Hard Cylinder Research Articles

A stress-dependent sliding wear model for bileaflet mechanical heart valves

Pyrolytic carbon (PyC) is a common material used in mechanical heart valves. This investigation studies the effects of surface finish on the the sliding wear between two PyC surfaces. The primary application being, the prediction of wear at articulating surfaces within bileaflet mechanical heart valves. An experimental apparatus is designed which allows a cylinder to rotate on a flat plate at a constant frequency and load. The cylinder is harder (greater modulus of elasticity) than the flat surface. Two surface finishes of a single (hard) cylinder and two flat surfaces of different hardnesses (single surface finish) are investigated, for a total of four cases. These four cases are studied at four sliding distances. The exerimental data is used to develop theoretical load and stress-dependent models for sliding abrasive wear. For the boron alloyed PyC material used in this investigation, the load-dependent wear model is most applicable for unpolished cylinders and the stress-dependent model is most applicable for polished cylinders. These two models are used to make theoretical predictions of pivot wear in a bileaflet mechanical valve of the same material. The predictions from the stress-dependent wear model was found to be quite accurate with actual wear measurements. The methods developed in this paper are generalized and applied to other valve designs and materials.

Experiment of static creep behavior of aggregate-asphalt interfaces

In order to investigate the fatigue failure of compacted asphalt mixtures, the static creep mechanical behavior of aggregate-asphalt interfaces was conducted which especially constructed the creep equation between the deformation-time of aggregate-asphalt interfaces. The hard sandstone cylinder specimens of 38 mm and 21 mm in diameter were used to measure the static creep and strength of aggregate-asphalt, respectively. Through the gravity of asphalt itself, the excess asphalt flowed away from the end face of samples. A thin layer film was adhered to the end surface of hard sandstone cylinder samples. Shear strength and direct tensile strength between the aggregate-asphalt interfaces were measured with the electronic universal testing machine (EUTM) at the loading velocity of 50 mm/min and at 15∘C and 25∘C, respectively. The shear creep between the aggregate-asphalt interfaces was firstly done with EUTM successfully. The direct tensile creep was done with the universal testing machine (UTM). The shear creep deformation-time of the aggregate-asphalt interfaces was the power function relation. The direct tensile creep deformation-time of the aggregate-asphalt interfaces was also the power function relation. These power function relations of the aggregate-asphalt interfaces contribute to the following research about the fatigue failure of compacted asphalt mixtures.

SAXS data modelling for the characterisation of ion tracks in polymers.

Here, we present new models to fit small angle X-ray scattering (SAXS) data for the characterization of ion tracks in polymers. Ion tracks in polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI) and polymethyl methacrylate (PMMA) were created by swift heavy ion irradiation using 197Au and 238U with energies between 185 MeV and 2.0 GeV. Transmission SAXS measurements were performed at the Australian Synchrotron. SAXS data were analysed using two new models that describe the tracks by a cylindrical structure composed of a highly damaged core with a gradual transition to the undamaged material. First, we investigate the 'Soft Cylinder Model', which assumes a smooth function to describe the transition region by a gradual change in density from a core to a matrix. As a simplified and computational less expensive version of the 'Soft Cylinder Model', the 'Core Transition Model' was developed to enable fast fitting. This model assumes a linear increase in density from the core to the matrix. Both models yield superior fits to the experimental SAXS data compared with the often-used simple 'Hard Cylinder Model' assuming a constant density with an abrupt transition.

Acoustic Waves Scattering from a Fluid-Saturated Porous Cylinder

This paper reports a study on plane waves in a fluid incident on an infinitely long fluid-saturated porous cylinder. With consideration of both the fluid dynamic viscosity and the inelastic loss of the frame of the porous media, as well as the application-wide frequency of the Biot-Stoll model, the theoretical calculation of acoustic scattering of an acoustic wave at oblique incidence is carried out. The acoustic backscattering spectrum is calculated and used to investigate the influence of the incident angle and the boundary conditions on the scattering characteristics. The results show that the position of the peak on the horizontal coordinate moves to higher frequency as the incident angle is increased. In the soft porous cylinder, whose shear wave velocity is lower than the velocity of the fluid, the change in the backscattering spectrum under the open-pore boundary condition is more obvious than that in the sealed-pore boundary condition. The influence of the incident angle is more obvious in a hard porous cylinder whose shear wave velocity is larger than the velocity of the fluid than it is in a soft porous cylinder.

