A Study on the Contact Pressure and Thermo-Elastic Behavior of a Brake Disc-Pad by Infrared Images and Finite Element Analysis

To understand the tribological characteristics of a frictional brake system, it is very important to measure the contact pressure between the brake disc and pads. But until now there have been no direct methods by which to measure the contact pressure. In this study, an attempt to indirectly estimate the contact pressure is proposed. Infrared thermal images and finite element analysis were used as tools. For the thermo-elastic finite element analysis, uniform, linear, quadratic, and quartic heat flux profiles in the radial direction were applied on the disc surface. Thermal and stress fields were obtained under various conditions in the disc fixing holes and on the contact faces of the two half discs. From the numerical results, it was found that the effect of the boundary conditions on the magnitude of thermal stress was about 10%. Numerical temperature data in the radial direction could be curve-fitted to functions with the same order as the heat flux profiles. The coefficients of correlation of the curve-fittings were more than 0.91. It could be concluded that using temperature profiles obtained with an infrared camera, contact pressure distributions on the disc surface could be inferred

Effect of Post-Weld Heat Treatment on the Fatigue Behavior of Medium-Strength Carbon Steel Weldments

Railway vehicle makers manufacture the bogie frame by welding medium-strength carbon steel sheets. It has been a long-standing practice to perform post-weld heat treatment (PWHT) to remove welding-residual stress, but rail car manufacturers are moving toward producing bogie frames without PWHT. Since securing the fatigue strength of the bogie frame is essential for vehicle operation safety, it is necessary to systematically evaluate the effects of PWHT on hardness, microstructure, mechanical properties, corrosion, fatigue strength, etc. In this study, small-scale welding specimens and full-size components were produced using S355JR used in general structures, automobiles, shipbuilding, railroad vehicles, etc. The effect of PWHT on material properties-the hardness of the base material, heat-affected zone and weld metal, microstructure, shock absorption energy, yield strength, tensile strength, and fatigue were investigated. When the weld specimen was annealed at 590 °C and 800 °C for 1 h, the yield strength and tensile strength of the specimen decreased, but the elongation increased. For specimens not heat-treated, the parent material’s yield strength, the yield strength in HAZ, and the yield strength of the weld metal were 350 MPa, 345 MPa, and 340 MPa. For specimens heat-treated at 590 °C, they were 350 MPa, 345 MPa, and 340 MPa. For specimens heat-treated at 800 °C, they were 350 MPa, 345 MPa, and 340 MPa. Annealing heat treatment of the specimen at 800 °C homogenized the structure of the weldments similar to that of the base material and slightly improved the shock absorption energy. For specimens not heat-treated, the Charpy impact absorption energies at 20 °C of the parent material and weld metal were 291.5 J and 187 J. For specimens heat-treated at 590 °C, they were 276 J and 166 J. For specimens heat-treated at 800 °C, the Charpy impact absorption energy at 20 °C of the parent material was 299 J. PWHT at 590 °C had the effect of slightly improving the fatigue limit of the specimen but lowered the fatigue limit by 10.8% for the component specimen

Microstructural Analysis and Wear Performance of Carbon-Fiber-Reinforced SiC Composite for Brake Pads

Carbon-fiber-reinforced silicon carbide (C/C-SiC) composite is widely used as a friction material owing to its good performance, even though it is more expensive than metallic materials. The light C/C-SiC composite is an ideal candidate for weight reduction of frictional parts. In this study, the friction and wear behavior of C/C-SiC composite was assessed using a ball-on-disk friction tester under dry reciprocating sliding conditions at different temperatures of 25, 100, and 200 °C. The disk specimens were made of C/C-SiC composite, while the mating counterpart pins were made of bearing steel. The microstructure and wear track of the specimens were characterized using a scanning electron microscopy (SEM) and Raman spectroscopy. The microstructural analysis of the wear track revealed that the wear mechanism was abrasive. The friction coefficient and wear behavior of the specimens was dependent on the temperature, where the friction coefficients and wear rate increased with increasing temperature

Effect of Welding Polarity on Mechanical Properties of Submerged Arc Welded Railway Vehicle Wheels

When a railway vehicle moves on a curved rail, sliding contact between the rail head side and wheel flange causes wear on the wheel flange. Traditionally, a wheel with thinned flange is machined to get a minimum flange thickness specified for structural safety. This operation reduces the rim thickness and shortens the life of the wheel. In the present study, the thinned flanges were hard-faced by submerged arc welding. A welding wire, which has good weldability to the base material of the wheel and does not generate thermal cracking, was developed. The effects of welding polarity on the microstructure, hardness, friction coefficient, and wear characteristics of the welded wheel were studied. The hardness of the wheel welded with reverse polarity was similar to that of welded with straight polarity. The wear rates of the wheel disc welded with reverse polarity and its counterpart rail disc were 11% and 27% lower than those welded with straight polarity. Delamination wear due to subsurface crack propagation and oxidation wear were mixed. The hardness of the rail before the wear test was in the range of 250–300 HV. After the wear test, it soared to 500 HV