Investigation on fatigue life of Rail-Wheel assembly using Finite Element Analysis
In recent years, the axle loads on railway cars is increasing due to increased transport of the goods and faster infrastructural growth. The rail wheels are subjected to high contact stresses of alternating magnitude due to rolling action of the wheels under these loads. The rail wheels should be able to sustain these variable loading for reasonably infinite life. Accidents due to fracture of rail wheels affects the safety of railway facility. Therefore more attention is paid to the quality of rail-wheel. The rail wheels are found to fail predominantly due to fatigue under these variable loadings whereas other modes of failure are damage to railway bogie, suspension failure and in some cases derailment of the vehicle. After all the advancements in design, materials and non-destructive inspection, the fatigue propagation and failure due to damage of railway components remains an important issue for safety engineering in railways. In this work, an attempt is made to investigate the occurrence of stresses in rail-wheel assembly due to high contact loads at the assembly points. The study involves the determination of equivalent stress (von-Mises), strain, safety factor using finite element method on ANSYS® 2016. An appropriate understanding of these mechanisms needs in depth knowledge of physical interactions between rail and wheel. The rail wheel assembly is assumed to operate under the designed load. The Goodman mean stress correction theory is used to obtain results. The results on the fatigue life are presented which are assumed to depend on these factors.
3-D Rail-Wheel contact analysis using FEA
Mechanics of the Rail-Wheel contact is one of the fundamental areas of the study in Railway Engineering, requiring both vast application expertise and dependable analysis approaches. Analytical formulations describing the physics of this phenomenon are only defined for certain type of simple contact geometries, therefore for more complicated geometries the analytical models utilizing closed formulations remain elusive. Remaining option is to utilize numerical computation methods. Railway engineers are, to the certain extent, successfully applied one of the numerical computation techniques known as Finite Element Analysis (FEA) into Rail-Wheel contact problems to validate their results by comparing them to their real life data obtained over the years. In the literature, most of the work on the Rail-Wheel contact FEA is either 2-dimensional axi-symmetric or simple 3D Rail-Wheel models with poor mesh count/quality or undesired Tet-mesh, latter known to exhibit stiff deformation characteristics during the deformation. Also, in majority of the FEA studies, boundary conditions and/or total load are applied with some approximations. This study focuses more on the fundamental way of handling Rail-Wheel contact problems from the FEA standpoint, and highlights required steps for more realistic 3D solutions to these types of problems. 3D FE analysis results obtained show good agreement with real life problems experienced at both railway Wheel and Rail.
HYPERGOLIC REACTION MECHANISMS OF CATALYTICALLY PROMOTED FUELS WITH ROCKET GRADE HYDROGEN PEROXIDE
Abstract The coupling of the physical and chemical processes controlling the ignition delays (τ ign ) of hypergolic propellants complicates the direct analysis of the transient ignition processes. The transport properties of both the propellants and the ambient gas, and the heat of vaporization and reaction affect τ ign and must be considered experimentally. Furthermore, since hypergolic ignition occurs, by definition, on contact, the mechanics of initial contact and subsequent mixing can affect τ ign and must also be considered. Experimental results from a study of the hypergolic ignition of a catalytically promoted fuel with rocket grade hydrogen peroxide (RGHP) are presented. Statistical analysis of the experimental data was conducted to evaluate the relative effects of RGHP concentration, initial ambient pressure, and the ambient gas on τ ign . At RGHP concentrations of less than 92% in water, stable ignition was difficult to achieve. At sufficiently high Lewis number, an oscillatory ignition process is observed. A phenomenological model comprising mixing, RGHP decomposition, fuel heating and vaporization, and auto-ignition is presented and compared to the experimental results.