【作者】 刘维华；

【导师】 陈文；

【作者基本信息】 武汉理工大学 ， 材料学， 2008， 博士

【摘要】 1-3型压电复合材料的厚度机电耦合系数与径向机电耦合系数的比值k_t/k_p远大于同类陶瓷材料,使其各向异性大,可提高换能器的分辨率、改善脉冲的响应时间。同时可以通过控制纤维体积含量大幅度提高静水压灵敏度,适合制作高灵敏度、宽带、窄脉冲的换能器,是医疗超声、无损探伤和水听器的理想材料。本文在分析1-3型压电复合材料研究现状的基础上,针对换能器应用对压电材料的性能要求,采用塑性聚合物方法制备压电纤维,排列-浇铸法制备1-3型压电复合材料。系统地研究了压电陶瓷组成、陶瓷固含量、纤维体积含量及长径比等因素对1-3型压电复合材料的压电、介电、铁电性能和声阻抗的影响,获得了压电相性能对复合材料性能的影响规律。通过有限元模拟计算,建立了1-3型压电复合材料的振动模型,得到了与实验结果相吻合的研究结论。（1）采用塑性聚合物方法分别制备了截面为圆形和方形的PZT5、PMnS-PZN-PZT及PSN-PZN-PZT压电纤维,研究了塑性聚合物方法制备塑性泥料的制备工艺、压电陶瓷纤维的成型工艺及环氧树脂的固化工艺,分析了泥料中陶瓷固含量、烧结条件对纤维结构与性能的影响。陶瓷固含量对材料的力学性能和铁电性能则产生非常大的影响,当陶瓷固含量为86%时,可获得可塑性较好、有一定强度的压电纤维素坯。经过1190～1280℃处理2～4h,压电纤维的强度较高、结构致密、晶粒大小均匀,约2～5μm,此时纤维力学性能和铁电性能均达到最佳;（2）纤维长径比对其压电与介电性能产生大的影响,当t/d=4左右时,各性能指标达最大值。纤维横截面形状对压电与介电性能及其随长径比的变化规律不产生任何影响,但纤维截面形状对其应力.应变行为产生大的影响,圆截面纤维比方形截面具有更大的应变。在同一应力作用下,PZT5纤维的应变非常大,而PMnS-PZN-PZT纤维的抗拉强度则可以达到43.5MPa,是PZT5纤维的2倍;（3）以甲基四氢苯酐为固化剂、邻苯二甲酸二辛脂为塑性剂和2,4,6-三-（二甲胺基甲基）-苯酚作促进剂组成的环氧树脂固化体系,固化温度及固化速度适中,固化后无气泡产生。随纤维体积含量φ的增加,介电常数、剩余极化强度与矫顽场增大,但均低于纯陶瓷,压电电压系数d₃₃、机电耦合系数k_p和k_t、声阻抗Z显著增大而压电应变系数g₃₃明显降低,且k_t和g₃₃值高于纯陶瓷的性能,Q_m比陶瓷相小很多,使得1-3复合材料具有较高的g₃₃/d₃₃和k_t/k_p,表现出很好的各向异性;（4）复合材料的长径比对径向谐振、厚度谐振及横向结构模都会产生很大影响,随压电纤维长径比的减小,横向结构振动模干扰减弱,此时,复合材料的串并联谐振频率f_s、f_p升高,带宽增加。因此,可以通过调整材料的厚度获得单纯的谐振模。但是压电纤维的长径比不能太小,长径比太小的复合材料的d₃₃值很低,压电性能太差,当压电纤维长径比位于2≤t/d≤4之间时,复合材料的性能较佳,且具有单纯的厚度振动模式。复合材料的介电常数和介电损耗受压电相性能的影响非常之大,复合材料的性能变化规律同压电纤维性能的变化规律相同,因此可以通过改变压电纤维的性能来调节复合材料的性能;（5）通过模型设计,采用有限元分析了1-3压电复合材料在电场作用下的应力应变情况,研究了纤维体积含量及长径比对1-3型压电复合材料的介电性能、压电性能的影响。结果表明:纤维的长径比对纤维振动模式产生大的影响,长径比较小时同时具有厚度振动与径向振动,长径比较大时同时具有厚度振动与弯曲振动,当长径比为t/d=2～4之间时,可获得单纯的厚度振动模式。压电纤维上的应变和应力均远大于环氧树脂上的应变和应力,而且在陶瓷纤维与环氧树脂的界面上出现了应力集中。压电常数d₃₃随着纤维体积含量的增加迅速增大,最后趋于饱和,介电常数随着纤维体积含量的增加几乎呈线性增加。有限元模拟结果与实验结果吻合,能够很好的指导材料设计和制备。更多还原

