The braided composite actuator is a pressure-driven muscle-like actuator capable of large displacements as well as large blocking forces. It consists of an elastomeric tube reinforced by a sleeve braided by high performance fibers. In addition to the actuation properties, this actuator can also exhibit a large change in stiffness through simple valve control when the working fluid has a high bulk modulus. Several analytical models have been previously developed that capture the geometrical and material nonlinearities, the compliance of the inner liner, and entrapped air in the fluid. The inter fiber yarn compaction in the fiber layer, which is shown to reduce the effective closed-valve stiffness, is studied. A new analytical model for uniformly deformed actuators is developed to capture the compaction effect. This model considers the inter fiber yarn compaction effect and the fiber extensibility as well as the material and geometric nonlinearities. Analysis and experimental results demonstrate that the new compaction model can improve the prediction of the response behavior of the actuator. The compaction model is improved by considering the yarn bending stiffness. The governing equations are derived and the solution algorithm is presented. / Ph. D.

Epoxy composite laminated piezoelectric stress-enhanced actuators (ECLIPSE) have been developed for potential applications by the United States Air Force and others. This class of actuators offers several advantages over other unimorph actuators such as lighter weight, design flexibility, and short production time. Anisotropic differential thermal expansion is utilized in the design of the actuators to achieve large out-of-plane curvature and place the brittle piezoelectric ceramic in residual compression. The numerous composite material choices and configurations can be used to control characteristics of the actuator such as radius of curvature and force output. ECLIPSE actuators were characterized during this study. They were made from layers of Kevlar 49/epoxy composite and a lead zirconate titanate ceramic (PZT) plate. All ECLIPSE actuators tested were built with a PZT plate with the same dimensions and material, but had different layup configurations. By changing the stacking order of the composite and PZT material, characteristics of the actuator were altered. The performance of each ECLIPSE actuator was compared. The maximum achievable displacement of each actuator was measured by cyclically applying an electric field at low frequency between zero and the maximum electric field allowable for the piezoelectric material. The frequency was also increased to a resonance condition to characterize the fatigue behavior of these actuators. In addition, the force output of various actuators was measured with a four-point bending apparatus. The experimental data was compared to a classical lamination theory model and an extended classical lamination theory model. These models were used to predict actuator behavior as well as to calculate the stress and strain distribution through the thickness of the actuator.

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