Michael Philen

Variable Stiffness Structures Utilizing Fluidic Flexible Matrix Composites

In this research, the capability of utilizing fluidic flexible matrix composites (F2MC) for autonomous structural tailoring is investigated. By taking advantage of the high anisotropy of flexible matrix composite (FMC) tubes and the high bulk modulus of the pressurizing fluid, significant changes in the effective modulus of elasticity can be achieved by controlling the inlet valve to the fluid-filled F2MC structure. The variable modulus F2MC structure has the flexibility to easily deform when desired (open-valve), possesses the high modulus required during loading conditions when deformation is not desired (closed-valve — locked state), and has the adaptability to vary the modulus between the flexible/stiff states through control of the valve. In the current study, a 3D analytical model is developed to characterize the axial stiffness behavior of a single F 2MC tube. Experiments are conducted to validate the proposed model, and the test results show good agreement with the model predictions. A closed/open modulus ratio as high as 56 times is achieved experimentally. With the validated model, an F2MC design space study is performed. It is found that by tailoring the properties of the FMC tube and inner liner, a wide range of moduli and modulus ratios can be attained. By embedding multiple F 2MC tubes side by side in a soft matrix, a multi-cellular F2MC sheet with a variable stiffness in one direction is constructed. The stiffness ratio of the multi-cellular F2MC sheet obtained experimentally shows good agreement with a model developed for this type of structure. A case study has been conducted to investigate the behavior of laminated [+60/0/-60] s multi-cellular F2MC sheets. It is shown that the laminate can achieve tunable, steerable, anisotropy by selective valve control.

Fibrillar Network Adaptive Structure with Ion-transport Actuation

The overall objective of this research is to create a new actuation system, emulating the ability of plants to generate large strains while carrying significant structural loads. Specifically, the authors aim to create high-authority active structures by exploring a revolutionary combination of two innovative ideas inspired by the mechanical, chemical, and electrical properties of the plants. The first idea, inspired by the fibrillar network in plant cell walls, is to create a high-mechanical-advantage actuator structure based on flexible matrix composites (FMCs). Through fiber—matrix tailoring of FMC tubes, one can cause the structure to actuate in certain desired directions when pressurized. Second, the actuator concept is combined with a novel electroosmotic (EO) transport mechanism to regulate pressure inside the FMC tube, inspired by the ion-transport and volume-control phenomena in plant cells. By adjusting the applied voltage across a charged porous membrane, one can control the internal pressure and actuator response. The performance of the system (pressure, response time, stroke, load, etc.) can be tuned by proper selection of the membrane (e.g., pore size, surface charge, membrane pore area, etc.) and FMC (materials, fiber angle, etc.) properties. The new system can use natural seawater (ideal for naval applications) or a small amount of onboard solution with appropriate properties for electroosmotic pumping. This approach has several advantages over traditional actuators, such as large stroke/force, design flexibility/scalability, and electrical activation with quiet operation and no moving parts. In this research, the FMC structure and EO pump (EOP) models are developed and validated, and the integrated model is analyzed to provide guidelines for designing the overall actuation system.

Pressurized artificial muscles

Pressurized artificial muscles are reviewed. These actuators consist of stiff reinforcing fibers surrounding an elastomeric bladder and operate using a pressurized internal fluid. The pressurized artificial muscles, known as McKibben actuators or flexible matrix composite actuators, can be applied to a wide array of applications, including prosthetics/orthotics, robots, morphing wing technologies, and variable stiffness structures. Analytical models for predicting the response behavior have used both virtual work methods and continuum mechanics. Various nonlinear control algorithms have been developed, including sliding mode control (SMC), adaptive control, neural networks, etc. In addition to traditional fluid-driving methods, innovative techniques such as chemical and electrical driving techniques are reviewed. With improved manufacturing techniques, the operational life of pressurized artificial muscles has been significantly extended, thus making them suitable for a vast range of potential applications.

Study of flexible fin and compliant joint stiffness on propulsive performance: theory and experiments

The caudal fin is a major source of thrust generation in fish locomotion. Along with the fin stiffness, the stiffness of the joint connecting the fish body to the tail plays a major role in the generation of thrust. This paper investigates the combined effect of fin and joint flexibility on propulsive performance using theoretical and experimental studies. For this study, fluid-structure interaction of the fin has been modeled using the 2D unsteady panel method coupled with nonlinear Euler-Bernoulli beam theory. The compliant joint has been modeled as a torsional spring at the leading edge of the fin. A comparison of self-propelled speed and efficiency with parameters such as heaving and pitching amplitude, oscillation frequency, flexibility of the fin and the compliant joint is reported. The model also predicts the optimized stiffnesses of the compliant joint and the fin for maximum efficiency. Experiments have been carried out to determine the effect of fin and joint stiffness on propulsive performance. Digital image correlation has been used to measure the deformation of the fins and the measured deformation is coupled with the hydrodynamic model to predict the performance. The predicted theoretical performance behavior closely matches the experimental values.

