Manuel Fonte - Academia.edu (original) (raw)

Papers by Manuel Fonte

International Journal of Fatigue, 1999

Forces in Mechanics, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Forces in Mechanics, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Theoretical and Applied Fracture Mechanics, 2016

Nickel-Titanium (NiTi) alloys with superelastic properties have been increasingly introduced as a... more Nickel-Titanium (NiTi) alloys with superelastic properties have been increasingly introduced as a substitute to more conventional alloys, such as stainless steel, in a variety of applications. In Dentistry, NiTi alloys are used in tools such as Endodontic rotary files, allowing the file to follow teeth root canals more easily than their stainless steel counterparts. Nevertheless, during surgery, the file is subjected to cyclic bending loading, since it is rotating while being deformed inside the curved canals and is prone to fracture due to fatigue, without showing any visible signals of degradation. Following a systematic approach, this work presents the results of rotary fatigue tests for several NiTi wires from different manufacturers (Memry and Euroflex). The formulation is presented, where the material strength reduction can be quantified from the determination of the strain and the number of cycles until failure. Experimental tests as well as numerical Finite Element Analysis (FEA) simulations are presented to better understand the fatigue fracture mechanisms present in NiTi alloys, showing that there is good agreement between the predicted strains (difficult to measure in such small wires) and the cycles to failure.

Theoretical and Applied Fracture Mechanics, 2016

Procedia Structural Integrity, 2016

During their operation, modern aircraft engine components are subjected to increasingly demanding... more During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.

Ultrasonic fatigue testing machine are being used to perform materials testing in the range of 10... more Ultrasonic fatigue testing machine are being used to perform materials testing in the range of 10 7 to 10 10 fatigue cycles. The so-called very high cycle fatigue regime is now an established technology in which concerns the layout of ultrasonic fatigue machines, but the accurate measurement of the parameters that influence fatigue life (load, strain, displacement,) at ultrasonic frequencies still is a matter of concern and continuous development. The objective of this paper is to describe the design and construction of a fully instrumented ultrasonic fatigue testing machine at 20 kHz working frequency. In order to achieve fully automated tests, a closed loop control system was developed to use monitored temperature and displacement to set the power and the cooling periods of the machine. The monitoring of the displacement, considered here in the bottom face of the specimen, is carried out using a high resolution laser. The specimen´s temperature is monitored online through a pyrometer. The cooling of the specimen is achieved with cooled dry air. To manage and process the data a data acquisition device working at 400 kHz from National Instruments is used. The software was developed in house using the LabView package.

El periodo de vida de estructuras sometidas a cargas cíclicas esta basado en las curvas S_N, que ... more El periodo de vida de estructuras sometidas a cargas cíclicas esta basado en las curvas S_N, que establecen un tiempo de vida infinito cuando el esfuerzo aplicado es menor que la resistencia limite. Estudios demuestran que el colapso debido a fatiga es alcanzado después de 10e7 ciclos, indicando que no hay resistencia límite de fatiga. Sin embargo, la obtención de estas cargas límite a través de máquinas servo hidráulicas requiere mucho tiempo. De esta manera, las maquinas ultrasónicas para predecir fatiga están diseñadas para conducir ensayos en un periodo de tiempo mucho menor. El presente trabajo describe el diseño y montaje de un dispositivo para ensayos ultrasónicos de fatiga a 20kHz.

