Two-point Contacts Research Articles

Fatigue analysis of 75 kg/m-12 heavy-haul railway frog based on finite element simulation

A comprehensive approach is developed for studying fatigue properties of heavy-haul railway frog at different sections by finite element simulation and structure optimization. Combined with experimental research, the fatigue properties of heavy-haul railway frog is analyzed by three finite element simulation methods including stress fatigue life analysis, strain fatigue life analysis and crack propagation life analysis. Finite element simulation results show that the contact relationships of standard 75 kg/m-12 heavy frog are “two-point contacts” between the wheel and rails at sections of point rail top width of 10 mm and 20 mm, while are “one-point contact” at other sections. The maximum contact stress shows the biggest value in the 20 mm section and the smallest value in the 50 mm section. The fatigue life distribution of fatigue life analysis and the stress distribution of static mechanical analysis shows same regular pattern at same cross section. Our results indicate that optimization of the wing rail by cutting work side 5 mm and moving 5 mm to the point rail and elevating its top surface, can significantly reduce the maximum contact stress and prolong the fatigue life of heavy frog.

Effects of Multi-Point Contacts during Object Contour Scanning Using a Biologically-Inspired Tactile Sensor.

Vibrissae are an important tactile sense organ of many mammals, in particular rodents like rats and mice. For instance, these animals use them in order to detect different object features, e.g., object-distances and -shapes. In engineering, vibrissae have long been established as a natural paragon for developing tactile sensors. So far, having object shape scanning and reconstruction in mind, almost all mechanical vibrissa models are restricted to contact scenarios with a single discrete contact force. Here, we deal with the effect of multi-point contacts in a specific scanning scenario, where an artificial vibrissa is swept along partly concave object contours. The vibrissa is modeled as a cylindrical, one-sided clamped Euler-Bernoulli bending rod undergoing large deflections. The elasticae and the support reactions during scanning are theoretically calculated and measured in experiments, using a spring steel wire, attached to a force/torque-sensor. The experiments validate the simulation results and show that the assumption of a quasi-static scanning displacement is a satisfying approach. Beyond single- and two-point contacts, a distinction is made between tip and tangential contacts. It is shown that, in theory, these contact phases can be identified solely based on the support reactions, what is new in literature. In this way, multipoint contacts are reliably detected and filtered in order to discard incorrectly reconstructed contact points.

Spin current pumping in helical Luttinger liquids

We study the DC spin current induced into an unbiased quantum spin Hall system through a two-point contacts setup with time dependent electron tunneling amplitudes. By means of two external gates, it is possible to drive a current with spin-preserving and spin-flipping contributions showing peculiar oscillations as a function of pumping frequency, electron-electron interaction and temperature. From its interference patterns as a function of the Fabry-Perot and Aharonov-Bohm phases, it is possible to extract information about the helical nature of the edge states and the intensity of the electron-electron interaction.

Transport Properties of Single Vanadium Oxide Nanowire

We measured I-V characteristics and electrical resistance, in the temperature range from room temperature to above 600K in order to obtain nanodevices. Measurements were taken on a single V2O5 nanowire deposited on a Si template, where two-point and four-point metallic contacts were previously made using e-beam lithography. In both two- and four-point probe measurements, the I-V curves were clearly linear and symmetrical with respect to both axes. Drastic reduction in electrical resistance and deviation from single valued activation energy with increasing temperature indicated phase transitions taking place in the nanowire. From temperature-dependent HR-Micro Raman measurements, reductions from V2O5 to VO2/V2O3 phases took place at a temperature as low as 500K, when electrons were injected to the nanowire through electrical contacts.

Mach-Zehnder Interferometer in the Fractional Quantum Hall Regime

We consider tunneling between two edges of quantum Hall liquids of filling factors nu(0,1)=1/(2m(0,1)+1), with m(0)>or=m(1)>or=0, through two-point contacts forming a Mach-Zehnder interferometer. A quasiparticle description of the interferometer is derived explicitly through the instanton duality transformation. For m(0)+m(1)+1 identical withm>1, tunneling of quasiparticles of charge e/m leads to nontrivial m-state dynamics of effective flux through the interferometer, which restores the regular "electron" periodicity of the current in flux. The exact solution available for equal propagation times between the contacts shows that the interference pattern depends on voltage and temperature only through a common amplitude.

