Body-in-White Joint Stiffness Sensitivity Analysis

The major objectives of a car design are reducing costs, maximizing performance, and improving fuel economy. The total mass of a car has a direct effect on all these objectives. Around 25% of the total mass of a car is typically accumulated in its body in white (BIW). Thus, reducing the total mass of the BIW while satisfying the target stiffness is of utmost importance in the early stages of design. Reducing the total mass of the BIW involves the identification of potential locations for mass reduction and stiffness improvement. The joints of the BIW are often the most critical locations that decide the overall stiffness of the BIW. Understanding the contribution of each joint toward the overall stiffness is thus of paramount importance toward improving the stiffness of the BIW. This paper describes a new approach of identifying the contribution of each joint in a BIW toward the overall stiffness of the BIW. The joints in the BIW are parametrized and Altair Optistruct [1] tool is used to find optimum value of each parameter. The contribution of different joints to the overall stiffness is different for different loads. This methodology was applied to a simplified BIW model for a combination of two load cases-static torsion and bending. The relative joint sensitivities of the joints in BIW have been identified and verified based on the results. The entire methodology has also been automated in a preprocessor to reduce the total time involved.