An experimental study on the hydrothermal aging effect on the free vibration properties of hybrid aramid/glass/epoxy composites: Comparison of sea water and distilled water

The purpose of this experimental work is to investigate the impact of hydro thermal aging on the viscoelastic characteristics of hybrid aramid/glass/epoxy composites. In addition to the hybrid composites prepared by vacuum infusion method in two different hybrid configurations ([G3A3](S), [A3G3](S)) and two non-hybrid composite groups ([G6]S, [A6]S) were included for comparison purposes. Composite samples were kept in 4 different aging environments (distilled water 25 degrees C, distilled water 70 degrees C, seawater 25 degrees C, and seawater 70 degrees C) for 6 weeks. To assess the dynamic properties (natural frequency and damping ratio) of composites, a free vibration test was conducted. The vibration test results of the samples were calculated by the half-power bandwidth method. The results revealed that hydrothermal aging did not have serious effects on first-mode natural frequency. It was observed that the damping ratios of hybrid composites increased after hydrothermal aging when compared with unaged samples. The results from dynamic aspects like the storage modulus E' and loss modulus E'' were consistent among themselves. The parameters of the storage modulus E' and loss modulus E'' have both decreased as a result of hydrothermal aging. In addition, the results proved that the rise in temperature accelerated the degradation in mechanically deteriorated composite materials. It was also found that aging in seawater was induced to more deterioration of hybrid and non-hybrid composite materials.