Analysis of nanometer-sized aligned conical pores using small-angle x-ray scattering

Small angle X-ray scattering (SAXS) was used to quantitatively study the morphology of aligned, mono-disperse conical etched ion tracks in thin films of amorphous silicon dioxide with aspect ratios of around 6:1, and in polycarbonate foils with aspect ratios of around 1000:1. This paper presents the measurement procedure and methods developed for the analysis of the scattering images and shows results obtained for the two material systems. To enable accurate parameter extraction from the data collected from conical scattering objects a model fitting the 2-D detector images was developed. The analysis involved fitting images from a sequence of measurements with different sample tilts to minimise errors which may have been introduced due to the experimental set-up. The model was validated by the exploitation of the geometric relationship between the sample tilt angle and the cone opening angle, to an angle observed in the features of the SAXS images. We also demonstrate that a fitting procedure for 1-D data extracted from the scattering images using a hard cylinder model can also be used to extract the cone size. The application of these techniques enables us to reconstruct the cone morphologies with unprecedented precision.

Finite Element based Transient Elastohydrodynamic Simulation of Translational Hydraulic Seals

Seals are crucial machine elements in hydraulic devices. However, especially with regard to dynamic seals – for example in cylinder applications – the physical understanding of the sealing mechanism is still insufficient. In this paper a physically based, transient elastohydrodynamic simulation for translational hydraulic seals is presented. The deformation of the seal is calculated in a dynamic finite element (FE) simulation, hyper- and viscoelastic material properties are taken into account. For the numerical calculation of the fluid film and its influences on the seal deformation the FE simulation is coupled with an implementation of the transient Reynold’s equation. For a physically based calculation of the solid contact, the FE-model is coupled with Persson’s theory of rubber friction and contact mechanics. Both, normal force and solid friction are implemented. In a simulation study the influence of the relative velocity in the contact between the elastic, highly deformable seal and a hard cylinder is investigated. The initial phase of motion is investigated in detail. The simulation results are compared to experimental data of a lubricated sliding contact between an nitrile butadiene rubber (NBR) O-ring and a rough steel surface.

Diffraction of acoustic waves at two-dimensional hard trilateral cylinders with rounded edges: First-order physical theory of diffraction approximation.

The paper explores diffraction of acoustic waves at a two-dimensional hard trilateral cylinder with rounded edges. It represents the extension of the physical theory of diffraction (PTD) for finite objects with rounded edges. A first-order PTD approximation is developed. Integral equations are formulated for acoustic fringe waves and solved by method of moments (MoM). Good agreement is observed with the exact solution found by MoM when the object size exceeds a few wavelengths.

Speeding up Monte Carlo simulation of patchy hard cylinders.

The hard cylinder model decorated with attractive patches proved to be very useful recently in studying physical properties of several colloidal systems. Phase diagram, elastic constants and cholesteric properties obtained from computer simulations based on a simple hard cylinder model have been all successfully and quantitatively compared to experimental results. Key to these simulations is an efficient algorithm to check the overlap between hard cylinders. Here, we propose two algorithms to check the hard cylinder overlap and we assess their efficiency through a comparison with an existing method available in the literature and with the well-established algorithm for simulating hard spherocylinders. In addition, we discuss a couple of optimizations for performing computer simulations of patchy anisotropic particles and we estimate the speed-up which they can provide in the case of patchy hard cylinders.

Analytical dependences of motion of working part in inertial cone crusher.

The article discusses the analytical dependence of the movement of the inertial cone crusher, which is a hard cylinder that is moving along the inner elliptic trajectory of the stationary cone of the inertial cone crusher.

A Lab‐Scale Experiment Approach to the Measurement of Wall Pressure from Near‐Field under Water Explosions by a Hopkinson Bar

