Tania Vodenitcharova

STRUCTURAL RESPONSE OF ALUMINIUM FOAM HYBRID SANDWICH PANELS UNDER THREE-POINT BENDING LOADING

The present study focuses on the structural response of sandwich panels consisting of a commercial closed-cell foam core and thin aluminium sheet skins under static three-point bending loading. Panels of different thicknesses and span lengths were tested, and the influence of the foam density, core thickness and skin type on the response was revealed. The failure modes in bending were greatly dependent on the span length but independent on the foam thickness. For short spans, the deformed shape at failure was asymmetric, as opposed to a symmetric mode for long spans. The density and thickness of the foam core, the presence of reinforcing face sheets and the beam span determined the failure load and bending strength of the sandwich panels.

Resistance of Thin Al Foam Panels to Deep Indentation

In recent years there has been a considerable amount of research into the deformation behaviour of metallic foams. The majority of this research has only addressed size-independent bulk material properties, obtained through uniaxial compression and indentation tests of thick blocks. There is little information in the literature on the indentation response of thin panels, which has motivated the current study. Thin panels of ALPORAS closed-cell foam of ~ 0.25 g/cm3 density were tested in uniaxial compression, and were indented with long flat-plate punches and long cylindrical punches. Cross-sectioning of the samples following interrupted testing revealed the plastic strain evolution process. The deformation was attributed to the progressive crushing of the cell bands, and the combined action of shearing and tearing resistance. Based on energy formalism, a model was developed to estimate the crushing force. By fitting the experimental loaddisplacement curves, the foam ligament tearing energy was deduced for all types of indentation. The absorbed energy was also calculated for the uniaxial compression and indentation experiments.

Optimized bio-inspired stiffening design for an engine nacelle

Structural efficiency is a common engineering goal in which an ideal solution provides a structure with optimized performance at minimized weight, with consideration of material mechanical properties, structural geometry, and manufacturability. This study aims to address this goal in developing high performance lightweight, stiff mechanical components by creating an optimized design from a biologically-inspired template. The approach is implemented on the optimization of rib stiffeners along an aircraft engine nacelle. The helical and angled arrangements of cellulose fibres in plants were chosen as the bio-inspired template. Optimization of total displacement and weight was carried out using a genetic algorithm (GA) coupled with finite element analysis. Iterations showed a gradual convergence in normalized fitness. Displacement was given higher emphasis in optimization, thus the GA optimization tended towards individual designs with weights near the mass constraint. Dominant features of the resulting designs were helical ribs with rectangular cross-sections having large height-to-width ratio. Displacement reduction was at 73% as compared to an unreinforced nacelle, and is attributed to the geometric features and layout of the stiffeners, while mass is maintained within the constraint.