The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform
S Lozanoperez - One of the best experts on this subject based on the ideXlab platform.
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observation and quantification of the diffusion induced grain boundary migration ahead of scc Crack Tips
Corrosion Science, 2019Co-Authors: Zhao Shen, Phani Karamched, Koji Arioka, S LozanoperezAbstract:Abstract Crack Tips prepared from Ni-based alloys after stress corrosion Cracking testing in simulated pressurized water reactor primary water have been studied by high-resolution characterization. Diffusion-induced grain boundary migration (DIGM) was observed in all the Cracks and its potential role on the Crack propagation is discussed in detail. The extent of DIGM observed changed with grain boundary type and alloy composition, which could lead to different extent of retardation effects on the Crack propagation. A method is proposed to quantify the role of DIGM on Crack propagation based on the results obtained in this work.
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atom probe tomography of stress corrosion Crack Tips in sus316 stainless steels
Corrosion Science, 2015Co-Authors: Martina Meisnar, Michael P Moody, S LozanoperezAbstract:Abstract Novel atom probe tomography (APT) data of an intergranular stress corrosion Crack tip has been acquired. Using APT for stress corrosion Cracking research, very small, localized features and their distribution around the Crack tip can be studied in 3D. This work details the development of a technique for the preparation of atom probe needles. Initial characterization via analytical transmission electron microscopy provides with a complementary analysis and accurately locates features that can be correlated with the reconstructed APT data. Ni enrichment and intergranular oxidation ahead of the Crack tip have been studied with APT in 3D and with near-atomic resolution.
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a guide on fib preparation of samples containing stress corrosion Crack Tips for tem and atom probe analysis
Micron, 2008Co-Authors: S LozanoperezAbstract:The preparation of samples containing stress corrosion Crack Tips for 3D atom-probe tomography and transmission electron microscopy is of ultimate importance for understanding the mechanisms controlling Crack propagation. In this paper, it will be shown that a focused ion beam machine equipped with an in situ micromanipulator is an ideal tool to systematically prepare such demanding samples. The methodology is described and discussed in detail, and several results are presented to demonstrate the potential of the technique.
Amand George - One of the best experts on this subject based on the ideXlab platform.
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dislocation nucleation and multiplication at Crack Tips in silicon
Physica Status Solidi (a), 1999Co-Authors: C Scandian, Gerard Michot, H Azzouzi, N Maloufi, Amand GeorgeAbstract:The brittle–ductile transition (BDT) has been studied in silicon single crystals of different orientations and purities. It is shown that the BDT temperature at a given loading rate can be significantly varied depending on structural parameters, especially the density of cleavage defects (steps, …). The critical BDT temperature is raised when the cleavage defect density is lowered. This is explained by observations at Crack Tips which prove that dislocation nucleation is highly inhomogeneous. A first preliminary attempt to identify nucleation sites by AFM is reported. In crystals containing highly perfect cleavage Cracks, dislocation formation prior to fracture in mode I loading could be suppressed. In such cases, a very small number of dislocations created on purpose from remote sources, sufficed to trigger the formation of a plastic zone as soon as they touched the Crack front. Experimental results are compared to theoretical models and recent numerical computations. La transition fragile–ductile a ete etudiee dans des monocristaux de silicium de differentes orientations et puretes. A une vitesse de chargement donnee, la temperature de transition depend fortement de parametres structuraux, en particulier de la densite de defauts que presente la surface de clivage. La temperature de transition fragile–ductile augmente quand la densite de ces defauts diminue. Ceci est explique par des observations au voisinage du front de fissure qui montrent que la nucleation des dislocations est tres inhomogene. Un premier essai de caracterisation par microscopie a force atomique en vue d'identifier les sites de nucleation est rapporte. Dans des cristaux contenant des fissures de clivage de grande qualite, la formation des dislocations avant rupture sous un chargement en mode I peut etre supprimee. Dans de tels cas, un tout petit nombre de dislocations creees a dessein a partir de sources distantes du front de fissure suffit a declencher la formation de la zone plastique au moment ou elles touchent le front de fissure. Ces resultats experimentaux sont compares aux modeles theoriques et a des simulations numeriques recentes.
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dislocation loops at Crack Tips control and analysis of sources in silicon
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1994Co-Authors: Gerard Michot, Angela Loyola M De Oliveira, Amand GeorgeAbstract:Abstract New observations of the nature and configuration of the very first dislocations emitted at Crack Tips in single-crystal silicon double-centilever-beam samples loaded in mode I are reported. An estimate of the shear stress acting in dislocation arrays was derived from the etch pit pattern on the Crack surface. The activated Burgers vectors could be assessed by X-ray topography. The emission of dislocations with Burgers vectors parallel to the Crack plane from the beginning of plastic relaxation is confirmed. Such non-blunting dislocations are shown to be important for Crack opening.
