Study of the dynamic fracture of hollow spheres under compression using the Discrete Element Method

Abstract

Hollow sphere structure (HSS) belongs to cellular solids that have been studied recently for its multiples properties. In our case, HSS aims to absorb soft impacts energy on an airliner cockpit. This structure is investigated because of its promises in term of specific energy dissipated (J.kg1) during impact. First of all, quasi- static and dynamic (v = 5mmmin_1 to v = 2ms4) uniaxial compression tests are conducted at room temperature on a single sphere (D = 30 mm). Rapid crack propagation (RCP) is observed to be predominant at macroscopic scale. The formalism of Linear Elastic Fracture Mechanics (L.E.F.M.) is therefore used to estimate the dynamic energy release rate GIdc . The crack tip location is measured during the crack propagation using a high speed camera. The Discrete Element Method (DEM) is used to simulate the dynamic fracture by implementing a node release technique to perform a generation phase simulation. The dynamic energy release rate can be determined using the experimentally measured crack history. In hollowed spherical structures the numerical results reveal a high proportion of energy dissipated through inertial effects as well as a dependence of the thickness of the skin over the range of 0.04 mm to 1.2 mm. At a crack tip velocity of 0.6 times the Rayleigh wave speed of the material, the dynamic correction factor is less than 0.05. Similar results have been shown for the longitudinal dynamic fracture of polymer pipes. The quantitative results of GIdc are in good agreement with the literature and the present model offers an alternative to the finite element method to simulate the rapid crack propagation.Its use reveals to be an interesting way to model the mechanical behavior of brittle materials.