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Description
Polymeric foams are ubiquitous in civilian and military applications for impact mitigation. While quasi-static testing elucidates the basic mechanical properties of foam such as specific toughness, specific stiffness, and specific strength, dynamic testing reports the energy absorbing and impact mitigation performance of foams. The objective of this research is divided in twofold. First, the novel fabrication of a polymeric, hierarchical, semi-closed-cell foam with superior relative mechanical properties. The novel foam was manufactured in two different densities and observed using scanning electron microscopy, where the cell size was found to have a statistical distribution with a wide spread. The foam was found to have a hierarchical structure, where the edges of semi-closed-cells were occupied with smaller completely closed-cells. The semi-closed-cells eliminated the effect of face stretching, and thus reduced the overall rigidity of the foam. This reduction is offset by the entrapped closed- cells in the edges. Second, standard quasi-static compression testing was performed on a 1kN load frame until the foam reached densification strain. The stress-strain curves were then used to calculate the basic mechanical properties as well as to predict the dynamic behavior of the foams. Alternatively, the dynamic impact mitigation properties were evaluated using a modified dart impact tester, which produced a dynamic impact with an energy level of approximately 7.13 J between the impactor head and the foam samples. The predictions from the quasi-static testing and dynamic impact testing were found to be in good agreement. The performance of the newly fabricated foam was compared to an industry-leading counterpart and was found to outperform in almost all metrics. A prominent application of the new foam is padding in football helmets to reduce the transmitted impact force, hence preventing concussion.
