Carlos C Engler-Pinto | Ecole Polytechnique Federale de Lausanne (original) (raw)

Papers by Carlos C Engler-Pinto

Materials at High Temperatures, 1995

... Alliage IN100. ; Application. ; Aube turbine. ; Turbine gaz. ; Alliage base nickel. ; Alliage... more ... Alliage IN100. ; Application. ; Aube turbine. ; Turbine gaz. ; Alliage base nickel. ; Alliage Ni60Co15Cr10Al6Ti5Mo3V1. ; Al Co Cr Mo Ni Ti. ; Mots-clés espagnols / Spanish Keywords. Fatiga térmica. ; Propiedad mecánica. ; Superaléación. ; Relación tensión deformación. ; ...

Materials Science and Engineering: A, 2013

Abstract The variability in fatigue life for a cast aluminum alloy has been investigated under bo... more Abstract The variability in fatigue life for a cast aluminum alloy has been investigated under both high-cycle and low-cycle fatigue. The fatigue cracks have initiated mostly near the surface from pores or oxide inclusions. The size of the initiation sites has been evaluated for all specimens and the statistical distribution has been determined. In addition, probabilistic fatigue life regression models have been used to characterize the observed scatter in fatigue life. The cumulative density function (CDF) of fatigue life was found to be approximately equal to the complementary value of the CDF of the near surface fatigue initiator size. Therefore, it has been concluded that the observed scatter in fatigue life is directly related to the distribution of casting defects within the alloy.

Superalloys 1996 (Eighth International Symposium), 1996

The interaction between creep and thermo-mechanical fatigue (TMF) is investigated on the CM247LC-... more The interaction between creep and thermo-mechanical fatigue (TMF) is investigated on the CM247LC-DS alloy. Out-of-phase TMF tests are performed between 600°C and 900°C on tubular specimens (1 mm wall). Creep rupture experiments are conducted at 900°C on the virein (as received) allov under 280 MPa on both solid and tubular s"pecimens. Sequential creep-TMF and TMFcreep experiments are performed. Creep cavities and internal cracks are initiated on carbides or residual eutectics. In addition, oxidation assisted crack initiation is observed at the surface of the specimens during creep. No noticeable change on the 7-r' structure is observed during TMF cvclina. Under creen. however. a V-raft structure develois perpendicul&ly to the stress axis. This v-rafting softens the pre-crept alloy and influences its non-isothermal cyclic stress-strain bv increasing the inelastic strain. Short cracks initiated during pre-creeping drastically reduce the TMF crack initiation neriod. On the other hand. short cracks (100 to 300 urn surface 'crack length) initiated during pre-TMF cycling do not affect the creep lifetime. A linear creep-fatigue damage cumulative law can predict the residual life of TMF specimens which have been precrept.

Thermo-mechanical Fatigue Behavior of Materials: Third Volume

This paper deals with the comparison between thermal fatigue (TF) and thermomechanical fatigue (T... more This paper deals with the comparison between thermal fatigue (TF) and thermomechanical fatigue (TMF) testing for SRR99 superalloy. First, a measured TF mechanical strain‐temperature (epsilon(m)‐T) profile between 200 degrees C and 1100 degrees C has been reproduced on a TMF specimen to allow for an estimation of the stresses and inelastic strains which occur during TF. Thermal‐fatigue‐base (TFB) epsilon(m)‐T profiles were determined based on the measured TF profiles. These TFB cycles, together with the well‐known out‐of‐phase profile, were employed for all of TMF tests. The comparison of the results reveals that the TF and TMF out‐phase tests are more damaging in terms both of the applied stress and strain range, while the TMF out‐of‐phase test is more severe if the comparison is made in terms of the inelastic strain range. Finally, it is shown that the results can be rationalized quite well by plotting the fatigue lives as a function of the maximum stabilized stress (sigma(max)).

Thermomechanical Fatigue Behavior of Materials: Second Volume

The thermal fatigue (TF) behaviour of two single crystal nickel-based superalloys, SRR99 and CMSX... more The thermal fatigue (TF) behaviour of two single crystal nickel-based superalloys, SRR99 and CMSX-4, is reported. Single edge wedge specimens are rapidly heated by induction heating of the wedge tip to a maximum temperature between 1000°C and 1175°C and cooled to 200°C by forced air. A constant cycle period is employed for all experiments. The strain distribution along the edge of the TF specimens is measured. Changing the induction frequency leads to different strain ranges. CMSX-4 shows crack initiation always on cast microporosities. SRR99 presents an additional oxidation/spalling/re-oxidation mechanism under low strain loading. An "integrated approach" combining TF and TMF (thermo-mechanical fatigue) is proposed. The applied TMF temperature-strain cycle is deduced from the measured TF-cycle. Under this new temperature-strain cycle the crack initiation life and the total life in TMF for SRR99 are compared with the TF results.

