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.

Experimental and numerical investigations on longitudinal vibration of suspended monorail trains induced by bogie pitching motion

The longitudinal harmonic vibrations found in the suspended monorail train (SMT) seriously affected the ride quality and dynamic behaviour. In this work, the experimental and simulated analyses are carried out to reveal the essential phenomenon, occurring mechanism and possible solutions to this issue. Firstly, the ride quality and vibration transmission of the tested SMT system are investigated. It is found that the longitudinal vibrations with the frequency of 2.7Hz occur to the carbody, bogie frame and suspension of the train system. Due to the secondary suspension is lower than the gravity center of the bogie frame, the bogie pitch motion with low damping ratio can be easily excited. The longitudinal components of the bogie pitch motion will transfer to the carbody and wheelset through traction rod and primary suspension, respectively. After that, the multibody dynamic model of a suspended monorail train is developed. Based on the numerical model, some parametric simulations, e.g. rubber stiffness, traction rod height and secondary damping, etc., are carried out to propose solutions to relieve the longitudinal vibrations. Finally, the field tests for the SMT arranging the longitudinal dampers are conducted to verify its improvement to longitudinal vibrations.

Evaluation of Stress and Fatigue of a Rail Vehicle Suspension Component

The article discusses the use of pivot bearing friction liners, made of selected materials, in railway freight wagons’ spherical centre bowls. Comparative studies on the effect of suspension dynamics on the equivalent stresses in the liner material were carried out using the finite element method and multibody simulation. The results show the magnitude and location of the highest stresses in the liner with varying input loads, friction coefficients and interacting materials. The analysis is a basis for a simulation method for predicting the fatigue life of the suspension friction liner placed in the centre bowl between the bogie frame and the vehicle body.