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Micro/nano unmanned aerial systems are an emerging class of vehicles uniquely suited to performing covert missions. A linear model for the heave dynamics of a robotic samara (winged seed) in hovering flight was identified from data collected external to the vehicle by a visual tracking system. Insight gleaned from the implementation of feedback control includes a characteristically overdamped system in climb, which differs from the underdamped descent characteristic observed. Identification and error estimation efforts used a frequency response-based system identification. The two robotic samara vehicles of differing scale compared in this study represent the first demonstration of controlled flight of a vehicle of this kind. DOI: 10.2514/1.47197

The concept of a dual stiffness sensor that measures material degradation at the micromechanics scale and introduces damage variables to reflect average material degradation at a macromechanics scale is developed. The idea of a mechanical multifunctional dual stiffness sensor for in situ real-time stiffness and energy density measurements is motivated by Eshelby's equivalent inclusion theorem. A complete analytical derivation is presented and the use of a dual stiffness/energy sensor to diagnose damage and to determine the remaining life of structures is evaluated. A numerical verification using finite element analysis is presented, and the results indicate that the sensor can be used for diagnostics and prognostics of structures. A distributed array of sensors is used to determine the onset and location of damage. Experimental results presented for uniaxial experimental tests under monotonic quasi-static loading conditions indicate that the concept can easily be implemented. For a sensor pair of known geometry and material properties, the Esheiby tensors are independent of the host: A methodology was thus developed to detect material properties of different hosts and was used to predict accurately elastic material properties of diverse materials.

This paper develops an analytical model to simulate the gear mesh contact for a spur gear pair with and without tooth damage. Three common gear tooth faults are simulated including pitting, wear and root cracks. The effect of tooth face width on detection sensitivity for pitting and the effect of crack width on detection sensitivity for crack are investigated. Using static performance measures, such as transmission error, results suggest that basic gear design parameters, such as diametral pitch, pressure angle and number of teeth, may have a significant effect on damage detection sensitivity. It appears that a decrease in diametral pitch will enhance damage detection sensitivity for all the three types of damage. An increase in pressure angle or number of teeth will enhance detection sensitivity for pitting damage, but tends to decrease the sensitivity to crack or wear damage. [DOI: 10.1115/1.1519275]

Damped periodic flight trajectories achieving optimal fuel savings for hypersonic flight include scramjet propulsion. Previous studies of periodic cruise have neglected to impose the constraint that the ratio of kinetic to potential energy stay the same at the endpoints of a period. The new parameterization together with energy ratio constraints leads to fuel savings of around 45% for a version of the HL-20 spaceplane vehicle.

In this paper, we investigate ultrasonic guided wave (GW) sensing performance of a magnetostrictive composite patch sensor (MCPS) in use of a structural health monitoring system for metallic plates. A composite patch of the MCPS consisted of magnetostrictive powders and binding epoxy, where flake- and granular-type Galfenol and spherical nickel particles were considered to examine the effect of particle shape on sensing capability and directional sensitivity. Galfenol flakes with the surface parallel to the (200) crystallographic planes exhibit good field sensitivities in magnetic and magnetostrictive properties when an in-plane field is applied. Shape anisotropy disappears for the conventional spherical shape, accompanying with a large magnetizing field and poor field sensitivity. The 60-kHz GW was successfully captured by the three different MCPSs. Among them, the MCPS with the Galfenol flakes showed the best sensing performance because of their excellent field sensitivities in magnetization and magnetostriction. In addition, the composite patch was configured into a uniaxial comb shape to promote the magnetic shape anisotropy feature of the magnetostrictive patch by itself. Due to the unique configuration of the Galfenol composite patch, the equivalent MCPS presented outstanding directional sensitivity for the GWs propagating along the orientation of the comb fingers. [ABSTRACT FROM AUTHOR]

