05/00916 Transient and stability analysis in single-phase natural circulation

Abstract

The paper presents a ratchetting model, based on the non-linear kinematic-isotropic hardening law of Leimatre and Chaboche, able to predict the shear strain accumulation during rolling contact loading and including wear as a competitive phenomenon. A procedure was proposed to calibrate the model with the material constants suitable for rolling contact problems, obtaining them from bi-disk contact tests.For this aim and to study the damage evolution at the wheel–rail interface, some twin disk rolling contact tests were carried out on a common wheel–rail material couple under a dry rolling–sliding condition typical of normal service. The tests were stopped at progressive cycles numbers for different couples of specimens, which were then cut and observed with optical and electron microscope in order to analyse the damage evolution in the zone near to the contact interface. A wear-rolling contact fatigue competition was observed with a progressive crack tip advance following a shear band cracking mechanism and crack tail removal due to wear.The numerical model allowed predicting the experimental strain profile along the depth as a function of contact cycles number, also demonstrating through the critical strain approach that in the analysed conditions wear was able to prevent deep crack formation.