Crash elements design analysis

The methods discussed earlier are applied to the seat-occupant-restraint system of an aircraft. A description of a computer-aided analysis environment, including a multibody model of the occupant and a nonlinear finite element model of the seat, is provided, which can be used to re-construct variety of crash scenarios. These detailed models are useful in studies of the potential human injuries in a crash environment, injuries to the head, the upper spinal column, and the lumbar area, and also structural behavior of the seat. The problem of reducing head injuries to an occupant in case of a head contact with the surroundings (bulkhead, interior walls, or instrument panels), is then considered. The head impact scenario is re-constructed using a nonlinear visco-elastic type contact force model. A measure of the optimal values for the bulkhead compliance and displacement requirements is obtained in order to keep the possibility of a head injury as little as possible. This information could in turn be used in the selection of suitable materials for the bulkhead, instrument panels, or interior walls of an aircraft. The developed analysis tool also allows aircraft designers/engineers to simulate a variety of crash events in order to obtain information on mechanisms of crash protection, designs of seats and safety features, and biodynamic responses of the occupants as related to possible injuries. 

Use of impact sled tests is the most common technique for determining the postcrash dynamic behavior of an aircraft occupant. The impact sled and target tracking facilities available at National Institute for Aviation Research (NIAR) were used to conduct a study on occupant responses in a crash environment. Parallel analysis capabilities, including a multibody dynamic model of the occupant and a finite element model of seat structures, have been developed. The analysis has been used to reasonably predict the Head Injury Criteria (HIC) as compart with the experimental impact sled tests for an occupant head impacting a panel. A nonlinear viscoelastic contact force model was shown to better predict the experimental data on the contact forces than the Hertzian models. Suitable values of the coefficients in the contact force model were obtained and the correlations between the coefficients, HIC, and maximum deformation of the front panel were determined. A non-sled test method of pendulum-type has been designed to determine the head injuries as well as the performance of each particular impact absorber. 

Many methods are available to the designers. The most common are [14, 15] based on the finite element, finite difference or dynamic relaxation lumped parameter and the limit state methods. Appendices A and B give the step-by-step approach of the finite element analysis, Chapter 3 and limited state method used for these vessels is given in this chapter. In some service and fault conditions it is required to consider the influence of external hazards and environmental conditions. Major external hazards are due to seismic disturbances, wind/local generated missiles and aircraft crashes. These are fully dealt with by a number of researchers or designers [231]. 

In general, full 3-D finite element analysis of the fluid domain (impulse, in the case of wind or explosions) or full impact analysis (impact, in the case of aircraft crash or tornado missiles) are not used in the design process for the derivation of a suitable load function. Very detailed research programmes have been carried out in the engineering community and in some cases simplified engineering approaches are now available for a reliable design process, on the basis of the interpretation of test data or data from numerical analysis. 

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