Dynamic Mechanical Characteristics of Expanded Polypropylene Foams

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/m³ 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.

Keywords

compression test absorbed energy expanded polypropylene foam split Hopkinson pressure bar.

Get full access to this article

View all access options for this article.

References

Bouix, R. , Viot, P. and Lataillade, J.L. Polypropylene Foam Behaviour Under Dynamic Loadings: Strain Rate, Density and Microstructure Effects, Int. J. Impact Eng., 2009: 36: 329-342.

Viot, P. , Bernard, D. and Plougonven, E. Polymeric Foam Deformation Under Dynamic Loading by the Use of the Microtomographic Technique, J. Mater. Sci., 2007: 42: 7202-7213.

Kolsky, H. 1963: Stress Waves in Solids, Dover Publications , New York.

Frey, T.J. and Vinson, J.R. ( 1991). High Strain Rate Effects on Mechanical Properties of Glass/Polyester and Carbon/Aluminum Composite Material, In: Collection of Technical Papers - AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference AIAA-91-0930, pp. 19-29.

Saha, M.C. , Mahfuz, H. , Chakravarty, U.K. , Uddin, M. , Kabir, M.E. and Jeelani, S. Effect of Density, Microstructure, and Strain Rate on Compression Behavior of Polymeric Foams, Mater. Sci. Eng. A, 2005 : 406: 328-336.

Subhash, G. , Liu, Q. and Gao, X.L. Quasistatic and High Strain Rate Uniaxial Compressive Response of Polymeric Structural Foams, Int. J. Impact Eng., 2006 : 32: 1113-1126.

Vinson, J.R. ( 1997). Effect of Specimen Geometry in High Strain-rate Testing of Graphite/Epoxy Composite, In: Collection of Technical Papers - AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference AIAA-97-1046, pp. 927-934.

Zhao, H. Testing of Polymeric Foams at High and Medium Strain Rates, Poly. Testing, 1997: 16: 507-516.

Zhao, H. and Gary, G. A New Method for the Separation of Waves. Application to the SHPB Technique for an Unlimited Duration of Measurement, J. Mech. Phys. Solids , 1997: 45: 1185-1202.

10.

Zhao, H. , Gary, G. and Klepaczko, J.R. On the Use of a Viscoelastic Split Hopkinson Pressure Bar, Int. J. Impact Eng., 1997: 19: 319-330.

11.

Hopkinson, B. A Method of Measuring the Pressure Produced in the Detonation of High Explosives or by the Impact of Bullets, Proc. R. Soc. Lond. A, 1913: 89: 411-413.

12.

Davies, R.M. A Critical Study of the Hopkinson Pressure Bar, Philos. Trans. Roy. Soc. London A, 1948 : 240: 375-457.

13.

Chen, W. , Zhang, B. and Forrestal, M.J. A Split Hopkinson Bar Technique for Low-impedance Materials, Experimental Mech., 1999: 39: 81-85.

14.

Wang, L. , Labibes, K. , Azari, Z. and Pluvinage, G. Generalization of Split Hopkinson Bar Technique to Use Viscoelastic Bars, Int. J. Impact Eng., 1994: 15: 669-686.

15.

Avalle, M. , Belingardi, G. and Montanini, R. Characterization of Polymeric Structural Foams Under Compressive Impact Loading by Means of Energy-absorption Diagram, Int. J. Impact Eng. , 2001: 25: 455-472.