Polystyrene bead foam mouldings were impacted with a hemispherical striker of radius equal to the moulding thickness. Localised densification was observed below the contact area. A number of annular cracks initiated at bead boundaries at the moulding surface; the inner one grew most and limited load spreading. The extent of the main crack is determined by the yielded zone size. The impact force versus deflection response was predicted considering the vertical compressive stresses and the gas-pressure hardening of the foam. This gave good predictions for all but the 80 kg m-3 density foams, where hardening is mainly due to plastic deformation of the polymer.
Get full access to this article
View all access options for this article.
References
1.
1. Shaw, M.C. and T. Sata, 1966, The plastic behaviour of cellular materials, Int. J. Mech. Sci.8, 469-478.
2.
2. Wilsea, M., Johnson, K.L. and M.E. Ashby, 1975, Indentation of foamed plastics, Int. J. Mech. Sci., 17, 457-460.
3.
3. Lockett, F. J., Cousins, R. R. and D. Dawson, 1981, Engineering basis for selection and use of crash padding materials, Plast. and Rubb. Proc. and Appl., 1, 25-37.
4.
4. Orringer, O., Knadle, K. T. and J. F. Mandell, 1984, Crash padding mechanical properties and impact response analysis, SAE Trans., 93, part 4, 257-271.
5.
5. Gale, A. and N.J. Mills, 1985, The effect of polystyrene foam density on motorcycle helmet shock absorption, Plast. Rubb. Proc. & Appl., 5, 101-108.
6.
6. Mills, N.J., 1990, Protective capacity of bicycle helmets, Br. J. Sport. Med., 24, 55-60.
7.
7. Stupak, P. R. and J. A. Donavan, 1991, The effect of bead fusion on the energy absorption of polystyrene foam, Part II: Energy absorption, J. Cell. Plastics, 27, 506-513.
8.
8. Stupak, P. R. and J. A. Donavan, 1994, Deformation and energy absorption of polymer foams as a function of 2-D indenter and absorber geometries, Poly. Eng. Sci., 34,857-864.
9.
9. Gilchrist, A. and N. J. Mills, 1996, Protection of the side of the head, Accid. Anal. and Prevent., 28, 525-535.
10.
10. Moosa, A. and N.J. Mills, 1998, Analysis of yielding and fracture in bend tests on polymer foams, Polymer Testing, 17, 357-578.
11.
11. Mills, N.J. and P. Kang, 1994, The effect of water immersion on the fracture toughness of polystyrene foam used in soft shell cycle helmets, J. Cell. Plast., 30,196-222.
12.
12. Mills, N.J. and H.X. Zhu, 1999, The high strain compression of closed-cell polymer foams, J. Mech. Phys. Solids, 47,669-695.
13.
13. Mills, N.J. and A. Gilchrist, 1995, Evaluation of foams for horse riders' body protectors, Cell. Polym., 14,461-483.
14.
14. Mills, N.J., 1994, Impact response, in Low Density Cellular Plastics, Eds. N. C. Hilyard & A. Cunningham, Chapman & Hall, 270-318.
15.
15. Zhang, J., Lin, Z., Wong, A., et al., 1997, Constitutive modelling and material characterisation of polymeric foams, Trans. ASME- J. Eng. Matl. & Tech., 119, 284-291.
16.
16. Mills, N.J., 1997, Time dependence of the compressive response of polypropylene bead foam, Cell. Polym., 16,194-215.
17.
17. Mills, N.J. and A. Gilchrist, 1997, The effect of heat transfer and Poisson's ratio on the compressive response of closed cell polymer foams, Cell. Polym., 16,87-119.
