Rigid, polyurethane foam filling is currently being used for NVH (Noise, Vibration and Harshness) improvement in many automobiles The improvement is typically achieved by the injection of the rigid polyurethane foam into the thin-walled, hollow sections of the body members such as the pillars and rocker panels The foam seals the cavities thereby blocking the transmission and amplification of wind, engine and road noises Also by increasing the stiffness of the members and the joints, the body natural frequencies are increased thereby reducing the vibration
Another potential application of the rigid polyurethane foam is strength improvement of the body structures Thin-walled, hollow sections are inherently susceptible to buckling due to section collapse When filled with the rigid polyurethane foam, the section collapse can be significantly reduced thereby increasing the strength of such structures, in addition to the demonstrated NVH improvement
Bending tests (4-point) of foam-filled steel sections were performed to show the effectiveness of various densities of foam in improving the strength in the flexural mode These tests were replicated in nonlinear finite element simulations to establish the appropriate material characteristics including fracture properties Additionally, these tests served to identify the appropriate density range for roof-crush strength improvement Subsequently, nonlinear finite element analyses were performed to simulate the roof crush test per FMVSS 216 (Federal Motor Vehicle Safety Standards) at the A-pillar roof joint The study shows that the strength can be improved substantially by using rigid polyurethane foam By using foam, it is possible to reduce the pillar sections, reduce the thicknesses or eliminate reinforcements inside the pillars and thereby offset the mass increase due to the foam filling Also, a possible design concept utilizing the foam filling in a B-pillar that could meet the interior head impact requirements (per the FMVSS 201 Head Impact Protection upgrade) is presented