Detection of material interfaces using a regularized level set method in piezoelectric structures

An algorithm to solve the inverse problem of detecting inclusion interfaces in a piezoelectric structure is proposed. The material interfaces are implicitly represented by level sets which are identified by applying regularization using total variation penalty terms. The inverse problem is solved iteratively and the extended finite element method is used for the analysis of the structure in each iteration. The formulation is presented for three-dimensional structures and inclusions made of different materials are detected by using multiple level sets. The results obtained prove that the iterative procedure proposed can determine the location and approximate shape of material sub-domains in the presence of higher noise levels.     

Nondestructive identification of multiple flaws using XFEM and a topologically adapting artificial bee colony algorithm

We present a novel algorithm based on the extended finite element method (XFEM) and an enhanced artificial bee colony (EABC) algorithm to detect and quantify multiple flaws in structures. The concept is based on recent work that have shown the excellent synergy between XFEM, used to model the forward problem, and a genetic‐type algorithm to solve an inverse identification problem and converge to the ‘best’ flaw parameters. In this paper, an adaptive algorithm that can detect multiple flaws without any knowledge on the number of flaws beforehand is proposed. The algorithm is based on the introduction of topological variables into the search space, used to adaptively activate/deactivate flaws during run time until convergence is reached. The identification is based on a limited number of strain sensors assumed to be attached to the structure surface boundaries. Each flaw is approximated by a circular void with the following three variables: center coordinates (x_c, y_c) and radius (r_c), within the XFEM framework. In addition, the proposed EABC scheme is improved by a guided‐to‐best solution updating strategy and a local search (LS) operator of the Nelder–Mead simplex type that show fast convergence and superior global/LS abilities compared with the standard ABC or classic genetic algorithms. Several numerical examples, with increasing level of difficulty, are studied in order to evaluate the proposed algorithm. In particular, we consider identification of multiple flaws with unknown a priori information on the number of flaws (which makes the inverse problem harder), the proximity of flaws, flaws having irregular shapes (similar to artificial noise), and the effect of structured/unstructured meshes. The results show that the proposed XFEM–EABC algorithm is able to converge on all test problems and accurately identify flaws. Hence, this methodology is found to be robust and efficient for nondestructive detection and quantification of multiple flaws in structures. Copyright © 2013 John Wiley & Sons, Ltd.     

铋层状结构无铅压电陶瓷的研究与进展--无铅压电陶瓷20年发明专利分析之三

铋层状结构无铅压电陶瓷因其居里温度高、介电常数低，介电击穿强度大及各向异性大等特征近年来受到广泛研究。本文归纳和分析了铋层状结构无铅压电陶瓷近20年的发明专利．着重介绍了主要体系的压电铁电性能．并对铋层状结构无铅压电陶瓷今后的发展与研究提出了一些建议。     

压电式纳米发电机及其混合器件的研究进展

随着化石能源的过度使用和开采,随之而来的能源和环境问题也日益尖锐,而人们对能源的需求不减反增,因此寻求一种新型的绿色可持续能源是非常必要的。环境中的能量十分丰富,因此从环境中收集能量进行转化是十分有前景的方法。压电材料在受到外界作用发生机械变形时,能实现机械能向电能的转化,因此,压电式纳米发电机作为一种潜在的可持续、绿色能源,近年来受到广泛关注。从压电材料的分类入手,结合其制备方法、结构和性能等,对近年来一些研究成果进行了概述,详细评价了不同制备方法、结构对压电式纳米发电机压电性能的影响,并对今后发展进行了展望。     

