On the efficiency of some analytic wrinkling models

International audience; The design of very lightweight aircraft sandwich structured composites requires a deep knowledge to tackle the failure modes. In this paper, we focus on the wrinkling which may be the primary cause of failure of such structures. Currently, lightweight sandwich structured composites are more and more used in the aeronautics industry and extend to primary structures such as control surfaces [1]. The engineer therefore needs an efficient and effective tool to prevent the occurrence of wrinkling. The ideal, from the engineer’s point of view, would be to define the local buckling phenomenon using an analytical formulation with as few parameters as possible. As a result, the formulation proposed by Hoff and Maunter in 1945 [2] for wrinkling in sandwich beams is still widely used today as it only depends on 3 parameters. However, modelling the complex behaviour of local buckling in a sandwich structure using a simple analytical formulation is not easy. Strong assumptions are required to linearize the system of equations and obtain a simple form expression. A telling example is the approach of Douville and Grognec [3]. The authors start from a complex 3D base and then linearize their system by reporting the problem in an isotropic 2D framework. It is understood that analytical modelling allows a simple and quick use, which ideal for the engineers. However, this comes at the price of important assumptions, sometimes far from reality. Here, a critical literature review of analytical wrinkling formulations is done (for example [2-5]), and the equations are compared first to 3D finite element models and then to a coupon’s tests campaign. About fifty sandwich coupons panels, with a design consistent with those used in lightweight aeronautics sandwich structured composites, were tested. The onset of wrinkling under compressive uniaxial loading, thanks to Digital Image Correlation (DIC) and high-speed camera were captured. Finally, the limitations and approximations of the models are identified and the relevance of simple wrinkling formulas for the design of sandwich structured composites (anisotropy, defects etc...) are discussed.