Amplitude‐dependent damping properties of ramie fiber‐reinforced thermoplastic composites with varying fiber content

Abstract

This work presented the experimental study on the free vibration characteristics of short ramie fiber‐reinforced polypropylene composites (RF/PPs). Effects of fiber content and vibration amplitude on damping properties of the fabricated RF/PP composites, such as damping ratio, natural frequency, and associated mode shape, were investigated based on the amplitude‐dependent damping tests and pulsed excitation modal analysis. The results showed that an increase in fiber content increased the damping properties of composites. It was also found that a critical amplitude (Ac) appeared on the amplitude‐dependent damping ratio curves, at which the damping ratio almost reached the maximum value because the highest amount of the fiber/matrix slippage happened in the composite system. The critical amplitudes for composites with 10, 20, and 30 wt% fiber content were of 6, 8, and 10 mm, respectively. Whereas, the vibration amplitude had negligible influence on the natural frequency of those RF/PP composites. The pulsed excitation test results indicated that both the first and second damping ratios presented an increasing trend with the increase of fiber content. And the second damping ratios were higher than their corresponding first damping ratios due to the lager vibration amplitude in the second mode shape, which could generate more fiber/matrix slippage in composites. Additionally, the tensile and flexural properties of the RF/PP composites improved with the increase of fiber content due to the fiber transferring force effect and good interface quality based on the scanning electron microscopy analysis. POLYM. COMPOS., 40:2681–2689, 2019. © 2019 Society of Plastics Engineers