Induced strain actuators have been integrated with conventional structural materials to serve as energy input devices or actuating elements in many engineering applications implementing intelligent material systems and structures concepts. In order to use the actuation mechanism produced by the integrated induced strain actuators efficiently, the mechanics of the mechanical interaction between the actuator and the host substructure must be understood and modeled accurately. A refined analytical model has been developed based on the plane stress formulation of the theory of elasticity for a surfacebonded induced strain actuator/beam substructure system. Closed-form solutions of the induced stress field were obtained in an approximate manner using the principle of stationary complementary energy. The model has also been extended to include the presence of adhesive bonding layers and applied external loads. The results of the current model were compared with those obtained by finite element analysis and the pin-force and Euler-Bernoulli models. It was shown that the current model is capable of describing the edge effects of the actuator on actuation force/moment transfer and interfacial shear and peeling stress distributions that the existing analytical models fail to describe. Good agreement was obtained between the current model and the finite element analysis in terms of predicting actuation force/moment transfer. The interfacial shear stress distribution obtained by the current model satisfies stress-free boundary conditions at the ends of the actuator, which the finite element model is not able to satisfy. The current model correctly describes the transfer of the actuation mechanism and the resulting interfacial stress distributions; thus, it can be used in designing integrated induced strain actuator/substructure systems. Moreover, a new induced strain actuator configuration, which includes inactive edges on the ends of the actuators, has been proposed to alleviate the intensity of the interfacial stresses. The effectiveness of the actuator on the interfacial stress alleviation was verified by the current analytical model and finite element analysis. It was shown that the proposed actuator configuration can significantly alleviate intensive interfacial shear and peeling stresses without sacrificing the effectiveness of the actuation mechanism. The chances of interfacial failure of the integrated structural system, fatigue failure in particular, can thus be reduced. / Ph. D.

In this thesis, the thermomechanical approach with internal variables has been thoroughly analyzed. This approach is based on the combination of thermodynamic principles and continuum mechanics. Therefore it reflects the physical essence of constitutive behavior of materials. Based on this approach, a one-dimensional constitutive model for the two-way shape memory effect and a one-dimensional constitutive model for piezoceramics have been developed, respectively. In modeling the two-way shape memory effect, a residual stress σ_re is introduced as a controlling parameter for the two-way shape memory effect. A further refinement of the transformation kinetics expression for two-way shape memory is derived. It is demonstrated that the material parameters required by this model can be calculated or measured using a standard materials testing apparatus. A numerical study is conducted and the effectiveness of this model is verified. In the constitutive modeling of piezoceramics, a new internal state variable is introduced to relate the macroscopic behavior of a piezoceramic with its micro-properties. A phenomenological formulation of polarization reversal is proposed, and then a fully-coupled thermo-electro-mechanical model is developed. It is shown that the theory developed can describe the electromechanical behavior of piezoceramics well. / Master of Science