Vibration damping of flax fibre-reinforced polypropylene composites

This work investigates the effects of fibre content and fibre orientation on the damping of flax fibre-reinforced polypropylene composites. Laminates of various fibre contents were manufactured by a vacuum bagging process; their dynamic behaviour were then found from the vibration measurements of beam test specimens using an impulse hammer technique to frequencies of 1 kHz. The frequency response of a sample was measured and the response at resonance was used to estimate the natural frequency and loss factor. The single-degree-of-freedom circle-fit method and the Newton's divided differences formula were used to estimate the natural frequencies as well as the loss factors. The damping estimates were also investigated using a carpet plot. Experiments were subsequently conducted on a range of samples with different fibre volume fractions and orientations. The results show significant variations in natural frequencies and loss factors according to the variations in fibre orientation. Composites containing 45A degrees, 60A degrees and 90A degrees fibre orientation exhibit approximately the same natural frequencies. Composites with differing fibre orientations exhibit different loss factors for the various modes of vibration, and the maximum loss factor is obtained for the case of 45A degrees fibre orientation, with the loss factor generally lying in the range of 2-7 %. It was found that the loss factor increases with increasing frequency and decreases slightly with increasing fibre content. These outcomes indicate that flax fibre-reinforced composite could be a commercially viable material for applications in which noise and vibration are significant issues and where a significant amount of damping is required.