Title: Finite element investigation of thermal-kinetic-mechanical evolutions during laser powder deposition as an innovative technique for rail repair

Abstract

Utilization of laser powder deposition (LPD) as an innovative repair tool for damaged steel components is increasingly growing in recent years. This paper investigates repairing a standard US light rail using LPD. No study has focused on repairing standard US rails thus far. Besides, this is the first time that a three-dimensional finite element model is developed where element-birth-and-kill technique is employed to study thermal-kinetic-mechanical evolutions during the LPD rail repair process. Exploration of hardness versus microstructure yielded a reverse correlation between hardness level and austenite volume fraction. The maximum hardness was found near rail-deposition interface with the minimum austenite concentration, while the topmost deposition layer with the highest austenite concentration showed the minimum hardness. Longitudinal residual stresses at the rail-deposition interface were significantly more than that of transversal and normal. Comparing the residual stress against deposition material yield strength showed a slight exceedance (~5%) of transversal stress from the maximum limit, no exceedance for normal stress, but an extreme exceedance of 50%for longitudinal stress. This fact suggested a high risk of cracking along longitudinal direction at the rail-deposition interface, while there existed only a minor risk of transversal cracking and almost no chance of layer delamination. The simulated results were compared against experimental results obtained via optical and scanning electron microscopy, hardness test, and X-ray diffraction stress measurement, where a maximum deviation of 10% proved the model accuracy. The validated model in this study would be a great backbone for future studies on different process parameters to increase hardness and reduce stress in an LPD repaired rail.