Characteristics Of Point Contacts Research Articles

A traction coefficient formula for EHL point contacts operating in the linear isothermal region

Many mechanical systems including rolling/sliding parts, require traction data across a spectrum of operating conditions to predict their motion effectively. Numerous studies have examined the thermal effects and shear-thinning concerning the traction curve, but only a few have focused on the traction coefficient in the linear isothermal regime for low SRR. In this work, we investigate traction coefficient characteristics of EHL point contacts in the linear isothermal regime, over a wide range of operational conditions. To this end, we conduct numerical simulations utilizing a fully-coupled finite element-based model, resulting in a prediction formula for the traction coefficient slope. With this formula, the traction coefficient slope could be predicted for the operating conditions considered.

Design method of rack-and-pinion pair with pure rolling variable transmission ratio

Rack-and-pinion pair with variable transmission ratio can achieve the unity of vehicle steering portability and sensitivity, and effectively reduce vehicle steering energy consumption. Therefore, they have gradually become the standard core components of steering system. However, the gear surface of rack-and-pinion pair with variable transmission ratio is seriously worn under long-term service, which leads to the degradation of performance and cannot achieve the theoretically variable transmission ratio. To solve these problems, a new configuration of rack-and-pinion pair for commercial vehicle with herringbone pure rolling variable transmission ratio is proposed in this paper. The tooth surface mathematical model of the fully-conjugate variable transmission ratio is established based on the variable speed envelope principle, and the formula for calculating pure rolling point of tooth surface with variable transmission ratio is derived. The tooth point deviation equation of fully-conjugate variable transmission ratio is proposed, and the method of constructing pure rolling variable transmission ratio tooth surface is formed. The finite element analysis shows that the design of the pure rolling rack-and-pinion pair with variable transmission ratio has good tooth surface quality without the phenomenon of contact spot intermittent and edge contact during the meshing process, and the contact ellipse center of the tooth surface is located at the theoretical pure rolling point of the tooth surface. The measured transmission ratio curve of the samples is in good agreement with the theoretical variable transmission ratio curve, and the transmission ratio error is within a reasonable range. The contact strips of tooth surface impression test are consistent with those of finite element analysis, which indicates that the designed rack-and-pinion pair with variable transmission ratio has the characteristics of pure rolling and point contact. The tooth surface wear test shows that the wear of pure rolling gear surface with variable transmission ratio is obviously less than that of traditional gear surface with variable transmission ratio. The above tests and simulation indicate the correctness of the design method.

A novelty mandrel supported thin-wall tube bending cross-section quality analysis: a diameter-adjustable multi-point contact mandrel

The mandrel plays a vital role in metal tube bending limit improvement and high-quality achievement. For the bending forming process of metal tubes with different diameters, the corresponding mandrel needs to be customized, which has the disadvantages of a long design cycle, high manufacturing cost, and low reuse rate. Therefore, a novelty concept of diameter adjustable mandrel (DAM) based on the multi-point contact was proposed to adapt different diameter tube bending processes. Since the point-contact characteristics of the DAM can lead to irregular cross-section deformation, the cross-sectional full profile radial error (FP-RE) model was proposed. As a more comprehensive evaluation model, the FP-RE model is used to measure the deformation degree of the whole bending cross-section. A diameter-adjustable DAM was adopted in the AISI 304L tubes (the inner diameter = 40–56 mm) bending experiments. The maximum absolute error of FP-RE was 0.11% compared with the ones obtained from FEA in Abaqus/explicit. In addition, the effects of the DAM characteristic parameters, viz., the support blocks amount, the effective magnification, and the effective support diameter, on the tube forming quality were discussed. The results indicated that (a) an even number of support blocks could prevent the collapse of the outer convex tube wall and improve the quality of the inner concave tube wall. (b) When the DAM was used in the larger inner diameter tube bending, the larger non-contact area would cause an increase in the roundness section distortion. (c) A larger DAM diameter would lead to a more minor cross-section deformation degree for the tubes with the same diameter, while the wall thinning was just the opposite. Finally, the result also proved that the DAM (the minimum effective diameter is 40 mm with six support blocks) could be used for tubes with an inner diameter of about 40–56 mm, and the forming quality was acceptable.

