Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 653-660 Published Online July 2012 (http://www.SciRP.org/journal/jmmce) Effect of Cell Size on the Fundamental Natural Frequency of FRP Honeycomb Sandwich Panels Sourabha S. Havaldar 1 , Ramesh S. Sharma 1* , Arul Prakash M. D. Antony 2 , Mohan Bangaru 2 1 Department of Mechanical Engineering, R. V. College of Engineering, Bangalore, India 2 Department of Production Technology, Madras Institute of Technology, Chennai, India Email: * rssharma25@yahoo.com Received January 7, 2012; revised February 10, 2012; accepted March 5, 2012 ABSTRACT In the present work, the effect of hexagonal cell size of the core on the fundamental natural frequency of FRP honey- comb sandwich panels has been analyzed both experimentally and by finite element technique. Experimental Modal tests were conducted on hexagonal cell honeycombs ranging in size from 8 mm to 20 mm maintaining the facing thick- ness constant at around 1 mm with two different boundary conditions viz C-F-F-F and C-F-C-F. The traditional “strike method” has been used to measure the vibration properties. The modal characteristics of the specimens have been ob- tained by studying its impulse response. Each specimen has been subjected to impulses through a hard tipped hammer which is provided with a force transducer and the response has been measured through the accelerometer. The impulse and the response are processed through a computer aided FFT Analyzing test system in order to extract the modal pa- rameters with the aid of software. Theoretical investigations have been attempted with appropriate assumptions to un- derstand the behavior of the honeycomb sandwich panels during dynamic loading and to validate experimental results. Finite Element modeling has been done treating the facing as an orthotropic laminate and Core as orthotropic with dif- ferent elastic constants as recommended in the literature. The results are presented which show that the theoretical model can accurately predict the fundamental frequency and how honeycombs with different cell size will perform un- der dynamic loads. Keywords: Honeycomb; Modal Testing; FRP; Impulse; Frequency 1. Introduction Sandwich structures that employ a honeycomb core be- tween two relatively thin skins are desirable in several engineering applications that require high strength to weight ratios. Because of their ability to absorb large amounts of energy, they are also often used as a “cush- ion” against external loads. Honeycomb sandwich struc- tures are currently being used in many engineering ap- plications, both within and outside of aerospace engi- neering. Lightweight honeycomb materials can be used in the construction of composite panels, shells, and tubes with high structural efficiency. In recent years, the researches pertaining to honey- comb sandwich structures have been focused on effective numerical modeling methods, vibration properties, crash- worthiness, damage, failure and impact response [1,2]. Burton and Noor [3,4] investigated the continuum mod- eling of honeycomb sandwich for computation. Nieh [5] also studied the processing and modeling of cellular sol- ids for lightweight structures. Maheri and Adams [6] investigated the damping of composite honeycomb sand- wich beams in steady-state flexural vibration using the method extended from that for monolithic beams. Gold- smith et al. [7,8] studied the crashworthiness of honey- comb under impact loads. Neilsen [9] discussed the con- tinuum representations of cellular solids, including hon- eycomb materials, to relate localized deformations to appropriate constitutive descriptions. But the role of ani- sotropic properties of honeycomb core in elasticity on the structure was not addressed. Damping contributions due to its components, par- ticular skin fiber orientations, were considered. They also investigated the dynamic shearing property of both No- mex and aluminum honeycomb core [10]. The dynamic shearing properties of honeycomb were shown to be dif- ferent in various directions from static properties. It has long been realized that honeycomb materials are anisot- ropic in nature. The ability to predict the properties of these cellular materials depends on the knowledge of microstructural mechanism that contributes to macro- scopic behavior. The traditional Nomex and aluminum cores have great capability of withstanding compression * Corresponding author. Copyright © 2012 SciRes. JMMCE