Crashworthiness of composite seats for civil aircraft

A study has been conducted into the design of civil aircraft seats which are forward-facing and use the lap-belt method of restraint. Within these terms of reference, the response of the seat restraint occupant system (SROS) to impact loading has been analysed using physical (dynamic testing) and analytical (computer simulation) modelling techniques. With the increasing use of fibre-reinforced polymer composites in aircraft for weight efficiency, and the consequent appearance of composite seats, attention must be given to the crash performance of these structures. Composite structures are characterised by brittle failure with low impact energy absorption, in comparison to the collapse of metal structures which may exhibit plastic deformation prior to failure. However, using the developing technology of composite sub-structures with high specific energy absorption capability, seat structures have been modified to incorporate composite load-limiting elements. The redesign process involved the compatibility of energy absorber loads with occupant dynamics to minimise injury potential, together with the alleviation of forces in the structural load path to reduce damage and preclude failure of the seat, floor track, and other components. Shortcomings of existing seat designs were assessed, and the dynamics of lap-belted occupants analysed, including secondary head impact with the forward seat structure. The computer' model created was validated against the results of dynamic tests, and then used in a parametric study of occupant dynamics. Conclusions and recommendations include guidlines relating to the future design of both metal and composite seats.