1,721,023 research outputs found
A failure assessment diagram for components subjected to rolling contact loading
No full textA failure assessment diagram for the evaluation of the safe working area of components subjected to rolling contact loading is proposed. Rolling contact fatigue limitation is treated in terms of non-propagation condition of inherent defects, following the El-Haddad model for the short-cracks growth threshold. Static fracture and ratchetting limitations are also added to the diagram. In this way, the approach gives an overview of the possible damage mechanisms, automatically indicating which is expected for a specific case. In particular way, the diagram presents different areas: a safe zone (infinite life), a rolling contact fatigue zone almost independent on defects content, a rolling contact fatigue zone dependent on defects, a ratchetting zone and a static fracture zone. Depending on material properties, operating conditions and inclusion content, a reference point can be drawn on this diagram, indicating in which area the component is working and, consequently, if it is safe or which damage mechanism is expected. Some experimental evidences referring to rolling contact tests carried out in the past where re-interpreted and verified by this approach, highlighting the role of working conditions, material properties and inclusion content in determining the damage mechanism
On Mechanical Properties of New Railway Wheel Steels for Desert Environments and Sand Caused Wheel Damage Mechanisms
No full textWorn railway wheels after service in the desert were investigated by means of failure analysis, hardness measurements, tensile tests, fracture toughness tests and low-cycle fatigue (LCF) tests. The results complete both previous small-scale laboratory experiments and FEM simulations performed by the authors on widely used steels and new steel grades allowing to better understand the main damage mechanisms due to the sand. These new steel grades were developed for forged-rolled solid wheels in alternative to AAR Class B/C/D steel grades and were designed to ensure high resistance to wear and rolling contact fatigue in the presence of sand, debris or gravel on the rails. This paper covers the in-depth mechanical characterization of wheels made of the new steels. Hardness measurements, tensile tests, fracture toughness tests and LCF tests were carried out. The results are compared with AAR Class B/C/D steels showing an excellent combination of fracture toughness, cyclic yield strength and ductility
Rolling contact fatigue damage detected by correlation between experimental and numerical analyses
No full textA study on vibrations related to rolling contact fatigue test bench and a possible way to correlate this mechanical behavior and damage of the specimens is presented. In particular it has been evaluated the possibility to detect and quantify, thanks to vibration analysis, the damage on two discs subjected to rolling contact fatigue in different working conditions. Paper is divided in two parts. In the first part there is a description of test bench and results of its static and modal analyses. Then, some tests were carried out changing working conditions and specimens' parameters and a procedure that allowed both to monitor the specimen's damage state and to record accelerometric data was implemented. A set of piezoaccelerometers was placed on the machine and a virtual instrument for automatic data handling and analysis was performed. Taking into account the FEM results derived from the first part of work, data were analyzed both using a standard approach and by implementing custom digital weighting filters for a windowed RMS in order to define, real-time during the measurement, a good estimator for the specimen damage state development
Lumped Parameter Models for Numerical Simulation of the Dynamic Response of Hoisting Appliances
No full textThe paper describes three lumped parameters models for the study of the dynamic behavior of a boom crane. The models here proposed allows to evaluate the fluctuations of the load arising from the rope and structure elasticity and from the type of the motion command imposed by the winch. A calculation software was developed in order to determine the actual acceleration of the lifted mass and the dynamic overload during the lifting phase. Some application examples are presented, with the aim of showing the correlation between the magnitude of the stress and the type of the employed motion command
Competition between wear and rolling contact fatigue at the wheel-rail interface: some experimental evidence on rail steel
No full textRecent studies of the rail–wheel interface have shown that wear and rolling contact fatigue (RCF) are competitive phenomena.Wear, by removing the material from the contact surface, tends to limit the propagation of cracks formedby cyclic contact stresses. Several parameters influence these phenomena. This article studies the effects of various working conditions on the surface damage of railway steels. The competition betweenwear and RCF is particularly strong in dry rolling–sliding contacts, in which the damage severity of our test cases can be adequately predicted using the shakedown map. In wet contacts, RCF is prevalent: cracks rapidly propagate into the subsurface layer in response to hydraulic pressure penetration and then branch towards the surface causing severe damage (macroscopic pitting). The severity of this phenomenon depends strongly on the applied load and cannot be inhibited by wear due to the low friction. On the basis of these results, a general procedure is proposed to the structural integrity of rails
Failure assessment of subsurface rolling contact fatigue in surface hardened components
No full textA failure assessment diagram for components subjected to rolling contact with hardness varying along the depth is presented.
The approach takes into account the influence of inherent defects on subsurface fatigue: considering a 2D plane strain model, crack propagation from inherent defects was assessed in terms of applied stress intensity factor; defect-free fatigue was assessed in terms of the Dang Van stress.
By analysing different combinations of loading condition, defect dimension and hardness profile, it was possible to obtain a general relationship for subsurface rolling contact fatigue prediction.
A good agreement was found between predicted contact pressure limit and some published experimental results
Un modello fenomenologico per la previsione della competizione tra usura e RCF nel contatto ciclico tra ruota e rotaia
No full textSviluppo di un programma di calcolo per la previsione dei fenomeni di danneggiamento nei problemi di contatto ciclico
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