Effect of the Wheel Geometric Design on the Nonlinear Dynamics of Railroad Vehicles

The effect of the geometry of a wheel profile that allows only a single point of contact with the rail is investigated in this study. The local geometric properties of this profile are compared with the local geometric properties of a profile that allows for two-point contacts in order to understand the basic differences between the two profiles. A simple model is first used to examine the effect of the profile geometry on the stability and nonlinear dynamics of a suspended wheel set. The results obtained using this simple model show that the geometry of the wheel profile can significantly alter the critical speed. A computational approach is then used to investigate and quantify the effect of the wheel geometry wheel on the dynamics and stability of railroad vehicles. Two methods, the contact constraint and elastic formulations, are used. The contact constraint method employs nonlinear algebraic kinematic constraint equations to describe the contact between the wheel and the rail. The contact kinematic constraints, which eliminate one degree of freedom and do not allow for wheel/rail separation, are imposed at the position, velocity and acceleration levels. The system equations of motion are expressed in terms of the generalized coordinates and the nongeneralized surface parameters. In the formulations based on the elastic approach, the wheel has six degrees of freedom with respect to the rail, and the normal contact forces are defined as a function of the penetration using Hertz’s contact theory or using assumed stiffness and damping coefficients. In the elastic approach that allows for wheel/rail separation, the locations of the contact points are determined by solving a set of algebraic equations. The distribution of the contact forces resulting from the use of the two profiles that have different geometric properties is investigated using the two methods. Numerical results are presented for a full railroad vehicle model and the effect of the wheel profile on the vehicle stability is investigated.

Molecular and crystal structures of N-arylglycopyranosylamines formed by reaction between sulfanilamide and d-ribose, d-arabinose and d-mannose

The X-ray crystal structures of three monosaccharide derivatives prepared by the reaction of sulfanilamide with d-ribose, d-arabinose, and d-mannose have been determined. The derivatives are N-( p-sulfamoylphenyl)-α- d-ribopyranosylamine ( 1), N-( p-sulfamoylphenyl)-α- d-arabinopyranosylamine ( 2), and N-( p-sulfamoylphenyl)-β- d-mannopyranosylamine monohydrate ( 3). The monosaccharide ring of 1 and 2 has the 1 C 4 conformation, stabilized in 1 by an intramolecular hydrogen bond from O-2 to O-4. Compound 3 has the 4 C 1 conformation at the monosaccharide ring and the gt conformation at the C-6O-6 side chain. Occupancy of the water molecule in the crystal of 3 actually examined was 22%. The degree of interaction between sulfamoyl groups and monosaccharide moieties varies from structure to structure. The packing arrangement of 2 involves hydrogen bonding between sulfamoyl groups and monosaccharide hydroxyl groups, but interactions of this type are fewer in 1, and in 3 the hydrogen bonds are either strictly between monosaccharide hydroxyl groups or strictly between sulfamoyl groups. Pairs of hydrogen bonds (two-point contacts) link neighboring molecules in all three structures, between screw-axially related molecules in 1 and 2 and between translationally related molecules in 3. The contact in 3 defined by the O-3H⋯O-5 and O-6H⋯O-4 hydrogen bonds is found in several other N-aryl-β- d-mannopyranosylamine crystal structures and is apparently an especially favorable mode of intermolecular interaction in these compounds.

Dynamics of excitation pulses in two coupled nerve fibers

In this paper, we study the phenomena of interaction of traveling pulses in a system of two coupled nerve fibers. Each fiber is modeled by a discrete chain of mutually coupled Fitz Hugh-Nagumo excitable elements. The interaction among the fibers can be distributed, homogeneous, and also localized at certain points in space. In the case of homogeneous interaction, we show the possibility of interfiber synchronization of pulses. For localized interactions, we study the dynamics of point and two-point contacts, allowing us to perform effective control over the propagation of excitation along the coupled fibers.

