System Reliability Analysis Of Piezoelectric Truss Structures

For a strong and increasing demand for vibration and shape control, intelligent structures receive a considerable interest in the field of aerospace, specially. Applications of intelligent structures consisting of large numbers of distributed sensors, actuators, and processors are found in a very broad range of industries. Intelligent structures are structural systems which include active materials, such as piezoelectrics, electrostrictives, magnetostrictives, or shape memory alloys etc. Because piezoelectric materials offer many advantages compared to other active materials, piezoelectric materials are increasingly used in various intelligent structures. As a storage dielectric or a brittle material for the applications, it is ineluctable that there are the problems of electrical failures and mechanical failures in it. Otherwise, because of the uncertainty factors of structure system or its work environment, the reliability analysis is becoming more difficult for piezoelectric intelligent structures. Along with the extension of their use, the reliability of intelligent structures has been an important issue. it is necessary to make stochastic analysis of piezoelectric structure and evaluate its reliability.The thesis has made some progress in reliability analysis of intelligent structure with the electrical/mechanical failure have been taken into account. The main areas covered by the thesis are:1. The performance of mechanics and electricity about piezoelectric crystal was discussed and studied. The drive techniques of piezoelectric actuators were introduced basing on the study of piezoelectric effect. Based on the thermodynamic principle, the generalized constitutive relations of piezoelectric materials were obtained. The interrelation of the each piezoelectric parameters were expatiated, also according to the IEEE Standard, the comparability and the bilateral coupling relationships between mechanical energy, electrical energy and thermal energy were discussed.2. The avalanche mechanism of dielectric materials was introduced, and the complexities of the process of electrical breakdown were explained, so the statistics methods act as a more and more important role in this field. Assuming a Maxwell-Boltzmann distribution of defect energies that can produce micro-shorts, the statistical formula of electrical breakdown of piezoelectric materials was presented. Moreover, the comparative analysis with the weak point theory was given, and the limitation of the weak point theory was also pointed out.3. The electro-mechanical coupling equations of spring-preloaded piezoelectric actuator were presented, the maximize displacement/force outputs were analyzed in theory. A numerical example was given to show the feasible range of stiffness ratio between the piezoelectric stack and the spring.4. With the principle of minimum potential energy for piezoelectric stack applied, solving formulae of the finite element method was established. On the basis of analysis above, the electro-mechanical coupling finite element formulation of piezoelectric active bar, which are commonly composed of a piezoelectric stack and two metallic bars, was particularly deduced.5. Combining the mechanical character of piezoelectric truss structure, the reliability analysis of piezoelectric truss structure was discussed, the safety margin functions for reliability analysis were established, adopting Advanced First Order Second Moment (AFOSM) and Taylor expansion Stochastic Finite Element Method (TSFEM), the method of reliability of piezoelectric truss structure was given, and using the theory of reliability, the reliability index of piezoelectric truss structure system was acquired by Probabilistic Network Evaluation Technique, (PNET). Finally, numerical example was presented to explain the detailed process and demonstrate the validity and effectiveness of the method.