New Curve Fitting Based Roller Modification Method for Spherical Roller Bearing

In the field of roller modification affecting the service life of rolling bearings, Different from point contact of ball bearing and line contact of cylindrical or tapered roller bearing, Spherical roller bearing is very special because it has the characteristics of point contact and line contact at the same time. To solve the problem that the spherical roller cannot be modified by line contact type roller modification method, this paper provides a new modification method of spherical roller. The spherical roller profile is divided into two parts: non modification profile and modification profile. The concept of gap space is put forward. Curve fitting is carried out in the non modified part, and then the fitting logarithmic curve is used in the modified part of the spherical roller. This method can provide reference for engineering application.

Investigation on Industrial Screen-Printed Aluminum Point Contact and Its Application in n-PERT Rear Junction Solar Cells

As compared with the traditional back surface field (BSF) solar cells, the n -type passivated emitter rear and totally diffused rear-junction ( n -PERT-RJ) solar cells have much lower carrier recombination losses on their rear sides. In order to obtain more benefits (higher open-circuit voltages) from the currently passivated rear sides, the implementation of the point contact concept is an intuitive solution. In this article, we present industrial screen-printed point contacts that are metallized with aluminum (Al) pastes containing silicon additives (Si-add). To understand the impacts of the Si-add on the performance our n -PERT-RJ solar cells, the detailed loss analysis on the open-circuit voltage ( $V_{OC}$ ), short-circuit current density ( $J_{SC}$ ), and fill factor are performed separately. The effect of Si-add and pitch of laser contact openings (LCO) on the point contact characteristics are also investigated. In the last part, we introduce an innovative “point-line” contact concept on the rear side, which is composed of dot-shaped LCO and Al metal finger design, resulting in an n -PERT-RJ solar cell to reach $V_{OC}$ of 692 mV and peak efficiency of 22%. The 60% bifaciality of the device opens the way for an additional power output on module level, which further reduces the levelized cost of electricity. These features make the rear-side point contact design more flexible to be applied in industrial mass production.

Effect of behavior of oil–air lubrication flow on characteristic of point contact sliding wear

PurposeThis paper aims to investigate the influence of oil–air lubrication flow behavior on point contact sliding wear characteristics.Design/methodology/approachOil–air lubrication equations between point contact counterparts were established on the basis of volume of fluid model. The effects of oil supply and injection azimuth on oil-phase volume fraction and its pressure distribution were simulated with commercial software Fluent. Characteristics of point contact sliding wear were then tested with an MFT-3000 friction tester under oil–air lubrication condition. The influence of flow behavior on wear characteristic was investigated combined with numerical and experimental results. The wear mechanism was revealed using SEM, EDS and ferrography.FindingsWhen air supply speed is constant, the oil-phase volume fraction increases with the increase in oil supply, which helps form continuous oil film and decrease the sliding wear evidently. The injection angle and distance considerably influence the oil–air flow behavior. When injecting at a certain distance and angle, the oil-phase volume fraction reaches its maximum, and the abrasion loss is minimal. Under the test conditions in this study, abrasive particles are mainly debris and a few spiral cuttings. The wear mechanism is abrasive wear.Originality/valueThe influence of the behavior of oil–air lubrication flow on the characteristic of point contact sliding wear is analyzed. This work provides guidance for the application of oil–air lubrication technology in point contact friction pairs.

Transport characteristics of InSb trench-type in-plane gate quantum point contact

An InSb quantum point contact (QPC) has been fabricated in a two-dimensional InSb heterostructure by using a trench-type in-plane gate. The magneto-transport characteristics show magneto-depopulation of 1D subbands under a perpendicular magnetic field and crossings of the 1D subbands under an in-plane magnetic field. The estimated effective g-factor has in-plane (|g*x| ∼ |g*y| ∼ 40) and out-of-plane (|g*z| ∼ 60) anisotropy. When a positive voltage is applied to the trench gate, the QPC device shows the typical characteristics of parallel channels, suggesting electron accumulation along the side walls of the trench.

