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The paper reviews the Cranfield Impact Centre (CIC) experience with dynamic simulation of the collapse behaviour of minibus and coach body structures in rollovers and frontal impacts and the interaction between occupants and seats in a variety of loading scenarios. This work supported development of the: a. ECE (UN-Geneva) and EEC (European Union) safety standards for rollover strength and safety of seats with belts; b. Rollover safety Type Approval method, combining numerical simulation and component tests; c. Safety structures for rollover protection and in passenger seats. Characteristic extracts from various projects demonstrate not only the usefulness and capability of dynamic simulation, but also the difficulties associated with this rapidly developing field of safety technology.

The paper presents the new ‘universal’ coach safety twin seat (patent pending). It carries three-point belts, but also protects occupants sitting behind whether empty or fully loaded and whether the rear occupants are unbelted or lap-belted. The extreme 12 g reverse acceleration pulse was applied with seat spacing of 750 mm and 650 mm. The ECE Regulation 80 injury criteria were met in both Hybrid II and Hybrid III dummies (50 %ile, 5 %ile and 95 %ile), as well as the Hybrid III neck injury levels. The seat passed the 76/115/EEC belt anchorage test. With mass of 36.3 kg, conventional materials and production methods, the technical and commercial concept feasibility of such seats was fully demonstrated.

In order to bring the advanced finite element programs closer to the requirements of the early design stages, a compound beam element with varying joint and hinge moment-rotation curves has been developed and implemented into the public version of program DYNA-3D. The new beam combines the existing Belytschko-Schwer beam element with rotary springs having very non linear moment-rotation curves in the elastic-plastic and deep collapse range. The element behaviour under uniaxial and biaxial bending presented using simple models where various effects can be easily traced.

The paper reviews the main results of the theoretical and experimental analysis of the multiaxial collapse modes in rectangular section tubes used in bus and other vehicle structures. The tubes were tested quasistatically to collapse under the uniaxial bending, biaxial bending, pure torsion, torsion combined with uniaxial bending and torsion combined with biaxial bending. Hinge characteristics under multiaxial loading were simulated by a combination of the uniaxial collapse data. The analytical model compared well with the experiments.

Bus superstructures may soon be subject to new rollover safety requirements. Increased rollover safety must be achieved with minimum weight or cost penalty; hence, optimisation has a significant practical relevance. This paper demonstrates the possibility of predicting the collapse performance of a bus superstructure by a completely theoretical model. The work described also created a basis for the option offered by the new regulations that allows type approval by calculation combined with some component tests. It also shows how a safety structure can be optimised from the weight or cost point of view by means of a special computer program.

In order to satisfy the various international safety standards which currently exist, it is necessary that nearly all new vehicles be subject to a number of destructive tests before being made available to the public on the open market. Development programmes involving a series of such tests are very expensive and there is a growing need that reliable and economical design/analysis methods be made available. This paper attempts to present such a method. Using a relatively simple finite element computer program which has been adapted to the particular needs of the motor industry, the analysis of a new prestige limousine is described. A background to the analytical method is presented, but the emphasis of the paper is on the engineering aspects of using the method. Reference is made to practical design considerations in several instances. The results of calculations predicting the performance of the structure when subject to FMVSS 214 and 216 are presented.

The performance of a vehicle structure in an accident situation can be estimated by determining the correct collapse mechanism and energy absorbing capacity of the deforming components. In most framework-type vehicle structures /buses, special purpose vehicles, passenger compartments in cars etc./ the bending failures of components are clearly dominant, and the energy absorbing material is usually concentrated in the relatively small "hinges" of the collapse mechanism. The paper discusses various modes of the bending collapse that have been observed in practice. The analytical method to estimate the moment-deflection relationship of box beams in bending is reviewed, and the results compared with data obtained by laboratory testing of components. The present results indicate that hinge properties have important effects on the energy absorption. The bending collapse mechanism of box beams is very repeatable in both static and dynamic conditions.