The implementation of smaller, lighter, and more agile military systems requires new actuation technologies that offer high power density in compact form factors. The Compact Hybrid Actuator Program (CHAP) is pursuing active material based, rectifying actuators to create new actuation solutions for these demanding applications. Our actuator approach is based on thin film NiTi membranes operating in parallel (high intrinsic power density, >125 kW/kg) combined with liquid rectification, MEMS passive check valves, and commercially available power electronics. Previous results demonstrated 8 micron thick membrane actuation with 150 Hz forced convection response and force output of 100N. This paper focuses on two developments critical in scaling up previous single membrane results to power levels sufficient for military applications. This first is the development of SOI MEMS fabricated microvalve arrays which exhibit high flow rate at high frequencies. The second focus area is the design, fabrication, and assembly of a form factor compact actuator. The initial prototype demonstration of this concept shows great promise for thin film NiTi based actuation both in military technologies and in other areas which demand extremely compact actuation such as embedded fluid delivery for biomedical applications.
This paper presents comprehensive studies on sensor performance of an embedded Extrinsic Fabry Perot Interferometer (EFPI) fiber optic strain sensor in an aerospace grade composite system to support fiber optic smart structures (FOSS) development for Structural Health Monitoring (SHM) System. A major portion of this study is focused on establishing the accuracy of the embedded EFPI sensors in a graphite epoxy composite material system at different stress levels under quasi-static loading conditions. The NASA Dryden calibrated EFPI's were used for accurate measurements. Two collocated surface-mounted strain gages and a calibrated surface-mounted EFPI sensor are used to validate the calibrated embedded EFPI sensor. Experimental results suggest that once calibrated, the embedded and surface-mounted EFPI sensors provide robust, reliable and accurate measurement for values up to ~5,400 με higher than sensor's durability limit ~3,000 με at 106 cycles. This validation provides evidence that the sensing information emanating from FOSS can be used to monitor accurate health information.
Nickel Titanium (NiTi) film shape memory alloy (SMA) is integrated with space-qualified polymer and mesh materials for potential use as deployment mechanisms and actuation of flexible space apertures. SMA thin film is successfully applied to Astromesh metal mesh, Kapton, Upilex, and CP-1 polymer films. Sputter deposition of NiTi onto the substrate is used to validate the material system process and demonstrate the NiTi deployment capability. Although successful, the relatively high processing temperatures required to crystallize NiTi onto the substrates requires care. A second approach is demonstrated that deposits NiTi onto a silicon substrate, followed by coating the NiTi with the desired polymer, e.g. CP-1. Micro-electro-mechanical (MEMS) processing steps are then used to remove the silicon substrate beneath the NiTi, thus freeing up the composite membrane (i.e. NiTi + CP-1). Using MEMS fabrication techniques, a hot-shaped small dome shape structure is shaped into the NiTi before deposition of the CP-1 polymer. Activation of the integrated SMA/CP-1 produces deformation of this composite structure without damage. The test articles demonstrate the feasibility to both grossly deploy and locally actuate space-qualified polymer materials.
In this paper, a thin film nickel-titanium (NiTi) shape memory alloy (SMA) was used to develop a prototype compact hybrid actuator. SMA was selected as an actuating mechanism because it had the highest work density among active materials. Combining this attribute with high frequency response of thin films resulted in large power output. High drive frequency was also possible in part from manipulating the liquid flow to directly cool the SMA membranes. The actuator reached a drive frequency of 100Hz while producing 2.6Watts. The results indicated that power output is linearly related to the drive frequency since the volume flow rate increased proportional to frequency.
