DYMAT 2009 (2009) 547-553
DOI: 10.1051/dymat/2009078

Impact behaviour of hollow sphere agglomerates with density gradient

H.B. Zeng¹, S. Pattofatto¹, H. Zhao¹, Y. Girard² and V. Fascio<sup>3

1</sup>  Laboratoire de Mécanique et Technologie, ENS Cachan/CNRS, UMR8535/UPMC/PRES, Université Sud Paris, 61 avenue du président Wilson, 94235 Cachan Cedex, France
²  EADS CCR, Quai Marcel Dassault, BP. 76, 92152 Suresnes Cedex, France
³  ATECA/Advanced Materials & Systems (AMS) Verlhaguet, 82000 Montauban, France

Published online: 15 September 2009

Abstract
This paper presents a study on the influence of the density gradient profile on the mechanical response of graded polymeric hollow sphere agglomerates under impact loading. Quasi-static, standard split Hopkinson pressure bar (SHPB) tests as well as higher speed direct impact Hopkinson bar tests and Taylor tests are performed on such hollow sphere agglomerates with various density gradient profiles. It is found that the density gradient profile has a rather limited effect on the energy absorption capacity from those tests. It is because the testing velocity performed (<50 m/s) is rather small with respect to its average sound wave speed (around 500 m/s) and the equilibrium stress state can be reached rather quickly. The high impact tests allow to generate a non-equilibrium state condition and the influence of density profiles is clearly observed by numerical study. It confirms the important influence of the density gradient profile under a non-equilibrium stress state situation. This study shows that placing the hardest layer as the first impacted layer and the weakest layer as the last layer has some benefits in terms of maximum energy absorption with a minimum force level transmitted to the protected structures.

© EDP Sciences 2009