Materials Performance and Characterization, 2014

Thermo-mechanical fatigue (TMF) resistance of engineering materials is extremely important for th... more Thermo-mechanical fatigue (TMF) resistance of engineering materials is extremely important for the durability and reliability of components and systems subjected to combined thermal and mechanical loadings. However, TMF testing, modeling, simulation, validation, and the subsequent implementation of the findings into product design are challenging tasks because of the difficulties not only in testing but also in results interpretation and in the identification of the deformation and failure mechanisms. Under combined high-temperature and severe mechanical loading conditions, creep and oxidation mechanisms are activated and time-dependent failure mechanisms are superimposed to cycle-dependent fatigue, making the life assessment very complex. In this paper, the testing procedures and results for high-temperature fatigue testing using flat specimens and thermal-fatigue testing using V-shape specimens are reported; emphasis is given to hold-time effects and the possible underlying mechanisms. The uncertainty nature and the probabilistic characteristics of the V-shape specimen test data are also presented. Finally, the impact of hold-time effect on current product design and validation procedure is discussed in terms of virtual life assessment.

European Structural Integrity Society, 2002

Stress-strain behavior and durability of cast 319 aluminum-copper alloys are studied at high temp... more Stress-strain behavior and durability of cast 319 aluminum-copper alloys are studied at high temperatures and under thermo-mechanical fatigue (TMF), exposing rate sensitivity and microstructural changes. The decrease in strength during cycling was attributed to the significant coarsening of the precipitates at high temperatures, which was confirmed with transmission electron microscopy. The results show that the stress-strain response is similar under

SAE Technical Paper Series, 2005

Page 1. Statistical Approaches Applied to Fatigue Test Data Analysis Carlos C. Engler-Pinto Jr. J... more Page 1. Statistical Approaches Applied to Fatigue Test Data Analysis Carlos C. Engler-Pinto Jr. John V. Lasecki Robert J. Frisch Sr Michael A. DeJack John E. Allison Page 2. 2 Paper #2005-01-0802 Motivation: Design for Fatigue ∎ High Cycle Fatigue Strength is one of the ...

SAE Technical Paper Series, 2004

The high temperature fatigue behaviors of three cast aluminum alloys used for cylinder head fabri... more The high temperature fatigue behaviors of three cast aluminum alloys used for cylinder head fabrication – 319, A356 and AS7GU – are compared under isothermal fatigue at room temperature and elevated temperatures. The thermo-mechanical fatigue behavior for both out-ofphase and in-phase loading conditions (100–300°C) has also been investigated. It has been observed that all three of these alloys present a very similar behavior under both isothermal and thermo-mechanical low-cycle fatigue. Under high-cycle fatigue, however, the alloys A356 and AS7GU exhibit superior performance.

International Journal of Fatigue, 1996

Thermomechanical Fatigue Behavior of Materials: 4th Volume

... H., Engler-Pinto Jr., C. C, Tang, CY., and Allison, JE," Thermomechanica... more ... H., Engler-Pinto Jr., C. C, Tang, CY., and Allison, JE," Thermomechanical Fatigue Analysis of Cast Aluminum Engine Components," Thermomechanical Fatigue Behavior of Materials: 4th Volume, ASTM STP 1428, MA McGaw, S. Kalluri, J. Bressers, and ... [4] Suresh, S.," Fatigue of ...

steel research international

International Journal of Fatigue

Abstract Fatigue tests for unidirectional (UD) CFRP composite specimens of various sizes are cond... more Abstract Fatigue tests for unidirectional (UD) CFRP composite specimens of various sizes are conducted under different stress ratios. The results show that the specimen size has considerable influence on the transverse tension-tension fatigue performance of UD laminates. The underlying fatigue mechanisms are also investigated through SEM observations. Moreover, a fatigue life prediction method considering size effects is presented, and a good correlation is observed between the prediction and the test data. Finally, to allow for an evaluation of the effects of mean stress, constant fatigue life diagrams for 0°, 10°, and 90° UD composites are established based on four-segment anisomorphic model.

