Journal of ASTM International, Vol. 3, No. 2, Feb 2006
The presence of multiple types of defect is a challenge for Extreme Value Inclusion Rating since ... more The presence of multiple types of defect is a challenge for Extreme Value Inclusion Rating since it can lead to serious underestimation of extreme inclusion size and it can in practice make methods less robust than expected. First the paper deals with the results being obtained by ESIS TC20 within two round-robins carried out on an automotive steel and a bearing steel. Results show the need for correct assessment of multiple types of particles. We present here a new method of analysis based on a “com- peting risks” model together with some practical exploitation in terms of: i evaluation of the minimum control area to be inspected by “block maxima” sampling; ii new implications for data collection based on image analysis; iii assessment of sensitivity to the distribution of different particles.
International Journal of Heavy Vehicle Systems, 2003
ABSTRACT This paper describes a mathematical model for the prediction of the dynamic loads induce... more ABSTRACT This paper describes a mathematical model for the prediction of the dynamic loads induced on a bridge structure by the passage of vehicles. The model is defined in the time domain and represents the bridge and the vehicles as dynamic systems interacting with each other via wheel–road contact forces. The numerical outcomes of the mathematical model are compared to measurements performed on an existing steel bridge, and show satisfactory agreement. The mathematical model was eventually applied to the estimation of load spectra corresponding to daily traffic. In particular, the load spectra corresponding to different vehicles and speeds were combined by using a statistical description of the traffic. It is shown that this procedure leads to results very close to the ones measured on the structure.
Railway axles, though designed for infinite life, are subject to failure due to various types of ... more Railway axles, though designed for infinite life, are subject to failure due to various types of surface damage (ballast hits, corrosion) that might occur during their very long service life (30years or 107km). This problem is dealt with by regular axle examinations in the form of nondestructive testing inspections, whose periodicity is calculated on the basis of the propagation lifetime
Proceedings of The Institution of Mechanical Engineers Part F-journal of Rail and Rapid Transit, 2004
Abstract: The reduction of the total life cycle cost of the whole wheelset requires an optimizati... more Abstract: The reduction of the total life cycle cost of the whole wheelset requires an optimization of inspection intervals for axles. Such components can, in most European countries, endure more than 30 years of service life. During this time, they are subjected to frequent ...
The fatigue of mechanical components can be explained by the growth of very small fatigue cracks,... more The fatigue of mechanical components can be explained by the growth of very small fatigue cracks, which lead to the final fracture of the component. It is, therefore, essential to try to describe the growth and the thresholds of small cracks. In this paper, the Strip-Yield model is used to analyse the fatigue thresholds of a mild-steel widely used for
... 1.1. Fatigue crack growth model for railway axles. Different algorithms for predicting life o... more ... 1.1. Fatigue crack growth model for railway axles. Different algorithms for predicting life of cracked components are available in literature. In the present work, NASGRO v.3.0.21 [10] will be considered. ... 4. Simulation of crack propagation in railway axles. 4.1. Load spectra. ...
The present work concentrates on the static and fatigue behaviour of tensile-shear loaded joints ... more The present work concentrates on the static and fatigue behaviour of tensile-shear loaded joints obtained by clinching, a rapidly developing cold welding technology for thin sheets used is in automobile, electronic and house hold appliances industries. The project primarily dealt with static, fatigue and residual strength tests, which showed a good fatigue behaviour of the clinched joints. Fractographic observations showed
Some typical fatigue failures of butt-welded rails consist of fractures of the web. In the early ... more Some typical fatigue failures of butt-welded rails consist of fractures of the web. In the early stage, the crack propagates parallel to the rail surface but, after a while, it tends to propagate with a slant surface. The aim of the present work is to analyse the mechanisms involved in crack propagation in rail webs and the crack path, which
In the present paper, the fatigue crack propagation of longitudinal flaws starting in butt-welded... more In the present paper, the fatigue crack propagation of longitudinal flaws starting in butt-welded joints of rails is analysed. Firstly Finite Element simulations are carried out, in order to determine the actual stress intensity factor histories caused by the passage of the wheel over the rail. Simulations show that fatigue crack growth is dominated by an out-of-phase Mode I–Mode II mechanism with an overlapping of about 180 degrees. Then, mixed-mode fatigue test experiments have been designed in order to reproduce in-service conditions at laboratory test level. For this purpose, tubular specimens have been subjected to mixed-mode loading (reversal torsion combined with axial tension/compression). The crack growth propagation dominated by the shear has been confirmed. At the end of the paper, the conditions to obtain the shear mode crack propagation are discussed and the kinetics data are presented.
