Abstract
Advances in rail materials from conventional rail steels to those with higher yield points and the potential of additively manufactured laser clad coatings to improve the durability of railway track components presents a new challenge in characterisation. Many of these new and novel materials have either limited test samples available or are more resistant to strain and therefore present challenges in characterisation. The method reported here uses twin disc tests to simulate cyclic loading experienced by rail steel in service. A sample from a single test condition is analysed, measuring the shear yield stress and the accumulated shear strain at multiple depths below the contact surface, from which a Shear Yield Stress – Plastic Shear Strain (SYS-PSS) relationship is extracted. Knowledge of the stress history of a rail sample is not required to apply the method and minimal samples are required, providing a technique which can be used on rail steel samples removed from service.
Highlights
Rail in service is subject to high compressive and shear loading on relatively small contact areas and a combination of rolling and sliding where it is contact with a wheel
Prior to rolling contact micro indentation testing with a 0.2 kg load was used to determine the hardness of Martensitic Stainless Steel (MSS), heat affected zone (HAZ) and R260 grade rail steel using a twin disc sample manufactured with a 1 mm MSS laser clad coating
A material response to load characterisation method has been developed in which a rail material sample from a single twin-disc test can provide all required data to derive the respective Shear Yield Stress – Plastic Shear Strain (SYS-PSS) curve
Summary
Rail in service is subject to high compressive and shear loading on relatively small contact areas (around 1 cm2) and a combination of rolling and sliding where it is contact with a wheel. Such loading results in stresses exceeding the rail material’s yield point and in plastic strain occurring. Repeated cyclic loading in this manner can result in accumulated plastic shear strain in a process referred to as ratchetting, leading to large scale plastic deformation within the rail, which, if left untreated, can lead to wear and crack initiation.[1] Regular maintenance of conventional rails, with methods such as grinding, is required to maintain rail safety. The characterisation of the Shear Yield Stress – Plastic Shear Strain (SYS-PSS) behaviour in rail materials is key to describing and modelling this material response to cyclic loading and is the subject of the research reported here
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