Product Dynamic Characteristics and Life Improvement through Spot-Weld Layout and Design Enhancements 2003-01-1326

Better dynamic characteristics and longer fatigue life implies a robust product which has a direct bearing on customer perception of quality in passenger vehicles, and is one of the major factors affecting customer loyalty. Traditional optimization of dynamic characteristics is first performed to improve fundamental bending and torsion frequencies of automotive body structures. Such analyses typically involve mass minimization for which gage sensitivities are used to identify critical parts.

It is recognized that most fatigue failures in an automobile body structure occur at spot welds, and almost none of the traditional optimization methods include the influence of spot weld layout on dynamic characteristics and durability. Also, load path identification tools currently available are not very effective for large & complicated parts such as body panels, floor panels, etc. since typically only small regions of such parts absorb energy. While a significant amount of time & effort is expended in the preparation of analytical models and load inputs, a relatively short amount of time is budgeted to review results and extract design directions. To date fully integrated tools that simplify and automate this painstaking process of load path identification and overall structural optimization are not commercially available. Moreover, currently available tools do not incorporate the intelligence needed to interpret large volumes of analytical results.

A new software N-hance.DOC has been developed to address this issue. This software provides an integrated design environment to optimize dynamic characteristics of a structure through (1) part design enhancement (for better load path and energy distribution, (2) fastener layout enhancement (for better connectivity between parts and fastener durability), followed by the traditional mass optimization. An overview of the method is presented followed by results from the optimization of the body-in-white structure of a typical passenger car.