Materials Science and Engineering: A

Abstract With the increase of exhaust temperature in automobiles resulting from the stricter envi... more Abstract With the increase of exhaust temperature in automobiles resulting from the stricter environmental and fuel consumption regulations, high temperature fatigue failure of exhaust manifolds is being a significant issue for safety concern. In this research, low cycle fatigue behavior of a Nb-bearing cast austenitic steel with the "Chinese-script" type primary Nb(C,N), was investigated in the temperature range of 600–950 °C. It is indicated that the fatigue lifetime was predominantly dependent on the inelastic strain amplitude, in spite of fatigue temperature. However, the change of deformation substructure from dislocation cells, slip bands to subgrains was observed from 600 °C to 950 °C, which was induced by the increased thermal recovery. Correspondingly, the cyclic stress amplitude changed from cyclic hardening at 600 °C to cyclic softening and cyclic stress saturation at 800 °C and 950 °C, respectively. Besides, strain heterogeneity was also noted between the dendrite core and the interdendritic region, thus regarded as a promotion for crack initiation. The generated data and the understanding will be helpful for alloy design and fatigue lifetime prediction next.

Procedia Engineering, 2015

Out-of-phase thermomechanical fatigue (OP-TMF) tests between 600 C and 950 C have been conducted ... more Out-of-phase thermomechanical fatigue (OP-TMF) tests between 600 C and 950 C have been conducted for three cast austenitic alloys with different metal-carbide (MC) morphologies: dense skeleton, sparse skeleton and blocky carbides. The alloy with dense skeleton-like MC exhibited longer TMF life than the other two, even though their chemical composition and casting process were similar. Fractography analysis indicated that the fatigue cracks initiated from the specimen surface for all the alloys in this study. The morphology of Nb(C,N) has an obvious effect on inelastic deformation. Alloys with skeleton-like Nb(C,N) precipitates have better ductility as compared to alloys with isolated blocky precipitates. Dense skeleton-like Nb(C,N) is found to delay OP-TMF crack initiation and propagation, resulting in longer TMF lives.

Procedia Engineering, 2015

In this paper, thermomechanical fatigue life (TMF) prediction is performed on an automotive exhau... more In this paper, thermomechanical fatigue life (TMF) prediction is performed on an automotive exhaust manifold using in-house postprocessor code (Hotlife) with four different constitutive models: elastoplastic model with kinematic hardening, two-layer viscoplastic model, and two unified elasto-viscoplastic models based on the equations proposed by Sehitoglu and Chaboche, respectively. Commercial FEA software Abaqus has been used for the analysis. The first two models are already available in Abaqus; the Chaboche and Sehitoglu models were implemented using a user material subroutine (UMAT, available in Abaqus). The stress and strain histories calculated by these four models are output to Hotlife for post-processing. The results from the prediction are then compared to the experimental TMF life obtained from a component thermal fatigue bench test. Result show the Hotlife calculations based on the two implemented elasto-viscoplastic models yield better correlation with test results.

Tecnologia em Metalurgia Materiais e Mineração, 2014

Os gradientes térmicos originados durante regimes transientes em operações de liga/desliga produz... more Os gradientes térmicos originados durante regimes transientes em operações de liga/desliga produzem complexos carregamentos mecânicos e térmicos de fadiga, que limitam a vida de palhetas de turbina e de outros componentes de motores que operam a altas temperaturas. Assim, torna-se imprescindível uma avaliação mais criteriosa e confiável da fadiga não isotérmica. Este trabalho investiga o comportamento em fadiga isotérmica de baixo ciclo (FBC) e fadiga termomecânica (FTM) de uma superliga à base de Ni, CM 247LC-DS, extensivamente utilizada a altas temperaturas. Os ensaios mecânicos foram realizados em temperaturas entre 600°C e 1.000°C. O comportamento mecânico da liga foi fortemente afetado no intervalo 800°C-1.000°C e o comportamento tensão-deformação cíclico observado para todo o intervalo de temperatura obedeceu à equação de Ramberg-Osgood. Um modelo simplificado de tensão-deformação não isotérmico, baseado no conceito de plasticidade linear foi proposto e descreveu o comportamento de fadiga termomecânica observado, tanto para ciclos em fase, como para fora de fase. Palavras-chave: Superliga; Fadiga isotérmica; Fadiga termomecânica.