International Journal of Fatigue, 2014

The fatigue limit of materials, due to the improvement of fatigue life of structures and mechanic... more The fatigue limit of materials, due to the improvement of fatigue life of structures and mechanical components should be extended from the traditional 10 6-10 7 cycles up to 10 9 and more, but with traditional testing hardware this is a difficult technical task due to the length of time needed for the completion of tests. Ultrasonic fatigue testing machines seem to be adequate for very high cycle fatigue (VHCF) tests. We propose here to evaluate the behavior of the hysteretic damping in an attempt to associate that with damage parameter. The approach here presented is based on the fact that the fatigue issue can be understood in terms of the energy available for irreversible process triggering. This nonconservative energy will be involved in micro-structural changes in the material before being dissipated as thermal energy. In fact, the balance between the energy supplied to and returned by the material is positive and the hysteretic damping factor represents the inelastic fraction of energy in each cycle. Aiming at building a model to correlate the hysteretic cycle parameters and the fatigue process, both energy loss and material response of the specimens are measured during the fatigue test. The fatigue tests are carried out with an ultrasonic machine test, operated at 20 kHz with amplitude or temperature control, under HCF and VHCF for copper specimens. The results show the behavior of hysteretic damping parameter during fatigue life, the equivalent dissipated energy per cycle and a good correlation between the hysteretic damping factor parameter and the fatigue process S-N curve, suggesting that factor as a promising fatigue life parameter useful for some cases of fatigue life prediction.

Engineering Fracture Mechanics, 1991

ABSTRACT

Engineering Failure Analysis, 2009

A case study of a catastrophic failure of a web marine crankshaft and a failure analysis under be... more A case study of a catastrophic failure of a web marine crankshaft and a failure analysis under bending and torsion applied to crankshafts are presented. A microscopy (eye seen) observation showed that the crack initiation started on the fillet of the crankpin by rotary bending and the propagation was a combination of cyclic bending and steady torsion. The crack front profile approximately adopts a semi-elliptical shape with some distortion due to torsion and this study is supported by a previous research work already published by the authors. The number of cycles from crack initiation to final failure of this crankshaft was achieved by recording of the main engine operation on board, taking into account the beachmarks left on the fatigue crack surface. The cycles calculated by the linear elastic fracture mechanics approaches showed that the propagation was fast which means that the level of bending stress was relatively high when compared with total cycles of main engine in service. Microstructure defects or inclusion were not observed which can conclude that the failure was probably originated by an external cause and not due to an intrinsic latent defect. Possible effects of added torsional vibrations which induce stresses are also discussed. Some causes are analyzed and reported here but the origin of the fatigue fracture was not clearly determined.

Procedia Engineering, 2015

Endodontic rotary file instruments used to treat root canals in dentistry suffered breakthrough t... more Endodontic rotary file instruments used to treat root canals in dentistry suffered breakthrough transformations in recent years when stainless steel was replaced by Nickel-Titanium (NiTi). NiTi alloys used in Endodontics possess superelastic properties at body temperature (37C) that bring many advantages on the overall performance of the root-canal treatment. They can follow curved root canals more easily than stainless steel instruments and have been reported to be more effective in the removal of the inflamed pulp tissue and protection of the tooth structure. However, these instruments eventually fracture under cyclic bending loading due to fatigue, without any visible signals of degradation to the practitioner. This problem brought new challenges on how new instruments should be tested, as NiTi alloys are highly non-linear and present a large hysteresis cycle in the Elastic domain. Current existing standards are only available for Stainless Steel testing. Thus, many authors have attempted to design systems that can test NiTi endodontic files under fatigue loads. However, no approach has been universally adopted by the community yet, as in most cases they are based on empirical set ups. Following a more systematic approach, this work presents the results of rotary fatigue tests for several NiTi wires from different manufacturers (MemryTM and EuroflexTM). The tests were done on a versatile fully automatic rotary bending testing machine. The formulation is also presented, where the material strength reduction can be quantified from the determination of the strain and the number of cycles until failure.

