A Novel Reciprocating Tribometer for Friction and Wear Measurements with High Contact Pressure and Large Area Contact Configurations

There are many moving machine assemblies with conformal tribological contacts at very high contact pressures, e.g., sliding bearings, propeller shaft bearings and machine guideways. Furthermore, applications such as trunnion and guide vane bearing in Kaplan turbines have very low sliding speeds and oscillatory types of motion. Although there is a vast selection of tribology test rigs available, there is still a lack of test equipment to perform friction and wear tests under high contact pressure, reciprocatory sliding and large area contact. The aim of this work is thus to develop a novel reciprocating tribometer and test method that enables friction and wear tests under low-speed reciprocatory sliding with contact pressures up to 90 MPa in a flat-on-flat contact configuration. First, a thorough description of the test rig design is given. Secondly, the influence of contact pressure and stroke length on the tribological properties of a stainless steel and polymer composite material combination is studied. The significance of considering creep, friction during the stroke and contact temperature is specifically highlighted. The novel tribometer can be used to screen different bearing and shaft material combinations and to evaluate the friction and wear performance of self-lubricating bearings for the specific operating conditions found in Kaplan turbines.

Determination of suitable traveller for definite yarn count: A comparative study

The traveller imparts twist to the yarn and enables winding of the yarn on the cop. Yarn quality parameters can be improved by proper traveller weight selection which results in reducing yarn breakage, mass variation, twist variation and hairiness. High contact pressure (up to 35N/mm) is generated between the ring travellers during winding, mainly due to centrifugal force the pressure includes strong frictional forces which in turn lead to significant generation of heat. This is the kernel of the ring/ traveller problem. The low mass of the traveller does not permit dissipation of the generated heat in the short time available. Uster Evenness Tester 5 was used to determine the yarn properties such as unevenness, percentage, imperfection index, hairiness, standard variation of hairiness. Traveller number 5/0 was the best for card 30 Ne compare between traveller number 4/0 Most preeminence fact is that, the traveller speed remained same both for 5/0 and 4/0.

MECHANICAL PROCESSES IN TRIBOTECHNICAL UNITS

The study examined the diffusion phenomenon caused by compressive forces in tribotechnical nodes adhering to each other under high contact pressure and the mechanism of rupture of surfaces during surface fatigue. As a result, for two metal surfaces, depending on the nature of the touch, the gravitational and repulsive forces generated during the interaction in any environment are determined based on the number of touches and an analytical expression is obtained to calculate them. Keywords: tribotechnical knot, mutual contact, diffusion phenomenon, surface attraction, molecular contact, mechanical contact.

Observation of Crack Originating from Non-Metallic Inclusions in Furnace-Induction Heated SUJ2 Steel under One-Point Rolling Contact Fatigue at High Contact Pressure

It is important to reveal the mechanism of crack growth from non-metallic inclusions because it commonly causes the origin of flaking fracture. In order to observe the cracks initiated from non-metallic inclusions under contact pressure, we performed one-point rolling contact fatigue tests using furnace-induction heated SUJ2 steel. We measured the hardness distribution of the furnace-induction heated (FIH) specimen and observed cracks with the inclusions at cross-sections.

Superlubricity under ultrahigh contact pressure enabled by partially oxidized black phosphorus nanosheets

Superlubricity has recently raised an increasing interest owing to its great potential in energy saving and environmental benefits. Yet how to obtain stable superlubricity under an ultrahigh contact pressure (>1 GPa) still remains a challenge. Here, we demonstrate that robust liquid superlubricity can be realized even under a contact pressure of 1193 MPa by lubrication with partially oxidized black phosphorus (oBP) nanosheets. The analysis indicates that the oBP nanosheets that absorb large amounts of water molecules are retained at the friction interface and transform the friction pairs interface to that between the oBP nanosheets. Molecular dynamics simulation demonstrates that water molecules could be retained at the friction interface even under the ultrahigh contact pressure owing to the abundant P=O and P–OH bonds formed on the oBP nanosheet surfaces, contributing to the achievement of stable superlubricity under the ultrahigh contact pressure. This work has the potential of introducing the liquid superlubricity concept in diverse industrial applications involving high-contact-pressure operating conditions.

Study of operational properties of steel friction pairs with antifriction coating from copper alloys produced by electric spark alloying

Improving the reliability, durability and safety of operation of heavily loaded friction units is an urgent problem in physics, chemistry and surface mechanics. The tribotechnical characteristics of coatings made of bronzes BrAZhMts10-3-1.5 and BrMtsF3-6, applied by electrospark alloying on bushings made of structural steel 30KhGSN2A for operation under conditions of high contact pressure under friction without lubrication, have been investigated. Modes of coating deposition from the standpoint of tribology (the value of the electric discharge current in a pulse, the value of the longitudinal electrode feed per one rotation of the part, the rotation speed of the workpiece, the number of passes during processing, finishing of the coating) have been developed. It was found that when applying bronze BrMtsF3-6 to obtain a high-quality coating, the process must be performed in a protective atmosphere of argon to prevent phosphorus burnout. The tribotechnical efficiency of coatings when working under dry friction conditions is shown. For the steady-state wear mode, the friction coefficient is 0.10 – 0.13 at a pressure of 200 – 250 MPa, the wear resistance of coated steel is doubled. Steel with a bronze coating BrAZhMts10-3-1.5 has a higher bearing capacity, with BrMtsF3-6 coating — a higher antifriction. The ways of increasing the service life of steel-coated steel friction pair are analyzed.

A New Combined Model for considering the Plasticity Effects in Contacting Asperities

Wheel-rail contact in railway engineering is an important topic. Due to different materials and surface roughness of wheel and rail, the contact characteristics can alter significantly. This article aims to investigate the effects of surface roughness and asperities on the contact parameters such as contact area, contact force, and contact stiffness. The lateral contacts between asperities are assumed to be the general contact condition. Azimuthal and contact angles distributions are assumed to be spherical harmonic distribution. This assumption is compatible with the asperity distribution on the wheel and the rail surfaces. Besides, a new combined model is developed to cover the stick-slip and the plasticity effects in contacting asperities. The results of the presented model offer very good estimations for the asperities contact characteristics, especially at the small-contact area and separation where high-contact pressure and plastic deformation usually exist.