钙钛矿型低铅压电陶瓷的制备与性能研究

采用传统陶瓷工艺制备了钙钛矿型低铅压电陶瓷xPbTi0.4716Zr0.4834（Mn1/3Sb2/3）0.0450O3-（1-x）（K0.485Na0.485Li0.03）NbO3[xPMS-（1-x）KNLN],研究了该陶瓷体系的结构和介电、压电与铁电性能以及这些结构和性能与工艺条件的关系。XRD分析表明,随着烧结温度的升高,陶瓷晶相由焦绿石相与赝立方钙钛矿相共存转变为单一的四方钙钛矿相;SEM分析表明,在烧结过程中产生了以（K0.485Na0.485Li0.03）NbO3组分为主的液相,并在烧结温度提高的过程中产生孔洞出现-孔洞消失的现象;电学测试表明,xPMS-（1-x）KNLN陶瓷具有良好的性能,在x=0.75、烧结温度为1250℃时,陶瓷的性能参数为压电常数d33=182pC/N,机电耦合系数kp=34.5%,居里温度TC=165℃,剩余极化强度Pr=21.2μC/cm2,矫顽场强Ec=1.47kV/mm,介电常数εr=1879,介电损耗tanδ=0.92%。     

铌酸钠钾基压电陶瓷的电场诱导介电特性

采用传统的固相反应合成法制备了0.9(K0.5Na0.5)NbO3-0.1LiSbO3(KNN-LS)无铅压电陶瓷,研究了它在不同直流偏置电场下的介电常数的频谱,并分析了直流偏置电场诱导下的相对介电常数变化值Δrε和调谐率K.随着偏置电场的增大,Δrε和K都变大,这与传统的钛酸锶钡陶瓷类的材料结果相反.同时,随着频率的增加,Δrε和K都减小.Δrε随偏置电压的增加而增大,意味着在高的电压下,样品的色散效应增大,其原因可以用空间电荷的极化理论来解释.另外,在外加偏置电压不高的情况下(3 kV/cm),就可以获得相对较大的调谐率1.17%.     

LiTaO3基压电陶瓷的制备与性能研究进展

介绍了LiTaO3的基本性质,综述了LiTaO3基压电陶瓷体系的制备方法、压电铁电性能及应用背景,指出了目前相关研究的重点和难点,并展望了LiTaO3基压电陶瓷今后的研究和发展方向.     

An approach for analysis of poled/depolarized piezoelectric materials with a crack

In this paper, the influence of dielectric medium inside a crack on crack growth, in an infinite poled or depolarized ceramic, has been studied by employing an electric boundary condition derived from the exact boundary conditions proposed by Sosa (1996). The effect of remanent polarization has also been examined. The results obtained show that electric displacement on crack surfaces is not always zero. Hence, for studying fracture problems of piezoelectric ceramics with cracks accurately, the exact boundary conditions should be implemented. In addition, the results indicate that the effect of remanent polarization is equivalent to that of a positive electric field and it cannot be neglected. It is also found that a positive electric field always has a tendency to open a crack, and a negative electric field tends to close a crack.     

凝胶注模在PMN-PZT压电陶瓷中的应用

将凝胶注模成型技术应用于三元系压电陶瓷PMN-PZT的制备工艺中,重点讨论了分散剂、浆料pH值和固相含量对注模浆料粘度的影响,制备出固相含量高达55%(体积分数)、粘度<1Pa.s的压电陶瓷悬浮体,使用该浆料可获得达理论密度95%以上的致密PMN-PZT压电陶瓷。     

LiNbO3基无铅压电陶瓷的研究与进展

LiNbO3基无铅压电陶瓷近年来受到各国学者的关注．已成为继BNT之后的又一重要的无铅压电陶瓷研究体系。本文结合近年来有关LiNbO3基无铅压电陶瓷的研究论文及近20年的发明专利公报,归纳和分析了LiNbO3基无铅压电陶瓷的研究开发进展,着重介绍了LiNbO3基无铅压电陶瓷的主要体系及制备方法、压电铁电性能,并对LiNbO3基无铅压电陶瓷今后的研究和发展提出一些建议。     

Punch problem for piezoelectric ceramic half-plane

Based on the theory of linear piezoelectricity, this study presents an exact solution for a two dimensional indentation on a piezoelectric ceramic half-plane with different contact conditions. The flat-ended indenters are assumed to be rigid. Besides, they can either be insulating or conducting. In addition, different contact conditions, including frictionless, frictional, and adhesive punches are investigated. Lekhnitskii's formulism and Fourier transforms are used to obtain the Green's function of a piezoelectric ceramic half-plane subjected to a point loading. Utilizing Green's half-plane function, we obtain the three integral equations by connecting generalized displacement gradients at the surface and surface loading. Both uncoupled and coupled integral equations can be transformed into a Fredholm integral equation. The analytical closed form solutions of the contact forces and the electric charges under the indenter can be derived by solving the Fredholm integral equations. Once the distributions of the contact forces and the electric charges on the surface are known, the electroelastic response in the half-plane can also be obtained.     

