Correlation between Barkhausen-noise and corrugation of railway rails

The magnetic Barkhausen-noise has been investigated on the running surface of a railway rail and a good correlation has been found between the noise and corrugation. The Barkhausen-noise showed minima and maxima at the hill and valley positions, respectively. This correlation can be used to observe or preindicate the corrugation process.     

Characterisation of residual stresses in heat treated,high strength aluminium alloy extrusions

Residual stresses were measured in rectilinear aluminium bars quenched using an aqueous polyoxyethylene glycol (PAG) solution or cold-water. Residual stresses were measured with neutron diffraction and a superposition-based method using mechanical strain release measurements. Three orthogonal stress components were measured along two transverse lines using neutron diffraction. The longitudinal residual stresses were mapped over a transverse cross-section using the contour technique. A primary slice removal technique mapped three orthogonal residual stresses over a transverse cross-section in the PAG extrusion. Residual stresses were found to vary from biaxial compressive in the part boundaries to triaxial tensile in the interiors. There was close correlation between the neutron diffraction and mechanical strain release techniques. PAG quenching demonstrated lower residual stresses.

This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.     

Effects of residual stresses on the failure micromechanisms in toughened epoxy systems

The residual stress-strain distributions in various toughened epoxy systems have been analysed and related to their failure micromechanisms. The thermal expansion mismatch between epoxy and dispersed fillers gives rise to either compressive or tensile radial stresses at the interface. The interplay of these and the crack-tip stresses can profoundly govern the nature of crack tip-filler interactions which in turn dictate the micromechanisms of failure. Control of these stresses may be tailored to improve the fracture resistance and crack growth stability of toughened epoxies.     

Using three-dimensional finite element analysis for simulation of residual stresses in railway wheels

One of the most important issues in railway wheels is residual stresses. It is desirable to produce less residual stresses when possible and to decrease the remaining residual stresses in the wheels. The objective of this paper is to provide an estimation of the residual stresses in the rail wheel caused by the stress field from heat treatment process of a railway wheel. A three-dimensional nonlinear stress analysis model has been applied to estimate stress fields of the railway mono-block wheel in heat treatment process. After forging or casting, railway wheels are heat-treated to induce the desirable circumferential compressive residual stress in the upper rim. Finite element analysis model is presented applying the elastic–plastic finite element analysis for the rail wheel under variable thermal loads. Calculative analysis applying a finite element method (FEM) has been used to predict residual stresses. The quenching and annealing segments of the wheel manufacturing process are simulated using a decoupled heat transfer and stress analysis. Three-dimensional finite element analysis results obtained show good agreement with those achieved in field measurements.     

Numerical study on fatigue crack growth in railway wheels under the influence of residual stresses

Accurate prediction of fatigue crack growth on railway wheels and the influence of residual stresses by finite element method (FEM) modeling can affect the maintenance planning. Therefore, investigation of rolling contact fatigue and its effect on rolling members life seem necessary. The objective of this paper is to provide a prediction of rolling contact fatigue crack growth in the rail wheel under the influence of stress field from mechanical loads and heat treatment process of a railway wheel. A 3D nonlinear stress analysis model has been applied to estimate stress fields of the railway mono-block wheel in heat treatment process. Finite element analysis model is presented applying the elastic–plastic finite element analysis for the rail wheel under variable thermal loads. The stress history is then used to calculate stress intensity factors (SIFs) and fatigue life of railway wheel. The effect of several parameters, vertical loads, initial crack length and friction coefficient between the wheel and rail, on the fatigue life in railway wheels is investigated using the suggested 3-D finite element model. Three-dimensional finite element analysis results obtained show good agreement with those achieved in field measurements.     

Stability of shot peening induced residual stresses and their influence on fatigue lifetime

Mechanical surface treatment methods such as shot peening may improve the fatigue strength of materials. In this study, the effect of shot peening on strain controlled constant amplitude fatigue loading of a near pearlitic microalloyed steel was investigated. The stress amplitudes throughout the whole lifetime were followed, in addition to detailed recording of stress-strain hysteresis loops, particularly at small cycle numbers. The detailed relaxation of residual stresses and the changes in full width of half maximum (FWHM) of the X-ray peak at the surface and in depth as function of the number of cycles and plastic strain were recorded. By these techniques, the onset as well as the rate of relaxation of residual stresses could be followed at different strain amplitudes. Pronounced increase in lifetime of the shot peened specimens tested at total strain amplitude smaller than 0.3% (corresponding to 0.034% plastic strain amplitude) was achieved. This coincides with reasonably stable residual stresses at the surface and in depth.     