Cast aluminum engine components are increasingly being used in the automobile industry. Due to hi... more Cast aluminum engine components are increasingly being used in the automobile industry. Due to high engine operating temperature, thermal fatigue during start-stop cycles is a very important design consideration. In this paper we will describe the application of newly developed analysis methods to analyze these complex problems. A user material subroutine for viseoplasticity stress analysis using the commercial FEA code ABAQUS has been developed. Stress and strain of engine heads during thermal cycle are thus analyzed and this code verified. The thermomechanical fatigue model developed by Neu and Sehitoglu, a damage accumulation model including fatigue, oxidation and fatigue damage, has been extended to three-dimensional state of stress by using the concept of critical planes. The enhanced damage model has been implemented in a FEA postprocessor for engine component life analysis. The predictions of thermal strains and fatigue life based on 3D FEA analysis are compared with measurements of engine component tests. Three different thermal loading cycles are considered. The thermal fatigue life predictions are within 30% error of actual component test data.

The thermal fatigue (TF) behaviour of two single crystal nickel-based super-alloys, SRR99 and CMS... more The thermal fatigue (TF) behaviour of two single crystal nickel-based super-alloys, SRR99 and CMSX-4, is reported. Single edge wedge specimens are rapidly heated by induction heating of the wedge tip to a maximum temperature between 1000~ and 1175~ and cooled to 200~ by forced air. A constant cycle period is employed for all experiments. The strain distribution along the edge of the TF specimens is measured. Changing the induction frequency leads to different strain ranges. CMSX-4 shows crack initiation always on cast microporosities. SRR99 presents an additional oxidation/spalling/re-oxidation mechanism under low strain loading. An "integrated approach" combining TF and TMF (thermo-mechanicai fatigue) is proposed. The applied TMF temperature-strain cycle is deduced from the measured TF-cycle. Under this new temperature-strain cycle the crack initiation life and the total life in TMF for SRR99 are compared with the TF results.

Materials at High Temperatures, 1995

... Alliage IN100. ; Application. ; Aube turbine. ; Turbine gaz. ; Alliage base nickel. ; Alliage... more ... Alliage IN100. ; Application. ; Aube turbine. ; Turbine gaz. ; Alliage base nickel. ; Alliage Ni60Co15Cr10Al6Ti5Mo3V1. ; Al Co Cr Mo Ni Ti. ; Mots-clés espagnols / Spanish Keywords. Fatiga térmica. ; Propiedad mecánica. ; Superaléación. ; Relación tensión deformación. ; ...

Materials Science and Engineering: A, 2013

Abstract The variability in fatigue life for a cast aluminum alloy has been investigated under bo... more Abstract The variability in fatigue life for a cast aluminum alloy has been investigated under both high-cycle and low-cycle fatigue. The fatigue cracks have initiated mostly near the surface from pores or oxide inclusions. The size of the initiation sites has been evaluated for all specimens and the statistical distribution has been determined. In addition, probabilistic fatigue life regression models have been used to characterize the observed scatter in fatigue life. The cumulative density function (CDF) of fatigue life was found to be approximately equal to the complementary value of the CDF of the near surface fatigue initiator size. Therefore, it has been concluded that the observed scatter in fatigue life is directly related to the distribution of casting defects within the alloy.

Superalloys 1996 (Eighth International Symposium), 1996

The interaction between creep and thermo-mechanical fatigue (TMF) is investigated on the CM247LC-... more The interaction between creep and thermo-mechanical fatigue (TMF) is investigated on the CM247LC-DS alloy. Out-of-phase TMF tests are performed between 600°C and 900°C on tubular specimens (1 mm wall). Creep rupture experiments are conducted at 900°C on the virein (as received) allov under 280 MPa on both solid and tubular s"pecimens. Sequential creep-TMF and TMFcreep experiments are performed. Creep cavities and internal cracks are initiated on carbides or residual eutectics. In addition, oxidation assisted crack initiation is observed at the surface of the specimens during creep. No noticeable change on the 7-r' structure is observed during TMF cvclina. Under creen. however. a V-raft structure develois perpendicul&ly to the stress axis. This v-rafting softens the pre-crept alloy and influences its non-isothermal cyclic stress-strain bv increasing the inelastic strain. Short cracks initiated during pre-creeping drastically reduce the TMF crack initiation neriod. On the other hand. short cracks (100 to 300 urn surface 'crack length) initiated during pre-TMF cycling do not affect the creep lifetime. A linear creep-fatigue damage cumulative law can predict the residual life of TMF specimens which have been precrept.

