AA AT5:1998

This document has been developed to provide the major relevant information about the behavior of aluminum in vehicle crash situations and how this behavior, combined with knowledge, experience and appropriate design, can be used to develop crashworthy structures for aluminum intensive vehicles. The fact that this is indeed possible has been convincingly demonstrated by the many crashworthy aluminum structured vehicle designs that have been developed in recent years, such as the aluminum intensive version of the Ford Taurus which meets all the relevant FMVSS crash safety requirements, the GM EV1, which also has an aluminum structure, and the Audi A8 aluminum space frame vehicle which meets all European and North American safety requirements for crashworthiness (1,2,3).
Aluminum, just like steel, absorbs energy in a vehicle crash by folding and bending deformation of the metal structure. Both steel and aluminum, when used for vehicle structures manage crash energy absorption and, hence, provide crashworthy structures for the vehicle occupants in exactly the same way. Therefore, there should be no mystery or indeed any surprise that aluminum can be used just as effectively as steel to provide crashworthy vehicle structures.
There are however, important physical and metallurgical differences between steel and aluminum; it is, for instance, much less dense than steel but it is typically used at about 1.5 times the steel thickness in equivalent structural components, e.g. in front rails. These provide the primary energy absorption in a frontal collision and the increased thickness for the aluminum results in more deformation and, hence, enhancement of its energy absorption. Conversely, automotive structural steels will generally deform more before fracturing than the corresponding aluminum materials and therefore the design of components and whole structures must take all such properties and characteristics into account to ensure that the vehicle structures have the requisite crashworthiness.
Crashworthiness is one of the most important aspects in vehicle design but there are many other aspects to be considered such as weight for the projected size of vehicle, structural stiffness which is key for good road holding and handling, occupant space and manufacturing cost and compromises have to be made to evolve viable vehicle designs. However, crashworthiness can not be compromised but adding weight is not the answer; a well designed military tank might be a safe vehicle for its occupants but likely would result in fatalities in any passenger vehicle in collision with the tank. And the tank would not meet any of the purchaser's expectation for speed, comfort and road holding. Thus the challenge for the designer is to develop vehicles which meet the customer's expectations for performance, road holding and space while, at the same time, having a crashworthy structure and one that is viable to manufacture and sell.
The purpose of this document therefore is to bring together in one place the relevant information on the choice of materials and the design and manufacturing of crashworthy aluminum vehicle structures for automotive designers and engineers in the auto companies and the parts and material supplier industries. The document covers the relevant government regulations, material properties, overall design approaches including available modeling techniques, design guidelines for individual structural members, experimental results from component testing under simulated crash conditions and, finally, crash test results from actual aluminum structured vehicles.
The data presented clearly demonstrates that appropriately designed aluminum vehicle structures are fully crashworthy, meeting or exceeding all the government safety requirements as well as meeting or exceeding the performance of equivalent steel structured vehicles.