Determining the angles of squat cracks via CT scanning and metallographic observations. (1st May 2020)

• Record Type: Journal Article
• Authors: Naeimi, Meysam; Li, Zili; Dollevoet, Rolf
• Is Part Of: Engineering fracture mechanics. Volume 230(2020)
• Publication Date: 2020-05-01
• Subjects: Squat -- Primary crack -- Secondary crack -- Crack angle -- Crack orientation -- CT scan -- Serial cutting; Fracture mechanics -- Periodicals; Rupture, Mécanique de la -- Périodiques; Fracture mechanics; Periodicals; 620.112605
• DOI: 10.1016/j.engfracmech.2020.107016
• Languages: English
• ISSNs: 0013-7944

Abstract

Highlights: A new 3D visualization method is presented. The necessary geometric definitions and conventions are provided. A combined CT - metallography method is used to reconstruct the crack networks. The angles and orientations of squat cracks are visually demonstrated and measured. Abstract: This study investigates the angles θ1, θ2, and θ3 that squat crack faces form with respect to three orthogonal planes: the rail top, the longitudinal-vertical cross-section and the lateral-vertical cross-section. Rail samples with squats of various severities are obtained from the field. Their three-dimensional crack networks are reconstructed using CT (computed tomography) scanning and serial cutting. A 3D visualization method, together with the necessary geometric definitions, is developed for enabling effective measurement and characterization of the squat cracks. It is found that the cracks can be characterized by four orientations (T1 – T4). The variation ranges of the crack angles are determined for each orientation that satisfies 132° ≤θ1 ≤ 150°, 6° ≤θ2 ≤ 36° and 67° ≤θ3 ≤ 81° . By investigating the occurrence frequency of the orientations, it is found that T4 and T1 together form the primary V-shaped cracks of the squats, and T2 and T3 together form the secondary V-shaped cracks. A finite element modelling of the wheel-track system, in combination with contact mechanics and multi-axial fatigue analysis, successfully relates the stress state to the RCF cracks.