Journal of ASTM International, Vol. 3, No. 2, Feb 2006
The presence of multiple types of defect is a challenge for Extreme Value Inclusion Rating since ... more The presence of multiple types of defect is a challenge for Extreme Value Inclusion Rating since it can lead to serious underestimation of extreme inclusion size and it can in practice make methods less robust than expected. First the paper deals with the results being obtained by ESIS TC20 within two round-robins carried out on an automotive steel and a bearing steel. Results show the need for correct assessment of multiple types of particles. We present here a new method of analysis based on a “com- peting risks” model together with some practical exploitation in terms of: i evaluation of the minimum control area to be inspected by “block maxima” sampling; ii new implications for data collection based on image analysis; iii assessment of sensitivity to the distribution of different particles.
International Journal of Heavy Vehicle Systems, 2003
ABSTRACT This paper describes a mathematical model for the prediction of the dynamic loads induce... more ABSTRACT This paper describes a mathematical model for the prediction of the dynamic loads induced on a bridge structure by the passage of vehicles. The model is defined in the time domain and represents the bridge and the vehicles as dynamic systems interacting with each other via wheel–road contact forces. The numerical outcomes of the mathematical model are compared to measurements performed on an existing steel bridge, and show satisfactory agreement. The mathematical model was eventually applied to the estimation of load spectra corresponding to daily traffic. In particular, the load spectra corresponding to different vehicles and speeds were combined by using a statistical description of the traffic. It is shown that this procedure leads to results very close to the ones measured on the structure.
Railway axles, though designed for infinite life, are subject to failure due to various types of ... more Railway axles, though designed for infinite life, are subject to failure due to various types of surface damage (ballast hits, corrosion) that might occur during their very long service life (30years or 107km). This problem is dealt with by regular axle examinations in the form of nondestructive testing inspections, whose periodicity is calculated on the basis of the propagation lifetime
Proceedings of The Institution of Mechanical Engineers Part F-journal of Rail and Rapid Transit, 2004
Abstract: The reduction of the total life cycle cost of the whole wheelset requires an optimizati... more Abstract: The reduction of the total life cycle cost of the whole wheelset requires an optimization of inspection intervals for axles. Such components can, in most European countries, endure more than 30 years of service life. During this time, they are subjected to frequent ...
The fatigue of mechanical components can be explained by the growth of very small fatigue cracks,... more The fatigue of mechanical components can be explained by the growth of very small fatigue cracks, which lead to the final fracture of the component. It is, therefore, essential to try to describe the growth and the thresholds of small cracks. In this paper, the Strip-Yield model is used to analyse the fatigue thresholds of a mild-steel widely used for
... 1.1. Fatigue crack growth model for railway axles. Different algorithms for predicting life o... more ... 1.1. Fatigue crack growth model for railway axles. Different algorithms for predicting life of cracked components are available in literature. In the present work, NASGRO v.3.0.21 [10] will be considered. ... 4. Simulation of crack propagation in railway axles. 4.1. Load spectra. ...
The present work concentrates on the static and fatigue behaviour of tensile-shear loaded joints ... more The present work concentrates on the static and fatigue behaviour of tensile-shear loaded joints obtained by clinching, a rapidly developing cold welding technology for thin sheets used is in automobile, electronic and house hold appliances industries. The project primarily dealt with static, fatigue and residual strength tests, which showed a good fatigue behaviour of the clinched joints. Fractographic observations showed
Some typical fatigue failures of butt-welded rails consist of fractures of the web. In the early ... more Some typical fatigue failures of butt-welded rails consist of fractures of the web. In the early stage, the crack propagates parallel to the rail surface but, after a while, it tends to propagate with a slant surface. The aim of the present work is to analyse the mechanisms involved in crack propagation in rail webs and the crack path, which
In the present paper, the fatigue crack propagation of longitudinal flaws starting in butt-welded... more In the present paper, the fatigue crack propagation of longitudinal flaws starting in butt-welded joints of rails is analysed. Firstly Finite Element simulations are carried out, in order to determine the actual stress intensity factor histories caused by the passage of the wheel over the rail. Simulations show that fatigue crack growth is dominated by an out-of-phase Mode I–Mode II mechanism with an overlapping of about 180 degrees. Then, mixed-mode fatigue test experiments have been designed in order to reproduce in-service conditions at laboratory test level. For this purpose, tubular specimens have been subjected to mixed-mode loading (reversal torsion combined with axial tension/compression). The crack growth propagation dominated by the shear has been confirmed. At the end of the paper, the conditions to obtain the shear mode crack propagation are discussed and the kinetics data are presented.
Laboratory tests are often carried out for demonstrating the reliability of a component by a limi... more Laboratory tests are often carried out for demonstrating the reliability of a component by a limited number of experiments. In this chapter the basic concepts for the confidence of parameter estimates for the Weibull distribution are firstly discussed and then the relationships for a correct dimensioning (sample size and duration) of reliability demonstration tests are obtained.
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Papers by Stefano Beretta