Electrical equivalent circuits with impedance elements modeling the electromechanical behavior of a thin plate with piezoelectric actuators are presented. The dynamic characteristics of a two-dimensional iezoelectric force actuator are represented by a 5×5 impedance matrix, which is equivalent to a five-port electric network. When the dual piezoelectric actuators are assumed to produce average bending momentsor a unit length along the edge at the interfacial surfaces, a 5×5 impedance matrix for these actuators is obtained. While the dual actuators are assumed to produce average bending moments for a unit area at the interfacial surfaces between the plate and the actuators, a 3×5 impedance matrix is presented. According to the theory of thin plates, the impedance of a rectangle thin plate with four simply supported edges is related with vibration amplitude of the plate. The continuity conditions between the actuators and the plates are established by using two approximate hypotheses we proposed. The system impedances are finally obtained by solving the impedance equations of the piezoelectric actuators and the plate. Four numerical examples are analyzed to illustrate the application of this modeling method, and the esults agree well with the results obtained by other methods. Equivalent electric circuits of thinplates with piezoelectric actuators are capable of dynamically analyzing of such complex electromechanical system with 2D piezoelectric actuators.

The electric admittance function of the piezoelectric atches bonded on a beam with an open crack is presented, for the purpose of theoretically evaluating the health conditions of he cracked beam. At first, a sandwich beam with two layers of piezoelectric actuators is regarded as a piezoelectric imorph, and the dynamics of the bimorph is represented by a 5×5piezoelectric impedance matrix. Secondly, the ynamics of the elastic beam is also represented by a 4×4 impedance matrix, which is a degenerative form of piezoelectric mpedance. Thirdly, the open crack is modeled as rotational massless spring and an expression of the equivalent stiffness is adopted, then the spring is used to connect the adjacent elastic beam segments. Furthermore, the cracked beam is represented by three elastic beam segments and one piezoelectric bimorph segment together with one spring. The admittance function of the piezoelectric elements is obtained by solving the linear impedance equations considering the mechanical-electric boundary conditions and the continuum conditions between the beam segments and the spring. Lastly, the effects of the crack depth and location on the admittance are examined in two numeric examples. It is found that the frequency changes and the admittance amplitude changes of the beam due to the crack can be predicted by the piezoelectric admittance function, and the modal frequencies calculated by the proposed method are accord with the results obtained by experiments and other methods. The possible application of the admittance function to detect the crack on the beam is discussed at the end of the paper as well.

由试验获得桥梁用钢14MnNbq 焊接件的疲劳裂纹扩展da/Dn、∆K数据点及其疲劳门槛值 ∆Kth，断裂韧性K。近似采用相同厚度母材试样得到的结果。采用四参数Forman公式利用多元线性回归法拟合试验数据，给出了14MnNbq焊挡件的全范围疲劳裂纹扩展的表达式。在应力比R=0.05,0.25,0.50条件下Forman公式拟合曲线与试验数据吻合较好；相对于母材而言，在疲劳开裂和稳定扩展初期焊接接件疲劳裂纹扩展速率较高。

分析了受一对分布双压电片激励产生弯曲的含裂纹行智能梁的动态特性。智能梁被划分为有限个电阻抗单元，在这些单元中包括双压电晶片梁阻抗单元和弹性梁阻抗单元。分别用一个5×5和4×4的阻抗矩阵表示。基于阻抗单元间和裂纹处的连续条件以及智能梁的边界条件，求解线性阻抗方程，建立裂纹参数及其他系统参数和压电片输入导纳间的关系，并方便地得到含裂纹智能梁受压电片激励的动态特性。通过数值算例，分别对含单边和双边对乐裂纹的智能梁的动态特性进行了讨论，并与已知实验比较，比较的结果说明了分析方法是有效的。

建立了武汉轻轨桥梁的三维有限元模型，对普通钢筋采用一种分层的等效方法，对预应力钢筋采用修正的等效载荷法，将结构要素都纳入到有限元模型中，计算了几种典型工况作用下轻轨桥梁的应力和变形，并对计算结果进行了详细的分析和对比。验证了该桥梁的安全性，提出了对于该桥梁设计及三维有限元方法应用于轻轨桥梁设计的一些建议。