This paper presents the external loading effects on an ultrasonic guided wave (GW) magnetostrictive sensor using a nickel disk patch permanently attached to a thin metallic waveguide plate. The circular magnetostrictive patch transducer (CMPT) consists of the surface-bonded nickel patch and a detachable magnetic circuit device enclosing a ring-shaped sensing coil and cylindrical biasing magnets. Various compressive and tensile stresses were applied to the nickel patch on account of the buckling response of the plate structure. Strain gauges attached to the nickel patch, a Hall effect sensing device, and a laser displacement sensor were utilized to verify the in-plane deformation and the corresponding magnetic flux density change of the nickel patch and the plate’s central deflection, respectively, under various external loading conditions of the plate. Several PZT wafers also mounted to the plate were individually used to generate a 30 kHz toneburst GW, which is less sensitive to local stiffness changes of the plate due to the buckling mode. The external loading effects on the CMPT were determined by evaluating the peak-to-peak amplitude variation of the direct arrival waveform of the GW signals acquired by the PZT and CMPT sensor networks. The experimental results demonstrate that the external load applied to the waveguide structure induces compressive and tensile stresses in the nickel patch, leading to distorted GW sensing performance and the directional pattern of the CMPT. Although the presented CMPT has an omnidirectional sensing profile due to its design configuration, the planar-stressed CMPT exhibits a specific directional sensing performance as a result of the stress-induced anisotropic magnetostriction of the nickel disk patch. [ABSTRACT FROM AUTHOR]

The vibratory response of a structure can be represented by the superposition of traveling waves propagating along a complex structural network. Wave dynamics generated at natural boundary conditions and subsequently reflected at geometric boundary conditions can lead to pole-zero characteristics of conventional reverberated transtar functions. However, by implementing model-based wave virtual controllers at each structural element, a dereverberated transfer function can be obtained from the measured reverberated transfer function response. Because the dereverberated transfer function represents the direct path of energy transmission across a structure, it can be used to infer damage in a structure by tracking how variations in local element properties affect the propagation of incident energy through the structure. A methodology is presented for obtaining the dereverberated transtar function response for four types of structural elements, including symmetric and asymmetric discrete spring mass elements and spectral rod and beam finite elements for continuous structures. The dereverberated transfer function response is obtained by attaching virtual controllers at the terminals of each structural element. A phase damage index method is proposed based on the relative phase propagation error from element to element to quantify the type and amount of damage. Analytical results on several simulated examples confirm that the dereverberated response can be used as a method for locating and quantifying damage in structures.

In this paper, we present a magnetostrictive phased array sensor (MPAS) with a polycrystalline nickel patch of a circular comb shape in order for the use of the ultrasonic guided Lamb wave inspection technique. The MPAS was comprised of two main components of the surface-mounted nickel patch and a mobile magnetic circuit device enclosing six sensing coils and center-positioned cylindrical biasing magnets. The magnetic circuit device detects the magnetic property change induced by the elastic wave propagation through the magnetostrictive nickel patch bonded to a thin aluminum plate. The individual sensing coils were configured to have directional preferences specified along the perpendicular direction of the coil winding, and they were arranged in a hexagon with a radius of 0.5" to form a compactsized phased array sensor. Although the magnetic circuit device contains only six physical sensing coils, the MPAS enables to increase the total numbers of sensing positions by altering the orientation of the magnetic circuit device. The enhanced directional sensing capability of the presented MPAS was achieved as a result of the combined effect on the high magnetic shape anisotropy feature along the individual comb finger directions of the nickel patch and the directional sensitivity of the hexagon magnetic circuit device itself. [ABSTRACT FROM AUTHOR]

This article presents the magnetic shape anisotropy effect on sensing performance and directional sensitivity in a directional magnetostrictive patch transducer using a uniaxial comb-shaped nickel patch, for the use of ultrasonic guided Lamb wave technology in metallic planar structure. The uniaxial comb patch was modified from a disc-shaped patch made of polycrystalline nickel, so that its comb fingers were aligned to a specific radial direction to promote the magnetic shape anisotropy in the nickel patch. Previously, it was found that a magnetostrictive patch transducer using a nickel disc patch appeared to have omnidirectional sensitivity for sensing guided Lamb waves in an aluminum plate due to the isotropic magnetostrictive nature of polycrystalline nickel. In this work, we initially investigated a theoretical approach to determine demagnetization factor change caused by the geometrical shape modification of a nickel patch, which strongly correlated with a specific magnetization characteristic of the patch. Then, experimental guided Lamb wave analysis was followed to demonstrate the directional guided Lamb wave sensitivity of magnetostrictive patch transducers using nickel patches with three different geometrical configurations. We verified from the experimental guided Lamb wave testing that the proposed magnetostrictive patch transducer using the uniaxial comb-shaped nickel patch exhibited excellent directional sensitivity along the comb fingers’ orientation in the aluminum plate. [ABSTRACT FROM AUTHOR]