THE PUBLISHING HOUSE PROCEEDINGS OF THE ROMANIAN ACADEMY, Series A, OF THE ROMANIAN ACADEMY Volume 16, Number 1/2015, pp. 70–79 EXPERIMENTAL DETERMINATIONS OF SOME MECHANICAL PROPERTIES FOR NEW TYPES OF COMPOSITE BARS WITH POLYPROPYLENE HONEYCOMB CORE Cristian Oliviu BURADA 1 ,Cosmin Mihai MIRIŢOIU 2 , Marius Marinel STĂNESCU 3 , Dumitru BOLCU 4 1,4 University of Craiova, Faculty of Mechanics, Dept. of Applied Mechanics and Civil Constructions Calea Bucureşti Street, Number 107, Code 200512, Craiova, Romania 2 University of Craiova, Faculty of Mechanics, Dept. of Transports and Industrial Engineering Calea Bucureşti Street, Number 107, Code 200512, Craiova, Romania 3 University of Craiova, Dept. of Applied Mathematics A.I. Cuza Street, Number 13, Code 200396, Craiova, Romania E-mail: cristian.burada@yahoo.com In this paper we have experimentally determined, using some known methods, the equivalent elasticity modulus for new types of sandwich bars characterized by: polypropylene honeycomb core, with a thickness of 20 mm, having the exterior layers made of epoxy resin reinforced (on the upper and lower sides) with 5 and 10 layers of steel wire mesh. We have considered as a reference method for elasticity modulus determination the modal analysis. We have determined the first three eigenmodes and used them to determine the elasticity modulus. The obtained results were checked with another experimental method characterized by bending loading of the bars in three points. In the last part of the paper, we have made a comparative study between the flexural rigidity values obtained from different sandwich structures with polypropylene honeycomb core that have thickness of 20 mm. The bars have different face sheets: bar 1 has one layer of fiber-glass with epoxy resin, bar 2 has two layers of fiber-glass with epoxy resin, bar 3 has five layers of steel wire mesh with epoxy resin and bar 10 has ten layers of steel wire mesh with epoxy resin. Starting from the first two eigenmodes of the bars, it is established a method used to determine the bars flexural rigidity. The results are validated by using an approximate experimental method. Key words: sandwich bars; eigenmodes; elasticity modulus; flexural rigidity; eigenfrequencies. 1. INTRODUCTION The sandwich bars and plates can be studied by various methods that mostly differ by the inclusions or neglecting the effects of angular deformation and respectively, the rotational inertia. A first theory, named as FSDT (First-Order Shear Deformation Theory), was presented in [1] and further developed in [2]. According to this theory, a straight line normal on the median plane before deformation remains straight without keeping the perpendicularity during deformation (on the median surface). The refined theories rely on a non- linear distribution of shear stresses along the thickness of the plate or bar. The inclusion of high order terms implies the inclusion of supplementary unknowns. Moreover, when fulfilling both the distribution of shear stresses in thickness are parabolic and if the limit conditions are accomplished on external surfaces, a correction factor is not necessary. Based on these assumptions, a HSDT (High-Order Shear Deformation Theory) theory was presented in [3]. According to this theory, the stresses and strains normal to the median plane are null. In [4] it was developed a theory that considers the stresses normal to the median plane. This theory removes a series of contradictions that appear in previous theories by accepting non linear factors of shear stresses in thickness. It is not neglected a part of the normal stresses obtained by the loading of the composite structure. A better characterization of sandwich bars can be obtained by using LWM (Layer-Wise Models) models. In [5, 6], it is considered each layer in a sandwich structure as a separate bar. The damped, forced and nonlinear vibrations for simply supported rectangular plates with viscoelastic core were studied in [7]. The core was modelled like a Voigt-Kelvin solid. There was also studied the influence of the layers thicknesses and material properties over the nonlinear plates response. There have also been made some