Browse Publications Technical Papers 1995-20-0016

A Front Rail Design for Efficient Crush Energy Absorption 1995-20-0016

Although there was a safety awareness from the earliest days of the automobile, systematic approaches to designing for safety became more widespread after 1950 when large numbers of vehicles came into use in both the United States and Europe, and governments in both continents undertook a widespread highway development. Industry response to safety objectives and also to government regulation has produced a large number of safety enhancing engineering developments, including radial tires, disc brakes, anti-lock brakes, improved vehicle lighting systems, better highway sign support poles, padded instrument panels, better windshield retention systems, collapsible hood structures, accident sensitive fuel pump shut-off valves, and other items.
A significant development was the design of the energy absorbing front structures. Recognizing that most vehicle collisions involve frontal impacts, engineers set about to design front structures that, while not adversely affected in performing other vehicle functions, would sacrificially collapse during a frontal impact to help protect the structural integrity of the passenger compartment while limiting the deceleration the occupant would experience. Before the advent of unitized body construction the principal energy absorbing member was the chassis frame rail. With unitized construction the principal energy absorbing element is the body lower front side member or, as referred to herein, the rail.
While designing the vehicle to enhance the safety of occupants under a wide variety of operational conditions and during a reasonable set of unintended or "accidental' events, the design engineer must also produce a vehicle capable of reasonable fuel efficiency, good performance, and acceptable cost. Fuel efficiency, performance, and cost are directly related to vehicle weight.
The achievement of the safety objective is a challenging engineering assignment. To do so at low weight even more so.
The purpose of this paper is to outline design criteria and principles for configuring the primary structural elements to more efficiently, i.e. at low weight, achieve the desired vehicle safety objectives


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