https://sam.ensam.eu:443 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Fri, 17 Apr 2026 13:08:19 GMT 2026-04-17T13:08:19Z http://hdl.handle.net/10985/26281 A probabilistic model to consider scale and gradient effects in the prediction of the fatigue life of Inconel 718 for turbine disk application GOULMY, Jean-Patrick; KAMINSKI, Myriam; LEROY, F.H.; KANOUTE, Pascale The aim of this paper is to implement and compare different fatigue post-processing approaches for fatigue life assessment of complex parts. Inconel 718 is taken as an example, as it can exhibit several factors influencing fatigue life, such as mean stress, stress gradient and scale effects. Tests on different specimen geometries to exacerbate these effects were carried out at 550°C. The range of service operating life is between 103 and 106 cycles. A modelling chain was then set up. A structural calculation was performed using an elasto-visco-plastic behavior law to obtain the mechanical fields at cycle stabilize. These values were finally exploited by applying a post-processing treatment approach to predict the fatigue life of the structure. Two main types of post-processing approach were investigated: standard and probabilistic. The way in which the different factors influencing fatigue life are considered, depending on the approach used, was discussed. Finally, the probabilistic volume approach yields better results, thanks to its ability to consider mean stress, stress gradient and scale effects in the proposed formulation. Thu, 01 May 2025 00:00:00 GMT http://hdl.handle.net/10985/26281 2025-05-01T00:00:00Z GOULMY, Jean-Patrick KAMINSKI, Myriam LEROY, F.H. KANOUTE, Pascale The aim of this paper is to implement and compare different fatigue post-processing approaches for fatigue life assessment of complex parts. Inconel 718 is taken as an example, as it can exhibit several factors influencing fatigue life, such as mean stress, stress gradient and scale effects. Tests on different specimen geometries to exacerbate these effects were carried out at 550°C. The range of service operating life is between 103 and 106 cycles. A modelling chain was then set up. A structural calculation was performed using an elasto-visco-plastic behavior law to obtain the mechanical fields at cycle stabilize. These values were finally exploited by applying a post-processing treatment approach to predict the fatigue life of the structure. Two main types of post-processing approach were investigated: standard and probabilistic. The way in which the different factors influencing fatigue life are considered, depending on the approach used, was discussed. Finally, the probabilistic volume approach yields better results, thanks to its ability to consider mean stress, stress gradient and scale effects in the proposed formulation. http://hdl.handle.net/10985/25381 A model for the influence of work hardening and microstructure on the evolution of residual stresses under thermal loading – Application to Inconel 718 GOULMY, Jean-Patrick; TOUALBI, L.; BOYER, V.; KANOUTE, P.; RETRAINT, D.; ROUHAUD, E. This study proposes a model for the influence of work hardening and microstructure on the thermal relaxation of residual stresses. To construct such a model, an experimental campaign is first conducted on shot peened samples of Inconel 718 to generate different levels of residual stress and work hardening. The effect of the grain size and the size of the strengthening precipitates is investigated by producing two modified microstructures. Two shot peening conditions are used to introduce several profiles of residual stress and work hardening. These profiles are evaluated using X-ray diffraction. A thermal loading is then applied at 550°C with varying holding times, leading to a rapid but not complete relaxation of the residual stresses and work hardening. The experimental results exhibit the fact that the work hardening levels have a significant influence on this relaxation while the grain size and the size of the strengthening precipitates have a very moderate influence. Based on these experimental results, a model is proposed that considers the influence of work hardening on the thermal relaxation of residual stresses with some predictive applications. It is therefore possible to estimate the relaxation of residual stresses at any point on a shot peened part. Sun, 01 Sep 2024 00:00:00 GMT http://hdl.handle.net/10985/25381 2024-09-01T00:00:00Z GOULMY, Jean-Patrick TOUALBI, L. BOYER, V. KANOUTE, P. RETRAINT, D. ROUHAUD, E. This study proposes a model for the influence of work hardening and microstructure on the thermal relaxation of residual stresses. To construct such a model, an experimental campaign is first conducted on shot peened samples of Inconel 718 to generate different levels of residual stress and work hardening. The effect of the grain size and the size of the strengthening precipitates is investigated by producing two modified microstructures. Two shot peening conditions are used to