Influence of the residual stresses induced by tool wear on the failure of brass electro-valves

Failure analysis was performed on different brass electro-valves body affected by unexpected phenomena of cracking. Through the application of optical and scanning electron microscopy, micro hardness Vickers test and X-ray diffraction, the causes of damage were identified. The study showed the dependence between roughness and residual stress associated to the tool wear. A solution to avoid the failure is finally proposed, based on the use combination of a tool with controlled wear and stress relieving heat treatment.     

Influence of the vibrotreatment of structural elements with residual stresses on their damping ability

We investigate the influence of the vibrotreatment of annular elements made of St. 3 steel on the kinetics of residual stresses and dissipation of energy in the material. By using the characteristic features of changes in the decrement of oscillations of the material and residual stresses, we substantiated the possibility of control over the completion of vibrotreatment by the time of stabilization of the characteristic of dissipation of energy in the material. The established decrease in the decrement of oscillations shows that specimens undergo plastic deformation in the course of this process. Translated from Problemy Prochnosti, No. 5, pp. 113–121, September–October, 1997.     

Influence of the vibrotreatment of structural elements with residual stresses on their damping ability

We investigate the influence of the vibrotreatment of annular elements made of St. 3 steel on the kinetics of residual stresses and dissipation of energy in the material. By using the characteristic features of changes in the decrement of oscillations of the material and residual stresses, we substantiated the possibility of control over the completion of vibrotreatment by the time of stabilization of the characteristic of dissipation of energy in the material. The established decrease in the decrement of oscillations shows that specimens undergo plastic deformation in the course of this process.     

The development of a crack propagation model for railway wheels and rails

Rolling contact fatigue (RCF) and wear of railway wheels and rails are the main phenomena that affect their maintenance costs. When crack propagation and wear rates can be predicted, maintenance planning can be optimised, and cost‐effective measures can be developed. Several RCF models exist, but none which can be used in combination with vehicle dynamics simulations and can predict the actual crack depth. This study shows the development of a crack propagation model that can be applied for both railway wheels and rails. Two unknown material parameters in the model were calibrated against crack measurements in a curve on the Dutch railways over a period of 5 years. Two different RCF models were used to calculate the stress magnitudes for the propagation model. The propagation model can be used in combination with vehicle‐track dynamics simulations and shows promise in predicting the actual crack depth and/or surface length. Further research is needed to determine the model's validity for other operational conditions.     

Influence of residual stresses on stable crack growth

Abstract

The influence of residual stresses resulting from thermal shock and pressure loading on the initiation and stable growth of cracks in pressure vessels and pipes is considered and preliminary calculations have been made. The residual stresses of a precracked vessel of a 0·22Cr–0·75Ni–0·7Mo–Cr steel at an arbitrarily chosen temperature transient have been analysed using the finite element method. After reheating to normal operating temperature, the influence of the remaining residual stresses on the initiation of the assumed crack is considered. The results provide the initial conditions for stable crack growth analysis based on the J–integral method, which is implemented into the non–linear finite element program ADINA.

MST/27     

A modern approach to principal stresses and strains

A simple formal method of evaluating principal stresses and directions using eigenvalues and eigenvectors of the stress matrix is presented. The method is equally applicable to 2–d and 3–d stress systems and does much to eliminate any risk of undetected errors in calculation or mistakes in assigning a principal stress to its corresponding direction. The method is extended to analysis of the 45strain gauge rosette.     

Determination of residual stresses in bimaterials

Residual stresses play a prominent role in the fracture process of bimaterials and therefore knowing these stresses prior to failure is important for understanding the mechanical behaviour of bimaterials. A critical assessment has been made of three methods for determining the residual stresses. These methods are: stress optical measurement, indentation method, and finite element method. With stress optical measurements the difference in the principal normal stresses, , can be determined. In the centre region adjacent to the interface, the measured stress values are in agreement with results from a simple analytical formula for the normal residual stresses parallel to the interface. Surface stresses at arbitrary locations can be obtained by the usual indentation technique. At the surface, stresses perpendicular to the interface are dominant and have the opposite sign to the stresses parallel to the interface. When there is no mechanical mismatch between the components the magnitude of the residual stresses can be estimated with the above-mentioned formula. Two-dimensional plane strain finite element calculations are in good agreement with the stress optical measurements.