European Structural Integrity Society, 2003

The influence of environment and micro structure is investigated on a high strength 7049 aluminiu... more The influence of environment and micro structure is investigated on a high strength 7049 aluminium alloy sheet cold rolled and heat-treated. This aluminium alloy was artificially aged to underaged (UA) and overaged (OA) conditions, resulting in approximately the same yield strength, but different mode of slip deformation. The UA alloy deforms by planar slip while the OA alloy by wavy

International Journal of Fatigue, 1999

Forces in Mechanics, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Forces in Mechanics, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Theoretical and Applied Fracture Mechanics, 2016

Nickel-Titanium (NiTi) alloys with superelastic properties have been increasingly introduced as a... more Nickel-Titanium (NiTi) alloys with superelastic properties have been increasingly introduced as a substitute to more conventional alloys, such as stainless steel, in a variety of applications. In Dentistry, NiTi alloys are used in tools such as Endodontic rotary files, allowing the file to follow teeth root canals more easily than their stainless steel counterparts. Nevertheless, during surgery, the file is subjected to cyclic bending loading, since it is rotating while being deformed inside the curved canals and is prone to fracture due to fatigue, without showing any visible signals of degradation. Following a systematic approach, this work presents the results of rotary fatigue tests for several NiTi wires from different manufacturers (Memry and Euroflex). The formulation is presented, where the material strength reduction can be quantified from the determination of the strain and the number of cycles until failure. Experimental tests as well as numerical Finite Element Analysis (FEA) simulations are presented to better understand the fatigue fracture mechanisms present in NiTi alloys, showing that there is good agreement between the predicted strains (difficult to measure in such small wires) and the cycles to failure.

Theoretical and Applied Fracture Mechanics, 2016

Procedia Structural Integrity, 2016

During their operation, modern aircraft engine components are subjected to increasingly demanding... more During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.

Ultrasonic fatigue testing machine are being used to perform materials testing in the range of 10... more Ultrasonic fatigue testing machine are being used to perform materials testing in the range of 10 7 to 10 10 fatigue cycles. The so-called very high cycle fatigue regime is now an established technology in which concerns the layout of ultrasonic fatigue machines, but the accurate measurement of the parameters that influence fatigue life (load, strain, displacement,) at ultrasonic frequencies still is a matter of concern and continuous development. The objective of this paper is to describe the design and construction of a fully instrumented ultrasonic fatigue testing machine at 20 kHz working frequency. In order to achieve fully automated tests, a closed loop control system was developed to use monitored temperature and displacement to set the power and the cooling periods of the machine. The monitoring of the displacement, considered here in the bottom face of the specimen, is carried out using a high resolution laser. The specimen´s temperature is monitored online through a pyrometer. The cooling of the specimen is achieved with cooled dry air. To manage and process the data a data acquisition device working at 400 kHz from National Instruments is used. The software was developed in house using the LabView package.

El periodo de vida de estructuras sometidas a cargas cíclicas esta basado en las curvas S_N, que ... more El periodo de vida de estructuras sometidas a cargas cíclicas esta basado en las curvas S_N, que establecen un tiempo de vida infinito cuando el esfuerzo aplicado es menor que la resistencia limite. Estudios demuestran que el colapso debido a fatiga es alcanzado después de 10e7 ciclos, indicando que no hay resistencia límite de fatiga. Sin embargo, la obtención de estas cargas límite a través de máquinas servo hidráulicas requiere mucho tiempo. De esta manera, las maquinas ultrasónicas para predecir fatiga están diseñadas para conducir ensayos en un periodo de tiempo mucho menor. El presente trabajo describe el diseño y montaje de un dispositivo para ensayos ultrasónicos de fatiga a 20kHz.

