Finite Element Dynamic Analysis of an Automotive Frame

Using several variations of a basic finite element model, the dynamic displacement response and mode shapes of an automotive frame have been predicted. Small improvements in accuracy were noted when higher-order mass representation and allowance for shear deformation were included in the analysis. Modeling accuracy was significantly increased, however, by including certain effects which are normally ignored. These include an allowance for the less-than-perfect rigidity of siderail-to-crossmember joints; for the torsional behavior of short, open cross-section beams; and for the reduction of flexural inertia in welded, double-channel cross-sections. With the introduction of these factors, the predicted natural frequencies for the first eight flexural modes can be correlated with test results to within 4%. For this level of agreement, the finite element model appears to be sufficiently accurate to be used in design evaluation of frames, prior to prototype construction.