Effect of Epoxy-Based Structural Foam on Energy Management: An Experimental & Analytical Investigation 2001-01-0473

The effect of epoxy-based structural foam on strength, stiffness, and energy absorption of foam filled structural components is investigated and implemented to formulate design guide-lines that can be used in enhancing weight reduction and engineering functions of systems.

An experimental approach is first utilized to identify design variables such as foam density, gage, and foam layer thickness, that are needed to enhance the weight/ performance ratio of structural hat-section components. A CAE approach using non-linear, large deformation finite element analysis is used to model the hat-section components. An acceptance level of confidence in the CAE analytical tools is then established based on comparisons of results between the two approaches. Upon that, the CAE analytical tools are deployed in a sensitivity study to quantify the crush/crash characteristics of foam-filled hat-section components with respect to the changes in the afore mentioned design variables. Design charts are presented, from which design variables can be selected for particular applications in order to establish the weight effectiveness of foam reinforcement.

In the foam thickness range investigated (5–8 mm), the axially absorbed energy increased between 50–125%, while the maximum axial strength increased by 10–25% only. On the other hand, the flexural energy absorption increased from 10–40%, while the maximum bending load registered an increase ranging from 25 to 80%. Therefore, the use of thin gages accompanied by foam layers in the 5 to 8 mm range would result in the most efficient energy absorbing axial structural components. In addition, maximum bending strength can also be increased with almost no weight penalty, by deploying similar thicknesses of the epoxy-based foam in beam components. The cut-off gages for the efficiency of the epoxy-based foam (in the studied foam thickness layers of 5–8 mm) ranges from 1.4-1.8 mm for flexural applications and from 2.0–2.2mm for axial applications.

The enhancement in the structural characteristics of columns and beams through structural foam deployment, is due to a delayed local buckling mechanism. On the other hand, foam deployment in beams has to be enhanced in density and location, where plastic hinges are likely to form. This enhancement in location will minimize the total weight of the component thus maximizing the total specific energy gain per that member.