Comments on "micro-scale abrasive wear testing of PVD coatings on curved substrates"

Previously published expressions for the wear volume in the micro-scale abrasion test for curved specimen surfaces (K.L. Rutherford and I.M. Hutchings, Tribology Letters 2 (1996) 1-11) were based upon erroneous assumptions about the wear-scar geometry. Accurate volumes have now been computed, and the errors in the use of the original analytical equations are shown to be negligibly small (<0.5% error) for all practical cases. © J.C. Baltzer AG, Science Publishers.

The deposition of small particles from a turbulent air flow in a curved duct

The paper describes an experimental and theoretical study of the deposition of small spherical particles from a turbulent air flow in a curved duct. The objective was to investigate the interaction between the streamline curvature of the primary flow and the turbulent deposition mechanisms of diffusion and turbophoresis. The experiments were conducted with particles of uranine (used as a fluorescent tracer) produced by an aerosol generator. The particles were entrained in an air flow which passed vertically downwards through a long straight channel of rectangular cross-section leading to a 90° bend. The inside surfaces of the channel and bend were covered with tape to collect the deposited particles. Following a test run the tape was removed in sections, the uranine was dissolved in sodium hydroxide solution and the deposition rates established by measuring the uranine concentration with a luminescence spectrometer. The experimental results were compared with calculations of particle deposition in a curved duct using a computer program that solved the ensemble-averaged particle mass and momentum conservation equations. A particle density-weighted averaging procedure was used and the equations were expressed in terms of the particle convective, rather than total, velocity. This approach provided a simpler formulation of the particle turbulence correlations generated by the averaging process. The computer program was used to investigate the distance required to achieve a fully-developed particle flow in the straight entry channel as well as the variation of the deposition rate around the bend. The simulations showed good agreement with the experimental results. © 2012 Elsevier Ltd.

Bifurcations and instability in the adhesion of intrinsically curved rods

Motivated by applications such as gecko-inspired adhesives and microdevices featuring slender rod-like bodies, there has been an increase in interest in the deformed shapes of elastic rods adhering to rigid surfaces. A central issue in analyses of the rod-based models for these systems is the stability of the predicted equilibrium configurations. Such analyses can be complicated by the presence of intrinsic curvatures induced by fabrication processes. The results in the present paper are used to show how this curvature can lead to shear-induced bifurcations and instabilities. To characterize potential instabilities, a new set of necessary conditions for stability are employed which cater to the possible combinations of buckling and delaminating instabilities. © 2013 Elsevier Ltd. All rights reserved.

In-plane critical current density measurements of straight and curved tracks in RABiTS-MOD coated conductors

Depending on the temperature and the magnitude and orientation of an external magnetic field, the critical current density, J c , of a coated conductor can be limited either by the properties of the grain boundaries or by those of the grains. In order to ascertain what governs J c under different conditions, we have measured straight and curved tracks, patterned into RABiTS-MOD samples, while a magnetic field was swept in the plane of the films. Significantly different results were obtained at different field and temperature ranges, which we were able to attribute to J c being limited by either grain boundaries or grains.

Parametric guidance for turbulent noise reduction from poroelastic trailing edges and owls

The interaction of a turbulent eddy with a semi-infinite, poroelastic edge is examined with respect to the effects of both elasticity and porosity on the efficiency of aerodynamic noise generation. The edge is modelled as a thin plate poroelastic plate, which is known to admit fifth-, sixth-, and seventh-power noise dependences on a characteristic velocity U of the turbulent eddy. The associated acoustic scattering problem is solved using the Wiener-Hopf technique for the case of constant plate properties. For the special cases of porous-rigid and impermeable-elastic plate conditions, asymptotic analysis of the Wiener- Hopf kernel function furnishes the parameter groups and their ranges where U5, U6, and U7 behaviours are expected to occur. Results from this analysis attempt to help guide the search for passive edge treatments to reduce trailing-edge noise that are inspired by the wing features of silently flying owls. Furthermore, the appropriateness of the present model to the owl noise problem is discussed with respect to the acoustic frequencies of interest, wing chord-lengths, and foraging behaviour across a representative set of owl species.

An energy-efficient hopping robot based on free vibration of a curved beam

This paper explores a design strategy of hopping robots, which makes use of free vibration of an elastic curved beam. In this strategy, the leg structure consists of a specifically shaped elastic curved beam and a small rotating mass that induces free vibration of the entire robot body. Although we expect to improve energy efficiency of locomotion by exploiting the mechanical dynamics, it is not trivial to take advantage of the coupled dynamics between actuation and mechanical structures for the purpose of locomotion. From this perspective, this paper explains the basic design principles through modeling, simulation, and experiments of a minimalistic hopping robot platform. More specifically, we show how to design elastic curved beams for stable hopping locomotion and the control method by using unconventional actuation. In addition, we also analyze the proposed design strategy in terms of energy efficiency and discuss how it can be applied to the other forms of legged robot locomotion. © 1996-2012 IEEE.

Hopping robot based on free vibration of an elastic curved beam

This study presents a novel approach to the design of low-cost and energy-efficient hopping robots, which makes use of free vibration of an elastic curved beam. We found that a hopping robot could benefit from an elastic curved beam in many ways such as low manufacturing cost, light body weight and small energy dissipation in mechanical interactions. A challenging problem of this design strategy, however, lies in harnessing the mechanical dynamics of free vibration in the elastic curved beam: because the free vibration is the outcome of coupled mechanical dynamics between actuation and mechanical structures, it is not trivial to systematically design mechanical structures and control architectures for stable locomotion. From this perspective, this paper investigates a case study of simple hopping robot to identify the design principles of mechanics and control. We developed a hopping robot consisting of an elastic curved beam and a small rotating mass, which was then modeled and analyzed in simulation. The experimental results show that the robot is capable of exhibiting stable hopping gait patterns by using a small actuation with no sensory feedback owing to the intrinsic stability of coupled mechanical dynamics. Furthermore, an additional analysis shows that, by exploiting free vibration of the elastic curved beam, cost of transport of the proposed hopping locomotion can be in the same rage of animals' locomotion including human running. © 2011 IEEE.

Determination of the tilt and twist angles of curved GaN layers by high-resolution x-ray diffraction

The full-width at half-maximum (FWHM) of an x-ray rocking curve (XRC) has been used as a parameter to determine the tilt and twist angles of GaN layers. Nevertheless, when the thickness of GaN epilayer reaches several microns, the peak broadening due to curvature becomes non-negligible. In this paper, using the (0 0 l), l = 2, 4, 6, XRC to minimize the effects of wafer curvature was studied systematically. Also the method to determine the tilt angle of a curved GaN layer was proposed while the Williamson-Hall plot was unsuitable. It was found that the (0 0 6) XRC-FWHM had a significant advantage for high-quality GaN layers with the radius curvature of r less than 3.5 m. Furthermore, an extrapolating method of gaining a reliable tilt angle has also been proposed, with which the calculated error can be improved by 10% for r < 2 m crystals compared with the (0 0 6) XRC-FWHM. In skew geometry, we have demonstrated that the twist angles deriving from the (2 0 4) XRC-FWHM are in accord with those from the grazing incidence in-plane diffraction (IP-GID) method for significantly curved samples.