Studies On Damping Modification Of Fiber Reinforced Composites

Fiber reinforced composites have good specific stiffness, specific strength, damping property and low density. As structural materials, composites have been used in aerospace, ships, automobile and other engineering fields. Damping properties of composites are 10-100 times higher than most of common metals, but not exceeding 2%. They need damping modification treatment. This paper improved damping properties of composites by fabricating hybrid fibers composites and structural damping composites, designed new structural damping composites.Carbon fiber/Kevlar fiber hybrid composites are prepared by wet hand lay-up and heat pressing. We tested loss factor by thermal dynamic mechanics analysis technique to evalute damping properties of composites, and studied the influences of the hybrid ratios, stacking sequences and hybrid modes on the damping and mechanical properties of hybrid composites. The results show that the category and quantity of outermost fibers have significant influence on the damping and mechanical properties of composites. When carbon fiber works as surface layer, composites have higher bending properties and lower damping properties. When Kevlar fiber works as surface layer, composites have lower bending properties and higher damping properties. Bending modulus of CF/KF hybrid composites are on the rise with carbon fiber volume fraction increasing. The more hybrid interface number, the better damping properties of interply hybrid composites.This paper studied the influences of frequency and amplitude on the damping and mechanical properties of composites. The results show the loss factor is on the rise with test frequency increasing and amplitude has little influence on damping properties.We fabricated structural damping composites by the co-curing process, studied the influences of moulding process, temperature, damping layer, damping layer thickness and perforated damping layer on structural damping composites. The results show viscoelastic damping layer can be embeded into composites as specific layer and co-cured with composites. It can improve damping properties of composites and decrease modulus of composites. Resin and viscoelastic damping layer have well combined interface. Damping properties of co-cured damping composites depend on dynamic properties of damping layer at different temperatures. The increase of damping layer thickness can improve damping properties of structural composites and reduce bending properties of composites. Prforated damping layer decreases damping properties of composites while the bending properties of composites have an improvement.Finally, we combined two damping modification methods and designed new structural damping composites. One method is conducted by constraint damping treatment on composites. This method improves damping properties efficiently and doesn't decrease stiffness, but increases some thickness and weight. Other method is embeding Kevlar fiber layers into structural composites with interleaved viscoelastic damping layer. This method can improve damping properties efficiently.