Development of Criteria for Analysis of Point-contact Sensor Characteristics in Complex Gas Media

The electric conductivity of point-contact multistructured sensors in a complex medium of the human breath gas has been studied. Considering a large number of parameters which characterize response curves of point-contact sensors, we proved the possibility of using a statistical procedure to assess the reproducibility of sensor operation. To select sensors with similar parameters from a studied set of sensors, the method of cluster analysis was employed. As a result, we first propose a criterion for selection of uniform sensors from sample sets based on sensing arrays, each containing over 200 point-contact sensing elements. We demonstrate the effectiveness of the proposed approach for the selection of uniform sensors in experiments with breath gas exhaled by a volunteer. In this case, pairs of random elements from the formed cluster show a good reproducibility of their sensor images. The selected elements are thus proved to be uniform samples which can be used to study complex gas media, for example, in clinical practice to develop methods of noninvasive diagnosis based on breath analysis.

A New Method for Controlling the Quantized Growth of Dendritic Nanoscale Point Contacts via Switchover and Shell Effects

We report on quantum electrical characteristics of dendritic copper point contacts (PCs) formed through an electrochemical process via a new cyclic switchover effect that is demonstrated by the occurrence of steps in the time dependence of the dendritic-PCs conductance. We show that this quantization of the electrical conductance is due to an electronic shell effect governing the dendrite growth. The cyclic variations of conductance during dendritic PCs electrosynthesis offer the possibility for forming nanostructures of preassigned sizes controlled through their electrical resistance.

Exploring point-contact spectra of Ba1−xNaxFe2As2in the normal and superconducting states

We present a study of the derivatives of current-voltage $I(V)$ characteristics of point contacts (PCs) based on Ba${}_{1\ensuremath{-}x}$Na${}_{x}$Fe${}_{2}$As${}_{2}$ ($x=0.25$) in the normal and superconducting states. The detailed analysis of $dV/dI(V)$ data (also given in Appendix A) shows that the thermal regime, when the temperature increases with voltage at a rate of about 1.8 K/mV, is realized in the investigated PCs at least at high biases $V$ above the superconducting (SC) gap $\ensuremath{\Delta}$. In this case, the specific resistivity $\ensuremath{\rho}(T)$ in the PC core is responsible for a peculiar $dV/dI(V)$ behavior, while a pronounced asymmetry of $dV/dI(V)$ is caused by the large value of thermopower in this material. A reproducible minima detected in $dV/dI(V)$ at low biases in the range $\ifmmode\pm\else\textpm\fi{}$(6--9) mV, well below the SC critical temperature ${T}_{c}$, could be connected with the manifestation of the SC gap $\ensuremath{\Delta}$. An evaluation of these Andreev-reflection-like structures on $dV/dI(V)$ points out to the preferred value of $2\ensuremath{\Delta}/{k}_{\mathrm{B}}{T}_{c}\ensuremath{\approx}6$. The expected second gap features in $dV/dI(V)$ are hard to resolve unambiguously, likely due to impurity scattering, spatial inhomogeneity, and transition to the mentioned thermal regime as the bias further increases. Suggestions are made how to separate the spectroscopic features in $dV/dI(V)$ from those caused by the thermal regime.

The Effect of Surface Defect on EHL Point Contact

In this paper, the lubrication of three-dimensional EHL point contact with surface defect was solved, the lubrication film shape and film pressure distribution were presented and the characteristics of EHL point contact with defect were analyzed, the effect of surface defect on EHL point contact was studied. The results were presented that convex defect could lead to film pressure peak increasing, there was obvious micro-EHL effect, concave defect could lead to film pressure hollow and peak, film pressure peak was also increasing. The results also shown that convex and concave defects would have negative impact on EHL lubrication, there was great influence of surface defect on EHL lubrication pressure, the significant fluctuation of local film pressure was caused by surface defect, and generating greater pressure peak, maximum film pressure was rapid growth with the defect size increasing, so any kind defect should be to avoid in EHL lubrication.

