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.
Science and Technology of Welding and Joining, 2009
Porosity is easily formed in welded joints during high power laser welding due to keyhole instabi... more Porosity is easily formed in welded joints during high power laser welding due to keyhole instability. Large pores have detrimental effects on the fatigue resistance of a component and cause many failures in welded parts. This paper is aimed at predicting the maximum pore dimension in long laser welded joints, starting from the sampling of large pores in shorter joints. Two sampling strategies and, consequently, two estimating techniques, both belonging to the statistics of extremes, were explored. The first approach, extreme value type, is used to estimate the size of the maximum pore in each of a series of steel samples. In each sample, the larger single pore or two large pores which are very close are the measured maximum pore. The second approach, threshold value type, is used to estimate the size of pores larger than a critical threshold in a single sample of steel. Both approaches lead to good estimates of the largest pore distribution in short laser welded joints. However, the first one is more adequate to describe the largest pore distribution, because it allows the synergetic effect of two adjacent pores to be considered. In particular, the Gumbel distribution adequately fits the experimental data even in the case of welded joints 10 times longer than the investigated bead length.
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 ...
Transportation authorities have to support high costs for track maintenance due to the wear of th... more Transportation authorities have to support high costs for track maintenance due to the wear of the rails and to crack generation at some particular points along the line. To set up the planning of the maintenance and inspection operations, a predictive approach could be very useful. Moreover, such an approach could help tramcar designers to design tramcars less aggressive towards the line. This paper deals with a numerical approach for the prediction of damage phenomena on tramline rails. In order to be able to foresee maintenance and inspection intervals, both wear and ratchetting analyses are carried out on the basis of load spectra that were determined with a validated multi-body tramcar model. Although the damage analysis is focused on a specific case (one single curve with a radius of 50 m), the approach is very general thus allowing to be used for assessing tramcar design.
In this paper a model for the fatigue strength prediction of rope wires is presented and discusse... more In this paper a model for the fatigue strength prediction of rope wires is presented and discussed. Within this method the fatigue process of wires is described in terms of propagation of the surface defects caused by cold drawing. In particular, the fatigue limit is related to the population of extreme defects and to the material properties expressed by cyclic yield strength and by crack propagation thresholds.
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 fatigue properties of railway axle steels have not yet been thoroughly studied even though a ... more The fatigue properties of railway axle steels have not yet been thoroughly studied even though a number of axle failures are undoubtedly due to the combined effects of corrosion and fatigue. In this paper, the effects of corrosion by rainwater on the fatigue behavior of A1N steel, has been studied. The analysis of the results enabled us to establish that even the presence of a mild corrosive environment eliminates the fatigue limit, thus causing failures in the high-cycle fatigue regime (>10 6 cycles). The pit-to-crack transition and the crack propagation mechanism were then analyzed together with crack growth measurements on surface cracks. A modified Murtaza and Akid model was used to obtain the description of corrosion-fatigue crack growth data thus allowing us to obtain a conservative prediction of the S-N diagram subjected to artificial rainwater.
Truck wheels are usually assessed against fatigue by experimental tests based on standardised loa... more Truck wheels are usually assessed against fatigue by experimental tests based on standardised load sequences (CARLOS load spectra) which reproduce a typical service life of the real component. The present paper deals with the effect of defects, caused by the manufacturing process, on the fatigue life of wheels subjected to block loading tests. The research was prompted by premature service failures of a batch of truck wheels. The investigation firstly dealt with fatigue and crack growth tests for the quality control of the material and then with the detection of defects at the origin of the unexpected failures. The data have been used to assess the acceptability of defects and to estimate life under proof tests using current crack propagation models. #
Plasticity-induced crack closure'' phenomenon is the leading mechanism of different effects (R-ra... more Plasticity-induced crack closure'' phenomenon is the leading mechanism of different effects (R-ratio, overload retardation, . . . ) acting on crack growth rate in many metallic materials. Experimental tests are carried out to quantify the physical phenomenon, while Strip-Yield analytical models have been developed for predicting life of components. In the present work, an additional module to be applied to a Strip-Yield model is proposed in order to derive the strains near the crack tip. Particularly, the module is based on the WestergaardÕs elastic complex potential. The presented algorithm allowed us to obtain the correlation between ''local compliance'' experimental results and the corresponding Strip-Yield analyses. This method can be taken as a semi-analytical procedure for calibrating the constraint factor, i.e., the most delicate parameter for Strip-Yield models.
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
Recent studies showed that fatigue failure of high-strength eutectoid steel wires originates from... more Recent studies showed that fatigue failure of high-strength eutectoid steel wires originates from surface flaws caused by the cold-drawing process. In this research we studied the short crack problem and analysed microcrack propagation and threshold. The study led to a description of the fatigue process from the characteristic nucleation sites of cold-drawn wires. The adoption of an EPFM crack propagation model allowed us to obtain fatigue life prediction from the experimental population of defects.
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
Failure analysis was applied to a hydraulic actuator piston made of aluminium alloy 7075 T6 which... more Failure analysis was applied to a hydraulic actuator piston made of aluminium alloy 7075 T6 which failed at a relatively low number of cycles. Cracks were seen to nucleate from some defects naturally present in the material, and their propagation lead to component failure before 100,000 cycles. Experimental tests were carried out to characterize the material by means of the cyclic curve and the fatigue threshold DK th . The resultant failure analysis showed the problem in terms of crack propagation thus justifying a fracture mechanics approach to the component failure. Finally, some design recommendations were suggested to increase the fatigue life of the component.