International Journal of Fatigue, 2014

The fatigue limit of materials, due to the improvement of fatigue life of structures and mechanic... more The fatigue limit of materials, due to the improvement of fatigue life of structures and mechanical components should be extended from the traditional 10 6-10 7 cycles up to 10 9 and more, but with traditional testing hardware this is a difficult technical task due to the length of time needed for the completion of tests. Ultrasonic fatigue testing machines seem to be adequate for very high cycle fatigue (VHCF) tests. We propose here to evaluate the behavior of the hysteretic damping in an attempt to associate that with damage parameter. The approach here presented is based on the fact that the fatigue issue can be understood in terms of the energy available for irreversible process triggering. This nonconservative energy will be involved in micro-structural changes in the material before being dissipated as thermal energy. In fact, the balance between the energy supplied to and returned by the material is positive and the hysteretic damping factor represents the inelastic fraction of energy in each cycle. Aiming at building a model to correlate the hysteretic cycle parameters and the fatigue process, both energy loss and material response of the specimens are measured during the fatigue test. The fatigue tests are carried out with an ultrasonic machine test, operated at 20 kHz with amplitude or temperature control, under HCF and VHCF for copper specimens. The results show the behavior of hysteretic damping parameter during fatigue life, the equivalent dissipated energy per cycle and a good correlation between the hysteretic damping factor parameter and the fatigue process S-N curve, suggesting that factor as a promising fatigue life parameter useful for some cases of fatigue life prediction.

Engineering Fracture Mechanics, 1991

ABSTRACT

Engineering Failure Analysis, 2009

A case study of a catastrophic failure of a web marine crankshaft and a failure analysis under be... more A case study of a catastrophic failure of a web marine crankshaft and a failure analysis under bending and torsion applied to crankshafts are presented. A microscopy (eye seen) observation showed that the crack initiation started on the fillet of the crankpin by rotary bending and the propagation was a combination of cyclic bending and steady torsion. The crack front profile approximately adopts a semi-elliptical shape with some distortion due to torsion and this study is supported by a previous research work already published by the authors. The number of cycles from crack initiation to final failure of this crankshaft was achieved by recording of the main engine operation on board, taking into account the beachmarks left on the fatigue crack surface. The cycles calculated by the linear elastic fracture mechanics approaches showed that the propagation was fast which means that the level of bending stress was relatively high when compared with total cycles of main engine in service. Microstructure defects or inclusion were not observed which can conclude that the failure was probably originated by an external cause and not due to an intrinsic latent defect. Possible effects of added torsional vibrations which induce stresses are also discussed. Some causes are analyzed and reported here but the origin of the fatigue fracture was not clearly determined.

Procedia Engineering, 2015

Endodontic rotary file instruments used to treat root canals in dentistry suffered breakthrough t... more Endodontic rotary file instruments used to treat root canals in dentistry suffered breakthrough transformations in recent years when stainless steel was replaced by Nickel-Titanium (NiTi). NiTi alloys used in Endodontics possess superelastic properties at body temperature (37C) that bring many advantages on the overall performance of the root-canal treatment. They can follow curved root canals more easily than stainless steel instruments and have been reported to be more effective in the removal of the inflamed pulp tissue and protection of the tooth structure. However, these instruments eventually fracture under cyclic bending loading due to fatigue, without any visible signals of degradation to the practitioner. This problem brought new challenges on how new instruments should be tested, as NiTi alloys are highly non-linear and present a large hysteresis cycle in the Elastic domain. Current existing standards are only available for Stainless Steel testing. Thus, many authors have attempted to design systems that can test NiTi endodontic files under fatigue loads. However, no approach has been universally adopted by the community yet, as in most cases they are based on empirical set ups. Following a more systematic approach, this work presents the results of rotary fatigue tests for several NiTi wires from different manufacturers (MemryTM and EuroflexTM). The tests were done on a versatile fully automatic rotary bending testing machine. The formulation is also presented, where the material strength reduction can be quantified from the determination of the strain and the number of cycles until failure.

European Structural Integrity Society, 2003

The influence of environment and micro structure is investigated on a high strength 7049 aluminiu... more The influence of environment and micro structure is investigated on a high strength 7049 aluminium alloy sheet cold rolled and heat-treated. This aluminium alloy was artificially aged to underaged (UA) and overaged (OA) conditions, resulting in approximately the same yield strength, but different mode of slip deformation. The UA alloy deforms by planar slip while the OA alloy by wavy