Enhancement of Mechanical Engineering Curriculum to Introduce Manufacturing Techniques and Principles for Bio-inspired Product Development

ABSTRACT Bio-inspired products and devices take their inspiration from nature 1. Insert a new sequence of instructional materials on bio-inspired concepts into the mechanical engineering curriculum. 2. Disseminate the materials developed for the new modules and course notes through a dedicated web site. As a result of the curriculum enhancement, a new generation of mechanical engineers will acquire the knowledge necessary to develop products and conduct research for a wide variety of applications utilizing bio-inspired concepts. The project (1) integrates emerging manufacturing technologies based on biological principles into the Mechanical Engineering curriculum, (2) utilizes multi-media technology for disseminating course content, and (3) trains graduate students and faculty participating in its implementation in an emerging technology and thereby contribute to faculty development. Specifically, curriculum is being developed that discusses the following manufacturing technologies and principles

Characterizing and modeling the enhancement of lift and payload capacity resulting from thrust augmentation in a propeller-assisted flapping wing air vehicle

Partial funding for Open Access provided by the UMD Libraries' Open Access Publishing Fund.Biologically-inspired flapping wing flight is attractive at low Reynolds numbers and at high angles of attack, where fixed wing flight performance declines precipitously. While the merits of flapping propulsion have been intensely investigated, enhancing flapping propulsion has proven challenging because of hardware constraints and the complexity of the design space. For example, increasing the size of wings generates aerodynamic forces that exceed the limits of actuators used to drive the wings, reducing flapping amplitude at higher frequencies and causing thrust to taper off. Therefore, augmentation of aerodynamic force production from alternative propulsion modes can potentially enhance biologicallyinspired flight. In this paper, we explore the use of auxiliary propellers on Robo Raven, an existing flapping wing air vehicle (FWAV), to augment thrust without altering wing design or flapping mechanics. Designing such a platform poses two major challenges. First, potential for negative interaction between the flapping and propeller airflow reducing thrust generation. Second, adding propellers to an existing platform increases platform weight and requires additional power from heavier energy sources for comparable flight time. In this paper, three major findings are reported addressing these challenges. First, locating the propellers behind the flapping wings (i.e. in the wake) exhibits minimal coupling without positional sensitivity for the propeller placement at or below the platform centerline. Second, the additional thrust generated by the platform does increase aerodynamic lift. Third, the increase in aerodynamic lift offsets the higher weight of the platform, significantly improving payload capacity. The effect of varying operational payload and flight time for different mixed mode operating conditions was predicted, and the trade-off between the operational payload and operating conditions for mixed mode propulsion was characterized. Flight tests revealed the improved agility of the platform when used with static placement of the wings for various aerobatic maneuvers, such as gliding, diving, or loops

A design framework for realizing multifunctional wings for flapping wing air vehicles using solar cells

Partial funding for Open Access provided by the UMD Libraries' Open Access Publishing Fund.Long flight durations are highly desirable to expand mission capabilities for unmanned air systems and autonomous applications in particular. Flapping wing aerial vehicles are unmanned air system platforms offering several performance advantages over fixed wing and rotorcraft platforms, but are unable to reach comparable flight times when powered by batteries. One solution to this problem has been to integrate energy harvesting technologies in components, such as wings. To this end, a framework for designing flapping wing aerial vehicle using multifunctional wings using solar cells is described. This framework consists of: (1) modeling solar energy harvesting while flying, (2) determining the number of solar cells that meet flight power requirements, and (3) determining appropriate locations to accommodate the desired number of solar cells. A system model for flapping flight was also developed to predict payload capacity for carrying batteries to provide energy only for power spikes and to enable time-to-land safely in an area where batteries can recharge when the sun sets. The design framework was applied to a case study using flexible high-efficiency (>24%) solar cells on a flapping wing aerial vehicle platform, known as Robo Raven IIIv5, with the caveat that a powertrain with 81% efficiency is used in place of the current servos. A key finding was the fraction of solar flux incident on the wings during flapping was 0.63 at the lowest solar altitude. Using a 1.25 safety factor, the lowest value for the purposes of design will be 0.51. Wind tunnel measurements and aerodynamic modeling of the platform determined integrating solar cells in the wings resulted in a loss of thrust and greater drag, but the resulting payload capacity was unaffected because of a higher lift coefficient. A time-to-land of 2500 s was predicted, and the flight capability of the platform was validated in a netted test facility

Targeted Feature Recognition Using Mechanical Spatial Filtering with a Low-Cost Compliant Strain Sensor

