Crashworthiness Challenges in Steel-to-Aluminum Front End Design

The search for weight reduction opportunities to improve corporate average fuel economy has led the auto industry to investigate light weight materials such as aluminum and magnesium. These materials can reduce vehicle weight while satisfying crash safety requirements of corporate, government, and independent insurance agencies. As a result, designs of several vehicles have been fully migrated from steel to aluminum while many other vehicles have opted to substitute lighter materials at the component and system levels. An investigation has been conducted on the front end principal crash energy absorbing rails to convert the original HSLA350 steel structural members into 5754NG aluminum. The investigation shows that while the substitution of aluminum at the right thickness can achieve lighter weight and higher specific energy, additional design parameters such as design load targets remain a major challenge. A comparison of steel versus aluminum mean crash loads, crash energy management, weight saved, specific energy, and design load target highlights some of these challenges. The results from an experimental investigation of stamped 5754NG aluminum sheet rails show the substitution of stamped 5754NG aluminum sheets for steel rails reduces the weight of each of the front rails by 3.3 (lb) and enhances the specific crash energy management efficiency by 38%. To solve the design load target challenge, the same investigation extends to higher strength 6xxx series extruded aluminum material using CAE modeling and demonstrates an increase in crash energy management efficiency of up to 80%.