Recently, there have been significant advances in using magnetostrictive particles in a polymer matrix; finding uses in many applications, both as an active transducer and a passive dumper. Termed magnetostrictive particulate composites (MPC), the material provides capabilities identical or superior to the monolithic material. Fortis Technologies has been pursuing improvements in the applications and fabrication of this innovative material. Specifically, this MPC technology provides a passive, broadband, large temperature range, high stiffness, damping material to be used where current technologies fall short. A novel manufacturing technique based on magnetic fields has been developed to distribute magnetostrictive particulates in a polymer resin and apply it in thin-layer on surfaces for vibration damping in environments typical of turbomachinery fan blades. These magnetostrictive particulates provide damping through domain wall switching, a non-conservative action which provides a high loss factor, and, in turn, significant vibration mitigation. The magnetostrictive damping composites can be easily fabricated into thin films, provide stiffness and strength while also incorporating damping capabilities which exceed in performance and temperature range viscoelastic materials, the current state of the art for applied blade damping. Analytical studies, a finite element analysis and experimental study of the new material in a typical turbomachinery blade loading condition has been conducted and has demonstrated the benefits of this technology.
This paper describes the development of a micro-machined passive check valve for an SMA-based compact hybrid actuator device (CHAD). The overall diameter of the valve is 12 mm and the thickness is 1 mm. The structure houses an array of 56 micro check valves. Each micro valve has a 250 μm diameter orifice covered by 10 mm thick nickel flap. Stoppers on each micro valves limit the displacement of the flaps during an opening. This design allows the Ni flaps to withstand high-pressure gradient created by the actuator while achieving high flow rate. A finite element analysis is used to characterize the static and dynamic behaviors of the valve flap for the prediction on flow rate. The prediction is found to be in good agreement with the experiment on static flow rate. The test results indicate that the flaps are able to withstand pressure difference of 0.28 MPa while achieving flow rate of 20 cc/sec. The valve also has low cracking pressure and reverse leakage.
The development of a piezoelectric hydraulic pump with innovative active valves is presented in this study. The pump structure basically consists of a diaphragm type piezoelectric stack actuator and two specially designed unimorph disc valves acting as inlet and delivery valves. Static and dynamic piezoelectric finite element analyses were used to maximize the delivered fluid volume per stroke and to predict the resonance characteristics of the pump, respectively. A structural optimization technique was performed to optimize the efficiency of the pump versus its geometrical dimensions. A transient CFD model was used to predict flow rates. Dynamic experiments were also conducted and results are in good agreement with those obtained from the simulation.
In this paper, a prototype SMA-based actuator for a compact kinetic energy missile was fabricated. Thin film nickel-titanium was selected as an actuating mechanism because it exhibited high power density compared to other smart materials. This study represents a proof of concept that high drive frequency and high power density can be both achieved with thin film SMA. The thin film reached a drive frequency of 80Hz while achieving a power density of 27900 Watts/kg. As for the pump, the power density was 2.93 Watts/kg, but obtaining higher value can certainly be achieved by reducing the chamber weight through optimization. In any case, CFD analysis revealed that the pump chamber had to be redesigned to change the flow profile because the present design created non-circulating dead zones immediately adjacent to the diaphragm. Therefore by redirecting the liquid flow to directly cool the SMA diaphragm improved the heat transfer and thus improved performance of the actuator can be achieved.
Experimental results on mechanical behavior of Extrinsic Fabry-Perot Interferometric Fiber Optic Strain Sensors (EFPI-FOSS) are presented in this paper. The goal of this study was to determine the accuracy, strength characteristics, and durability properties of both bare (non-embedded) EFPI sensors, and embedded EFPI optical fiber sensors in either a neat resin or aerospace grade composite laminate. Experimental results suggest that the embedded EFPI sensors provide reliable strain measurements for values exceeding 10,000 (mu) (epsilon) under static loading conditions. A major portion of this study focused on evaluating the long term tension-tension fatigue behavior of optical fiber sensors. Test data suggest the EFPI sensors provide reliable data up to 1 million cycles at fatigue strain levels below 3,000 (mu) (epsilon) . For fatigue strain levels above this value, failure of the fiber optic sensor was observed. While the sensor failed it did not influence the strength and fatigue life of the composite coupons. Considering the design strains used in aerospace components, these results provide evidence that the EFPI sensors will survive during the life of typical aerospace structures.