Issue 49

A. Bendada et alii, Frattura ed Integrità Strutturale, 49 (2019) 655-665; DOI: 10.3221/IGF-ESIS.49.59 664 E FFECT OF DELAMINATION continuous effort was addressing to study the vibrational behaviour of damaged composite plate using the numerically predicted parameters. The damages are inevitable in structures [22-23]; delamination is a common type of the honeycomb sandwich panel damage. In this work the detection of modal parameters of damaged honeycomb sandwich panel was carried out. We created a delamination of different size in one face only of sandwich panel. The natural frequencies and the mode shapes of a damaged model structure are obtained and presented in Tab. 13. The results show that the natural frequencies are very influenced by this defect (reduced rigidity) and new mode shapes appear in each delamination size. C ONCLUSION rediction study for determining the accurate orthotropic parameters of honeycomb aluminum core were investigated. According to the numerical equivalent properties a finite element model of honeycomb sandwich panel was created to extract the dynamical characteristic (frequencies and mode shapes), Experimental modal analysis was carried out to validate the numerical achievements. The important error between the computational results and experimental modal analysis led to introduce the double thickness wall in the Representative Volume Elements for determining the precise properties. The good agreement of frequencies and also corresponding mode shapes between numerical and experimental results after introducing the double thickness walls shows that:  The neglect of double wall in the characterization of pure core gives not efficient elastic properties which affects the mechanical analysis results of honeycomb sandwich panel.  The numerical homogenization method using RVE can provide accurate equivalent elastic constants of honeycomb core.  Non-destructive experimental method based on a precise contact free–free measurement system is very effective to validate the numerical achievements. According to the efficient parameters, a numerical study of damaged panel model is carried out to examine the influence of delamination on the modal parameters of the structure. The results show that the natural frequencies became lower which can be explained by the degradation of structural rigidity due to delamination. R EFERENCES [1] Hohe, J., Becker, W. (2002). Effective stress-strain relations for two-dimensional cellular sandwich cores: homogenization, materials models and properties, Appl. Mech, 55(1), 61. [2] Kelsey, S., Gellatly, R A., Clark, B W. (1958). The shear modulus of foil honeycomb cores, Aircraft engineering, 30, pp.294–302. [3] Gibson, L., Ashby, M F. 2 nd éd., (1999). Cellular Solids: Structure and Properties, Cambridge: Cambrige Solid State Series. [4] Masters, I G., Evans, K E. (1996). Models for the elastic deformation of honeycombs, Composite Structure, 35, pp. 403–422. [5] Xu, X F., Qiao, P. (2002). Homogenized elastic properties of honeycomb sandwich panels with skin effect, Journal Solids and Structures, 39, pp.2153–2188. [6] Chen, A., Davalos, J. (2005). Solution including skin effect for stiffness and stress field of sandwich honeycomb core, J Solids and Structures, 42, pp. 2711–2739. [7] Meraghni, F., Desrumaux, F., Benzeggagh, M L. (1999). Mechanical behavior of cellular core for structural sandwich panels, Composites: Part A, 30, pp. 767–779. [8] Hu, H., Belouettar, S., Daya, E M. (2006). Evaluation of Kinematic formulations for viscoelastically damped sandwich beam modeling, J Sandwich struct Master, 8, pp.477–495. [9] Mujika, F., Pujana, J., Olave, M. (2011). On the determination of out-of-plane elastic properties of honeycomb sandwich panels, Polymer Testing, 30(2), pp.222–228. A P