suction in order to reduce the aerodynamic drag. BWB aircraft design concepts profit from a structurally beneficial distribution of lift and weight and allow a better utilization of interior space over conventional layouts. A structurally efficient design concept for the pressurized BWB cabin is a vaulted layout that is, however, aerodynamically disadvantageous. A suitable remedy is a multi-shell design concept with a separate outer skin. The synergetic combination of such a multi-shell BWB fuselage with a LFC via perforation of the outer skin to attain a drag reduction appears promising. In this work, two relevant structural design aspects are considered. First, a numerical model for a ribbed double-shell design of a fuselage segment is analyzed. Second, fatigue aspects of the perforation in the outer skin are investigated. A design making use of controlled fiber orientation is proposed for the perforated skin. The fatigue behavior is compared to perforation methods with conventional fiber topologies and to configurations without perforations.

Strength of fiber reinforced polymers (FRPs) under compression loads is typically limited by a shear localization failure mode called microbuckling which is highly sensitive to fiber misalignment. In addition to the magnitude of fiber misalignment, the dimensionality of fiber misalignment also plays a prominent role in the prediction of compression strength. Therefore, a comparison between 1D, 2D, and 3D fiber misalignment is carried out in a finite element setting with a homogenized representation of fiber and matrix materials. In real FRP structures, fiber misalignment is spread in a correlated random manner throughout the material volume resulting in a distribution of compression strength. Spectral representation method is used for developing the volumetric representation of fiber misalignment in numerical models, thus preserving the spatial correlations of fiber misalignment. As an input to the spectral representation method, two different functional forms of spectral density of the fiber misalignment are considered. The results of model series based on functional forms of spectral density are also compared against a reference model series based on experimental measurements of the fiber misalignment. Finally, a simple relation is proposed for prediction of compression strength at different percentiles of distribution of failure strengths with regard to scaling of mean square spectral density.