Modeling of translational motion between two flexible bodies connected via three points

A dynamic model is presented in this paper for modeling the translation of a flexible body over another flexible body with three load transmission points between them. The three contact points on one of the bodies continuously change as one body translates with respect to the other. No software tools currently exist for simulating the dynamic response of this two-body system. In the present model, six degrees of freedom are allowed between the two bodies and then contacts are modeled using constraints that account for the relative motion. The small, elastic deformation of each body is modeled using the method of assumed modes. Numerical results presented demonstrate the dynamic interactions. The steps needed for implementation in multibody dynamics codes are outlined. The Mobile Transporter-Space Station system is a direct application for the present model. YNAMICS formulations13 and software analysis tools such f as TREETOPS4 and DISCOS5 model the relative motion between two bodies in an articulated, flexible multibody system through a hinge that can permit up to six degrees of freedom (DOFs). In such models, the relative translational motion is defined as that occurring between two points, one each fixed in each of the bodies, and the relative rotational motion as that between two reference frames, one each attached at the same two points in the respective bodies. A typical hinge definition is shown in Fig. 1. This definition facilitates the modeling of open-loop, articulated flexible multibody systems such as the Shuttle Remote Manipulator System (SRMS) and typical spacecraft with articulating flexible solar arrays. In the case of closed-loop systems, a cut joint is introduced to render the system open loop, with the joint definition the same as above, and then loop closure constraints are imposed. A consequence of the above definition for a joint connecting two bodies is that the dynamics of a flexible beam translating over two rigid supports, studied by Buffinton and Kane,6 cannot be modeled using the above formulations or software. This is because the points on the flexible beam that are in contact with the two rigid supports continuously change as the beam translates. The translation joint modeling in Refs. 1-5 assumes that the translation occurs along a rigid appendage, although the bodies themselves may be flexible. Although not incorporated into TREETOPS,4 Li and Likins7 extended the approach of Singh et al.4 to include travel along a curved flexible path, with a single point contact between the flexible guide and the body traveling on it. Hwang and Haug8 modeled one- and two-point contacts between two flexible bodies but presented numerical results only for the single-point contact case. Another system that cannot be modeled using the above joint definition alone is shown in Fig. 2. Body j and body L(y) in this figure are in contact at three locations and body j travels over a pair of parallel tracks that are fixed to body L(j). Two of the three contacts between the bodies occur over one rail whereas the third contact occurs over the other rail. Both the bodies are flexible. The interaction dynamics with multipoint contact between flexible bodies and with a relative DOF has not been modeled in the literature and cannot be simulated using the available multibody dynamics software. Single- and multipoint contact studies in the literature912 investigate how a flexible body will react to a given set of moving point

Desisn of wheel and rail profiles without hish contact pressure and two-point contacts.

Desisn of wheel and rail profiles without hish contact pressure and two-point contacts.

Electrical and Structural Properties of Amorphous Metal—Metal-Oxide Systems

Amorphous mixtures of Al-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$, Sn-Sn${\mathrm{O}}_{2}$, Ta-${\mathrm{Ta}}_{2}$${\mathrm{O}}_{5}$, and Ni-NiO were sputtered in various concentrations at room temperature. The resistivity was measured as a function of temperature between 1 and 300 \ifmmode^\circ\else\textdegree\fi{}K in three different ways; two-point and four-point contacts in a planar geometry and in a capacitance configuration. The most extensive measurements conducted on the Al-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ and Sn-Sn${\mathrm{O}}_{2}$ systems showed that, over nine orders of magnitude in resistance the resistivity could be described by $\ensuremath{\rho}={\ensuremath{\rho}}_{0}{e}^{{(\frac{{T}_{0}}{T})}^{\frac{1}{n}}}$ with $n=4$ over a wide range of compositions in the Al-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ system. This resistivity behavior along with the current's voltage dependence and the ac resistivity measurements indicate that the conduction mechanism in such films may be similar to the thermally activated hopping mechanism described in other amorphous materials.