Thermo-mechanical Fatigue Behavior of Materials: Third Volume

This paper deals with the comparison between thermal fatigue (TF) and thermomechanical fatigue (T... more This paper deals with the comparison between thermal fatigue (TF) and thermomechanical fatigue (TMF) testing for SRR99 superalloy. First, a measured TF mechanical strain‐temperature (epsilon(m)‐T) profile between 200 degrees C and 1100 degrees C has been reproduced on a TMF specimen to allow for an estimation of the stresses and inelastic strains which occur during TF. Thermal‐fatigue‐base (TFB) epsilon(m)‐T profiles were determined based on the measured TF profiles. These TFB cycles, together with the well‐known out‐of‐phase profile, were employed for all of TMF tests. The comparison of the results reveals that the TF and TMF out‐phase tests are more damaging in terms both of the applied stress and strain range, while the TMF out‐of‐phase test is more severe if the comparison is made in terms of the inelastic strain range. Finally, it is shown that the results can be rationalized quite well by plotting the fatigue lives as a function of the maximum stabilized stress (sigma(max)).

Thermomechanical Fatigue Behavior of Materials: Second Volume

The thermal fatigue (TF) behaviour of two single crystal nickel-based superalloys, SRR99 and CMSX... more The thermal fatigue (TF) behaviour of two single crystal nickel-based superalloys, SRR99 and CMSX-4, is reported. Single edge wedge specimens are rapidly heated by induction heating of the wedge tip to a maximum temperature between 1000°C and 1175°C and cooled to 200°C by forced air. A constant cycle period is employed for all experiments. The strain distribution along the edge of the TF specimens is measured. Changing the induction frequency leads to different strain ranges. CMSX-4 shows crack initiation always on cast microporosities. SRR99 presents an additional oxidation/spalling/re-oxidation mechanism under low strain loading. An "integrated approach" combining TF and TMF (thermo-mechanical fatigue) is proposed. The applied TMF temperature-strain cycle is deduced from the measured TF-cycle. Under this new temperature-strain cycle the crack initiation life and the total life in TMF for SRR99 are compared with the TF results.

Materials Performance and Characterization, 2014

Thermo-mechanical fatigue (TMF) resistance of engineering materials is extremely important for th... more Thermo-mechanical fatigue (TMF) resistance of engineering materials is extremely important for the durability and reliability of components and systems subjected to combined thermal and mechanical loadings. However, TMF testing, modeling, simulation, validation, and the subsequent implementation of the findings into product design are challenging tasks because of the difficulties not only in testing but also in results interpretation and in the identification of the deformation and failure mechanisms. Under combined high-temperature and severe mechanical loading conditions, creep and oxidation mechanisms are activated and time-dependent failure mechanisms are superimposed to cycle-dependent fatigue, making the life assessment very complex. In this paper, the testing procedures and results for high-temperature fatigue testing using flat specimens and thermal-fatigue testing using V-shape specimens are reported; emphasis is given to hold-time effects and the possible underlying mechanisms. The uncertainty nature and the probabilistic characteristics of the V-shape specimen test data are also presented. Finally, the impact of hold-time effect on current product design and validation procedure is discussed in terms of virtual life assessment.

European Structural Integrity Society, 2002

Stress-strain behavior and durability of cast 319 aluminum-copper alloys are studied at high temp... more Stress-strain behavior and durability of cast 319 aluminum-copper alloys are studied at high temperatures and under thermo-mechanical fatigue (TMF), exposing rate sensitivity and microstructural changes. The decrease in strength during cycling was attributed to the significant coarsening of the precipitates at high temperatures, which was confirmed with transmission electron microscopy. The results show that the stress-strain response is similar under

SAE Technical Paper Series, 2005

Page 1. Statistical Approaches Applied to Fatigue Test Data Analysis Carlos C. Engler-Pinto Jr. J... more Page 1. Statistical Approaches Applied to Fatigue Test Data Analysis Carlos C. Engler-Pinto Jr. John V. Lasecki Robert J. Frisch Sr Michael A. DeJack John E. Allison Page 2. 2 Paper #2005-01-0802 Motivation: Design for Fatigue ∎ High Cycle Fatigue Strength is one of the ...

