Tip vortex induces downwash movement, which reduces the effective angle of attack of a wing. For a low-aspect. ratio, low-Reynolds-number wing, such as that employed by the micro air vehicle (MAV), the induced drag by the tip vortex substantially affects its aerodynamic performance. In this paper we use the endplate concept to help probe the tip-vortex effects on the MAV aeredynamic characteristics. The investigation is facilitated by solving the Navier-Stokes equations around a rigid wing with a root-chord Reynolds number of 9 x 10 4
A whole-field micromechanical deformation analysis was performed on a thick [90 2 /0] n graphite/epoxy laminate. Rail-shear loading conditions were used and deformations were measured by high-sensitivity moire interferometry. Shear strains were determined in in dividual plies and in the resin-rich zones between plies. Nominally equivalent plies exhibited dramatic differences in shear strains. Large shear strains occurred in the resin- rich zones. Relationships were developed to extract average or representative strain values and shear moduli were calculated from these. Effective interlaminar moduli, for design purposes, are given for 0 deg and 90 deg plies as G 13 = 3.2 GPa (470,000 psi) and G 23 = 2.4 GPa (350,000 psi), respectively, and for the laminate as G = 2.7 GPa (390,000 psi).
Prior work has shown that Macro Fiber Composites (MFCs) used in a unimorph configuration provide the largest actuation when bonded to a thin substrate with a high elastic modulus. However, when studying the load bearing capability of the unimorph, research has shown that the optimum solution is not as clear. A large deflection may not correlate with the largest deflection under loading. The work included in this paper studies the bending moment produced when a unimorph, consisting of an MFC bonded to a substrate, is actuated in a four point bend test. The goal of this research is to develop an optimal unimorph layup to provide large deflections and relatively high blocking force for active flight control on Micro Air Vehicles (MAVs). Wind tunnel tests and Digital Image Correlation (DIC) results are presented and discussed.
This work is concerned with wind tunnel testing of an elastic membrane wing intended for micro air vehicles. Erratic flow conditions are a particular problem for the smooth controllability of such vehicles, and so stiff batten structures are imbedded into the trailing edge of the membrane wing, intended to passively washout under aerodynamic loading. This passive deformation is not always effective however, particularly at higher angles of attack, and so this work is intended to provide some understanding of the complex role of wing structure and flight speed upon aerodynamic performance of membrane wings. Several disparate wing structures are fabricated, with varying batten thicknesses and spacing. Data, in terms of measured aerodynamic loads and structural deformation, is given for a wide range of relatively low Reynolds numbers. Drastic changes in lift slopes, stalling conditions, and deformation patterns are found for certain combinations of flight speed and wing structure.
Out of many exciting and unique micro air vehicles (MAVs) being developed at the University of Florida, one MAV design utilizes a bendable wing concept. To minimize the storage volume, the wing is rolled and the MAV is stored inside a canister. To predict the shape of the wing and consequently initial strain produced in the wing, when it is stored inside canister, energy method principal is used. An analytical model is developed which predicts the shape and initial strains in the wing by modeling the wing as a one dimensional composite beam. Results of the analytical model prediction are compared with the experimental observations.
Purpose This paper aims to present the methodology and results of the experimental characterization of three-dimensional (3D) printed acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) parts utilizing digital image correlation (DIC). Design/methodology/approach Tensile and shear characterizations of ABS and PC 3D-printed parts were performed to determine the extent of anisotropy present in 3D-printed materials. Specimens were printed with varying raster ([+45/−45], [+30/−60], [+15/−75] and [0/90]) and build orientations (flat, on-edge and up-right) to determine the directional properties of the materials. Tensile and Iosipescu shear specimens were printed and loaded in a universal testing machine utilizing two-dimensional (2D) DIC to measure strain. The Poisson’s ratio, Young’s modulus, offset yield strength, tensile strength at yield, elongation at break, tensile stress at break and strain energy density were gathered for each tensile orientation combination. Shear modulus, offset yield strength and shear strength at yield values were collected for each shear combination. Findings Results indicated that raster and build orientations had negligible effects on the Young’s modulus or Poisson’s ratio in ABS tensile specimens. Shear modulus and shear offset yield strength varied by up to 33 per cent in ABS specimens, signifying that tensile properties are not indicative of shear properties. Raster orientation in the flat build samples reveals anisotropic behavior in PC specimens as the moduli and strengths varied by up to 20 per cent. Similar variations were observed in shear for PC. Changing the build orientation of PC specimens appeared to reveal a similar magnitude of variation in material properties. Originality/value This article tests tensile and shear specimens utilizing DIC, which has not been employed previously with 3D-printed specimens. The extensive shear testing conducted in this paper has not been previously attempted, and the results indicate the need for shear testing to understand the 3D-printed material behavior fully.
A major challenge in the identification of material properties is handling different sources of uncertainty in the experiment and the modelling of the experiment for estimating the resulting uncertainty in the identified properties.
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