Experimental Study of Effects of the Third Medium on the Maximum Friction Coefficient between Wheel and Rail for High-Speed Trains

The changes of the friction coefficient between wheel and rail affect the wheel-rail adhesion characteristics of high-speed trains. The adhesion state in the wheel-rail contact area could be distinguished by the maximum friction coefficient between wheel and rail. The wheel-rail adhesion is of great significance for high-speed train traction. In order to study the influence of water, oil, fallen leaves, quartz sand, or their mixtures on the maximum friction coefficient between high-speed wheel and rail, a wheel-rail contact test bed is built to carry out the wheel-rail contact test and wheel-rail friction contact test. The comparative analysis of the test results shows that the axle load has little influence on the maximum friction coefficient between wheel and rail. Water, oil, and fallen leaves would reduce the maximum friction coefficient. Quartz sand could increase the maximum friction coefficient in a short time, while the excessive static friction coefficient would damage the wheel and rail. Besides, the maximum friction coefficient of water, oil, and fallen leaves mixing in pairs is lower than each of them existing alone. Both water and oil could increase the adhesion of quartz sand, and the effect of water is better. Therefore, when the sand still could not meet enough traction, it could be considered to add some water to increase the wheel-rail adhesion.

A Comparative Evaluation of Frictional Resistance of Conventional, Teflon and Epoxy Coated Stainless Steel Archwires in Metal, Ceramic Brackets – An In vitro Study

Aim and Objectives: To evaluate the frictional resistance of Conventional, Teflon, and Epoxy coated stainless steel archwires in Metal, Ceramic brackets. Materials and Methods: 0.019” x 0.025” Stainless steel arch wire. (G & HTM) – 30n, 0.019” x 0.025” Teflon coated stainless steel archwire. (D-TechTM) – 30n, 0.019” x 0.025” Epoxy coated stainless steel archwire. (G & HTM) – 30n, 0.22 MBT Stainless steel (Gemini- 3M UnitekTM,) lower incisor brackets – 30n, 0.22 MBT Ceramic (Gemini- 3M UnitekTM), lower incisor brackets – 60n. The wires are cut into 5cm long and are ligated to bracket using 0.010- inch ligature wire. Acrylic block is placed in lower arm of Instron universal testing machine, free end of wire is pulled with upper arm of universal testing machine, at a rate of 10 mm/ min while the wire is placed parallel to long axis of bracket and tooth, and a load of 50 kg was used to measure frictional forces. Results: Stainless steel bracket combined with Stainless Steel wire showed maximum Friction 2.640N (mean) and minimum was 0.307N (mean) with a SD of ±1.2275 (0.6618). Stainless-steel bracket combined with Epoxy coated SS wire showed maximum Friction of 10.3N and minimum was 5.62N with a SD of ± 7.3513 (1.8975). Stainless steel bracket combined with Teflon coated SS wire maximum Friction noted was 5.59N and minimum was 1.66N with a SD of ± 1.8652 (0.9545). Ceramic brackets combined with Stainless Steel wire showed maximum Friction 10.88N and minimum 4.29N with a SD of ± 6.55529 (1.6081). Ceramic brackets combined with Epoxy coated SS wire showed maximum Friction 14.88N and minimum 5.62 with a SD of ± 9.3305 (2.4077) Ceramic brackets combined with Teflon coated SS wire showed maximum Friction of 6.93N and minimum 4.31N with a SD of ±6.3483 (1.2302) Conclusions: Stainless steel brackets combined with stainless steel archwires or Teflon coated archwires may be used effectively in sliding mechanics, rather than ceramic brackets and tooth-colored epoxy coated archwires.

Thermo-Mechanical Coupling Analyses for Al Alloy Brake Discs with Al2O3-SiC(3D)/Al Alloy Composite Wear-Resisting Surface Layer for High-Speed Trains

In the present work, a theoretical model of three-dimensional (3D) transient temperature field for Al alloy brake discs with Al2O3-SiC(3D)/Al alloy wear-resisting surface layer was established. 3D transient thermo-stress coupling finite element (FE) and computational fluid dynamic (CFD) models of the brake discs was presented. The variation regularities of transient temperature and internal temperature gradient of the brake discs under different emergency braking conditions were obtained. The effects of initial braking velocity (IBV) and thickness of Al2O3-SiC(3D)/Al alloy composite wear-resisting layer on the maximum friction temperature evolution of the disc were discussed. The results indicated the lower temperature and thermal stress distributed uniformly on the wear-resisting surface, which was dominated by high conductivity and cooling ability of the Al alloy brake disc. The maximum friction temperature was not obviously affected by the thickness of the wear-resisting layer. The maximum friction temperature of the brake discs increased with the increase of the IBV, the maximum friction temperature and thermal stress of the brake discs is about 517 °C and 192 MPa at IBV = 97 m/s considering air cooling, respectively. The lower thermal stress and fewer thermal cracks are produced during the braking process, which relatively decrease the damage. The friction behavior of the tribo-couple predicted using FE method correlated well with the experimental results obtained by sub-scale testing.

Improvement of Polymer Surface Properties Using the Deposition with Thin Metal Alloy Layers

The paper describes the advantages of material deposition using the resistive vaporization method, so that new very thin layer, which is about ìm, could be used on polymer base structure. Due to the new properties involving the friction coefficient on plane surface, where some dynamic forces are acting, we may better control the performances. By analyzing the theoretical aspects of entropy rate production, we may determine the maximum friction providing the stability of wear avoiding the material deterioration during the process.

A Review on Important Factors Affecting Dry Sliding Friction

Friction is the resistance faced by one body when it slides or rolls over another body. The friction is not a property of material. It is a response observed during sliding or moving. The maximum friction is required in some applications such as automobile tires on the road, machining the materials, brakes, clutches etc., Alternatively, the friction should be low in some applications like bearings, sliding parts of machineries etc., Most of material failure is occurred due to improper observation of friction and wear behaviors. Hence, understanding of the frictional behaviors of various metal pairs is essential to design any engineering tools and equipment. Therefore, in this paper, the important factors affecting the sliding friction are described in detail.