Study of Damping in Composite Beams

Abstract

The vibrations produced in the structures or components are the primary source of problems in machine tools, aircraft and automobile structures. Vibration produces detrimental stresses in these components. These problems can be overcome by introducing damping in these structures. Damping is the dissipation of energy stored due to oscillatory motions. This is one of the vital parameters in the design of a dynamic system in order to enhance their service life. A recent method to improve the damping ability of structures is by fabricating these with composites. In addition, composites are found to have superior strength, stiffness, improved corrosion and fatigue resistance. Composite materials, particularly fiber reinforced (FR) composites are widely used in aerospace and automotive applications due to their less weight and high damping characteristics. The damping of FR composites depends on the structure, diameter and orientation of fiber in matrix. Damping at the fiber-matrix interface dissipates a significant amount of energy. In the current investigation, damping of structural composite beams has been studied to estimate the damping ratios and natural frequencies. The various composite beams used are Glass Fibre Reinforced Epoxy (GFE), Glass Fibre Reinforced Polyester (GFP) and Carbon Black Filled Epoxy (CBFE). To accomplish the requirements of the projected investigation, composite beams of 170 mm cantilever length has been used. The cantilever beams are mounted on a heavy and rigid framework. The frame has provisions to hold the fixed end of the beam rigidly, thus ensuring perfect cantilever condition. Forced vibration is imparted to the cantilever beam using a vibration exciter. A contact type accelerometer is used to obtain the signal and feed it to a digital storage oscilloscope (DSO). Logarithmic decrement method is used to evaluate the damping parameters from the obtained amplitude versus time plots. The damping ratio and natural frequency values are found to be 0.2281 and 1664.94 rad/s respectively for CBFE. CBFE has highest damping property as compared to GFE and GFP