Research On Multi-field Coupling Performance Of 3-D Braided Piezoelectric Ceramic Matrix Composites

In recent decades,because of excellent electro-mechanical coupling properties,piezoelectric composites have been widely used in aerospace,military,medical,robot,micro-electro-mechanical systems(MEMS)and many other precision control fields.Nowadays,piezoelectric composites have become an indispensable advanced intelligent material which occupies an important position in the field of smart materials.Compared to pure piezoelectric ceramic material that has the shortcomings of high brittleness and low shock resistance,piezoelectric composites inherits the excellent piezoelectric properties of piezoelectric ceramics and has good mechanical properties of polymer materials.With the wide application of piezoelectric composites in different fields,the mechanical defects of traditional piezoelectric composites,for instance,the weak performance interlayer easily lead to layer,crack and fail,are increasingly prominent.Connectivity is a key factor that determines the performances of piezoelectric composites.The interface combination mode between piezoelectric phase and non-piezoelectric phase in traditional piezoelectric composites design pattern essentially belongs to traditional laminate design pattern.This paper introduces 3-D braided structure which has excellent overall performance and can completely overcome the phenomenon of delamination into the structural design of piezoelectric composites and designs the 3-D braided piezoelectric composites structure.Improve the mechanical properties of traditional piezoelectric composites by using the three dimensional braided structure.The thesis is summarized as follows.(1)From the aspects of theory,experiment and numerical simulation,the research status of 3-D braided composites and piezoelectric composites are introduced in detailed.The existing problems in the research of piezoelectric composites are pointed out.The necessity of the research is analyzed and FEM is used to study the project in this paper.(2)In this paper,the three-dimensional(3-D)four-step(1×1)rectangular braided procedure,internal yarn spatial topology and internal yarn mechanical model are analyzed in detail.A new geometric model,which uses a cubic spline curve is used to fit yarn trajectory,is established.The unit cell model that can describe braided preform microstructure after fitted using a cubic spline curve has been given.Based on the new proposed geometric model and the stiffness averaging theory,the corresponding elastic constants are predicted.The predicted numerical results are calculated,and compared with the experimental results.The numerical calculations well agree with the experimental results and verify the validity and accuracy of the new geometrical model.(3)This paper introduces 3-D braided structure into the structural design of piezoelectric composites and has designed 3-D braided piezoelectric composites structure that changes the connectivity mode of traditional piezoelectric composites.The novel braided piezoelectric composites model designed in this paper has excellent structural integrity and better mechanical properties.For special electro-mechanical coupling properties of 3-D braided piezoelectric composites,FEM is used to analyze the displacement field mode and electric field mode separately.Then,based on the basic electro-mechanical coupling equations of piezoelectric materials and virtual work principle,the governing equation of coupled FEM model of 3-D braided piezoelectric composites is established.Finally,the analysis of macroscopic mechanical performance,sensing performance and driving performance of 3-D braided piezoelectric ceramic matrix composites are carried out.(4)The effect of temperature field on the properties of piezoelectric composites was studied.According to the constitutive model of the piezoelectric ceramic material,high order shear deformation theory,two order electric potential distribution model,high order temperature field theory and Hamilton variational principle,the finite element governing equation of piezoelectric ceramic force-thermal-electric are established.The influence of temperature field on the sensing performance and driving performance of the braided piezoelectric composites is numerically simulated.