Search

Abstract: This paper presents evidences obtained by field monitoring, measurement and survey to show the validity of some numerical predictions about squat growth. The predictions concerns a postulated squat growth process, the relationship between the dynamic contact force and the corrugation-like wave pattern that often follows squats, the high frequency wheel–rail interaction related to squats, and the influence of tangential force on squat growth. The observations reveal signature tunes of squats which may be used for early detection of squats, show the necessity to include high frequency dynamic wheel–rail interaction in squat-related analyses, and provide evidence of relationship between rolling stock performance and squat initiation and growth. In validating the numerical results the model is also verified for its applicability to analyses of squat-related problem and other problems similar in nature. The model can be employed for the solution of three-dimensional frictional rolling contact problems. It can also be used for analyses of loading conditions of wheel–rail contact at short wave defects, and the associated damages such as wear, plastic deformation, fatigue and corrugation. [Copyright &y& Elsevier]

Abstract: Short track defects cause large dynamic contact forces at the wheel–rail interface, leading to fast deterioration of the track. Early detection of such defects is very important for timely maintenance. The track technical state can be assessed with the aid of axle box acceleration measurements, which can indicate short track defects like squats, welds with poor finishing quality, insulated joints, corrugation, etc. As a first attempt to determine a quantitative relationship between the characteristics of the accelerations and the track defects, axle box acceleration at a squat and a thermite weld were simulated through finite-element modeling. The magnitude and frequency contents of axle box acceleration at squats agreed with measurements. The results for welds had some discrepancies, which were mainly attributed to the fact that the modeled geometry of the weld deviated from the real one. [Copyright &y& Elsevier]

Abstract: Nowadays squats are a severe rolling contact problem on some railways. The root causes of it are not yet clear. From railway operation and maintenance points of view, root causes have to be known so that effective maintenance policies and plans can be made based on measurements and prediction. In the present work first a correlation analysis is performed based on measured data and field observations, and then a relation between squat occurrence and some parameters of the vehicle–track system is identified. Subsequently a transient finite element model of vehicle–track interaction is built up to analyze the contact forces and the resulting stresses and strains. The numerical results show good correspondence with observed phenomena at squats, and suggest certain relation between squat development and some eigen frequencies of the coupled vehicle–track system. A squat growth process is accordingly postulated. [Copyright &y& Elsevier]