introduce several profiles of residual stress and work hardening. These profiles are evaluated using X-ray diffraction. A thermal loading is then applied at 550°C with varying holding times, leading to a rapid but not complete relaxation of the residual stresses and work hardening. The experimental results exhibit the fact that the work hardening levels have a significant influence on this relaxation while the grain size and the size of the strengthening precipitates have a very moderate influence. Based on these experimental results, a model is proposed that considers the influence of work hardening on the thermal relaxation of residual stresses with some predictive applications. It is therefore possible to estimate the relaxation of residual stresses at any point on a shot peened part. http://hdl.handle.net/10985/24561 Classification of the acquisition conditions driving the accuracy of strain measurements during in situ DIC with scanning electron microscope GOULMY, Jean-Patrick; GUITTONNEAU, Fabrice; JÉGOU, Sébastien; BARRALLIER, Laurent Performing in situ scanning electron microscope (SEM) tests is an interesting way to visualise strain heterogeneities under mechanical loading. An essential step before performing the tests is to define the acquisition conditions. The aim of this paper is to propose a classification of the acquisition conditions that are most important for the accuracy of strain measurements using digital image correlation (DIC) in in situ SEM tests. More than 200 image pairs were acquired using a field emission gun SEM. The influence of different acquisition conditions was investigated: acceleration voltage, probe current, working distance, magnification, number of integrated images, image resolution, integration and number of integrated images, scan speed, contrast, brightness and exposure time of the sample in a given area. The methodology implemented in this work is an interesting tool for detecting scan line shift, drift distortion, spatial distortion and rastering artefacts. It allows the optimization of SEM acquisition conditions for strain measurements. Finally, optimal acquisition conditions for in situ testing are proposed and used to perform a tensile test on pure copper. The main factors highlighted include the size of the subset used in the DIC, the beam stabilisation time before image acquisition and the size of the images, which play a significant role in the results. It is recommended to apply the methodology to each device to optimise the acquisition conditions. Thu, 13 Jul 2023 00:00:00 GMT http://hdl.handle.net/10985/24561 2023-07-13T00:00:00Z GOULMY, Jean-Patrick GUITTONNEAU, Fabrice JÉGOU, Sébastien BARRALLIER, Laurent Performing in situ scanning electron microscope (SEM) tests is an interesting way to visualise strain heterogeneities under mechanical loading. An essential step before performing the tests is to define the acquisition conditions. The aim of this paper is to propose a classification of the acquisition conditions that are most important for the accuracy of strain measurements using digital image correlation (DIC) in in situ SEM tests. More than 200 image pairs were acquired using a field emission gun SEM. The influence of different acquisition conditions was investigated: acceleration voltage, probe current, working distance, magnification, number of integrated images, image resolution, integration and number of integrated images, scan speed, contrast, brightness and exposure time of the sample in a given area. The methodology implemented in this work is an interesting tool for detecting scan line shift, drift distortion, spatial distortion and rastering artefacts. It allows the optimization of SEM acquisition conditions for strain measurements. Finally, optimal acquisition conditions for in situ testing are proposed and used to perform a tensile test on pure copper. The main factors highlighted include the size of the subset used in the DIC, the beam stabilisation time before image acquisition and the size of the images, which play a significant role in the results. It is recommended to apply the methodology to each device to optimise the acquisition conditions. http://hdl.handle.net/10985/21499 A calibration procedure for the assessment of work hardening Part II: Application to shot peened IN718 parts GOULMY, Jean-Patrick; KANOUTE, P.; ROUHAUD, E.; TOUALBI, L.; KRUCH, S.; BOYER, V.; BADREDDINE, Jawad; RETRAINT, D. The objective of this paper is to discuss the application of the calibration methodology exposed in the previous part to shot-peened Inconel 718 specimens. Shot peening is commonly used to increase the fatigue life of critical parts such as Inconel 718 turbine discs. This surface treatment induces residual stresses, work hardening and possibly, gradients of microstructures that, in turn, affect fatigue life. Work hardening is a quantity that represents a set of physical and mechanical phenomena related to the level of disorder reached in the microstructure of the