Both nucleation and propagation of fatigue cracks in fcc metals are investigated, using 3D discre... more Both nucleation and propagation of fatigue cracks in fcc metals are investigated, using 3D discrete dislocation dynamics (DDD) simulations. Firstly, DDD simulations explain the mechanisms leading to the formation of persistent slip bands in surface grains loaded in fatigue. Extrusions are evidenced where the bands intercept the free surface. The extrusion growth rate is estimated for different material parameters and loading conditions. Energy and stress calculations performed inside the simulated grain lead to a possible scenario for the crack initiation at the interface between the band and the matrix, as reported in the literature. Secondly, a crack is inserted at the persistent slip band interface and the crack tip slip displacement evolutions are evaluated. It is shown that the crack growth rate is strongly related to the grain size and to the distance to the grain boundary; the smaller the grain, the faster the crack growth. Finally, the crack propagation to the next grain is ...
A 3D dislocation dynamics study to ascertain the probable path of stage-I fatigue crack propagati... more A 3D dislocation dynamics study to ascertain the probable path of stage-I fatigue crack propagation across the persistent slip band (PSB) in austenitic stainless steel is presented. Cyclic plasticity and the resulting crack tip slip displacement (CTSD) are evaluated for cracks of varying length introduced at PSB-center and at two PSB-matrix interfaces. CTSD attains high value at either of the two interfaces irrespective of the proximity of crack front to the grain boundary. Further, a difference in microcrack propagation rate is also observed among the two interfaces. The present results assert microcrack propagation preferrentially along one of the two PSB-matrix interfaces rather than at the PSB-center. A preexisting PSB dislocation structure localises the cyclic slip for crack lengths up to approximately half of the grain depth for an applied strain range of 2 × 10 −4 .
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. 3D Discrete Dislocation Dynamics Investigations of Fatigue Crack Initiation and Propagation C Déprés, C. Robertson, M. Fivel
DOI : 10.12762/2015.AL09-01 Both nucleation and propagation of fatigue cracks in fcc metals are i... more DOI : 10.12762/2015.AL09-01 Both nucleation and propagation of fatigue cracks in fcc metals are investigated, using 3D discrete dislocation dynamics (DDD) simulations. Firstly, DDD simulations explain the mechanisms leading to the formation of persistent slip bands in surface grains loaded in fatigue. Extrusions are evidenced where the bands intercept the free surface. The extrusion growth rate is estimated for different material parameters and loading conditions. Energy and stress calculations performed inside the simulated grain lead to a possible scenario for the crack initiation at the interface between the band and the matrix, as reported in the literature. Secondly, a crack is inserted at the persistent slip band interface and the crack tip slip displacement evolutions are evaluated. It is shown that the crack growth rate is strongly related to the grain size and to the distance to the grain boundary; the smaller the grain, the faster the crack growth. Finally, the crack propa...
Micro-crack initiation in thermal fatigue — an analysis based on experimental and DD simulation results
Transactions of the Indian Institute of Metals, 2010
ABSTRACT The combined effect of cyclic thermal shocks and static tensile loading is investigated ... more ABSTRACT The combined effect of cyclic thermal shocks and static tensile loading is investigated in 304L stainless steel specimens. Damage obtained at the end of the tests is analyzed by means of experimental observations and dislocation dynamics (DD) simulations. The calculations, carried out using representative loading conditions (δZZ = δθθ), show that the dominant slip systems do not necessarily have the largest activation ratio. Rather, the dominant slip directions b has specific orientations with respect to the free surface, maximizing the “surface connected volume” (SCV) of the active slip systems. During the tests, a marked effect of the superimposed static tensile loading (or mean stress) is also noted. This effect is also analyzed with the help of DD simulations, performed with a positive mean stress. These calculations show that slip irreversibility in the individual persistent slip bands systematically augments with increasing mean stress.
A Three Dimensional Discrete Dislocation Dynamics Analysis of Cyclic Straining in 316L Stainless Steel
Materials Science Forum, 2005
The early stages of the formation of dislocation microstructures in low strain fatigue are analys... more The early stages of the formation of dislocation microstructures in low strain fatigue are analysed,using three-dimensional discrete dislocation dynamics modelling (DDD). A detailed analysis of the simulated microstructures provide a detailed scheme for the persistent slip band formation, emphasizing the crucial role of cross-slip for both the initial strain spreading inside of the grain and for the subsequent strain localization in the form of slip bands. A new ad-hoc posttreatment tool evaluates the surface roughness as the cycles proceed. Slip markings and their evolutions are analysed, in relation to the dislocation microstructure. This dislocation-based study emphasizes the separate contribution of plastic slip in damage nucleation. A simple 1D dislocation based model for work-hardening in crystal plasticity is proposed. In this model, the forest dislocations are responsible for friction stress (isotropic work-hardening), while dislocation pile-ups and dislocation trapped in Pe...
