Preparation And Properties Of Piezoelectric Ceramic/Conductive Particles/Epoxy Damping Composites

Damping materials have been widly used in aerospace shuttles,buildings, machines and communication fields.In research and development of damping material fields,the piezo-damping materials have received much attention for the novel energy loss mechanism.In this dissertation,the diglycidyl ether of bisphenol-A (DGEBA)epoxy resin(EP)was chosen as the resin matrix in composites preparation for its good damping property,lead magnesium niobate-lead zirconate-lead titanate (PMN)was used as piezoelectric material,and conductive carbon black(CB)and carbon nano fibers(CNFs)were taken as conductive materials.The 0-3 PMN/CBEP and PMN/CNFs/EP composites were prepared by resin casting moulding method.The microstructures,mechanical properties,dielectric properties and damping properties of the composites were investigated and the energy loss mechanism of the 0-3 composites was revealed in this dissertation.The conclusions of the work may provide important theoretical basis for the study and application of intelligent piezo-damping materials.The following important conclusions were received in this dissertation.The piezoelectric ceramic and conductive materials take great effects on structure and mechanical properties of the 0-3 piezoelectric ceramic/conductive materials/epoxy resin composites.When the ceramic volume fraction is less than 20%, the piezoelectric ceramic paticles and conductive powders scatter well in the epoxy resin matrix,and the flexural strength of the composites increase with the ceramic fraction increasing.When the ceramic volume fraction is more than 30%,the flexural strength of the composites decreases with the ceramic fraction increasing.The flexural strength of PMN/CB/EP composite rises a little with CB content increasing then decreases with CB content increase.The flexural strength of PMN/CNFs/EP composite steps down to a maximum value then rise gradually for the reinforcement of CNFs with the increase of CNFs contents.In addition,the 0-3 PMN/CB/EP and PMN/CNFs/EP composites have high modulus,about 2～6GPa,so the composites can act as structural damping materials or be used together with structural materials. Piezoeletric ceramic greatly affects the dielectric property of PMN/EP composite. With the increase of PMN volume fraction,the dielectric constantεof PMN/EP composite increases nonlinearly and the dielectric loss rantδdecreases.When the PMN volume fraction increases from 0%to 50%,εincreases form 4.7 to 29.87.Dielectric constant e decreases with the increase of frequency,and the higher PMN fraction the more decrease of dielectric constant.The particle size of PMN ceramic also greatly affects the dielectric constant of PMN/EP composites.Dielectric constant of PMN/EP composite prepared with large particles is higher than that with small particles.With the increase of temperature,the dielectric constant shows a little increase,andε-T curve is rather flat in the testing temperature range 20～150℃.Conductive particles greatly affect the electric property of composites.With the increase of conductive particles,the electric resistance of composites fells rapidly.The PMN/CB/EP and PMN/CNFs/EP composites show an insulator to semiconductor transition respectively when the CB content is 6%of epoxy resin and CNFs content is 0.6%of epoxy resin and the electric risistivity is about 10~8Ω·m.The conductive particles content of insulator-semiconductor transition is called percolation threshold. With the increase of conductive particles,the dielectric constantεand dielectric loss tan6 increase,εand tanδincrease rapidly at the percolation threshold content.At the frequency range 1kHz～1MHz,εand tanδwith frequency increase,especiallyεand tanδdecrease rapidly when the frequency is lower than 10~5 Hz.Piezoeletric ceramic content affects the damping property of PMN/EP composite. When PMN partical size is 7～35μm and volume fraction is 20%,PMN/EP composites show the best damping property with the damping loss factor peak value (βmax),the integral area between loss factor curve and temperature axis(TA)and the damping temperature range(△T)all reaching to maximum.In PMN/EP composites, the damping mechanism consists of 3 parts:visoelastic damping of epoxy resin, interface friction loss and dielectric loss.The damping loss factor increase when the PMN/EP composites were modified by conductive particles.Because of the piezo-damping contribution,the PMN/CB/EP and PMN/CNFs/EP composites show the best damping properties when the conductive particles content is of percolation threshold.Dynamic load and frequency take some effects on composites and the piezo-composites may realize some active damping control.The optimum condition of piezo-damping is that the electric resistance of compsites lies in insulator-semiconductor transition,and the electric risistivity is about 10~8Ω·m.At the percolation threshold the conductive particles can form good conductive net and transform the electric charge to thermal energy efficiently.In piezoelectric ceramic/conductive particles/epoxy resin composites,the piezo-damping,dielectric loss,viscoelastic damping and interface friction energy loss contribute the damping properties synergetically.