The effect of polyurethane structural foam on strength, stiffness, and energy absorption of foam filled structural components is investigated to formulate design directions that may be used in weight reduction and engineering functions of vehicle systems.
An experimental/testing approach is first utilized using Taguchi’s DOE to identify design variables [foam density, gage, and material type], that are needed to determine the weight/performance ratio of structural hat-section components. An analytical CAE approach is then used to analyze the hat-section components using non-linear, large deformation finite element analysis. An accepted level of confidence in the CAE analytical tools is then established based on comparison of results between the two approaches. Upon that, the CAE analytical tools are deployed in a sensitivity study to quantify crush/crash characteristics of foam-filled hat-section components with respect to the changes in the design variables; namely, foam density, gage, and steel material strength. Design charts are then generated for a spectra of design variables aimed at particular applications in order to help establish the weight effectiveness of foam filling.
Increasing the gage from 0.65 to 1.0 mm will increase energy absorption, but it will be accompanied by significant weight increase thus reducing the effectiveness of foam. Therefore, the use of thin gages accompanied by foam fillings in the 5 to 9 pcf range would result in efficient energy absorbing structural components. Strength and energy absorption can also be increased with no weight penalty, by changing the material type from mild to high strength steel.
The peak and mean loads (strength) of columns and beams increased by foam-filling, is due to a delayed local buckling mechanism. On the other hand, foam usage in beams requires a trade-off in density and location, where plastic hinges are likely to form. This trade-off in location will help minimize the total weight of the component thus maximizing the total specific energy gain per that member.