4. Unnotched material: mechanical properties and energy absorption
Typical stress–strain curves are shown in Fig. 2(a) for the Alporas foam and in Fig. 2(b) for the Alcan foam. We note that the overall shapes of the tensile and compressive stress–strain curves are insensitive to the choice of material. Alporas foam was found to be almost isotropic, with a variation of 915% in modulus and yield strength with regard to specimen orientation. In contrast, the Alcan foam is orthotropic; the tensile and compressive stiffness and strength are least in the through-thickness (TT) direction. In compression, both foams show a local peak stress at yield, followed by a fairly constant plateau stress. The plateau stress spl was taken as the average compressive stress for compressive nominal strains within the range 5–30%. In tension, both materials strain harden within the plastic range, prior to tearing at a strain of only a few percent. We found that the ultimate tensile strength sUTS is within 25% of the compressive plateau stress spl for both foams. The unloading Young’s modulus E in both tension and compression tests was measured from the slope of the unloading curve after a small plastic strain, of the order of 1%; it was found that the tensile and compres
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4. Unnotched material: mechanical properties and energy absorptionTypical stress–strain curves are shown in Fig. 2(a) for the Alporas foam and in Fig. 2(b) for the Alcan foam. We note that the overall shapes of the tensile and compressive stress–strain curves are insensitive to the choice of material. Alporas foam was found to be almost isotropic, with a variation of 915% in modulus and yield strength with regard to specimen orientation. In contrast, the Alcan foam is orthotropic; the tensile and compressive stiffness and strength are least in the through-thickness (TT) direction. In compression, both foams show a local peak stress at yield, followed by a fairly constant plateau stress. The plateau stress spl was taken as the average compressive stress for compressive nominal strains within the range 5–30%. In tension, both materials strain harden within the plastic range, prior to tearing at a strain of only a few percent. We found that the ultimate tensile strength sUTS is within 25% of the compressive plateau stress spl for both foams. The unloading Young’s modulus E in both tension and compression tests was measured from the slope of the unloading curve after a small plastic strain, of the order of 1%; it was found that the tensile and compressive
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