Marija Molodova

Differential wear and plastic deformation as causes of squat at track local stiffness change combined with other track short defects

Squats have become a major problem in the track of many railways. In the quest for the root causes of squats, it is observed that they are occasionally found at locations of track stiffness changes such as at fish-plated insulated joints and at switches and crossings. Obviously, there should be other factors in the track, which, together with the stiffness change, have played important roles otherwise there will be squats at all such locations. A validated hybrid multibody-finite element model of vehicle–track vertical interaction is extended to simulate the frictional dynamic rolling contact at a fish-plated insulated joint in order to identify such factors. Elastic–plastic rail material property is taken into account. It is found that it is track short defect in the preload condition of the bolts and the contact between the fishplates and the rail head, which together with the stiffness change, causes large normal and longitudinal contact force variation at the fishplate end so that differential wear and differential plastic deformation may accumulate at a fixed location. With proper wavelength, the accumulated rail top geometry deviation may grow into a squat. The significance of the present work lies in that other track short defects such as damaged and improper railpads and fastening, and ballast voids may also have such effects, which may be responsible for a large portion of the many squats in the tracks. This gives the direction for further work.

Squat Treatment by Way of Minimum Action Based on Early Detection to Reduce Life Cycle Costs

Squats are a type of rolling contact fatigue on the top of rails of straight tracks or shallow curves. In some countries they have become a major type of rail damage. Although it is widely recognized that preventive and early corrective actions are cheaper than late remedies such as rail replacement, timely treatment is hindered by the lack of automatic detection of early squats. So far, the treatment of squats has mainly been dependent on ultrasonic detection, which detects deep cracks and is applicable only to severe squats. The life cycle costs (LCC) of squat-infected track are therefore high. The operational safety and availability of the networks are also adversely affected. Based on a new method which detects initiating squats, this paper proposes a methodology for squat related LCC reduction. First a squat classification is introduced that facilitates early identification of squats. Then the growth phases of squats are discussed; typical growth rate of squats is analyzed, and thereupon based threshold values for minimum action by rail grinding are proposed. After a review of the currently available detection methods, the new detection method is presented, with results of field test demonstrating the capability of the method to detect light squats. Finally, a case study of the LCC of a monitored squat-infected track section shows that the proposed treatment can significantly reduce the LCC. In addition, operational safety and network availability can also be improved.© 2010 ASME