A tunneling spectroscopy study of the pairing symmetry in the electron-dopedPr1−xLaCexCuO4−y

We have performed scanning tunneling spectroscopy and point contactspectroscopy measurements on the electron-doped superconductorPr1−xLaCexCuO4−y (x = 0.12, K). We address the question of the symmetry of the order parameter andof the amplitude of the energy gap. We compare three possible scenarios,i.e. isotropic s-wave, ‘anisotropic’ s-wave, and d-wave. Evidence for a d-wavesymmetry of the order parameter is given. From the temperature evolution of thedI/dV versusV characteristics we extract a BCS-like temperature dependence of the superconducting energy gapΔ. Despitethe variety of measured spectra we give a consistent explanation for the whole set of data, indicatingΔ = (3.6 ± 0.2) meV and a ratio . In particular, point contact characteristics showing gap-like features at higher voltageshave been interpreted by considering the formation of an intergrain Josephson junction inseries with the point contact junction. Further confirmation of the correctness of themodel is given by the behavior of the critical current of the intergrain Josephsonjunction versus temperature which follows the Ambegaokar–Baratoff behavior.

Broadband microwave spectroscopy of a GaAs point contact

We use a novel broadband microwave spectroscopy measurement to study the source–drain current characteristics of a GaAs quantum point contact (QPC) within the tunnelling regime. The experimental setup was based on the Corbino approach with the notable difference that it was non-invasive to the sample and swept a frequency range between 1 and 10 GHz at low temperatures. Highly aperiodic but completely reproducible conductance fluctuations were observed close to pinch-off as well as regions of negative conductance. We account these fluctuations to be due to quantum interference of ballistic electron trajectories, trapped within the QPC, being modified by the radiation source and influencing the tunnelling rates through a complex potential well structure.

The study on the design of spiral bevel gear sets with circular-arc contact paths and tooth profiles

In this paper, the spiral bevel gear sets which can be manufactured by cup-shape grinder or milling cutter on a general purpose four-axis milling machine is proposed. The general meshing constraint equation of bevel gear sets was first presented in our previous publication to be followed again as a continuation of designing and constructing solid model. In order to derive the meshing constraint equation of bevel gear sets with point-contact characteristics, the degeneration condition is set. Because of occurrence of just one contact point in each instant, there exists a contact path on each tooth surface. After configuring the designed parameters, the contact path can be designed as an approximate to circular-arc curve. Finally, the torus surface is used to construct the tooth surface. According to the idea described in this paper, a new approach of manufacturing the spiral bevel gear is developed. The major merit of this spiral bevel gear is only single axis motion has to be controlled during the cutting process.

Point contact spectroscopy on ferromagnetic/superconducting heterostructures

The interplay between superconductivity and ferromagnetism is an interesting subject of experimental and theoretical research. The observation of this effect became possible only recently due to the great progress in the preparation of high-quality hybrid ferromagnet/superconductor (F/S) systems. In this paper we present conductance characteristics of point contact junctions realized between a normal Pt–Ir tip and YBa 2Cu 3O 7− x /La 0.7Ca 0.3MnO 3 (YBCO/LCMO) bilayers. The point contact characteristics show a zero bias conductance peak, as a consequence of the formation of Andreev bound states at the YBCO Fermi level. The temperature evolution of the spectra reveals a depressed zero bias peak and a reduced superconducting energy gap. We had already observed similar effects in the conductance spectra on polycrystalline RuSr 2GdCu 2O 8 pellets. By comparing spectra on both materials, we can thus conclude that these features are explainable in terms of spin polarization effects due to the ferromagnetic layer.

Asymmetry of point-contact characteristics of RECu 5 (RE: heavy rare earth) compounds

We present the study of an asymmetry of point-contact characteristics of the heterocontacts RECu 5–Cu (RE=Tb, Dy, Ho, Er, Tm and Yb). Point-contact spectroscopy, in the case of normal metals, gives direct information about the electron–quasiparticle interaction (EQI). We have determined the asymmetry and have explained its origin within model taking into account the thermopower effects.

