2002 Pontiac Montana Frequency Improvements Employing Structural Foam 2001-01-1609
This paper documents a joint development process between General Motors and Dow Automotive to improve primary body structure frequencies on the GM family of midsize vans by utilizing cavity-filling structural foam. Optimum foam locations, foam quantity, and foam density within the body structure were determined by employing both math-based modeling and vehicle hardware testing techniques.
Finite element analysis (FEA) simulations of the Body-In-White (BIW) and “trimmed body” were used to predict the global body structure modes and associated resonant frequencies with and without structural foam. The objective of the FEA activity was to quantify frequency improvements to the primary body structure modes of matchboxing, bending, and torsion when using structural foam.
Comprehensive hardware testing on the vehicle was also executed to validate the frequency improvements observed in the FEA results. BIW modal tests were performed before and after the addition of structural foam to confirm the FEA predictions. A production vehicle was also foamed and modal tested to verify that improvements to the BIW were also comprehended at the full vehicle level. Hardware measurements from road response testing were also incorporated into the evaluation matrix. Acceleration measurements (Power Spectral Density or PSD) at the steering wheel and seat track, and sound pressure level (SPL) measurements in the passenger compartment were collected to further evaluate the affect of structural foam on overall vehicle performance.
BIW test results of a current production van yielded a first structural mode frequency increase of 11% using 8pcf (pounds per cubic foot) density foam and 35% using 24pcf density foam. Additional advantages to foaming the vehicle were also observed in terms of improvements to interior sealing and reductions in low frequency interior noise levels.