N-hance.DOC: Software for Enhancing Structural Dynamic Characteristics Through Spot Welds 2004-01-0815

Structural dynamic characteristics such as fundamental structural modes and the corresponding frequencies are the most important factors in determining the robustness of a product design. Vehicle vibrations have a direct bearing on customer perception of quality, comfort and reliability in passenger vehicles, and play a key role in retaining customer loyalty.

The conventional wisdom to enhance the fundamental frequencies of a vehicle is to optimize the body structure for the best stiffness-compliance combination for a given vehicle line. In the process, considerable mass is often added to the body-in-prime structure for enhancing the structural frequencies by about 0.5-1.0 Hz. On the other hand, the process is often technically challenging involving complex computational methods and software for optimization, and requires a priori knowledge of every component of the product regarding its influence on the overall dynamic performance of the structure.

On the other hand, recognizing that the spot welds play a key role in the load transfer mechanism and the structural performance under dynamic loads, indigenous methods are developed [1, 2] and incorporated into a user-friendly software (N-hance.DOC) for assisting product designers to enhance the structural frequencies by redesigning the welds for efficient load transfer. The method is based on a family of indigenously developed set of rules based on strength, compliance and failure modes as well as an ever growing set of heuristics based on experience in the field. The method being based on the routine linear solutions (static, eigen and forced responses) does not call for additional technical know-how and hence is simple to adapt. In addition, the software is highly automated relieving the user from the difficult and time-consuming analysis-decision iterations as well as the routine jobs such as report/presentation generation.

The new software, N-hance.DOC, has been applied on several car and truck body structures and has been proven to produce consistently robust results assisting design enhancement upfront.

In this paper, a brief overview of the method is presented followed by a brief introduction to the software from NVH perspective. The results from some typical automotive structural assemblies are presented to demonstrate the consistency and robustness of the method as well as the capability and usefulness of the software.