Vinayak Ranjan

ROLLING CONTACT FATIGUE LIFE OF RAIL FOR DIFFERENT SLIP CON-DITIONS

A THREE-DIMENSIONAL ELASTIC-PLASTIC FINITE ELEMENT ANALYSIS (FEA) IS CARRIED OUT TO ESTIMATE THE ROLLING CONTACT FATIGUE (RCF) CRACK INITIATION LIFE FOR VARIED SLIP RANGE ON THE RAIL ARISING FROM OPERATIONAL VARIATIONS. THE WHEEL LOAD PRODUCES HERTZIAN CONTACT PRESSURE. VARIATION IN ENGINE TRACTION INDUCES SLIP VARIATIONS THAT EVOLVES THERMAL LOAD IN TERMS OF HEAT FLUX. THE APERIODIC ROLLING OF WHEEL ON RAIL DEVELOPS NON-PROPORTIONAL MULTIAXIAL FATIGUE LOADING. PRESENT STUDY COMBINES THESE EFFECTS BY TRANSLATING THE WHEEL LOAD ON RAIL FOR MULTIPLE (TWELVE) PASS IN PRESENCE OF THERMAL LOAD, CONTACT PRES-SURE AND TRACTION THROUGH A PROPOSED SIMULATION. THE TEMPERATURE DEPENDENT CHABOCHE MATERIAL MODEL WITH NONLINEAR KINEMATIC HARDENING LAW IS IMPLEMENTED TO ESTIMATE THE STRESSES AND PLASTIC STRAINS GOVERNING THE MULTIAXIAL FATIGUE CONDITION AT THE INTERFACE. THE LOCATION OF MAXIMUM VON MISES STRESS, FOUND AT A MATERIAL POINT ON OR A LAYER BELOW THE RAIL-HEAD, CONTEMPLATES THE FATIGUE CRACK INITIATION SITE. A CODED SEARCH ALGORITHM HELPS TO IDENTIFY THE CRITICAL PLANE OF CRACK INITIATION CORRESPONDING TO THE MAXIMUM FATIGUE PARAMETER (FP). IN CONTRAST TO AVAILABLE PREDICTIONS OF RCF LIFE CONSIDERING CONTACT PRESSURE AND/OR TRACTION OR FRICTIONAL HEAT IN ISOLATION, PRESENT STUDY COMBINES ALL THESE LOADS TOGETHER AND PROVIDES A MORE REALISTIC RESULT BY NUMERICAL SIMULATION.

A Comparison of Vibroacoustic Response of Isotropic Plate with Attached Discrete Patches and Point Masses Having Different Thickness Variation with Different Taper Ratios

A comparison of sound radiation behavior of plate in air medium with attached discrete patches/point masses having different thickness variations with different taper ratio of 0.3, 0.6, and 0.9 is analysed. Finite element method is used to find the vibration characteristics while Rayleigh integral is used to predict the sound radiation characteristics. Minimum peak sound power level obtained is at a taper ratio of 0.6 with parabolic increasing-decreasing thickness variation for plate with four discrete patches. At higher taper ratio, linearly increasing-decreasing thickness variation is another alternative for minimum peak sound power level suppression with discrete patches. It is found that, in low frequency range, average radiation efficiency remains almost the same, but near first peak, four patches or four point masses cause increase in average radiation efficiency; that is, redistribution of point masses/patches does have effect on average radiation efficiency at a given taper ratio.

Effects of thermal load on wheel–rail contacts: A review

ABSTRACT This article presents a technical review on the effects of thermal loads evolved at the wheel–rail–brake contact interfaces. These dynamic contact interfaces develop heat transfer conditions of widely varied thermal level. Their modeling to identify the sources for a variety of defect formation, observable on wheel tread or rail surface, is very important. The railway system, in general, has to bear axle load, friction load, and thermal load arising from their contact conditions in addition to traction and dynamic loads. The defects arising from the interaction of thermal load and other loadings may be identified as hot spots, shelling, spalling, rolling contact fatigue (RCF), and corrugation. The mechanisms for the formation of such defects are pivoted over the existing thermal environment of dynamic interacting surfaces. This review summarizes the works of early investigations and recent advances in modeling the heat transfer conditions required to estimate the temperature distribution at the contact zone. The heat partitioning method for both drag and stop braking conditions, in the presence of rail chill effect, is emphasized. Thermal gradient, introduced by localized temperature rise in the contact zone, in the presence of variable friction coefficient, promotes the RCF process. These alter the residual stresses in the contact region to cause a structural shakedown, aggravate plastic flow and activates ratchetting phenomenon in rails. The evolution of thermomechanical surface and subsurface fatigue cracks are also discussed for the completeness of this article. The effect of all such defect formation, emerging from thermal loading condition, and their countermeasures for defect mitigation are presented in this review. This abridged technical documentation envisions attracting more research in the area to improve wheel–rail set design and performance standards to extend enhanced safety and comfort to rail transport operation. It is opined that the thermomechanical loading, their effects on promoting defect formation and propagation should be studied in combination instead of the current practice of treating them separately.

