Mechanism Analysis of Spalling Defect on Rail Surface under Rolling Contact Conditions

Abstract

Under the wheel/rail contact loading conditions, the microcracks on the rail surface propagate, leading to spalling defect or rail fracture and threatening the travelling safety of high-speed railway directly. In order to analyze the mechanism of the crack propagation on the rail surface, the calculation model of the wheel/rail contact fatigue was established, and the variation of the stress intensity factor at the crack tip when the crack length was increased from 0.1 mm to 2 mm was obtained. Based on the mixed-mode fracture criterion and Paris growth theory, the mechanism of the crack propagation on the rail surface was analyzed. The results show that when the microcrack grows to macrocrack, the mode of the fatigue crack on the rail surface is mixed including sliding mode and open mode. With the increase of the crack length, the stress intensity factor KI increases first and then decreases gradually, and the relative dangerous location of the open-mode crack moves from the inner edge of the contact area to the outer edge, while the factor KII is increasing during the whole propagation process, and the relative dangerous location of the sliding-mode crack remains unchanged basically. The main failure mode of crack is open during the initial stage and then transforms into sliding mode with the crack length increasing. The crack tends to propagate upward and leads to spalling defect when the crack length is between 0.3 and 0.5 mm. This propagation path is basically identical with the spalling path of the service rail. The research results will provide a basis for improving the antifatigue performance of rail and establishing the grinding procedure.

Caracterização do defeito spalling e correlação com a região da solda aluminotérmica em trilho ferroviário

“…de trilhos e rodas ferroviárias [5][6][7]. Devido ao excesso de tensões decorrentes do contato entre a roda e o trilho, pode ocorrer a iniciação e a propagação de trincas na superfície dos trilhos, as quais podem originar defeitos e fraturas, dentre esses, destaca-se o spalling no boleto [8][9][10][11][12].…”

“…De acordo com [13], o spalling na superfície de contato dos trilhos é um defeito típico de RCF que interfere na manutenção da via além de acentuar as interações dinâmicas no sistema roda-trilho. O defeito surge com alguns milímetros de profundidade na pista de rolamento do trilho evoluindo gradativamente à medida que a roda ferroviária passa sobre sua região de localização [7,12]. Esta irregularidade na via causa vibração anormal no veículo ferroviário [13].…”

Use of the fatigue index to study rolling contact wear

“…Although the different plots are not aligned, it has to be taken into account that FI has been calculated using λ = 1 for all the tests and the Tresca criterion and not the shear yield strength from actual tests. Furthermore, as the value of the yield strength was not found in the papers, it was estimated using, when available, the minimum value the standards demand from the steels or a value from other papers ( [48] for the U71Mn steel). One last but very important problem is that the traction coefficients used to draw figure 15 could be the maximum or the final ones and not one value more representative of the whole test as the one selected in this study, as no information is given about that in the studied papers.…”

Evaluation of Numerical Simulation Approaches for Simulating Train–Track Interactions and Predicting Rail Damage in Railway Switches and Crossings (S&Cs)

“…S&C rail faults whose main failure mechanism is RCF include spalling, shelling, cracks in the rail, head checks and squats. Spalling is identifiable by cavities and subsequent fracture on the railhead and is initiated through recurring extrusion from high wheel-rail contact stresses, resulting in the initiation and propagation of micro-cracks [6]. Shelling is identifiable as material peeling off the rail surface and initiates by a small crack on the rail surface, reducing the structural integrity on subsequent multiplication and merging [6].…”

“…Spalling is identifiable by cavities and subsequent fracture on the railhead and is initiated through recurring extrusion from high wheel-rail contact stresses, resulting in the initiation and propagation of micro-cracks [6]. Shelling is identifiable as material peeling off the rail surface and initiates by a small crack on the rail surface, reducing the structural integrity on subsequent multiplication and merging [6]. Head checks are observed in the form of parallel cracks on the rail gauge corner and initiate from RCF on the surface rail [7].…”