SAE Technical Paper Series, 2004

The high temperature fatigue behaviors of three cast aluminum alloys used for cylinder head fabri... more The high temperature fatigue behaviors of three cast aluminum alloys used for cylinder head fabrication – 319, A356 and AS7GU – are compared under isothermal fatigue at room temperature and elevated temperatures. The thermo-mechanical fatigue behavior for both out-ofphase and in-phase loading conditions (100–300°C) has also been investigated. It has been observed that all three of these alloys present a very similar behavior under both isothermal and thermo-mechanical low-cycle fatigue. Under high-cycle fatigue, however, the alloys A356 and AS7GU exhibit superior performance.

International Journal of Fatigue, 1996

Thermomechanical Fatigue Behavior of Materials: 4th Volume

... H., Engler-Pinto Jr., C. C, Tang, CY., and Allison, JE," Thermomechanica... more ... H., Engler-Pinto Jr., C. C, Tang, CY., and Allison, JE," Thermomechanical Fatigue Analysis of Cast Aluminum Engine Components," Thermomechanical Fatigue Behavior of Materials: 4th Volume, ASTM STP 1428, MA McGaw, S. Kalluri, J. Bressers, and ... [4] Suresh, S.," Fatigue of ...

steel research international

International Journal of Fatigue

Abstract Fatigue tests for unidirectional (UD) CFRP composite specimens of various sizes are cond... more Abstract Fatigue tests for unidirectional (UD) CFRP composite specimens of various sizes are conducted under different stress ratios. The results show that the specimen size has considerable influence on the transverse tension-tension fatigue performance of UD laminates. The underlying fatigue mechanisms are also investigated through SEM observations. Moreover, a fatigue life prediction method considering size effects is presented, and a good correlation is observed between the prediction and the test data. Finally, to allow for an evaluation of the effects of mean stress, constant fatigue life diagrams for 0°, 10°, and 90° UD composites are established based on four-segment anisomorphic model.

Materials Science and Engineering: A

Abstract With the increase of exhaust temperature in automobiles resulting from the stricter envi... more Abstract With the increase of exhaust temperature in automobiles resulting from the stricter environmental and fuel consumption regulations, high temperature fatigue failure of exhaust manifolds is being a significant issue for safety concern. In this research, low cycle fatigue behavior of a Nb-bearing cast austenitic steel with the "Chinese-script" type primary Nb(C,N), was investigated in the temperature range of 600–950 °C. It is indicated that the fatigue lifetime was predominantly dependent on the inelastic strain amplitude, in spite of fatigue temperature. However, the change of deformation substructure from dislocation cells, slip bands to subgrains was observed from 600 °C to 950 °C, which was induced by the increased thermal recovery. Correspondingly, the cyclic stress amplitude changed from cyclic hardening at 600 °C to cyclic softening and cyclic stress saturation at 800 °C and 950 °C, respectively. Besides, strain heterogeneity was also noted between the dendrite core and the interdendritic region, thus regarded as a promotion for crack initiation. The generated data and the understanding will be helpful for alloy design and fatigue lifetime prediction next.

Procedia Engineering, 2015

Out-of-phase thermomechanical fatigue (OP-TMF) tests between 600 C and 950 C have been conducted ... more Out-of-phase thermomechanical fatigue (OP-TMF) tests between 600 C and 950 C have been conducted for three cast austenitic alloys with different metal-carbide (MC) morphologies: dense skeleton, sparse skeleton and blocky carbides. The alloy with dense skeleton-like MC exhibited longer TMF life than the other two, even though their chemical composition and casting process were similar. Fractography analysis indicated that the fatigue cracks initiated from the specimen surface for all the alloys in this study. The morphology of Nb(C,N) has an obvious effect on inelastic deformation. Alloys with skeleton-like Nb(C,N) precipitates have better ductility as compared to alloys with isolated blocky precipitates. Dense skeleton-like Nb(C,N) is found to delay OP-TMF crack initiation and propagation, resulting in longer TMF lives.

