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Successful automotive weight reduction with high strength-to-weight ratio steels has caused re-evaluation of the basic structural design parameters. This paper introduces the new concept of “Kinetic Modulus” which describes the nature of materials in motion. Kinetic modulus is influenced by stress and strain amplitude, yield strength and the number of loading cycles. The scope of kinetic modulus encompasses: elastic, secant, dynamic and tangent moduli; each of which is a specific case of kinetic modulus at a particular condition. Theoretical and experimental results are presented to support this concept. They show that high strength steel has higher dynamic stiffness and improved vibration response in structures as compared to that of lower strength steel. Thus, high strength steel (“Stiff Steel”) can be used advantageously in stiffness controlled automotive structures to achieve greater weight reductions.

The substantial development efforts made by the steel and aluminum industries have resulted in high strength-to-weight ratio materials that can be employed to achieve significant vehicle weight reduction. This total vehicle weight reduction is the sum of the initial weight savings attributable to lightweight material substitution and the iterative weight savings resulting from component weight interactions. The theoretical concept of vehicle interactive weight reduction was presented in a previous work. The present work reviews this theoretical concept and presents an experimental application: Charger XL, a lightweight materials development vehicle. Charger XL is 630 lb. (286 kg) lighter than its current, standard production counterpart. Lightweight materials substitution accounts for 375 lb (171 kg) while the interacting savings accounts for the remaining 255 lb (115 kg).

The use of aluminum in automobiles can significantly reduce vehicle weight. This paper discusses factors that relate to why aluminum will be used in automobiles. These factors are fuel economy, fuel cost, federal regulations, and increasing weight trends. The cost of reducing weight is analyzed by the overall economy concept. Overall economy includes operating cost and initial purchase price. The role of inertia weight class and interacting weight reduction are discussed and exemplified by two vehicles. One is a production vehicle, the Feather Duster and the other is a prototype called the Charger XL. The substitution of aluminum into conventional applications sometimes requires the developing of new technology in design and manufacturing. These aspects of how aluminum will be used in automobiles is also discussed.