A numerical study on effects of friction-induced thermal load for rail under varied wheel slip conditions

A finite element-based simulation was carried out to investigate the effects of friction-induced thermal load on rail under varied wheel slip conditions. The surface temperature rise from six different percentage slips (1%, 1.5%, 2%, 5%, 8.5%, and 10%) at the contact interface was examined for eight-wheel pass. The residual stresses and accumulated plastic strains evolved by the effect of localized temperature rise are estimated. Analytical formulation for conduction mode of heat transfer at the contact patch is used to estimate the temperature distribution. The interaction of thermal-elastic-plastic field conditions is obtained by a proposed simulation model. This is implemented in commercial finite element software ANSYS 14.0. In order to capture the steep thermal gradient beneath the contact surface, refined mesh is used in the upper layers up to a depth of 2 mm of the simulation domain. For better manifestation of thermally affected material layers, a temperature dependent bilinear-kinematic hardening material condition is applied. Results indicate the maximum temperature rise at about 0.6a from the trailing end in the contact ellipse of semi-major axis a. At higher slippage conditions the initial pearlitic rail steel gets converted to martensite which is often observed on rail surface as white etching layer known to be associated with rolling contact fatigue. The study reveals the mechanisms of thermally induced defects observable on rail surface. The outcomes, in addition, can provide useful information for the development of thermo-mechanically superior rail steels.

Vibration analysis of a thin functionally graded plate having an out of plane material inhomogeneity resting on Winkler–Pasternak foundation under different combinations of boundary conditions

In the present research article, classical plate theory has been adopted to analyze functionally graded material plate, having out of plane material inhomogeneity, resting on Winkler–Pasternak foundation under different combinations of boundary conditions. The material properties of the functionally graded material plate vary according to power law in the thickness direction. Rayleigh–Ritz method in conjugation with polynomial displacement functions has been used to develop a computationally efficient mathematical model to study free vibration characteristics of the plate. Convergence of frequency parameters (nondimensional natural frequencies) has been attained by increasing the number of polynomials of displacement function. The frequency parameters of the functionally graded material plate obtained by proposed method are compared with the open literature to validate the present model. Firstly, the present model is used to calculate first six natural frequencies of the functionally graded plate under all possible combinations of boundary conditions for the constant value of stiffness of Winkler and Pasternak foundation moduli. Further, the effects of density, aspect ratio, power law exponent, Young’s modulus on frequency parameters of the functionally graded plate resting on Winkler–Pasternak foundation under specific boundary conditions viz. CCCC (all edges clamped), SSSS (all edges simply supported), CFFF (cantilever), SCSF (simply supported-clamped-free) are studied extensively. Furthermore, effect of stiffness of elastic foundation moduli (kp and kw) on frequency parameters are analyzed. It has been observed that effects of aspect ratios, boundary conditions, Young’s modulus and density on frequency parameters are significant at lower value of the power law exponent. It has also been noted from present investigation that Pasternak foundation modulus has greater effect on frequency parameters as compared to the Winkler foundation modulus. Most of the results presented in this paper are novel and may be used for the validation purpose by researchers. Three dimensional mode shapes for the functionally graded plate resting on elastic foundation have also been presented in this article.

Burst strength analysis of gas turbine disc based on deformation characteristics

In aircraft gas turbine engine, the rotating turbine disc is highly stressed component. The demand of high strength to weight ratio for each component of aeroengine makes the disc, a critical compo...

Effect of volume fraction index and mass ratio on natural frequency of clamped functionally graded plate with attached point mass

This study is concerned with the effect of volume fraction index and mass ratio on natural frequency of clamped functionally graded plate having different aspect ratio with point mass attached at the center using Rayleigh-Ritz method. According to the power law distribution, the mechanical properties of the functionally graded plate are continuously varying along the thickness of the plate. Rayleigh-Ritz procedure of energy variation formulation is used to obtain the eigen equation. Some of the results of natural frequencies associated with functionally graded plates are validated with the published results.