Experimental investigation of static and fatigue behaviour of composites honeycomb materials using four point bending tests S. Belouettar a, * , A. Abbadi a,b , Z. Azari b , R. Belouettar c , P. Freres d a Centre de Recherche Public Henri Tudor, 29, Avenue John F. Kennedy, L-1855 Luxembourg, G.D of Luxembourg, Luxembourg b Laboratoire de Fiabilite ´ Me ´canique, Ecole des Inge ´nieurs de Metz, Ile du Saulcy, F-57045 Metz, France c De ´partement de Ge ´nie Civil, Universite ´ Badji Mokhtar de Annaba, BP 12 Sidi Amar, DZ 23000 Annaba, Algeria d EURO-COMPOSITES Ò , S.A. Zone Industrielle, L-6401 Echternach, G.D of Luxembourg, Luxembourg Available online 12 February 2008 Abstract In this study static and fatigue behaviours of honeycomb sandwich composites, made of aramide fibres and aluminium cores, are investigated through four-point bending tests. Damage and failure modes are reported and discussed. Global and local parameters were considered to evaluate the fatigue life of the analysed sandwich composites. Effects of core densities and the cell orientation (L or W) on the maximum load and on the damage processes (initiation and evolution) are also investigated. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Sandwich beam; Fatigue; Aramide fibres; Aluminium honeycomb; Damage 1. Introduction The use of sandwich structure continues to increase rap- idly due to the wide fields of their application, for instance: satellites, aircraft, ships, automobiles, rail cars, wind energy systems, and bridge construction to mention only a few. The sandwich composites are multi-layered materials made by bonding stiff, high strength skins facings to low- density core material (see Fig. 1). The main benefits of using the sandwich concept in structural components are the high stiffness and low weight ratios. These structures can carry both in-plane and out-of-plane loads and exhibit good stability under compression, keeping excellent strength to weight and stiffness to weight characteristics. The many advantages of sandwich constructions, the devel- opment of new materials and the need for high perfor- mance and low-weight structures insure that sandwich construction will continue to be in demand. Sandwich con- structions are being considered for application to aircraft primary structures, where durability and damage tolerance is a first rank consideration, therefore, understanding the adverse effect of in-service events. In fact, expansion of composite structure to sensitive fields, where high reliabil- ity is demanded, such as civil aviation, was so far restricted by the poor knowledge of their behaviour under complex dynamic loads. For widespread application and in order to introduce sandwich in primary structures several chal- lenges must be meet. Therefore, the structure needs to be evaluated in order to prove that damage occurring during the service life will not lead to failure or excessive structural deformation until the damage is detected. In order to use these materials in different applications, the knowledge of their static and fatigue behaviours are required and a better understanding of the various failure mechanisms under sta- tic and fatigue loadings conditions is necessary and highly desirable. The strength of the sandwich is a result of a combination of properties from the skin, core and interface. Any dam- age accumulated in one, or more, of these base materials will have an overall effect on the properties of the sand- wich. It is imperative to understand how potential damage occurs in service will affect structural performance. The 0263-8223/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.compstruct.2008.01.015 * Corresponding author. Tel.: +352 54 55 80 500; fax: +352 42 59 91 333. E-mail address: salim.belouettar@tudor.lu (S. Belouettar). www.elsevier.com/locate/compstruct Available online at www.sciencedirect.com Composite Structures 87 (2009) 265–273