【作者】 赵星；

【导师】 钱征华； 刘金喜；

【作者基本信息】 南京航空航天大学 ， 固体力学， 2020， 博士

【摘要】 压电-压磁夹层结构是层状复合材料或器件的重要结构形式之一,其优点是制备工艺简单,且通过调整材料的极化方向可以显著提高复合材料的磁电转换效应。根据磁电转换机理可知,层状结构磁电耦合效应的实现主要依赖于两个先决条件:一是结构边界必须有机械约束来确保主动变形可以传递;二是层间完美的界面连接来保证主动变形可以传递给被动层。前者一般通过结构边界固支或铰支来实现。对于后者,由于层间变形不协调性,在器件生产和服役过程中,界面处很容易发生脱胶、剥离或开裂,从而降低磁电转化效率,甚至导致器件断裂失效。因此,掌握压电-压磁夹层结构断裂失效机理,分析界面裂纹的断裂特性对磁电器件的抗断裂设计具有重要意义。本文利用积分变换和奇异积分方程技术,忽略压电材料中的磁场和压磁材料中的电场,研究了固支边界条件下压电-压磁-压电夹层结构在电场作用下界面裂纹的断裂特性,主要内容包括:界面裂纹静态断裂问题、冲击响应问题以及界面运动裂纹问题。通过数值算例分析了外加电荷载作用下,结构几何参数、材料极化方向及材料性能对界面断裂行为的影响。主要结论为:(1)对于静态断裂问题,当组份比确定时,增加结构层厚度可以有效抑制裂纹扩展;对于有限尺寸的复合材料,主动变形材料所占组份比越大,界面越容易发生开裂。对于平面应变问题,主动变形材料极化方向可以改变界面裂纹的开裂方式,同时也可以影响应力强度因子的大小。材料性能对断裂行为的影响,既依赖于其在变形过程中所扮演的角色,也和界面裂纹的开裂方式有关。(2)对于界面裂纹冲击响应问题,调整主动变形层的极化方向,选择合理的几何参数以及调整组份材料软硬均有助于提高结构的抗断裂性能,其影响规律和静态断裂问题的结论是相似的。(3)对于Yoff型界面运动裂纹问题,裂纹的开裂方式主要依赖于主动变形材料的极化方向;当界面裂纹为I型开裂时,运动速度的增加会促进裂纹扩展;当界面为II型开裂时,运动速度的增加会抑制裂纹扩展。更多还原

【Abstract】 Piezoelectric(PE)-piezomagnetic(PM)sandwich structures consisting of PE and PM layers are one of common forms in layered magnetoelectric(ME)composites or devices.The PE-PM sandwich structures are easily manufactured,and their ME coupling effect can be greatly enhanced by adjusting the polling direction of PE or PM material.According to the ME conversion mechanism,two prerequisites should be essential for the performances of ME devices.One is the mechanical constrain applied at the structure boundary,and the other is the perfect interface coupling between component materials.The former can be easily achieved by the simply supported or clamped boundary.For the latter,due to the incompatibility of the interlaminar deformation,the debonding and cracking easily occur at the interfaces of layered structures in the process of manufacture and service,which would give rise to a reduction of ME conversion coefficient and even lead to fracture failure.Therefore,the interface fracture analyses of PE-PM sandwich structures are significant for the anti-fracture designs of related ME devices.Ignoring the magnetic field in PE layers and the electric field in a PM layer,this dissertation investigates the interface fracture behaviors of PE-PM sandwich structure by integral transform and singular integral equation techniques.The main content includes the static fracture problems,the impact reponses and the moving crack problems.Some numerical examples are presented to show the influences of the structure geometries,poling directions and the material properties on the interface fracture properties.The conclusions can be summarized as follows.(1)When the volume fraction is fixed,increasing the thickness of the structure can suppress the crack growth,whereas for a fixed thickness of the structure,increasing the component ratio of active material can promote the crack growth.The polling direction of the active material can not only change the cracking mode of the interface crack,but also affect the magnitude and direction of the normal and tangential stresses.Additionally,the influences of the material constants on the SIFs are dependent on the roles played by PE and PM medium during the deformation process as well as the cracking mode of interface crack.(2)For the transient responses of the interface crack,the dynamic anti-fracture ability can be improved by adjusting the polling direction,geometric parameters and the material properties.These conclusions are similar to the static fracture problems.(3)For the interface moving crack problem,the cracking mode of the interface crack mainly depends on the polling direction of the active material.The increasing of crack moving velocity can promote the growth of mode-I crack,whereas retard the propagation of mode-II crack.更多还原