Direct measurement of the wall pressure loading subjected to the near‐field underwater explosion is of great difficulty. In this article, an improved methodology and a lab‐scale experimental system are proposed and manufactured to assess the wall pressure loading. In the methodology, a Hopkinson bar (HPB), used as the sensing element, is inserted through the hole drilled on the target plate and the bar’s end face lies flush with the loaded face of the target plate to detect and record the pressure loading. Furthermore, two improvements have been made on this methodology to measure the wall pressure loading from a near‐field underwater explosion. The first one is some waterproof units added to make it suitable for the underwater environment. The second one is a hard rubber cylinder placed at the distal end, and a pair of ropes taped on the HPB is used to pull the HPB against the cylinder hard to ensure the HPB’s end face flushes with loaded face of the target plate during the bubble collapse. To validate the pressure measurement technique based on the HPB, an underwater explosion between two parallelly mounted circular target plates is used as the validating system. Based on the assumption that the shock wave pressure profiles at the two points on the two plates which are symmetrical to each other about the middle plane of symmetry are the same, it was found that the pressure obtained by the HPB was in excellent agreement with pressure transducer measurements, thus validating the proposed technique. To verify the capability of this improved methodology and experimental system, a series of minicharge underwater explosion experiments are conducted. From the recorded pressure‐time profiles coupled with the underwater explosion evolution images captured by the HSV camera, the shock wave pressure loading and bubble‐jet pressure loadings are captured in detail at 5 mm, 10 mm, …, 30 mm stand‐off distances. Part of the pressure loading of the experiment at 35 mm stand‐off distance is recorded, which is still of great help and significance for engineers. Especially, the peak pressure of the shock wave is captured.

Hydrodynamic mobility of a sphere moving on the centerline of an elastic tube

Elastic channels are an important component of many soft matter systems, in which hydrodynamic interactions with confining membranes determine the behavior of particles in flow. In this work, we derive analytical expressions for Green’s functions associated with a point-force (Stokeslet) directed parallel or perpendicular to the axis of an elastic cylindrical channel exhibiting resistance against shear and bending. We then compute the leading order self- and pair mobility functions of particles on the cylinder axis, finding that the mobilities are primarily determined by membrane shear and that bending does not play a significant role. In the quasi-steady limit of vanishing frequency, the particle self- and pair mobilities near a no-slip hard cylinder are recovered only if the membrane possesses a non-vanishing shear rigidity. We further compute the membrane deformation, finding that deformation is generally more pronounced in the axial (radial) directions, for the motion along (perpendicular to) the cylinder centerline, respectively. Our analytical calculations for Green’s functions in an elastic cylinder can serve as a fundamental building block for future studies and are verified by fully resolved boundary integral simulations where very good agreement is obtained.

Quantum scattering from cylindrical barriers

We solve the two-dimensional Schrödinger equation for particles with momentum px=ℏk scattering off of a hard circular cylinder using the finite element method; we compare our results with the exact analytic solution. The quantity of interest to experimentalists is the differential cross section σ(ϕ)=|fk(ϕ)|2, which represents the final angular distribution of only the scattered particles. Here, we are also interested in the interference between the incident and scattered wave, which can be seen in the probability density for the total wave function, ρ(x,y)=|ψk(x,y)|2. We also apply the finite element method to the problem of particles scattering off of a hard rectangular cylinder, for which there is no analytic solution.

Scattering reduction of an acoustically hard cylinder covered with layered pentamode metamaterials.

Transformational acoustics offers the theoretical possibility of cloaking obstacles within fluids, provided metamaterials having continuously varying bulk moduli and densities can be found or constructed. Realistically, materials with the proper, continuously varying anisotropies do not presently exist. However, discretely layered cloaks having constant material parameters within each layer may be a viable alternative in practice. The present work considers a range of cloaks, from those comprised of fluid layers that are isotropic in bulk moduli with anisotropic density (inertial cloaks) to those having anisotropic bulk moduli and isotropic density (pentamode cloaks). In this paper an analytical solution is obtained for the case of plane wave scattering from a submerged rigid cylinder covered with a multilayered cylindrical cloak composed of discrete anisotropic fluid layers. An investigation of the parameter space defining such cloaks is undertaken with the goal of minimizing the far-field scattered pressure, using layer constituent anisotropic properties (density and bulk modulus) constrained to lie within reasonable ranges relative to those of water.

Rolling friction—models and experiment. An undergraduate student project

In this paper the rolling friction (rolling resistance) model is studied theoretically and experimentally in undergraduate level fundamental general physics courses. Rolling motions of a cylinder along horizontal or inclined planes are studied by simple experiments, measuring deformations of the underlay or of the rolling body. The rolling of a hard cylinder on a soft underlay as well as of a soft cylinder on a hard underlay is studied. The experimental data are treated by the open source software Tracker, appropriate for use at the undergraduate level of physics. Interpretation of results is based on elementary considerations comprehensible to university students—beginners. It appears that the commonly accepted model of rolling resistance based on the idea of a warp (little bulge) on the underlay in front of the rolling body does not correspond with experimental results even for the soft underlay and hard rolling body. The alternative model of the rolling resistance is suggested in agreement with experiment and the corresponding concept of the rolling resistance coefficient is presented. In addition to the obtained results we can conclude that the project can be used as a task for students in practical exercises of fundamental general physics undergraduate courses. Projects of similar type effectively contribute to the development of the physical thinking of students.