Partial funding for Open Access provided by the UMD Libraries' Open Access Publishing Fund.A tactile sensing architecture is presented for detection of surface features that have a particular target size, and the concept is demonstrated with a braille pattern. The approach is akin to an inverse of mechanical profilometry. The sensing structure is constructed by suspending a stretchable strainsensing membrane over a cavity. The structure is moved over the surface, and a signal is generated through mechanical spatial filtering if a feature is small enough to penetrate into the cavity. This simple design is tailorable and can be realized by standard machining or 3D printing. Images of target features can be produced with even a low-cost compliant sensor. In this work a disposable elastomeric piezoresistive strain sensor was used over a cylindrical “finger” part with a groove having a width corresponding to the braille dot size. A model was developed to help understand the working principle and guide finger design, revealing amplification when the cavity matches the feature size. The new sensing concept has the advantages of being easily reconfigured for a variety of sensing problems and retrofitted to a wide range of robotic hands, as well as compatibility with many compliant sensor types

Hard Film Coatings for High-Speed Rotary MEMS Supported on Microball Bearings

Abstract: Titanium Nitride (TiN) and Silicon Carbide (SiC) coatings deposited on the surface of silicon raceways are evaluated in a microturbine. Nanoindentation is employed to study the properties of the hard-thinfilm/silicon raceway system and the tribological platform is evaluated through turbine operation curves. TiN films are shown to stay intact over the speeds and forces in the range relevant to future power and energy applications applications, (500-10,000rpm and 10-50mN, respectively), while SiC films wear almost instantaneously. Evaluation of the dynamic friction torque versus normal load relationship between the TiN and bare Si systems suggest the gradual generation of wear debris, comprised of either the raceway or microballs, is negating the benefits of enhanced mechanical properties in TiN

Design, Manufacturing, and Testing of Robo Raven

Most current bird-inspired flapping wing air vehicles (FWAVs) use a single actuator to flap both wings. This approach couples and synchronizes the motions of the wings while providing a variable flapping rate at a constant amplitude or angle. Independent wing control has the potential to provide a greater flight envelope. Driving the wings independently requires the use of at least two actuators with position and velocity control. Integration of two actuators in a flying platform significantly increases the weight and hence makes it challenging to achieve flight. We used our successful previous designs with synchronized wing flapping as a starting point for creating a new design. The added weight of an additional actuator required us to increase the wing size used in the previous designs to generate additional lift. For the design reported in this paper, we took inspiration from the Common Raven and developed requirements for wings of our platform based on this inspiration. Our design process began by selecting actuators that can drive the raven-sized wing independently to provide two degrees of freedom over the wings. We concurrently optimized wing design and flapping frequency to generate the highest possible lift and operate near the maximum power operating point for the selected motors. The design utilized 3D printed parts to minimize part count and weight while providing a strong fuselage. The platform reported in this paper, known as Robo Raven, was the first demonstration of a bird-inspired platform doing outdoor aerobatics using independently actuated and controlled wings. This platform successfully performed dives, flips, and buttonhook turns demonstrating the capability afforded by the new design

Quasi-static and dynamic constitutive characterization of beryllium bearing bulk metallic glasses

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Metallic glasses were first discovered by Pol Duwez in 1960 using the fabrication technique of splat quenching. The mechanical behavior of metallic glasses were first characterized in 1969 from tensile tests conducted on thin ribbons. From these tests it was apparent that metallic glasses possessed tensile fracture strengths of approximately [...], which approach theoretical limits. Compressive mechanical data became available in 1974 with the fabrication of small cylindrical rods of [...]. This data indicated that the quasi-static yield behavior of metallic glasses may obey a pressure insensitive von Mises yield criterion. In 1983, Mechanical tests were conducted on [...] in multi-axial stress states which further confirmed the von Mises yield behavior. However, in 1988, mechanical tests performed on [...] indicated that metallic glasses may instead obey a pressure sensitive Mohr-Coulomb criterion. There is some ambiguity in interpreting the results of mechanical tests performed on metallic glasses. The data from these tests were obtained by testing specimens whose sizes do not guarantee a well-defined stress state. Furthermore, the mechanical behavior of metallic glasses may depend on composition. In order to properly determine the yield behavior of metallic glasses in multi-axial stress states, it was necessary to fabricate specimens with geometries suitable for generating well-defined stress states. In 1993, a new beryllium bearing bulk metallic glass with the nominal composition of [...] was discovered at Caltech. This metallic glass can be cast as cylindrical rods as large as 16 mm in diameter. Specimens could then be fabricated with geometries that conformed to ASTM testing standards. These specimens were then tested in quasi-static compressive, tensile, and torsional stress states at strain rates of [...] to [...] in order to properly characterize the yield behavior of the metallic glass. From these tests it was determined that the beryllium bearing bulk metallic glass obeys a von Mises yield criterion. In addition it was discovered that the ductility of this metallic glass could be altered by adding Boron and varying the quench rate. For the first time, the dynamic compressive yield behavior of a metallic glass could be characterized at strain rates of [...] to [...] by using the split Hopkinson pressure bar. High-speed infrared thermal detectors were also used to determine if adiabatic heating occurred during dynamic deformation of the metallic glass. From these tests it appears that the yield stress of the metallic glass is insensitive to strain rate and no adiabatic heating occurs before yielding