A phenomenological investigation of squat defects is performed. The surface-breaking crack pattern, which is either linear or branched (V-shaped), shows a typical position and orientation in the running band. Particular characteristics are asymmetry of this pattern, with the presence of a leading and a trailing branch, and crack reflection at the running band border. Bending tests reveal a 3D internal crack pattern, with a pair of crack planes or 'wings' enclosing a wedge. Microstructural analysis of the rail upper layer show metallurgical principles of crack initiation: edge delamination of white etching shelves, embedded in the surface, and transverse fracture of white etching material. This analysis moreover reveals an anisotropic 3D texture of the upper layer under combined bi-directional shear surface tractions. Mechanical interpretation of the crack morphology shows that the leading or single branch of the surface-breaking crack pattern is a shear-induced fatigue crack, following the anisotropic microstructure when growing into the rail. The trailing crack of a branched squat is explained as the result of a subsequent transverse, wedge-shaped brittle failure mechanism of the surface layer of the rail, developing within the actual elliptical Hertzian contact patch - or the envelope of potential contact ellipses at the leading crack position. It is driven by the transverse shear loading towards the rail gauge face.


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    Title :

    Squat formation on train rails: Origination


    Contributors:


    Publication date :

    2012


    Size :

    16 Seiten, 15 Bilder, 21 Quellen




    Type of media :

    Conference paper


    Type of material :

    Storage medium


    Language :

    English




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