Development of Multi Layer Composite Energy Absorber Blocks for Aircraft Crashworthine

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

Development of a New Composite Energy-Absorber System for Aircraft and Helicopter Sub-Floors

Considerable research interest has been directed towards the use of composite for crashworthiness applications, because they can be designed to provide impact energy absorption capabilities which are superior to those of metals when compared on weight basis. The use of composite parts in structural and semi-structure applications is becoming more widespread throughout the automotives, aircraft and space vehicles. In this study, an innovative lightweight composite energy-absorbing keel beam system has been developed to be retrofitted in aircraft and helicopter in order to improve their crashworthiness performance. The developed system consists of everting stringer and keel beam. The sub floor seat rails were designed as everting stringer to guide and control the failure mechanisms at pre-crush and post crush failure stages of composite keel beam webs and core. Polyurethane foam was employed to fill the core of the beam to eliminate any hypothesis of global buckling. The numerical prediction was obtained using commercially available finite element analysis software. The experimental data are correlated with predictions from finite element model and analytical solution. An acceptable agreement between the experimental and computational results was obtained. For all structures considered classical axial collapse eigen values were computed. The results showed that the crushing behaviour of the developed system is found to be sensitive to the change in keel beam core cross-section. Laminate sequence has a significant influence on the failure mode types, average crush loads and energy absorption capability of composite keel beam. The desired energy absorbing mechanism revealed that the innovated system can be used for aircraft and helicopter and meet the requirements, together with substantial weight saving