AbstractThe energy‐absorbing characteristics of a foam are determined by its load–compression response, and hence reflect the geometric structure and physical properties of the matrix material. In this report, the energy‐absorbing characteristics are expressed in terms of three dimensionless quantities: (1)K, the energy‐absorbing efficiency, (2)I, the impact energy per unit volume divided byEf, and (3)I/K, the maximum decelerating force per unit area divided byEf, whereEfis the apparent Young's modulus. Using the calculation procedures described in this report, it is now possible to delineate the geometric structure and physical properties a foam matrix must possess to meet a given energy absorption specification. This approach shows that: (1) the energy‐absorbing characteristics of a brittle foam are superior to those of a ductile foam, (2) the optimum energy‐absorbing foam has a large cell size, a narrow cell size distribution, and a minimum number of reinforcing membranes between the cells, (3) foam composites offer no significant advantage over a single foam, and (4) the optimum energy‐absorbing region obtains over a tenfold change in impact velocity and can be extended in a given system only if the foam stiffness increases while the impact velocity is increased, as in a flu
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