USING EXPERIMENTAL MODAL ANALYSIS TO CHARACTERIZE AUTOMOBILE BODY JOINTS AND IMPROVE FINITE ELEMENT ANALYSIS

摘要

When using Finite Element Analysis to obtain the dynamics of an automobile, it becomes a problem for the modeler to develop an accurate representation of the many different joints, simple and complex, which exist within the body. Not only are the fastening techniques quite varied (i.e., spot- and butt-welded, glued, and bolted), but the various complex shapes introducing rigidness and/or flexibility become difficult to accurately model. The purpose of this research is to utilize experimental and analytical modal analysis tools to obtain a "best overall" model of the body joints. Detailed "mini-medals" are performed on loaded and unloaded joints to obtain accurate experimental models using well-established modal testing techniques. Analytical modal analysis methods such as Structural Dynamics Modification (SDM) and Modal Assurance Criterion (MAC) as well as a newer Perturbed Correlation Coefficient (PCC) can be used to extract and define specific stiffness and damping values associated only with the joint. A data base of joint properties can then be compiled to use in perturbation of values within the finite element model. It is not necessary to add new degrees-of-freedom to the model, only to perturbate current values in the calculated dynamic matrix until correlation between natural frequencies and mode shapes is optimal, through an iterative process.