Tribology of The Sock-Skin Interface – The Influence of Different Fabric Parameters On Sock Friction

The purpose of this parametric design of experiments was to identify and summarize how the influence of knit structure (single jersey vs. terry), fiber composition (polyester vs. cotton), fiber linear density (30/1 Ne vs. 18/1 Ne & 1/150/34 vs. 2/150/34), and yarn type (filament vs. spun) affected the frictional profile across the sock-skin interface, and then relate these factors to friction blister incidence. Friction testing trials were completed against both a polypropylene probe and a synthetic skin material (Lorica soft®) to determine if there was a difference in friction based on interface interaction. Friction testing was completed by sliding a probe across the inside bottom surface of the sock (the part that is usually in-contact with the bottom of the foot) while instantaneously measuring the frictional force every tenth of a second. For both trials (plastic probe and synthetic skin), in the dry condition, knit structure was found to be the most prominate fabric parameter affecting the frictional force experienced at the sock-skin interface. It was also determined that fiber linear density, and yarn type are tertiary factors affecting the frictional force measured at the sock-skin interface. Finally, in the dry state, it was determined that fiber composition had seemingly no effect on the frictional force experienced at the sock-skin interface.

Surface integrity and wear evolution of high strength aluminum alloy after high-speed oblique cutting

In this paper, we present an experimental study on the surface frictional wear mechanism of the high-strength aluminum alloy after high-speed milling. We use a surface profilometer and an X-ray stress tester to characterize the milled surface integrity of the material, and UMT-3 friction testing machine to obtain its surface roughness, oxygen content, hardness, and wear morphology during different wear stages. The results show that milling-induced residual tensile stress makes the cut surface more prone to fatigue cracking and consequently abrasive wear in the initial wear stage. The larger the angle between the friction pair movement direction, the greater the chance of adhesive wear and abrasive wear. A complete friction stage pattern can be obtained at a high load (15 N) and a low sliding speed (0.6 mm/s). The friction pair enters a stable wear stage after 20 sliding cycles. Work hardening constitutes the main driver of stable wear.

UNDERSTANDING TEMPERATURE EFFECTS ON FRICTION AT TOOL – CFRP WORKPIECE INTERFACE USING OPEN-LOOP FRICTION TESTING

Cutting processes of carbon fibre reinforced polymer (CFRP) material generate significant energy in the form of heat which can be detrimental to final surface and sub-surface quality. By artificially changing the temperature of the workpiece to simulate cutting temperatures, thermal effects on friction metrics can be understood. Feed rate and CFRP pre-heating for macro and nanoscale open loop pin on plate friction testing has been completed for two aerospace grade CFRP materials with steel, carbide and coated carbide pins to give an insight to fundamental tool wear that occurs in CFRP machining.

A Tribological Comparison of Facet Joint, Sacroiliac Joint, and Knee Cartilage in the Yucatan Minipig

Objective Pathology of the facet and sacroiliac (SI) joints contributes to 15% to 45% and 10% to 27% of lower back pain cases, respectively. Although tissue engineering may offer novel treatment options to patients suffering from cartilage degeneration in these joints, the tribological characteristics of the facet and SI joints have not been studied in either the human or relevant large animal models, which hinders the development of joint-specific cartilage implants. Design Cartilage was isolated from the knee, cervical facet, thoracic facet, lumbar facet, and SI joints of 6 skeletally mature Yucatan minipigs ( Sus scrofa). Tribological characteristics were assessed via coefficient of friction testing, interferometry, and immunohistochemistry for lubricin organization. Results Compared with the knee, the coefficient of friction was higher by 43% in the cervical facet, 77% in the thoracic facet, 37% in the lumbar facet, and 28% in the SI joint. Likewise, topographical features of the facet and SI joints varied significantly, ranging from a 114% to 384% increase and a 48% to 107% increase in global and local surface roughness measures, respectively, compared with the knee. Additionally, the amount of lubricin in the SI joint was substantially greater than in the knee. Statistical correlations among the various tribological parameters revealed that there was a significant correlation between local roughness and coefficient of friction, but not global roughness or the presence of lubricin. Conclusion These location-specific tribological characteristics of the articular cartilages of the spine will need to be taken into consideration during the development of physiologically relevant, functional, and durable tissue-engineered replacements for these joints.