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.
Science and Technology of Welding and Joining, 2009
Porosity is easily formed in welded joints during high power laser welding due to keyhole instabi... more Porosity is easily formed in welded joints during high power laser welding due to keyhole instability. Large pores have detrimental effects on the fatigue resistance of a component and cause many failures in welded parts. This paper is aimed at predicting the maximum pore dimension in long laser welded joints, starting from the sampling of large pores in shorter joints. Two sampling strategies and, consequently, two estimating techniques, both belonging to the statistics of extremes, were explored. The first approach, extreme value type, is used to estimate the size of the maximum pore in each of a series of steel samples. In each sample, the larger single pore or two large pores which are very close are the measured maximum pore. The second approach, threshold value type, is used to estimate the size of pores larger than a critical threshold in a single sample of steel. Both approaches lead to good estimates of the largest pore distribution in short laser welded joints. However, the first one is more adequate to describe the largest pore distribution, because it allows the synergetic effect of two adjacent pores to be considered. In particular, the Gumbel distribution adequately fits the experimental data even in the case of welded joints 10 times longer than the investigated bead length.
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 ...
Transportation authorities have to support high costs for track maintenance due to the wear of th... more Transportation authorities have to support high costs for track maintenance due to the wear of the rails and to crack generation at some particular points along the line. To set up the planning of the maintenance and inspection operations, a predictive approach could be very useful. Moreover, such an approach could help tramcar designers to design tramcars less aggressive towards the line. This paper deals with a numerical approach for the prediction of damage phenomena on tramline rails. In order to be able to foresee maintenance and inspection intervals, both wear and ratchetting analyses are carried out on the basis of load spectra that were determined with a validated multi-body tramcar model. Although the damage analysis is focused on a specific case (one single curve with a radius of 50 m), the approach is very general thus allowing to be used for assessing tramcar design.
In this paper a model for the fatigue strength prediction of rope wires is presented and discusse... more In this paper a model for the fatigue strength prediction of rope wires is presented and discussed. Within this method the fatigue process of wires is described in terms of propagation of the surface defects caused by cold drawing. In particular, the fatigue limit is related to the population of extreme defects and to the material properties expressed by cyclic yield strength and by crack propagation thresholds.
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 fatigue properties of railway axle steels have not yet been thoroughly studied even though a ... more The fatigue properties of railway axle steels have not yet been thoroughly studied even though a number of axle failures are undoubtedly due to the combined effects of corrosion and fatigue. In this paper, the effects of corrosion by rainwater on the fatigue behavior of A1N steel, has been studied. The analysis of the results enabled us to establish that even the presence of a mild corrosive environment eliminates the fatigue limit, thus causing failures in the high-cycle fatigue regime (>10 6 cycles). The pit-to-crack transition and the crack propagation mechanism were then analyzed together with crack growth measurements on surface cracks. A modified Murtaza and Akid model was used to obtain the description of corrosion-fatigue crack growth data thus allowing us to obtain a conservative prediction of the S-N diagram subjected to artificial rainwater.
Truck wheels are usually assessed against fatigue by experimental tests based on standardised loa... more Truck wheels are usually assessed against fatigue by experimental tests based on standardised load sequences (CARLOS load spectra) which reproduce a typical service life of the real component. The present paper deals with the effect of defects, caused by the manufacturing process, on the fatigue life of wheels subjected to block loading tests. The research was prompted by premature service failures of a batch of truck wheels. The investigation firstly dealt with fatigue and crack growth tests for the quality control of the material and then with the detection of defects at the origin of the unexpected failures. The data have been used to assess the acceptability of defects and to estimate life under proof tests using current crack propagation models. #
Plasticity-induced crack closure'' phenomenon is the leading mechanism of different effects (R-ra... more Plasticity-induced crack closure'' phenomenon is the leading mechanism of different effects (R-ratio, overload retardation, . . . ) acting on crack growth rate in many metallic materials. Experimental tests are carried out to quantify the physical phenomenon, while Strip-Yield analytical models have been developed for predicting life of components. In the present work, an additional module to be applied to a Strip-Yield model is proposed in order to derive the strains near the crack tip. Particularly, the module is based on the WestergaardÕs elastic complex potential. The presented algorithm allowed us to obtain the correlation between ''local compliance'' experimental results and the corresponding Strip-Yield analyses. This method can be taken as a semi-analytical procedure for calibrating the constraint factor, i.e., the most delicate parameter for Strip-Yield models.
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
Recent studies showed that fatigue failure of high-strength eutectoid steel wires originates from... more Recent studies showed that fatigue failure of high-strength eutectoid steel wires originates from surface flaws caused by the cold-drawing process. In this research we studied the short crack problem and analysed microcrack propagation and threshold. The study led to a description of the fatigue process from the characteristic nucleation sites of cold-drawn wires. The adoption of an EPFM crack propagation model allowed us to obtain fatigue life prediction from the experimental population of defects.
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
Failure analysis was applied to a hydraulic actuator piston made of aluminium alloy 7075 T6 which... more Failure analysis was applied to a hydraulic actuator piston made of aluminium alloy 7075 T6 which failed at a relatively low number of cycles. Cracks were seen to nucleate from some defects naturally present in the material, and their propagation lead to component failure before 100,000 cycles. Experimental tests were carried out to characterize the material by means of the cyclic curve and the fatigue threshold DK th . The resultant failure analysis showed the problem in terms of crack propagation thus justifying a fracture mechanics approach to the component failure. Finally, some design recommendations were suggested to increase the fatigue life of the component.
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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