Procedia Engineering, 2015

In this paper, thermomechanical fatigue life (TMF) prediction is performed on an automotive exhau... more In this paper, thermomechanical fatigue life (TMF) prediction is performed on an automotive exhaust manifold using in-house postprocessor code (Hotlife) with four different constitutive models: elastoplastic model with kinematic hardening, two-layer viscoplastic model, and two unified elasto-viscoplastic models based on the equations proposed by Sehitoglu and Chaboche, respectively. Commercial FEA software Abaqus has been used for the analysis. The first two models are already available in Abaqus; the Chaboche and Sehitoglu models were implemented using a user material subroutine (UMAT, available in Abaqus). The stress and strain histories calculated by these four models are output to Hotlife for post-processing. The results from the prediction are then compared to the experimental TMF life obtained from a component thermal fatigue bench test. Result show the Hotlife calculations based on the two implemented elasto-viscoplastic models yield better correlation with test results.

Tecnologia em Metalurgia Materiais e Mineração, 2014

Os gradientes térmicos originados durante regimes transientes em operações de liga/desliga produz... more Os gradientes térmicos originados durante regimes transientes em operações de liga/desliga produzem complexos carregamentos mecânicos e térmicos de fadiga, que limitam a vida de palhetas de turbina e de outros componentes de motores que operam a altas temperaturas. Assim, torna-se imprescindível uma avaliação mais criteriosa e confiável da fadiga não isotérmica. Este trabalho investiga o comportamento em fadiga isotérmica de baixo ciclo (FBC) e fadiga termomecânica (FTM) de uma superliga à base de Ni, CM 247LC-DS, extensivamente utilizada a altas temperaturas. Os ensaios mecânicos foram realizados em temperaturas entre 600°C e 1.000°C. O comportamento mecânico da liga foi fortemente afetado no intervalo 800°C-1.000°C e o comportamento tensão-deformação cíclico observado para todo o intervalo de temperatura obedeceu à equação de Ramberg-Osgood. Um modelo simplificado de tensão-deformação não isotérmico, baseado no conceito de plasticidade linear foi proposto e descreveu o comportamento de fadiga termomecânica observado, tanto para ciclos em fase, como para fora de fase. Palavras-chave: Superliga; Fadiga isotérmica; Fadiga termomecânica.

Cast aluminum engine components are increasingly being used in the automobile industry. Due to hi... more Cast aluminum engine components are increasingly being used in the automobile industry. Due to high engine operating temperature, thermal fatigue during start-stop cycles is a very important design consideration. In this paper we will describe the application of newly developed analysis methods to analyze these complex problems. A user material subroutine for viseoplasticity stress analysis using the commercial FEA code ABAQUS has been developed. Stress and strain of engine heads during thermal cycle are thus analyzed and this code verified. The thermomechanical fatigue model developed by Neu and Sehitoglu, a damage accumulation model including fatigue, oxidation and fatigue damage, has been extended to three-dimensional state of stress by using the concept of critical planes. The enhanced damage model has been implemented in a FEA postprocessor for engine component life analysis. The predictions of thermal strains and fatigue life based on 3D FEA analysis are compared with measurements of engine component tests. Three different thermal loading cycles are considered. The thermal fatigue life predictions are within 30% error of actual component test data.

The thermal fatigue (TF) behaviour of two single crystal nickel-based super-alloys, SRR99 and CMS... more The thermal fatigue (TF) behaviour of two single crystal nickel-based super-alloys, SRR99 and CMSX-4, is reported. Single edge wedge specimens are rapidly heated by induction heating of the wedge tip to a maximum temperature between 1000~ and 1175~ and cooled to 200~ by forced air. A constant cycle period is employed for all experiments. The strain distribution along the edge of the TF specimens is measured. Changing the induction frequency leads to different strain ranges. CMSX-4 shows crack initiation always on cast microporosities. SRR99 presents an additional oxidation/spalling/re-oxidation mechanism under low strain loading. An "integrated approach" combining TF and TMF (thermo-mechanicai fatigue) is proposed. The applied TMF temperature-strain cycle is deduced from the measured TF-cycle. Under this new temperature-strain cycle the crack initiation life and the total life in TMF for SRR99 are compared with the TF results.

Thèse No. 1496 (1996), 1996

This dissertation reports the elevated temperature fatigue behavior of 3 nickel based superalloys... more This dissertation reports the elevated temperature fatigue behavior of 3 nickel based superalloys: a polycrystalline alloy (IN738LC), a directionally solidified alloy (CM247LC_DS), and a single crustal alloy (SRR99).