About the Dynamic Behaviour of Composite Bars Reinforced with Cotton or Hemp Fibers

In this paper, the authors designed several green composites with natural reinforcements (hemp and cotton fibers) and the matrix is a synthetic resin (epoxy resin). On having produced the samples, the authors determined the dynamic mechanical characteristics. The dynamic parameters were determined from the bar free vibrations. The next experimental rig was used: the bars were clamped at one end and left free at the other end. At the free end, a Bruel&Kjaer accelerometer with 0.04 pC/ms-2 sensitivity was placed, in order to record the beam dynamic response. A force was applied at the free end to bend the beams, and after bending, the force was cancelled and the beams were left to vibrate freely. The accelerometer was connected to a Nexus signal conditioner, and the signal conditioner was connected to a SPIDER 8 data acquisition system made by Hottinger Baldwin Messtec. The acquisition system was connected to a notebook and the experimental parameters were obtained through the CATMAN EASY software. From the free vibrations recording, the next mechanical parameters were determined: the eigenfrequency of the first eigenmode, the damping factors per mass unit and per unit length, the loss factor and the dynamic Young modulus and stiffness. From the results obtained, it can be concluded that the materials with epoxy resin reinforced with hemp have better vibration damping properties as compared to the composites made from epoxy reinforced with cotton fibers.