THE PUBLISHING HOUSE PROCEEDINGS OF THE ROMANIAN ACADEMY, Series A, OF THE ROMANIAN ACADEMY Volume 16, Number 4/2015, pp. 522–530 ASSESMENT OF SANDWICH BEAMS WITH RIGID POLYURETHANE FOAM CORE USING FAILURE-MODE MAPS Emanoil LINUL, Liviu MARŞAVINA “Politehnica” University of Timisoara, Department of Mechanics and Strength of Materials, 1 Mihai Viteazu Avenue, 300 222 Timisoara, Romania E-mail: linul_emanoil@yahoo.com The failure-mode maps of composite sandwich beams can provide useful information about the influence of different design parameters on the failure behaviour of such components. Failure mode of sandwich beams with different cores and different faces were investigated in the experimental program. Foams with 40 and 200 kg/m 3 densities were used as core material, while Glass-Fibre Reinforced Polymer (GFRP), polyester, epoxy and aluminium are the faces materials. Three-point bending tests were carried out for sandwich beams. In order to characterize these sandwich materials first were carried out a statistical analysis of the cellular structure for two different densities of the core material above mentioned. The sandwich core morphology and cells dimensions were studied before testing through scanning electron microscopy (SEM) and pore diameter versus frequency of pores histogram were plotted. After statistical analysis were performed static compression tests. These compression tests have had as objective the determining of the main mechanical properties such as Young’s modulus and yield stress values. The results obtained from the static compression tests were used for the analytical determination of failure-mode maps of sandwich beams. Finally, the failure- mode maps were constructed for five considered sandwich types and validated by the experimental results. Each failure-mode map is characteristic for a family of sandwich beam designs. Key words: sandwich beam, polyurethane foams, failure-mode maps, three-point bending tests. 1. INTRODUCTION Composite structural members made of two thin, stiff faces separated by a weak, light-weight core are known as sandwich panels. Separation of the stiff faces by the core increases the moment of inertia of a sandwich beam or plate with little increase in weight, enhancing the properties in bending and buckling. Sandwich structures are widely used because of its ability to provide high bending moment stiffness coupled with light weight. Because of this, sandwich panels are often used in applications where weight-saving is critical: in aviation applications in recent years for flooring, helicopter rotor blades, and tail and wing components. Panels for aircraft structures almost invariably employ fibre composite faces with metal or paper-resin honeycomb or corrugated [1–4]. Their good energy absorbance combined with high flexural rigidity, furthermore makes them ideal for the manufacture of large panels and modern sports equipment: the decks and ship hulls of racing yachts, and water and snow skis [5–9]. Also, the automobile industry is beginning to use the concepts developed by the aircraft industry for sandwich construction in the cars of the future. In the non-residential building market sandwich panel roofing is gaining increasing popularity because of its low weight. Other constructions applications include: portable buildings and fold-up bridges (of potential use to the Army) [1]. In most applications the panel must have some required minimum stiffness, it must not fail under some maximum service loading and it must be as light as possible. Its design can be formulated as an optimization problem: the goal is the panel with minimum weight which meets the requirements for stiffness and strength. The optimization can be carried out with respect to the: core and skin dimensions, the core and skin materials and to the core density. The obvious attraction of sandwich structures is that they are light and stiff. But stiffness is not enough. The beam or panel must also have strength: it must carry the design loads without failing. At least five different failure modes are possible; a given sandwich will fail by the one which occurs