BNT基无铅压电陶瓷的研究与进展--无铅压电陶瓷20年发明专利分析之二

Bi0．5Na0．5TiO3(BNT)基无铅压电陶瓷是目前研究最广泛、最具吸引力的无铅压电陶瓷体系。本文分析了BNT基无铅压电陶瓷近20年的发明专利，着重讨论了相关体系的压电铁电性能，并展望了BNT基压电陶瓷今后的发展趋势。     

深油井超声探测用的压电陶瓷换能器的研究

超声压电陶瓷换能器可以探测5000m以下深处的地质结构和油井固实程度。用于压电陶瓷换能器的PT－PSN陶瓷性能参数是，Tc=380℃,kt=45%,εr=420,tanδ=1.5%，Qm=2200，Ec=733V/mm。经实验测量和现场试验表明，在温度高达200℃时压电陶瓷换能器的性能稳定，测量精度高。     

复杂结构的压电陶瓷成型工艺研究

快速成型和凝胶注模的有机结合是制备复杂结构陶瓷体的有效方法,该工艺的关键是制备高固相、低黏度的注模浆料.采用快速成型和凝胶注模制备复杂结构的PMN-PZT压电陶瓷,重点讨论了分散剂、浆料pH值和球磨时间对注模浆料黏度的影响,并对该工艺和传统模压成型工艺制备的样品进行了形貌分析和电学性能测定.结果表明:当分散剂用量在0.9%~1.1%,pH值为10.5~11.5,球磨时间为8 h时,可以制备出固相含量为55%,黏度小于1 Pa.s的压电陶瓷浆料.使用该浆料制备的复杂结构压电陶瓷体与模压成型工艺相比,显微结构均匀致密、晶粒大小与晶界分布均匀,气孔率更小,电学性能更均匀.     

压电陶瓷的非线性特性校正研究

讨论了非线性对正弦相位调制Fabry-Perot(F-P)干涉术的影响.当用分块积分讨论相调F-P干涉术的输出光强,并作近似处理时,就可以给出类似的结果,所以把这种方法进一步推广到对相调F-P干涉术的研究中.同时提出了两种测量压电陶瓷非线性系数的方法,在实际测量得到的非线性系数基础上,完成`影响大小的数值计算和实验研究.最后证明提出,相调F-P干涉术的初相位应选择在π/4附近以及它可用于测量精细表面的粗糙度或其轮廓.     

Damage identification in framed structures using natural frequencies

A novel procedure for damage identification of framed structures is proposed, where both the location and the extent of structural damage in framed structures can be correctly determined using only a limited number of measured natural frequencies. No knowledge of the modal shapes of the damaged structure is required. On the basis of the characteristic equations for the original and the damaged structure, a set of equations is generated. Two computational techniques, the direct iteration (DI) technique and the Gauss–Newton least-squares (GNLS) technique, are utilized to determine structural damage from the derived equations. Finally, different numerical examples are used to demonstrate the effectiveness of the proposed method. © 1997 John Wiley & Sons, Ltd.     

失谐压电周期结构中波动的局部化

针对压电周期结构中弹性波的局部化问题进行了研究。采用传递矩阵方法推导了结构中相邻单胞间的传递矩阵,采用W o lf方法给出了结构中局部化因子的表达式,给出了数值算例,并分析了压电材料各参数对局部化因子的影响。分析表明,对于不同的压电材料,结构中的频带性质和局部化程度有很大不同,可以通过调整结构的材料特性来改变弹性波的局部化程度,从而改变波动在结构中的传播特性。