material. Work hardening is seldom taken into account in fatigue life assessment mainly because it is not possible to characterize this quantity directly. We propose to use the calibration methodology (see part I of this paper [1]) on samples shot peened with several conditions. The three complementary experimental techniques (microhardness, XRD and EBSD) are then used to determine through correlation curves the work hardening gradients. The meth-odology for characterizing the work hardening within shot peened specimens is first presented. A dis-cussion of the applicability of the method in this context is then provided. The results obtained for the different characterization methods and microstructural effects are analyzed in two different sections. Finally, the influence of shot peening conditions on residual stresses and on work hardening is dis-cussed, showing the interest of the proposed procedure to obtain a real picture of the mechanical state after shot peening. Fri, 01 Jan 2021 00:00:00 GMT http://hdl.handle.net/10985/21499 2021-01-01T00:00:00Z GOULMY, Jean-Patrick KANOUTE, P. ROUHAUD, E. TOUALBI, L. KRUCH, S. BOYER, V. BADREDDINE, Jawad RETRAINT, D. The objective of this paper is to discuss the application of the calibration methodology exposed in the previous part to shot-peened Inconel 718 specimens. Shot peening is commonly used to increase the fatigue life of critical parts such as Inconel 718 turbine discs. This surface treatment induces residual stresses, work hardening and possibly, gradients of microstructures that, in turn, affect fatigue life. Work hardening is a quantity that represents a set of physical and mechanical phenomena related to the level of disorder reached in the microstructure of the material. Work hardening is seldom taken into account in fatigue life assessment mainly because it is not possible to characterize this quantity directly. We propose to use the calibration methodology (see part I of this paper [1]) on samples shot peened with several conditions. The three complementary experimental techniques (microhardness, XRD and EBSD) are then used to determine through correlation curves the work hardening gradients. The meth-odology for characterizing the work hardening within shot peened specimens is first presented. A dis-cussion of the applicability of the method in this context is then provided. The results obtained for the different characterization methods and microstructural effects are analyzed in two different sections. Finally, the influence of shot peening conditions on residual stresses and on work hardening is dis-cussed, showing the interest of the proposed procedure to obtain a real picture of the mechanical state after shot peening. http://hdl.handle.net/10985/21476 Towards an image quality criterion to optimize Digital image correlation. Use of an analytical model to optimize acquisition conditions GOULMY, Jean-Patrick; JÉGOU, Sébastien; BARRALLIER, Laurent Digital image correlation (DIC) is expanding in many fields. In particular, it requires that the acquisition conditions and speckle be adapted to each application. A new methodology allowing to define the quality of the images in a fast and precise way is proposed. An analytical model based on mean intensity gradient of speckle pattern criterion and the standard deviation of displacement on images has been proposed. The model can be used on the whole image or by creating subsets in the image. Standard deviation maps of displacement are obtained. The methodology makes it possible to save a considerable amount of time compared to the full DIC calculation to optimize the image acquisition conditions, the speckle and the DIC parameters. Sat, 01 Jan 2022 00:00:00 GMT http://hdl.handle.net/10985/21476 2022-01-01T00:00:00Z GOULMY, Jean-Patrick JÉGOU, Sébastien BARRALLIER, Laurent Digital image correlation (DIC) is expanding in many fields. In particular, it requires that the acquisition conditions and speckle be adapted to each application. A new methodology allowing to define the quality of the images in a fast and precise way is proposed. An analytical model based on mean intensity gradient of speckle pattern criterion and the standard deviation of displacement on images has been proposed. The model can be used on the whole image or by creating subsets in the image. Standard deviation maps of displacement are obtained. The methodology makes it possible to save a considerable amount of time compared to the full DIC calculation to optimize the image acquisition conditions, the speckle and the DIC parameters. http://hdl.handle.net/10985/21475 A calibration procedure for the assessment of work hardening part I: Effects of the microstructure and load type GOULMY, Jean-Patrick; ROUHAUD, E.; KANOUTE, P.; TOUALBI, L.; KRUCH, S.; BOYER, V.; BADREDDINE, Jawad; RETRAINT, D. This paper presents a methodology to define and quantify the level of work hardening locally in a material. The methodology is proposed after a thorough experimental study based