The Effect of Mean Stress and Thermo-Mechanical Induced Stress on Micro-Crack Initiation: An Analysis Based on Experiments and DD Simulation Results
Materials Science Forum, 2007
The combined effect of cyclic thermal shocks and static tensile loading is investigated, in a 304... more The combined effect of cyclic thermal shocks and static tensile loading is investigated, in a 304L stainless steel. During these experiments, the stress state in the cylindrical specimen walls is nearly equi-biaxial (σZZ ≈ σθθ). In dislocation dynamics (DD) simulations carried out with σZZ = σθθ, the predominant slip directions b are nearly aligned with the free surface normal vector n, regardless of their associated activation ratio (A.R.). This effect is related to the "surface connected volume" (SCV) of the predominant slip systems. Hence, surface grains with n = <110> possess "large SCV slip systems" and therefore, constitute preferential sites for micro-crack initiation in thermal fatigue. During the tests, a marked effect of the superimposed static tensile loading (or mean stress) is also noted. This effect is explained with the help of DD simulations performed with a positive mean stress: slip irreversibility in the individual persistent slip bands s...
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Public Domain
Plasticity of cristalline materials: from dislocations to continuum
This book details recent advances in all aspects related to scale transition in crystal plasticit... more This book details recent advances in all aspects related to scale transition in crystal plasticity and damage, with a particular focus on the challenges associated with the characterization and modeling of this class of complex interactions. The following topics are included: - Innovative characterization techniques (multi-scale characterization, SEMTEM coupling, TEM-micro-diffraction coupling, in-situ mechanical tests, localization, image correlation, displacement field measurements, tomography, etc.). - Computational crystal plasticity and damage (dislocation dynamics and ab initio calculations, microstructure evolution of polycrystals, comparison between FE, fast Fourier transform and self-consistent approaches, intragranular slip, heterogeneities, discrete approaches, etc.). The book gathers together selected papers from the invited lectures presented at the 3rd and 4th US-France Symposia organized by the editors under the auspices of the International Center for Applied Computational Mechanics (ICACM)
Both nucleation and propagation of fatigue cracks in fcc metals are investigated, using 3D discre... more Both nucleation and propagation of fatigue cracks in fcc metals are investigated, using 3D discrete dislocation dynamics (DDD) simulations. Firstly, DDD simulations explain the mechanisms leading to the formation of persistent slip bands in surface grains loaded in fatigue. Extrusions are evidenced where the bands intercept the free surface. The extrusion growth rate is estimated for different material parameters and loading conditions. Energy and stress calculations performed inside the simulated grain lead to a possible scenario for the crack initiation at the interface between the band and the matrix, as reported in the literature. Secondly, a crack is inserted at the persistent slip band interface and the crack tip slip displacement evolutions are evaluated. It is shown that the crack growth rate is strongly related to the grain size and to the distance to the grain boundary; the smaller the grain, the faster the crack growth. Finally, the crack propagation to the next grain is ...
A 3D dislocation dynamics study to ascertain the probable path of stage-I fatigue crack propagati... more A 3D dislocation dynamics study to ascertain the probable path of stage-I fatigue crack propagation across the persistent slip band (PSB) in austenitic stainless steel is presented. Cyclic plasticity and the resulting crack tip slip displacement (CTSD) are evaluated for cracks of varying length introduced at PSB-center and at two PSB-matrix interfaces. CTSD attains high value at either of the two interfaces irrespective of the proximity of crack front to the grain boundary. Further, a difference in microcrack propagation rate is also observed among the two interfaces. The present results assert microcrack propagation preferrentially along one of the two PSB-matrix interfaces rather than at the PSB-center. A preexisting PSB dislocation structure localises the cyclic slip for crack lengths up to approximately half of the grain depth for an applied strain range of 2 × 10 −4 .
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. 3D Discrete Dislocation Dynamics Investigations of Fatigue Crack Initiation and Propagation C Déprés, C. Robertson, M. Fivel
DOI : 10.12762/2015.AL09-01 Both nucleation and propagation of fatigue cracks in fcc metals are i... more DOI : 10.12762/2015.AL09-01 Both nucleation and propagation of fatigue cracks in fcc metals are investigated, using 3D discrete dislocation dynamics (DDD) simulations. Firstly, DDD simulations explain the mechanisms leading to the formation of persistent slip bands in surface grains loaded in fatigue. Extrusions are evidenced where the bands intercept the free surface. The extrusion growth rate is estimated for different material parameters and loading conditions. Energy and stress calculations performed inside the simulated grain lead to a possible scenario for the crack initiation at the interface between the band and the matrix, as reported in the literature. Secondly, a crack is inserted at the persistent slip band interface and the crack tip slip displacement evolutions are evaluated. It is shown that the crack growth rate is strongly related to the grain size and to the distance to the grain boundary; the smaller the grain, the faster the crack growth. Finally, the crack propa...