Point Contact Spectra on YBa2Cu3O7−x/La0.7Ca0.3MnO3 bilayers

We present conductance characteristics of point contact junctions realized between a normal Pt-Ir tip and YBa2Cu3O7−x/La0.7Ca0.3MnO3 (YBCO/LCMO) bilayers. The point contact characteristics show a zero bias conductance peak, as a consequence of the formation of Andreev bound states at the YBCO Fermi level. The temperature evolution of the spectra reveals a depressed zero bias peak and a reduced superconducting energy gap, both explainable in terms of spin polarization effects due to the LCMO layer.

Deformation of a charge density wave in the vicinity of a point contact with a normal metal

The current-voltage characteristics of Cu-K0.3MoO3 point contacts between a metal and a semiconductor with a charge density wave (CDW) are studied for various diameters of the contacts in a wide range of temperatures T and voltages V. In the interval 80 K ≲ T ≲ 150 K, the current-voltage characteristics are correctly described in the framework of a semiconductor model: screening of an external electric field causes CDW deformation, shifts the chemical potential of quasiparticles, and changes the point contact resistance. It is shown that the chemical potential is above the middle of the Peierls gap in equilibrium and approaches the middle upon an increase in temperature. The current-voltage characteristics of point contacts with a diameter d ≳ 100 A exhibit a sharp decrease in resistance for |V| > V t , which is associated with the beginning of local CDW sliding within the contact region. The V t (d, T) dependence can be explained by the size effect in the CDW phase slip.

Current-driven magnetic rearrangements in spin-polarized point contacts

A new method for investigating the dynamics of atomic magnetic moments in current-carrying magnetic point contacts under bias is presented. This combines the non-equilibrium Green's function (NEGF) method for evaluating the current and the charge density with a description of the dynamics of the magnetization in terms of quasistatic thermally-activated transitions between stationary configurations. This method is then implemented in a tight-binding (TB) model with parameters chosen to simulate the main features of the electronic structures of magnetic transition metals. We investigate the domain wall (DW) migration in magnetic monoatomic chains sandwiched between magnetic leads, and for realistic parameters find that collinear arrangement of the magnetic moments of the chain is always favorable. Several stationary magnetic configurations are identified, corresponding to a different number of Bloch walls in the chain and to a different current. The relative stability of these configurations depends on the geometrical details of the junction and on the bias, however we predict transitions between different configurations with activation barriers of the order of a few tens of meV. Since different magnetic configurations are associated to different resistances, this suggests an intrinsic random telegraph noise at microwave frequencies in the I-V characteristics of magnetic atomic point contacts at room temperature. Finally, we investigate whether or not current induced torques are conservative.

Tip-induced nano-writing/machining of Si and DLC surfaces – “anodic” versus thermal oxidation?

Tip-induced oxidative manipulation of conducting surfaces, e.g., Si and some metals, has conventionally been described by a field-induced anodic mechanism. Likewise, in the case of electrically conducting graphitic and diamond-like carbon (DLC) films, tip-induced conversion of carbon to CO2 was initially thought to be due to an ionisation process. There is now mounting evidence for thermal activation playing an important role. The state of the tip is a critical, but largely disregarded, factor in such experiments. The present project has been prepared and characterized by I–V analysis, tips with different initial characteristics (e.g., H-termination , Au-coating, native oxide). Likewise, several surfaces have been prepared (e.g., Si plus termination by either native or thermal oxide, or plus H-termination, DLC and Au), and also subjected to I–V analysis. The resultant point-contact characteristics were found to range from ohmic to non-ohmic (the latter due to either direct or Fowler–Nordheim tunnelling). The various combinations were tested with respect to oxidative yield and tip durability. It was found that the presence of a tunnelling barrier at the point of contact is essential for enhancing yield. Tip durability, on the other hand, is promoted by the barrier being located in the surface thus localizing thermal deposition in the surface rather than in the tip.