Journal of Mechanical Engineering and Automation 2016, 6(5A): 22-27 DOI: 10.5923/c.jmea.201601.05 Processing and Testing of Hybrid Sandwich Composites for Vibration Damping and Mechanical Properties Sushmita 1 , M. Rajesh 2 , Hemanth K. 2 , Ravikantha Prabhu 1 , Sharath Meloth C. 1 , Binu K. G. 1,* 1 Department of Mechanical Engineering, St Joseph Engineering College, Vamanjoor, India 2 Department of Mechanical Engineering, NITK, Surathkal, India Abstract Natural fibers due to their low cost, high specific strength, recyclability, and environmental friendliness, are finding increasing applications in automotive, aerospace, bio-medical, and sports equipment. In the present work, hybrid sandwich composites using Jute and Glass fibers in Polyester polymer, namely: Jute-Glass-Jute (JGJ) and Glass-Jute-Glass (GJG), were prepared by curing under pressure using compression moulding technique. The prepared sandwich composites were subjected to tensile and flexural testing. Their vibration and damping characteristics were studied using free vibration and forced vibration test rigs. Further, the influence of using Magneto Rheological (MR) fluid on vibration damping properties of the composite samples have also been investigated. The tensile and flexural strengths of GJG composites were found to be higher than that of JGJ and plain jute composites. In terms of their free vibration response, JGJ composites showed slightly higher natural frequency for first 3 modes while GJG showed better damping factors. Under forced vibration test, the effect of MR fluid was observed to be better for JGJ composites which showed 8% higher reduction in amplitude in comparison to GJG composites. Keywords Natural Fibres, Hybrid sandwich composite, Modal analysis, MR fluid 1. Introduction In the last 20 years, natural fibers have received more attention from the materials research community worldwide. These fibers are considered to be excellent alternatives to synthetic fibers due to advantages such as: low cost, low density, high strength to weight ratio, recyclability, and better environmental performance. These enhanced properties have led to the increased use of natural fiber reinforced composites in the fields of aircraft, military, home appliances, automotive or transportation, civil infrastructure, construction, corrosion resistant equipment, electrical gadgets, biomedical fields and sports equipment etc. K Senthil Kumar et al. [1] carried out experiments using impulse hammer method to analyze the vibration and damping characteristics of banana fiber polyester composite(BFPC) and sisal fiber polyester composite(SFPC). Experimental investigations showed that SFPC due to its dispersion ability offers good mechanical bonding and hence exhibits better mechanical strength and free vibration properties compared to BFPC. Akash D A et al. [2] investigated the damping factors and the mode shapes for the * Corresponding author: binuk@sjec.ac.in (Binu K. G.) Published online at http://journal.sapub.org/jmea Copyright © 2016 Scientific & Academic Publishing. All Rights Reserved cantilevered rectangular symmetric plate of hybrid jute-sisal fabric reinforced polyester composite with different fiber orientations using FFT based spectrum analyzer. It was found that the average damping factor obtained for fundamental frequency of hybrid jute-sisal laminate is 1.15 times higher than that of jute laminate. Iqbal Mokhtar et al. [3] carried out experiments to characterize the mechanical behavior of basalt/HDPE composite under in-vitro condition. The study indicated that the synthetic fiber (carbon) combines well with HDPE as a composite material and gave excellent consistent performance in mechanical testing. Also the basalt fibre as a natural fibre showed good results and better than E-glass fibre in overall mechanical evaluation. 1.1. Vibration and Damping Vibration is the motion of a particle or a body or system of connected bodies displaced from a position of equilibrium. Most vibrations are undesirable and particularly in machines and structures because they produce increased stresses, energy losses, cause added wear, increase bearing loads, induce fatigue, create passenger discomfort in vehicles, and absorb energy from the system. Damping is the resistance offered by a body to the motion of a vibratory system. The resistance may be internal or external and externally through a liquid or solid. The main advantage of providing damping in mechanical systems is to control the amplitude of vibration so that the failure occurring due to resonance could be avoided. Vibration