Preparation And Damping Properties Of Epoxy Resin Composites Containing Piezoelectric And Conductive Phases Particles

High-speed railway system has been developed rapidly in recent years; it makes strong market demand for efficient noise and vibration reduction materials. Piezoelectric damping material is a new research hotspot in this field because of its specific energy loss mechanism. In this thesis, epoxy resin (EP) was chosen as the resin matrix in such kind of composites, The niobium-magnesium lead zirconate titanate (PMN) and conductive carbon black (CB) were taken as piezoelectric phase and conductive phase, respectively. The agricultural straw fibers were added, hoping to improve some properties. Multilayer-structured design was also considered to uprate the damping effect. The mechanical and electrical properties, as well as the morphology of the as-prepared materials were studied, and some influencing factors on damping property were discussed.Firstly, we determined the optimal processing conditions for epoxy based composites by experimental studies. Effects of the conductive fillers and their loadings on the properties of the composites were investigated systematically. The results indicated that EP/CB composite reaches the percolation threshold when CB is16wt%which was regarded as the appropriate loading, and that higher conductivity could be obtained by a long time ultrasonic dispersion getting uniform distribution of CB in the composites. A similar result was also obtained using5wt%of carbon nanotubes having larger aspect ratio than CB. Based on the principle of equivalent impedance, a electrical-thermal energy model was proposed for theoretically analysis of the conversion of electrical to thermal energy. The analyses showed that the best efficiency of conversion could be achieved by reducing the imaginary part of the impedance and matching the frequency, and the optimal damping effect at a certain frequency required the resistivity of conductive phase satisfying the condition of R=1/(ωC).Using PMN as the piezoelectric phase, CB as the conductive phase, EP based composites were prepared for further investigations. The formulating experiments showed that the first-order damping ratio reached0.263when PMN is25wt%. Reducing the particle size of the piezoelectric phase PMN could get a better damping effect, and a good effect, the first-order damping ratio of0.269, could be got as the PMN particle size was0.67μm.Agricultural straw fiber was added to the piezoelectric damping material. It was found that the straw fiber could effectively improve the damping ratios, and the largest value of the first-order damping ratio is0.302when straw fiber was4wt%. Exceeding that, with the loading of the straw fiber increasing, the damping effrect of the composites turned worse. The damping property was found to be affected slightly by the size of the fillers, and the best effect was obtained when its size was150-250μm. The piezoelectric damping materials retained their mechanical strengths after adding straw fiber. SEM showed that the straw fibers and the epoxy resin had a good interface when straw fiber was4wt%and8wt%. However, the interfacial binding became worse when the loading of the straw fiber increased up to12wt%, resulting in lowering the strength of the composite.Finally, we preliminarily proposed a multilayered design for improving the damping properties of such kind of the materials containing piezoelectric and conducting phases. In the case of a fixed thickness, a multilayer structure was positive to the damping efficiency of the composites, and when the number of layers was four, the first-order damping ratio could reach the maximum value of0.293.