Core crush criterion to determine the strength of sandwich composite structures subjected to compression after impact

Abstract

In this study a core crush criterion is proposed to determine the residual strength of impacted sandwich structures. The core of the sandwich is made of a Nomex Honeycomb core and the faces are laminated and remain thin. The mechanism of failure of this kind of structure under post-impact compressive loading is due to interaction between three mechanical behaviors: geometrical nonlinearity due to the skin's neutral line offset in the dent area, nonlinear response of the core and damages to the skins. For the type of sandwich analysed in this study, initially the core crushes at the apex of the damage. Using a finite element discrete modelling of the core previously proposed by the authors, the load corresponding to the crushing of the first cell can be computed and it gives the value of the residual strength for our criterion. Some geometric and material hypotheses are assumed in the damaged area mainly based on nondestructive inspection (NDI). The criterion is then applied to tests modelled by Lacy and Hwang [Lacy TE, Hwang Y. Numerical modelling of impact-damaged sandwich composites subjected to compression after impact loading. Compos Struct 2003;61:115-128]. It is shown that the criterion allows a good prediction of the tests except in the case of very small dents. Several sensitivity studies on the assumptions were made and it is shown that using this approach, the criterion is robust.

Validation and modeling of aeronautical composite structures subjected to combined loadings: The VERTEX project. Part 1: Experimental setup, FE-DIC instrumentation and procedures

“…These tests have demonstrated that asymmetrical sandwich structures have exceptional compressive and impact behavior. In particular, the boundary conditions of these structural tests are very different from those of conventional Compression After Impact (CAI) tests [37] and are very conservative because, once the damage has initiated, it quickly propagates to the free edges. Tests at this level have the characteristic of being less conservative and more representative than the normalized uniaxial tests.…”

Sandwich Structure Based On Corrugated-Core: A Review

“…Stiff and simultaneous light component is very important in nowadays industries. To achieve lightweight and high stiffness component, sandwich structure construction is develop [1][2][3][4].…”

“…The advantages of sandwich structures include great stiffness to weight ratios [2][3][4][5] , improved fatigue life, steadiness under compressive forces, good thermal and acoustic isolation properties. These benefits determine the fact that the use of composites has improved ominously in a wide range of structural applications and first of all in aerospace manufacturing [6][7][8][9].…”

Experimental and numerical analysis of the shear nonlinear behaviour of Nomex honeycomb core: Application to insert sizing

“…In the related literature, the main topic is clearly the compressive response, a phenomenon that has been studied for a long time (see McFarland since 1965 [12] or Wierzbicki [13]). Many authors have studied the compressive behavior -mainly to analyse the energy absorbing capabilities of honeycomb ( [12][13][14][15][16][17] for example) or, more precisely, the crush behavior of the core after a low-velocity/low-energy impact on a sandwich [17][18][19][20][21][22][23][24]. Today, the tendency is to use very refined finite element analysis with explicit code to model the complex failure mode following crushing of the Nomex Honeycomb core.…”

“…However, by understanding the structural behavior of the hexagonal cell and by making an analogy with the postbuckling of stiffened structures [22], it is possible to propose simplified discrete models that are very accurate [22][23][24].…”