Force Tracking Control of Fluidic Flexible Matrix Composite Variable Stiffness Structures

Active valve control is investigated for force tracking of fluidic flexible matrix composite (F2MC) variable stiffness structures through analytical and experimental studies. F2MC structures are based upon fluid-filled flexible matrix composite tubes, and previous investigations have shown that several orders of magnitude change in stiffness can theoretically be achieved by opening and closing the inlet valve to the tubes. In this article, a simple analytical model of the F2MC system is developed that captures the dynamics of the composite tube, the servovalve, and the flow of the fluid through the valve. A combined observer/ regulator control system is determined using linearized equations of motion and is applied to the non-linear system. Analysis and experimental results demonstrate that the F2MC system can track a desired force—displacement curve using active valve control.

Fluidic flexible matrix composites for autonomous structural tailoring

In this research, the capability of utilizing fluidic flexible matrix composites (F2MC) for autonomous structural tailoring is investigated. By taking advantages of the high anisotropy of flexible matrix composite (FMC) tubes and the high bulk modulus of the pressurizing fluid, significant changes in the effective modulus of elasticity can be achieved by controlling the inlet valve to the fluid filled F2MC structure. The variable modulus F2MC structure has the flexibility to easily deform when desired (open valve), possesses the high modulus required during loading conditions when deformation is not desired (closed valve - locked state), and has the adaptability to vary the modulus between the flexible/stiff states through control of the valve. In the current study, a closed-form, 3-dimensional, analytical model is developed to model the behavior of a single F2MC tube structure. Experiments are conducted to validate the proposed model. The test results show good agreement with the model predictions. A closed/open modulus ratio as high as 56 times is achieved experimentally thus far. With the validated model, an F2MC design space study is performed. It is found by tailoring the properties of the FMC tube and inner liner, a wide range of modulus and modulus ratios can be attained.

Guided Wave Beamsteering using MFC Phased Arrays for Structural Health Monitoring: Analysis and Experiment

Phased array beamsteering is an effective tool for damage detection and assessment method in a guided wave structural health monitoring system. Monolithic piezoceramic (PZT) actuators have been widely utilized for beamsteering by assuming omnidirectional point sources for each actuator. However, this assumption can lead to erroneous results for a phased array of actuators with anisotropic actuation, such as macro-fiber composites (MFC). The MFC actuators are investigated in this research for beamsteering considering the main lobe width, main lobe magnitude, and side lobe levels and compared to equivalently sized PZT actuators. Analytical models of the MFC and PZT actuators attached to an isotropic plate structure are presented and the genetic algorithm is used to determine the optimal timing sequences of the phased array elements for beamforming enhancement. The analysis results show that the MFC phased arrays have reduced the main lobe width and side lobe levels compared to the PZT phased arrays for a range of beamsteering angles. The area ratios of the MFC arrays are also found to be greater than the PZT arrays for these beamsteering angles. Experiments using the PZT and MFC phased arrays on an aluminum plate are performed and compared to the analysis results. The experiment results agree with the analysis results and demonstrate improved beamsteering of the MFC phased arrays for specific applications.

Variable Modulus Materials Based Upon F2MC Reinforced Shape Memory Polymers

The performance of a new variable modulus composite material based upon shape memory polymer (SMP) reinforced with fluidic flexible matrix composite (FMC) tubes is investigated in this research. The new composite material is a unique combination of shape memory polymers acting as the matrix material with reinforcing embedded FMC tubes. The recently developed FMC tubes are small diameter tubes capable of potentially achieving more than three orders of magnitude change in effective stiffness through utilization of anisotropic flexible matrix composite (FMC) tubes, a high bulk modulus internal working fluid, and simple valve control. Similarly shape memory polymers can achieve more than three orders of magnitude change in stiffness through temperature regulation. To investigate the SMP-FMC variable modulus composite material, an analytical model of the SMP-FMC variable stiffness composite material is developed and design studies are performed. The results demonstrate that the new material system can achieve a wider range and greater selection of modulus values than the SMP or FMC systems alone. Experimental results show good agreement with analysis.

Investigating the energy harvesting capabilities of a hybrid ZnO nanowires/carbon fiber polymer composite beam

Hybrid piezoelectric composite structures that are able to convert mechanical energy into electricity have gained growing attention in the past few years. In this work, an energy harvesting composite beam is developed by growing piezoelectric zinc oxide nanowires on the surface of carbon fiber prior to forming structural composites. The piezoelectric behavior of the composite beam was demonstrated under different vibration sources such as water bath sonicator and permanent magnet vibration shaker. The beam was excited at its fundamental natural frequency (43.2 Hz) and the open circuit voltage and the short circuit current were measured to be 3.1 mV and 23 nA, respectively. Upon connecting an optimal resistor (1.2 kΩ) in series with the beam a maximum power output 2.5 nW was achieved.

Fluidic flexible matrix composite semi-active vibration isolation mounts

Variable stiffness f2mc are investigated for vibration isolation through analysis and experiments. The f2mc are novel structures that have been shown to achieve significant changes in stiffness through simple valve control. The objective of this research is to develop analysis tools to investigate the f2mc variable modulus system for semi-active vibration isolation and to validate the results through experiments. A non-linear analytical model of an isolation mount based on the f2mc tube with a proportional valve is developed. Analysis results indicate that the f2mc-based isolation mount is effective for reducing the force transmitted to the foundation and that the transmissibility ratio can be tuned via proportional valve control. Experimental results agree with analysis results and validate semi-active vibration isolation using a proportional valve.