Abstract
Expanded polypropylene (EPP) foams have been widely used as protective materials in automotive bumpers, safety helmets, etc., but their dynamic behavior is not well defined. In the current study, quasi-static compression tests and dynamic tests using a split Hopkinson pressure bar were performed to investigate the effect of material density on the absorption of impact energy and the stress—strain curve. Three kinds of EPP specimen with densities of 20, 30, and 60 kg/m3 were tested. With the increase in the strain rate from 0.17 to 1857 s-1, the stiffness of the 20 kg/m3 specimen remarkably increased, whereas that of the 60 kg/m3 specimen did not. It is also shown that when the strain rate increased from 0.17 to 1857 s-1, the energy absorption became 3.7 times in 20 kg/m3 specimens whereas 2 times in 60 kg/m 3 specimens. A higher density of EPP foam resulted in a greater absorption of energy. The energy that is absorbed during dynamic loading is much higher than that during static loading. These results are important in the development of a protective structure with polymer foams in views of the service energy and the level of service stress.
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