Rolling Friction: Comparison of Analytical Theory with Exact Numerical Results

We study the contact mechanics of a smooth hard cylinder rolling on a flat surface of a linear viscoelastic solid. Using the measured viscoelastic modulus of unfilled and filled (with carbon black) nitrile rubber, we compare numerically exact results for the rolling friction with the prediction of a simple analytical theory. For the unfilled rubber, the two theories agree perfectly while some small difference exists for the filled rubber. The rolling friction coefficient depends nonlinearly on the normal load and the rolling velocity.

Flexible stop and double-cascaded stop to improve shock reliability of MEMS accelerometer

Flexible stop could provide shock protection for MEMS accelerometer. By modeling and simulation, the paper studied the response of a closed-loop MEMS accelerometer with stop under shock of different amplitudes and pulse width. Contact force plays an important role and the shock response shows strong nonlinearity due to the contact mechanism. A kind of double-cascaded stop is proposed to mitigate high-frequency shock failure. MEMS accelerometers with flexible stop and with double-cascaded stop are both designed and fabricated based on SOG (silicon on glass) technology. Compared with shock tests of accelerometers with hard cylinder stop, flexible stop could withstand more than 1e4g shock with about 100μs pulse width. Double-cascaded stop is more robust to high frequency shock.

Theory of viscoelastic lubrication

We study the lubricated (wet) contact mechanics of a smooth hard cylinder sliding on a randomly rough nominally flat surface of a linear viscoelastic solid. We calculate the rolling and sliding friction, and study the transition from the boundary lubrication to the elasto-hydrodynamic lubrication regime. For the viscoelastic contact the minimum (average) separation does not monotonically increase with the sliding velocity, and the Stribeck curve exhibits new structures not shown for elastic solids.

The effect of an aircraft’s boundary layer on propeller noise

This study concerns the influence of the boundary layer at an aircraft’s fuselage, simulated by an infinite hard cylinder, on propeller noise in the acoustic far field. Also studied is the effect of the boundary layer on noise as a function of the thickness and profile of the mean velocity of the boundary layer, the Mach number of the incident flow, and the rotation speed of the propeller. It is shown that the boundary layer at the fuselage can substantially modify propeller noise in the far field and should therefore be taken into account in calculating community noise.

Scattering reduction of an acoustically hard cylinder covered with layered pentamode metamaterials

Unlike traditional target strength reduction coatings that rely on energy dissipation or other mechanisms to mitigate reflection, a coating comprised of metamaterials would behave as an acoustic waveguide that diverts sound energy around the object, thus reducing scattered energy. The majority of the literature has featured theoretical ideal metamaterial designs that have unrealizable properties, i.e., infinite mass, vanishing bulk modulus. However, our analysis has suggested that it may be possible to obtain effective scattering reductions with realizable material properties in a layered configuration using metafluids. In this context, realizable implies material properties that are constrained to lie within reasonable ranges relative to the density and bulk modulus of water. The multistatic scattering reduction of an acoustically hard cylinder covered with layered metafluids for plane wave incidence is analyzed. A range of coatings are considered, from those comprised of fluid layers that are isotropic in bulk moduli with anisotropic density (inertia) to those having anisotropic bulk moduli and isotropic density (pentamode). [Work supported by NAVSEA Division Newport ILIR.]

2A2-J08 能動スコープカメラのための柔軟性を有する直動アクチュエータの開発(アクチュエータの機構と制御)

We developed the Active Scope Camera by the Ciliary Vibration Drive as a snake type Rescue Robot. Moreover, to make it possible for Active Scope Camera to run on the soft road and intense ruggedness road where the it cannot run by the Ciliary Vibration Drive, we also developed the Inch-worm Drive used frictional anisotropy. However, the flexibility of the Active Scope Camera decreases because it uses the hard Pneumatic Cylinder as a Linear Actuator. In this paper, we propose a Flexible Cylinder to solve this problem. In addition, we made the prototype of Flexible Inch-warm Drive used the Flexible Cylinder and valuate driving performance of it by comparing with the past, Active Scope Camera.