Abstract
This paper deals with the characterization and the numerical modelling of the collapse of composite hollow spherical structures developed to absorb energy during high velocity impacts. The structure is composed of hollow spheres (ϕ=2–30 mm) made of epoxy resin and mineral powder. First of all, quasi-static and dynamic (v=5 mm·min−1 to v=2 m·s−1) compression tests are conducted at room temperature on a single sphere to study energy dissipation mechanisms. Fracture of the material appears to be predominant. A numerical model based on the discrete element method is investigated to simulate the single sphere crushing. The stress-strain-time relationship of the material based on the Ree-Eyring law is numerically implemented. The DEM modelling takes naturally into account the dynamic fracture and the crack path computed is close to the one observed experimentally in uniaxial compression. Eventually, high velocity impacts (v>100 m·s−1) of a hollow sphere on a rigid surface are conducted with an air cannon. The numerical results are in good agreement with the experimental data and demonstrate the ability of the present model to correctly describe the mechanical behavior of brittle materials at high strain rate.
Highlights
Hollow sphere structure (HSS) belongs to cellular solids that have been studied recently for their multiple properties [1].Compared to foam structure, HSS has both closed and open porosity
Before optimizing an assembly of HSS as shown in Figure 1(a) to dissipate more energy when crushed, the present paper focuses on the investigation of one sphere crushing
Considering that the failure is reached at a strain of 1.5%, the velocity threshold occurs at V = 11 m⋅s−1 which is consistent with the results found for both models
Summary
Hollow sphere structure (HSS) belongs to cellular solids that have been studied recently for their multiple properties [1].Compared to foam structure, HSS has both closed and open porosity. HSS aims to absorb soft impacts energy on an airliner cockpit. Many materials and structures have been tested to absorb energy of external impacts such as aluminium honeycombs [8], polymer [9], and metallic [10] foams and composite materials [7]. CELPACT [11] and MANSART [12] projects have recently focused on cellular structures designed for energy absorption. HSS is investigated through the SAMBA (Shock Absorber Material for Bird-shield Application) project because of its promises in terms of specific energy dissipated (J⋅kg−1) during impact [13]. The commonly used bird-shield structure measures approximately one square meter and ten centimeters thick which represents 10–12 kg
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