【Abstract】 The ratio of thickness model electromechanical coupling factor to radial model electromechanical coupling factor of 1-3 piezoelectric composites is much larger the that of similar piezoelectric ceramic.This leads to the anisotropism of the composites, and will raise the transducer’s resolution to improve the response time of the pulse. Additionally,the hydrostatic pressure sensitivity of the composites can be improved by changing the fiber volume fraction.So,this kind of material is suitable for transducers with high sensitivity,wide bend and narrow pulse,which have been widely used in medical ultrasonic,nondestructive test and hydrophone.In this article,the development of 1-3 composites was discussed.PZT5 fibers were fabricated by viscous polymer processing（VPP）.1-3 piezoelectric composites were prepared by arranging ceramic fibers and casting epoxy resin.Based on its use for transducer,the influences of ceramic composition,solid content,ceramic volume fraction and aspect ratio on piezoelectric properties,dielectric properties,ferroelectric properties and acoustic impedance were studied,and the influence of piezoelectric phase on the properties of 1-3 composites was achieved.Vibration mode of 1-3 piezoelectric composites was built and calculated by finite element method,and the results was consistent with the experimental result.（1） PZT5,PMnS-PZN-PZT and PSN-PZN-PZT ceramic fibers were fabricated by viscous polymer processing（VPP）.The procedure of VPP,the formation of piezoelectric ceramic fiber and the solidify of epoxy were studied.The affects of organic and sintering condition on fiber structures and properties were analyzed.The solid content has significant impact on the mechanical and ferroelectric properties,and the green ceramic fiber with good strength and plasticity,was obtained when solid content is 86%.After being sintered at 1190-1280℃for 2-4h,the fiber was dense,the crystal size was uniform（about 2～5μm）,and the mechanical and ferroelectric properties of fibers were best.（2） The influences of aspect ratio t/d on properties of 1-3 composites were tremendous, and all the properties parameter reached maximum value at t/d～4.Fiber cross-section shape has significant impact on the stress-strain behavior of the fibers,but no influence on the piezoelectric and dielectric properties.The tensile strength of PMnS-PZN-PZT fiber is 43.5MPa,which is 2 time than that of PZT5 fiber. （3） After cured at a suitable temperature,it was found that the structure of epoxy resin was tight and almost had no pore when the curing agent was methyl tetrahydrophthalic anhydride（THPA）,plasticizer was dioctyl phthalate（DOP） and promoter was 2,4,6-c-（dimethyl-amino） -phenol as.With increasing the ceramic volume fraction,the relative permittivity constant rose linear,remnant polarization P_r and coercive field E_c, piezoelectric strain constant d₃₃,electromechanical coupling factors k_p and k_t and acoustic impedance Z gained prominently but the piezoelectric voltage constant g₃₃ decreased.And k_t and g₃₃ of the composites were both higher than those of pure ceramics, but Q_m was smaller.These lead to 1-3 piezoelectric composites has high values of g₃₃/d₃₃ and k_t/k_p,and has great anisotropic property.（4） Aspect ratio has significant impact on the planar-mode,thickness-mode and lateral-mode resonances of the composites.With the aspect ratio decreasing,reducing lateral-mode resonances disturbance and the series and parallel resonant frequency,f_s and f_p, increased at the same time,which expanded the bandwidth.This implied that single resonance mode can be obtained by changing the thickness of the composites.But if the aspect ratio is too small,the d₃₃ value of the composites will be too low for using.When 2≤t/d≤3,the composites has single resonance mode and fine properties.The dielectric constant and loss of the composites varied with the properties of the piezoelectric ceramic, so the properties of composites can be controlled by changing fiber’s properties.（5）After designing and building modes,the stress-strain of 1-3 piezoelectric composites under the electric field was analyzed by the FEM simulation.The influences of fiber volume fraction and aspect ratio on dielectric and piezoelectric properties were studied.The simulation results shown that the aspect ratio has significant impact on the resonance modes,small aspect ratio leads to thickness-mode and planar-mode resonances, while large ratio leads to thickness-mode and bend-mode resonances.When t/d=2～4,there is single thickness-mode resonance.The stress and strain on the piezoelectric ceramic fiber are much bigger than those on epoxy and stress focus appeared on the interface between fiber and epoxy.With increasing the ceramic volume fraction,d₃₃ increased until it reaches a saturation value the and relative permittivity constant rose linear.The results of FEM simulation was consistent with the experimental result,which were useful for designing and fabrication of the composites.更多还原