on three complementary experimental techniques for microstructural characterizations: microhardness, X-ray diffraction (XRD) and Electron Backscatter Diffraction (EBSD) applied on Inconel 718 samples. In our analysis, several loading histories including single tension, single compression, high strain rates and low cycle fatigue have been investigated. The effects of the microstructure have been further investigated by modifying the size of the grains and the size of the strengthening precipitates. Experimental tests have also been simulated to choose a model variable able to represent work hardening. A reciprocal link between work hardening and experimental characterizations has then been established. Correlation curves have been proposed that enable to quantify the level of work hardening from the knowledge of the experimental data. Accuracy and complementarity of the three experimental approaches are discussed as well as the impact of the microstructure of the material on the measured quantities. Fri, 01 Jan 2021 00:00:00 GMT http://hdl.handle.net/10985/21475 2021-01-01T00:00:00Z GOULMY, Jean-Patrick ROUHAUD, E. KANOUTE, P. TOUALBI, L. KRUCH, S. BOYER, V. BADREDDINE, Jawad RETRAINT, D. This paper presents a methodology to define and quantify the level of work hardening locally in a material. The methodology is proposed after a thorough experimental study based on three complementary experimental techniques for microstructural characterizations: microhardness, X-ray diffraction (XRD) and Electron Backscatter Diffraction (EBSD) applied on Inconel 718 samples. In our analysis, several loading histories including single tension, single compression, high strain rates and low cycle fatigue have been investigated. The effects of the microstructure have been further investigated by modifying the size of the grains and the size of the strengthening precipitates. Experimental tests have also been simulated to choose a model variable able to represent work hardening. A reciprocal link between work hardening and experimental characterizations has then been established. Correlation curves have been proposed that enable to quantify the level of work hardening from the knowledge of the experimental data. Accuracy and complementarity of the three experimental approaches are discussed as well as the impact of the microstructure of the material on the measured quantities. http://hdl.handle.net/10985/24001 Crystal Plasticity simulations of in situ tensile tests: A two-step inverse method for identification of CP parameters, and assessment of CPFEM capabilities DEPRIESTER, Dorian; GOULMY, Jean-Patrick; BARRALLIER, Laurent As the computational capability of modern computers increases, the Crystal Plasticity Finite Element Method (CPFEM) becomes more and more popular in materials science to model the mechanical behaviour of polycrystals. Indeed, such analysis provides extensive information about local mechanical fields (such as plastic strain and stress), which can be useful for understanding the behaviour of bulk materials. However, estimating the parameters of the CP constitutive laws is still challenging because they are not directly related to the macroscopic behaviour of the polycrystalline aggregates. Thus, one way to identify such parameters is by inverse analysis from CPFEM simulations. However, such approach is usually extremely time consuming. This paper proposes a two-step optimization scheme to determine these coefficients. The first step is based on a simple model, similar to that proposed by Sachs back in 1928. The second step is based on CPFEM simulations, to be compared with experimental data acquired by an in situ tensile test and full-field measurements made by High-Resolution Digital Image Correlation (HRDIC). The uniqueness of the solution found by inverse analysis is studied and ways to solve the local minima issues are provided. Finally, the ability of CPFEM to replicate an in situ tensile test is assessed. The source code used for CPFEM inverse analysis is available at: https://github.com/DorianDepriester/OptiPRISMS Fri, 01 Sep 2023 00:00:00 GMT http://hdl.handle.net/10985/24001 2023-09-01T00:00:00Z DEPRIESTER, Dorian GOULMY, Jean-Patrick BARRALLIER, Laurent As the computational capability of modern computers increases, the Crystal Plasticity Finite Element Method (CPFEM) becomes more and more popular in materials science to model the mechanical behaviour of polycrystals. Indeed, such analysis provides extensive information about local mechanical fields (such as plastic strain and stress), which can be useful for understanding the behaviour of bulk materials. However, estimating the parameters of the CP constitutive laws is still challenging because they are not directly related to the macroscopic behaviour of the polycrystalline aggregates. Thus, one way to identify such parameters is by inverse analysis from CPFEM simulations. However, such approach is usually extremely time consuming. This paper proposes a two-step optimization