Mechanical Properties of White Metal on SCM440 Alloy Steel by Laser Cladding Treatment

The bearing is a machine element that plays an important role in rotating the shaft of a machine while supporting its weight and load. Numerous bearings have been developed to improve durability and life, depending on the functions and operating conditions in which they are desired. White metal is one of method to improve durability that is soft and bonded to the inner surface of the bearing to protect the bearing shaft. Currently, the centrifugal casting process is used as a white metal lamination method, but it involves problems such as long processing times, high defect rates and harmful health effects. In this paper, a laser cladding treatment is applied to bond powdered white metal to SCM440 alloy steel, which is used as bearing material in terms of replacing the risks of a centrifugal process. In order to understand whether laser cladding is a suitable process, this paper compares the mechanical properties of white metal produced on SCM440 alloy steel by centrifugal casting and the laser cladding process. The laser power, powder feed rate and laser head speed factors are varied to understand the mechanical properties and measure the hardness using micro Vickers and conduct field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and friction testing to understand the mechanical properties and surface characteristics. Based on the results, the hardness values of the cladding (white metal) layer ranged between 24 and 26 HV in both the centrifugal casting and laser cladding methods. However, the hardness of the white metal produced by laser cladding at about a depth of 0.1 mm rose rapidly in the cladding process, forming a heat-affected zone (HAZ) with an average hardness value of 200 HV at a laser power of 1.1 kW, 325 HV at 1.3 kW and 430 HV at 1.5 kW. The surface friction testing results revealed no significant differences in the friction coefficient between the centrifugal casting and laser cladding methods, which allows the assumption that the processing method does not significantly influence the friction coefficient.

Effect of tip size and experimental conditions on nano-scale friction testing

Assessment of nano-tribological properties (friction and wear) on polymer surface helps to understand their scratch, mar and wear properties. More polymers are used now for automotive, electronics, appliances, and building and constructions industries due to aesthetics and design freedom. Owing to their lower mechanical properties, polymers are vulnerable to surface damage and deteriorate their morphology, functionality, and aesthetics with time. In this study, nano-indenter was used for measuring friction and wear properties varying test parameters and indenter tips. A Berkovich tip (B-tip) with radius of ∼50 nm and a conical tip (C-tip) with 60° cone angle and tip radius of 1000 nm were used. Polyoxy methylene (POM) with additives were chosen for friction testing. Higher coefficient of friction (COF) for C-tip was observed compared to B-tip and this explained based on the higher tip-material interactional area for C-tip. COF was decreased with higher additive concentration and same trend was followed for wear depth for the B-tip. For C-tip, COF was increased with the testing loads and corresponding wear depth were higher for higher load. Change of COF with test velocity was not showing any specific trend. Shallow wear depth using B-tip compared to C-tip may be better for probing top surface of the materials. Nano-scale tribo-mechanical evaluation techniques are uniquely suited for fundamental understanding and screening many additives quickly. Observed wear properties not only depend on the additives added to the formulation, but may also be influenced by the geometry of the tip.

The composition and friction-reducing properties of leaf layers

Every autumn rail networks across the world suffer delays, accidents and schedule changes due to low friction problems caused by leaves landing on the rails. These leaves form a layer that can reduce the friction between the wheel and the rail to a similar level as that between ice and an ice-skate ( μ = 0.01 – 0.05 ). Previous works have generated several hypotheses for the chemical reactions and low friction mechanism associated with these layers. In this work, the reaction between an aqueous extract of sycamore leaves and metallic iron is investigated. This reaction has been shown to produce a black precipitate, which matches field observations of leaf layers, while friction tests with these extracts produce characteristic ultra low friction. The reaction is investigated through FTIR, XPS, CHNS and ICP-MS analysis as well as wet chemical testing. The impact of the reaction on friction is investigated through three rounds of tribological testing. The results indicate that the black precipitate produced is iron tannate, formed by complexation of tannins with dissolved iron ions. Friction testing showed that eliminating tannins from the leaf extract resulted in a significant increase in the friction coefficient compared with the control.

A tribometer and methodology for wear and friction testing of porous journal bearings at elevated temperatures

Purpose This paper aims on a methodology to overcome the fact that conventional service life testing of porous journal bearings (PJBs) requires long test times and is not economical. Design/methodology/approach This paper sketches out a pathway to strongly accelerated life tests for PJBs enabled by high load and elevated temperature, which saves months or even years of testing. The testing time is not only reduced to a few weeks, but the results are also statistically secured via a multiple test rig construction of a custom-made tribometer. Findings An exemplary bearing-lubricant combination is tested in the mixed lubrication regime, where the coefficient of friction is monitored during the test. Originality/value A Weibull curve is fitted to the experimental results to show the survival probability of the combination over time. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2019-0351/