Research On Structural Design And Properties Of Three-dimensional Braided Piezoelectric Composites

Thanks to the unique piezoelectric properties,piezoelectric composites have been widely used in sensor,drive,vibration control,structural health monitoring,micro-electro-mechanical systems and other high-tech fields.With the development of the research on piezoelectric composites,the disadvantages of mechanical properties are becoming more and more obvious,such as the poor adhesion between the piezoelectric materials and no-piezoelectric materials,easy to split,easy to crack and rapid crack growth.Piezoelectric ceramic matrix composites have high brittleness,low toughness,high sensitivity,and unable to withstand mechanical shock and other defects.In order to improve the mechanical defects of piezoelectric composites,three-dimensional(3-D)braided piezoelectric composites is designed by combining the 3-D braiding technique with the piezoelectric composite technology.Compared with the existing piezoelectric composites,the 3-D braided piezoelectric composites have great advantages in microstructure and macroscopic properties.The main contents of this dissertation are outlined as follows.(1)The current research status of the piezoelectric composites and microstructure of 3-D braided composites are introduced in detail.The problems existing in the research work of piezoelectric composites and 3-D braided composites are briefly summarized,and the design basis of 3-D braided piezoelectric composites is pointed out.The main research contents,purpose and significance of this paper are explained.(2)Based on the 3-D four-step rectangular braiding process,the variation of the cross section and the spatial orientation of braided fiber bundles are analyzed.The geometric model of 3-D braided preform is established by using the conic to fit the internal fiber bundle.The microstructure of 3-D braided piezoelectric composites was studied.According to the mixing rule and the stiffness averaging theory,a numerical analysis model of 3-D braided composites is established.The effective elastic constants of braided composites are numerically predicted.(3)According to the theory of electro-mechanical coupling and finite element method,a numerical analysis model of the effective electro-elastic constants of 3-D braided piezoelectric composites is established.The effect of fiber volume fraction on the effective electro-elastic properties of 3-D braided piezoelectric composites is investigated.In addition,the difference of the effective electro-elastic properties of 3-D braided piezoelectric composites and continuous straight fiber reinforced piezoelectric composites is analyzed.(4)The electro-mechanical coupling properties of 3-D braided piezoelectric composites are systematically studied through the cantilever beam structure and intelligent wing structure.According to the inverse method and the finite element method,the mechanical and electrical responses of the piezoelectric cantilever beam in the electro-mechanical coupling field are theoretically and numerically analyzed respectively.The microscopic and macroscopic mechanical properties of different piezoelectric materials cantilever structures are investigated.The braided piezoelectric composites is applied to the smart wing structure,and the sensing performance and driving performance are studied.