Dynamic Analysis of Sandwich Composite Beam with Magnetorheological Fluid Core

Abstract

Magnetorheological fluid (MRF) is a smart fluid which can change its rheological properties under the influence of an applied magnetic field. Sandwich structures with MRF as core have unique characteristics permitting to vary the stiffness and damping properties under the influence of the applied magnetic field. Hence, MRF core sandwich structures can be effectively utilized to suppress the vibration and enhance the life of the structures. This study, investigates the dynamic characterization of MRF core sandwich beams with two types of composite face layers viz. polymer matrix composite and metal matrix composite. The two-layer, four-layer and six-layered chopped strand mat glass fiber reinforced unsaturated polyester resin polymer matrix composites (CGRP-PMC) were prepared by the hand layup method. The tensile, flexural, impact, inter-laminar shear strength (ILSS), fracture toughness properties were evaluated. The results have revealed that the four-layered CGRP-PMC material has high impact strength, ILSS and fracture toughness compared to two-layer and six-layered CGRP-PMC material. Free vibration analysis was carried out to determine the natural frequency and damping ratio of the CGRP-PMC materials. The result obtained from free vibration analysis indicated that the natural frequency of six-layered CGRP-PMC is higher than two-layer and fourlayered CGRP-PMC materials. The density, tensile strength, flexural strength, impact strength, absorbed energy, ILSS, fracture toughness, and damping ratio results of the CGRP-PMC specimens were considered as attributes for the selection of the optimal composite using multi-attribute decision making (MADM) techniques. The six-layered CGRP-PMC material was selected as the optimal PMC based on the results of MADM techniques. The Al6082 and Al7075 aluminum alloy reinforced with (0, 1, 2, 3, 4, 5, 7.5, 10, 15 and 20) different weight percentages (wt%) of silicon carbide particles (SiCp) metal matrix composites (MMCs) were fabricated through stir casting method. The mechanical and dynamic properties such as density, hardness, tensile strength, impact strength, natural frequencies and damping ratio of the MMCs were determined. Thevi mechanical tests and free vibration analysis results revealed that the addition of SiCp reinforcement increased the strength and stiffness of the MMCs. 15% SiCp/Al7075 MMC was selected as the best MMC based on the results obtained from MADM techniques. The MRF is prepared in-house at room temperature and contains 30% volume carbonyl iron powder and 70% volume silicone oil. The rheological properties of the MRF with and without the magnetic flux density were determined. The viscosity of MRF increased with an increase in magnetic flux density and saturated at 0.63 T. The shear stress of MRF increased and viscosity of MRF decreased with an increase in the shear rate at zero magnetic flux density. Since the MRF is used as the core for sandwich beams, the frequency sweep analysis was performed in the rheometer. The complex shear modulus, storage modulus, loss modulus, shear stress and complex viscosity properties of MRF increased with an increase in the applied magnetic flux densities. The loss factor of MRF decreased with an increase in the magnetic flux densities. The complex viscosity of MRF decreased with an increase in oscillatory frequency and increased with increase in the applied magnetic flux density. The two-layer, four-layer and six-layered CGRP-PMC prepared using hand layup technique is used as top and bottom layers of the sandwich beams and the in-house prepared MRF is used as the middle core layer of the sandwich beams. The dynamic characterization of CGRP-PMC sandwich beams enclosed MRF core is experimentally investigated. The effect of various parameters such as magnetic flux density, the thickness of CGRP-PMC layers and MRF core layer on the natural frequencies, damping ratio and vibration amplitude suppressions of the CGRP-PMC-MRF core sandwich beams are examined. From free vibration analysis, it was observed that the natural frequency of the CGRP-PMC-MRF core sandwich beams decreases with increase in the thickness of the MRF core layer. However, the damping ratio of the CGRP-PMC-MRF core sandwich structure increased with increase in the thickness of the MRF core layer. Also, the experimental forced vibration results reveal that CGRPPMC-MRF core sandwich beams have excellent vibration amplitude suppression capabilities.vii Dynamic characterization of (0, 5, 10, 15 and 20%) SiCp reinforced Al6082 alloy MMC sandwich beam with MRF core is experimentally investigated. The MRF core of the sandwich beam is activated using a non-homogeneous magnetic field using permanent magnets. The natural frequency, damping ratio and frequency amplitude response of the MMC-MRF core sandwich beams were determined through experimental free and forced vibration analysis at 0, 200, 400 and 600 gauss magnetic flux densities. Vibration amplitude suppression capabilities of the MMC-MRF core sandwich beams subjected to varying magnetic flux densities are determined. The experimental results revealed that the natural frequency, damping ratio and vibration amplitude suppression capabilities of the MMC-MRF core sandwich beams improved with the increase in the applied magnetic flux density. The experimental forced vibration results reveal that MMC-MRF core sandwich beams have excellent vibration amplitude suppression capabilities.