scheme to determine these coefficients. The first step is based on a simple model, similar to that proposed by Sachs back in 1928. The second step is based on CPFEM simulations, to be compared with experimental data acquired by an in situ tensile test and full-field measurements made by High-Resolution Digital Image Correlation (HRDIC). The uniqueness of the solution found by inverse analysis is studied and ways to solve the local minima issues are provided. Finally, the ability of CPFEM to replicate an in situ tensile test is assessed. http://hdl.handle.net/10985/23782 Mechanical behavior of polycrystals: Coupled in situ DIC-EBSD analysis of pure copper under tensile test GOULMY, Jean-Patrick; DEPRIESTER, Dorian; GUITTONNEAU, F.; JÉGOU, Sébastien; BARRALLIER, Laurent Understanding the mechanisms at the microstructure scale is of great importance for modeling the behavior of materials at different scales. To this end, digital image correlation (DIC) is an effective measurement method for evaluating the strains generated by various loading conditions. The objective of this paper is to describe the experimental setup and the use of high resolution digital image correlation (HRDIC) during in situ Scanning Electron Microscope (SEM) tests in order to provide a coupling between polycrystalline modeling and experiment in the near future. The HRDIC technique is used to evaluate the tensile behavior of a pure copper polycrystal at room temperature. Several magnitudes are investigated in order to discuss the representativeness of the results with respect to the macroscopic scale. The selected image correlation parameters are discussed regarding the ability of the technique to define inter- and intra- granular strain heterogeneities. Finally, based on EBSD analyzes, the impact of grain orientation on the mechanical behavior is discussed. The Schmid factor, calculated from a macroscopic stress, appears to be the determining factor concerning the orientation of the location bands. On the other hand, it is not sufficient to define the mean strains in the grains. Thu, 01 Dec 2022 00:00:00 GMT http://hdl.handle.net/10985/23782 2022-12-01T00:00:00Z GOULMY, Jean-Patrick DEPRIESTER, Dorian GUITTONNEAU, F. JÉGOU, Sébastien BARRALLIER, Laurent Understanding the mechanisms at the microstructure scale is of great importance for modeling the behavior of materials at different scales. To this end, digital image correlation (DIC) is an effective measurement method for evaluating the strains generated by various loading conditions. The objective of this paper is to describe the experimental setup and the use of high resolution digital image correlation (HRDIC) during in situ Scanning Electron Microscope (SEM) tests in order to provide a coupling between polycrystalline modeling and experiment in the near future. The HRDIC technique is used to evaluate the tensile behavior of a pure copper polycrystal at room temperature. Several magnitudes are investigated in order to discuss the representativeness of the results with respect to the macroscopic scale. The selected image correlation parameters are discussed regarding the ability of the technique to define inter- and intra- granular strain heterogeneities. Finally, based on EBSD analyzes, the impact of grain orientation on the mechanical behavior is discussed. The Schmid factor, calculated from a macroscopic stress, appears to be the determining factor concerning the orientation of the location bands. On the other hand, it is not sufficient to define the mean strains in the grains. http://hdl.handle.net/10985/25601 Slip identification from HR-DIC/EBSD: Incorporating Crystal Plasticity constitutive laws DEPRIESTER, Dorian; GOULMY, Jean-Patrick; BARRALLIER, Laurent It is well known that dislocation slip plays a major role in plastic deformation of polycrystals. Depending on the crystal’s symmetry, only a limited number of Slip Systems (SSs) are possible, and their activities depend on the crystal orientation with respect to the applied stress. High Resolution Digital Image Correlation (HR-DIC) can be used to get the full-field measurements of displacement fields on the surface of the strained material during an in situ tensile test, whereas the EBSD technique provides local crystallographic orientations. Therefore, coupling them can lead to full description of the local slip activities. Recently, an algorithm (named SSLIP) was proposed in the literature to automatically estimate the plastic activity from HR-DIC and EBSD data. The aim of the present paper is first to improve this algorithm so that it works for incremental straining, and to propose a way to take account for the anisotropic behaviour through a well-known set of Crystal Plasticity (CP) constitutive laws. It is shown that slip identification, together with those CP laws, can be used to estimate the tensile stress at grain scale. The influence of the DIC resolution is investigated and ‘‘correction rules’’ for small grains are proposed. Finally, the