A recent report "Considerations in the Selection of Advanced High-Strength Steels for ULSAB-AVC" from the ULSAB-Advanced Vehicle Concepts (AVC) Consortium underscores the successful use of simultaneous engineering between the steel industry and vehicle designers to achieve mass, performance and other technical goals for its advanced concepts vehicle. ULSAB-AVC is the most recent addition to the global steel industry's initiatives offering steel solutions to the challenges facing automakers around the world. The challenges are to increase the fuel efficiency of automobiles, improve safety and performance and maintain affordability, as well as make environmentally friendly vehicles. The program follows the UltraLight Steel Auto Body (ULSAB) program, which was successfully completed in 1998.
The ULSAB-AVC Consortium set mass, performance and other targets for its advanced concepts vehicle to build the next generation of safe, affordable and fuel-efficient vehicles. Selection of steels for ULSAB-AVC was made to facilitate an optimum balance between structural strength, crash resistance, formability, joinability and total economy. Porsche Engineering Services (PES) Inc., Troy, Mich. provided design and engineering management for ULSAB-AVC as it did with the ULSAB Program, using a holistic approach to develop a new vehicle architecture that offers cost-efficient steel solutions to mass-reduction challenges.
Design and materials teams worked closely throughout the design process to ensure that design was optimized and that the steels selected, either conventional or advanced high-strength steels (AHSS), were used to their full potential. The simultaneous-engineering approach was essential because the development of advanced lightweight vehicles like ULSAB-AVC involves an inherent high degree of complexity and strong interaction between component design and materials selection.
In the materials selection process used for the body structure in ULSAB-AVC, the design was based on static mechanical properties using commonly available materials largely to validate the concepts. However, in looking to the future, materials selection also took into consideration materials under development and those anticipated being commercially available by 2004 from ULSAB-AVC Consortium members. Materials recommended were evaluated together with their associated high stress strain rate properties, and they were then applied to the initial C-Class and PNGV-Class body structure concept designs. Specific grades of AHSS were selected for use in the final design in a manner that best matched their unique mechanical properties with the crash and structural demands of specific ULSAB-AVC components.
The AHSS family of steels is based on multiphase microstructures, which provide high-strength and enhanced formability. This combination of strength and formability arises primarily from high strain-hardening capacity as a result of a lower yield strength (YS)-to-ultimate tensile strength (UTS) ratio (YS/UTS). This phenomenon makes AHSS ideal for use in mass (weight) reduction applications by using lighter thickness than could be used with less formable conventional steel.