Micro-crack initiation in thermal fatigue — an analysis based on experimental and DD simulation results
Transactions of the Indian Institute of Metals, 2010
ABSTRACT The combined effect of cyclic thermal shocks and static tensile loading is investigated ... more ABSTRACT The combined effect of cyclic thermal shocks and static tensile loading is investigated in 304L stainless steel specimens. Damage obtained at the end of the tests is analyzed by means of experimental observations and dislocation dynamics (DD) simulations. The calculations, carried out using representative loading conditions (δZZ = δθθ), show that the dominant slip systems do not necessarily have the largest activation ratio. Rather, the dominant slip directions b has specific orientations with respect to the free surface, maximizing the “surface connected volume” (SCV) of the active slip systems. During the tests, a marked effect of the superimposed static tensile loading (or mean stress) is also noted. This effect is also analyzed with the help of DD simulations, performed with a positive mean stress. These calculations show that slip irreversibility in the individual persistent slip bands systematically augments with increasing mean stress.
A Three Dimensional Discrete Dislocation Dynamics Analysis of Cyclic Straining in 316L Stainless Steel
Materials Science Forum, 2005
The early stages of the formation of dislocation microstructures in low strain fatigue are analys... more The early stages of the formation of dislocation microstructures in low strain fatigue are analysed,using three-dimensional discrete dislocation dynamics modelling (DDD). A detailed analysis of the simulated microstructures provide a detailed scheme for the persistent slip band formation, emphasizing the crucial role of cross-slip for both the initial strain spreading inside of the grain and for the subsequent strain localization in the form of slip bands. A new ad-hoc posttreatment tool evaluates the surface roughness as the cycles proceed. Slip markings and their evolutions are analysed, in relation to the dislocation microstructure. This dislocation-based study emphasizes the separate contribution of plastic slip in damage nucleation. A simple 1D dislocation based model for work-hardening in crystal plasticity is proposed. In this model, the forest dislocations are responsible for friction stress (isotropic work-hardening), while dislocation pile-ups and dislocation trapped in Pe...
The Effect of Mean Stress and Thermo-Mechanical Induced Stress on Micro-Crack Initiation: An Analysis Based on Experiments and DD Simulation Results
Materials Science Forum, 2007
The combined effect of cyclic thermal shocks and static tensile loading is investigated, in a 304... more The combined effect of cyclic thermal shocks and static tensile loading is investigated, in a 304L stainless steel. During these experiments, the stress state in the cylindrical specimen walls is nearly equi-biaxial (σZZ ≈ σθθ). In dislocation dynamics (DD) simulations carried out with σZZ = σθθ, the predominant slip directions b are nearly aligned with the free surface normal vector n, regardless of their associated activation ratio (A.R.). This effect is related to the "surface connected volume" (SCV) of the predominant slip systems. Hence, surface grains with n = <110> possess "large SCV slip systems" and therefore, constitute preferential sites for micro-crack initiation in thermal fatigue. During the tests, a marked effect of the superimposed static tensile loading (or mean stress) is also noted. This effect is explained with the help of DD simulations performed with a positive mean stress: slip irreversibility in the individual persistent slip bands s...
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Public Domain
Plasticity of cristalline materials: from dislocations to continuum
This book details recent advances in all aspects related to scale transition in crystal plasticit... more This book details recent advances in all aspects related to scale transition in crystal plasticity and damage, with a particular focus on the challenges associated with the characterization and modeling of this class of complex interactions. The following topics are included: - Innovative characterization techniques (multi-scale characterization, SEMTEM coupling, TEM-micro-diffraction coupling, in-situ mechanical tests, localization, image correlation, displacement field measurements, tomography, etc.). - Computational crystal plasticity and damage (dislocation dynamics and ab initio calculations, microstructure evolution of polycrystals, comparison between FE, fast Fourier transform and self-consistent approaches, intragranular slip, heterogeneities, discrete approaches, etc.). The book gathers together selected papers from the invited lectures presented at the 3rd and 4th US-France Symposia organized by the editors under the auspices of the International Center for Applied Computational Mechanics (ICACM)
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