Effect of Cell Size on the Fundamental Natural Frequency of FRP Honeycomb Sandwich Panels

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