Piezohydraulic actuation is the use of hydraulic fluid to rectify the high frequency, small stroke oscillation movement of the piezoceramic stack into a unidirectional movement at a specific combination of stroke and force. In recent years, piezohydraulic pumps have been studied and developed by several groups. This paper presents two steady flow models based on different approximations of the hydraulic fluid. In the first model we assume a fully developed incompressible viscous flow, and in the second model we incorporate the compressibility of hydraulic fluid into our model. These two models are derived based on the energy equations for hydraulic flow in a circular pipe. Major and minor losses are identified and incorporated into the models. Assumptions and approximations were made to minimize computation effort while achieving good accuracy. A piezohydraulic actuation system with active valves is then built and tested. Comparison with test results shows that the simulations accurately predict system performance under loads at which value leakage is not present. The results reveal that friction losses due to viscosity are a major limitation of performance for the current test setup when operating at higher frequencies. Timing studies of the active vales show the valve timing is important to the performance of the system.

Biological systems such as plants produce large deformations due to the conversion of chemical energy to mechanical energy. These chemomechanical energy conversions are controlled by the transport of charge and fluid across permeable membranes within the cellular structure of the biological system. In this paper we analyze the potential for using biological transport mechanisms to produce materials with controllable actuation properties. An energetics analysis is performed to quantify the relationship between the introduction of chemical energy in the form of ATP to the resulting osmotic pressure variation within an enclosed membrane. Our analysis demonstrates that pressure variations of between 5 and 15 MPa are achievable. The pressure variations are then coupled to a finite element analysis to determine the ability of organized arrays to produce extensional and bending actuation in thin membranes. Our analysis demonstrates that internal pressure variations on the order of 10 MPa can produce actuation materials with extensional energy density on the order of 100 kJ/m3 and bending energy density on the order of 10 kJ/m3.

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Microcapsules are micron-sized hollow particles that can be synthesized with fluid encapsulated in the interior. The microcapsules can be used as a potential actuation technique by incorporating stimulus-responsive materials, such as permeselective, light-sensitive and electrically sensitive materials. The microcapsules range from 10 to 80 microns in diameter and wall thickness normalized to radius might range from 0.05 to 0.5. The actuation concept is to control the size of the microcapsules by varying the interior fluid pressure using an external stimulus. This paper presents efforts to model the performance and capabilities of microcapsules as micro actuators. We assume the pressure of the fluid inside of the microcapsules can be controlled by certain technique, such as thermal, electro or optical stimulus to the fluid. This paper will focus at modeling the performance of microcapsules under known pressure variation of fluid inside. First the paper compares a thin-wall model to a thick-wall model and identifies that thin-wall theory is not accurate enough for microcapsules. Simulation results show that energy density inthe order of 3J/cm3 is theoreticaly achievable for thick microspheres. Two type of materials are studied as the materials encapsulated in microcapsules. Their constitutive equations are then incorporated into the thick-wall model. Simulations show hydrocarbon solvents are much more efficient than ideal gas in terms of actuation performance.