Issue 47

M.F. Funari et alii, Frattura ed Integrità Strutturale, 47 (2019) 277-293; DOI: 10.3221/IGF-ESIS.47.21 289 1) a uniformly distributed opening force applied along the upper skin of the panel (Fig. 10(a)). 2) a point opening force applied at the cracked edge of the panel (Fig. 10(b)); The idealized sandwich structure presents glass/polyester skins and a Divinycell H100 foam core, therefore the material and interface properties are the same as the ones listed in Tab. 3 with reference to the MMB test. The fracture parameters 1 C K and 2 C K experimentally determined Divinycell H100 foams, as detailed in the experimental section of this paper, are employed in this analysis. (a) (b) (c) Figure 10 : (a) uniformly distributed opening force applied along the upper skin of the panel; (b) point opening force applied at the cracked edge of the panel (b) ; detail of the mesh discretization in the core (c) . Modelling The 2D model involves a discretization of each face sheet by means of shear deformable beam elements, whereas the foam core is modelled by plane stress triangular elements. Both skin and core elements features cubic interpolation functions and a linear elastic constitutive behavior of the materials. ALE equations are introduced at each skin/core interfaces, in view of possible debonding phenomena, and in the core, to predict the propagation of the pre-existing crack length. Linear interpolation functions are assumed for the ALE variables. The numerical discretization used for the face sheet is assumed to be generally uniform with an element length D  equal to 5mm . A coarse discretization is adopted at the interface, in absence of any pre-existing interfacial defects. With reference to the core modelling, a high number of computational points is condensed around the crack tip region, whereas a coarse discretization is adopted in the remaining domain (Fig. 10(c)). The analysis is developed in displacement control mode, with the aim to ensure a stable crack propagation. (a) (b) Figure 11 : Load-displacement response: (a) uniformly distributed opening force; (b) point opening force.