Development of Multi Layer Composite Energy Absorber Blocks for Aircraft Crashworthine
Taher, Siavash Talebi (2009) Development of Multi Layer Composite Energy Absorber Blocks for Aircraft Crashworthine. PhD thesis, Universiti Putra Malaysia.
In this study, a novel concept of lightweight multi-layered composite energy-absorber blocks and beams have been developed that potentially can be retrofitted in aircraft and helicopter sub-floors in order to improve their crashworthiness performance. This novel structure encompassed of fibreglass fabric wrapped around two or three foam layer cores. This technique eventually prevented from core-to-facing debonding, especially during axial crashing, whereby the debonding tendency is controlled by a hoop stresses in fibreglass layers. Manufactured block can be used alone as an energy-absorber element in structure or a series of blocks integrate in the form of beam. Inline assembly of the fibre-reinforced blocks is covered with fabric glass fibre reinforcement in order to integrate the blocks in a beam configuration. Two types of triggering modifications had been applied to the developed composite structures and they are "bevel trigger" and "groove trigger". In the experimental work the composite blocks and beams were subjected to a quasi-static crushing load. After obtaining the load-displacement curves and determination of crashworthy parameters, a fmite element explicit dynamic analysis code module, incorporeity ANSYS/LS-DYNA implemented to the simulation of the quasi-static crash behaviour and energy absorption characteristics of the developed crashworthy composite structure. The results from the fmite element analysis were validated against the experimental results and good agreement between two approaches was observed. A dynamic crash analysis was also conducted numerically in order to simulate the dynamic crash event and estimating crash behaviour and energy absorption characteristics of the multi-layered structures which are subjected to high velocity impacts. It has been 0 bserved that by increasing the crushing speed load and energy absorption of the structures will inherently magnify. From this research work, it has been demonstrated that, the double-layered and triple-layered block and beam sandwich design concept is a practical means of producing cost-effective sandwich structures, that crush in a stable, progressive manner with high crush force efficiency. Crush force efficiency (CFE) for all specimen types changed between 0.5 to 0.78 and specific absorption energy (SAE) up to 12.78 kJ/ kg for blocks and 23.53 kJ/ kg for beams were recorded. Moreover the obtained quasi-static numerical results of axial compression model of composite blocks and beams are compared with actual experimental data of crash energy absorption, load-displacement history and crush zone characteristics, showing very good agreement with and without use of two types of the collapse trigger mechanisms. On the other hand, dynamic simulations also showed a stable, progressive crushing with high crush force efficiency but less than quasi-static condition. Increasing the crushing speed magnified the resistant load and consequently energy absorption of the structures. For example, in a non-triggered beam with quasistatic SAE equal to 14.37 kJI kg, a magnification factor equal to 5.46 achieved in 20 mis, i.e. SAE of structure was 78.5 kJI kg that is an excellent value in composite sandwich structures. High CFE and SAE of new design is desired feature of composite structures in crashworthiness applications.
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