experimental results are compared against those found using the CP Finite Element Method (CPFEM), showing good consistency, specially in terms of active SSs and local stress. Sun, 01 Dec 2024 00:00:00 GMT http://hdl.handle.net/10985/25601 2024-12-01T00:00:00Z DEPRIESTER, Dorian GOULMY, Jean-Patrick BARRALLIER, Laurent It is well known that dislocation slip plays a major role in plastic deformation of polycrystals. Depending on the crystal’s symmetry, only a limited number of Slip Systems (SSs) are possible, and their activities depend on the crystal orientation with respect to the applied stress. High Resolution Digital Image Correlation (HR-DIC) can be used to get the full-field measurements of displacement fields on the surface of the strained material during an in situ tensile test, whereas the EBSD technique provides local crystallographic orientations. Therefore, coupling them can lead to full description of the local slip activities. Recently, an algorithm (named SSLIP) was proposed in the literature to automatically estimate the plastic activity from HR-DIC and EBSD data. The aim of the present paper is first to improve this algorithm so that it works for incremental straining, and to propose a way to take account for the anisotropic behaviour through a well-known set of Crystal Plasticity (CP) constitutive laws. It is shown that slip identification, together with those CP laws, can be used to estimate the tensile stress at grain scale. The influence of the DIC resolution is investigated and ‘‘correction rules’’ for small grains are proposed. Finally, the experimental results are compared against those found using the CP Finite Element Method (CPFEM), showing good consistency, specially in terms of active SSs and local stress. http://hdl.handle.net/10985/23781 Modeling of the shot peening of a nickel alloy with the consideration of both residual stresses and work hardening GOULMY, Jean-Patrick; BOYER, V.; RETRAINT, D.; KANOUTE, P.; TOUALBI, L.; ROUHAUD, E. Shot peening of turbine disk engines is performed in the aerospace industry in order to enhance fatigue life. This surface enhancement method generates beneficial modifications like superficial compressive residual stresses that are known to delay crack initiation and propagation. In the same way, work hardening is also introduced at the surface of the part during shot peening and can have a significant influence on fatigue crack initiation. Taking this parameter into account in the fatigue design of parts, in addition to the residual stresses, is a real challenge to be the most predictive. One possibility for this is to be able to predict it during the modeling of the shot peening process. In the present work, various peening conditions are considered in order to be able to propose a model able to account for the influence of coverage and Almen intensity on residual stresses and work hardening. The studied material is Inconel 718, commonly used for aeronautical parts. The X-ray diffraction method is used to obtain the in-depth residual stress and work hardening profiles. A three-dimensional numerical model is proposed to predict these quantities. Efforts are made to consider all recent advances in three-dimensional simulation of the process, in terms of coverage assessment, shot and treated part modeling. The numerical results are compared to the experimentally measured residual stresses and work hardening. Wed, 01 Mar 2023 00:00:00 GMT http://hdl.handle.net/10985/23781 2023-03-01T00:00:00Z GOULMY, Jean-Patrick BOYER, V. RETRAINT, D. KANOUTE, P. TOUALBI, L. ROUHAUD, E. Shot peening of turbine disk engines is performed in the aerospace industry in order to enhance fatigue life. This surface enhancement method generates beneficial modifications like superficial compressive residual stresses that are known to delay crack initiation and propagation. In the same way, work hardening is also introduced at the surface of the part during shot peening and can have a significant influence on fatigue crack initiation. Taking this parameter into account in the fatigue design of parts, in addition to the residual stresses, is a real challenge to be the most predictive. One possibility for this is to be able to predict it during the modeling of the shot peening process. In the present work, various peening conditions are considered in order to be able to propose a model able to account for the influence of coverage and Almen intensity on residual stresses and work hardening. The studied material is Inconel 718, commonly used for aeronautical parts. The X-ray diffraction method is used to obtain the in-depth residual stress and work hardening profiles. A three-dimensional numerical model is proposed to predict these quantities. Efforts are made to consider all recent advances in three-dimensional simulation of the process, in terms of coverage assessment, shot and treated part modeling. The numerical results are compared to the experimentally measured residual stresses and work hardening.