Anisotropy in pearlitic steel subjected to rolling contact fatigue - modelling and experiments
Doktorsavhandling, 2014

In rails and wheels subjected to severe rolling/sliding contact, large plastic deformations accumulate in the surface layer. This decreases the fatigue resistance of components and makes this layer prone to formation of common rolling contact related defects. In pearlitic steel railway components, accumulated plastic deformations result in microstructural changes which, in turn, lead to anisotropic characteristic of properties like fracture toughness. The aim of the thesis is to investigate the influence of material anisotropy on damage mechanisms of pearlitic rail steels subjected to rolling/sliding contact. The interaction between the pearlitic microstructure and cracks in the surface layer of rail samples is studied. Based on microstructural investigations, an anisotropic fracture surface model is proposed to account for the directional dependence of resistance against crack propagation. The fracture surface model is employed in a computational framework where propagation of planar cracks is simulated. The simulation results show that the degree of anisotropy in the surface layer has a significant influence on the crack propagation path. In particular isotropic material characteristics will result in crack propagation towards the surface. This is a fairly benign type of fracture as compared to the transversal rail breaks that may result if the propagation deviates into the bulk material. To include large plastic deformations and the resulting anisotropy in simulations, a hybrid micro-macromechanical material model for pearlitic steels is proposed. Results from High Pressure Torsion (HPT) tests were used to calibrate the model. In HPT tests, samples are deformed under similar loading conditions to that of the rail-wheel contact i.e. a high compressive force and simultaneous large torsional straining. The HPT deformation procedure is simulated in the commercial finite element package ABAQUS. Numerical results agree well with experimental data demonstrating the high potential of the proposed material model in analyses including large deformations of pearlitic steel. In addition, the influence of different homogenization techniques in the material model is investigated. Two models proposed for a pearlitic colony are calibrated against micro-compression test data. The macroscopic response of a 3D model of pearlitic steel during simple shear deformation is compared with the response predicted by the developed hybrid material model. The hybrid model was found to give stress-strain responses that are qualitatively similar, but around 12% lower in stress magnitudes compared to the other two models. This should be contrasted towards the superior computational performance of the hybrid model.

pearlitic steel

crack propagation

Rolling Contact Fatigue

Anisotropy

plasticity

High Pressure Torsion

Virtual Development Laboratory (VDL)
Opponent: Professor Stefanie Reese, RWTH Aachen University, Germany

Författare

NASIM LARIJANI

Chalmers, Tillämpad mekanik, Material- och beräkningsmekanik

The effect of anisotropy on crack propagation in pearlitic rail steel

Wear,; Vol. 314(2013)p. 57-68

Artikel i vetenskaplig tidskrift

Interaction between cracks and microstructure in three dimensions for rolling contact fatigue in railway rails

Fatigue and Fracture of Engineering Materials and Structures,; Vol. 37(2014)p. 280-289

Artikel i vetenskaplig tidskrift

Hybrid micro-macromechanical modelling of anisotropy evolution in pearlitic steel

European Journal of Mechanics, A/Solids,; Vol. 38(2012)p. 37-47

Artikel i vetenskaplig tidskrift

Styrkeområden

Transport

Materialvetenskap

Ämneskategorier

Teknisk mekanik

ISBN

978-91-7597-031-8

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie

Virtual Development Laboratory (VDL)

Opponent: Professor Stefanie Reese, RWTH Aachen University, Germany

Mer information

Skapat

2017-10-07