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dislocation loops at Crack Tips nucleation and growth an experimental study in silicon
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1993Co-Authors: Gerard Michot, Amand GeorgeAbstract:Abstract The nucleation of dislocation loops at Crack Tips and the development of the plastic zone were studied in single-crystal silicon samples preCracked at room temperature and loaded at T ⩾ 900 K under well-controlled conditions (mode I loading, constant loading rate). Several crystallographic orientations with different cleavage planes and Crack front orientations were investigated. In situ observations by synchrotron X-ray topography were supplemented by chemical etching after fracture. Special attention was paid to the early stages of plastic zone formation. Dislocation nucleation appeared to be very heterogeneous along the Crack front and may be favoured at free surfaces and cleavage edges. Activated slip systems and dislocation arrangements are discussed. It is shown that considerations based on the Crack tip stress field to not suffice to account for the observed slip systems. The ledge Crack mechanism of Zhou and Thomson has probably been observed but cannot be proved to be the main emission mechanism.
Gerard Michot - One of the best experts on this subject based on the ideXlab platform.
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dislocation nucleation and multiplication at Crack Tips in silicon
Physica Status Solidi (a), 1999Co-Authors: C Scandian, Gerard Michot, H Azzouzi, N Maloufi, Amand GeorgeAbstract:The brittle–ductile transition (BDT) has been studied in silicon single crystals of different orientations and purities. It is shown that the BDT temperature at a given loading rate can be significantly varied depending on structural parameters, especially the density of cleavage defects (steps, …). The critical BDT temperature is raised when the cleavage defect density is lowered. This is explained by observations at Crack Tips which prove that dislocation nucleation is highly inhomogeneous. A first preliminary attempt to identify nucleation sites by AFM is reported. In crystals containing highly perfect cleavage Cracks, dislocation formation prior to fracture in mode I loading could be suppressed. In such cases, a very small number of dislocations created on purpose from remote sources, sufficed to trigger the formation of a plastic zone as soon as they touched the Crack front. Experimental results are compared to theoretical models and recent numerical computations. La transition fragile–ductile a ete etudiee dans des monocristaux de silicium de differentes orientations et puretes. A une vitesse de chargement donnee, la temperature de transition depend fortement de parametres structuraux, en particulier de la densite de defauts que presente la surface de clivage. La temperature de transition fragile–ductile augmente quand la densite de ces defauts diminue. Ceci est explique par des observations au voisinage du front de fissure qui montrent que la nucleation des dislocations est tres inhomogene. Un premier essai de caracterisation par microscopie a force atomique en vue d'identifier les sites de nucleation est rapporte. Dans des cristaux contenant des fissures de clivage de grande qualite, la formation des dislocations avant rupture sous un chargement en mode I peut etre supprimee. Dans de tels cas, un tout petit nombre de dislocations creees a dessein a partir de sources distantes du front de fissure suffit a declencher la formation de la zone plastique au moment ou elles touchent le front de fissure. Ces resultats experimentaux sont compares aux modeles theoriques et a des simulations numeriques recentes.
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dislocation loops at Crack Tips control and analysis of sources in silicon
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1994Co-Authors: Gerard Michot, Angela Loyola M De Oliveira, Amand GeorgeAbstract:Abstract New observations of the nature and configuration of the very first dislocations emitted at Crack Tips in single-crystal silicon double-centilever-beam samples loaded in mode I are reported. An estimate of the shear stress acting in dislocation arrays was derived from the etch pit pattern on the Crack surface. The activated Burgers vectors could be assessed by X-ray topography. The emission of dislocations with Burgers vectors parallel to the Crack plane from the beginning of plastic relaxation is confirmed. Such non-blunting dislocations are shown to be important for Crack opening.
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dislocation loops at Crack Tips nucleation and growth an experimental study in silicon
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1993Co-Authors: Gerard Michot, Amand GeorgeAbstract:Abstract The nucleation of dislocation loops at Crack Tips and the development of the plastic zone were studied in single-crystal silicon samples preCracked at room temperature and loaded at T ⩾ 900 K under well-controlled conditions (mode I loading, constant loading rate). Several crystallographic orientations with different cleavage planes and Crack front orientations were investigated. In situ observations by synchrotron X-ray topography were supplemented by chemical etching after fracture. Special attention was paid to the early stages of plastic zone formation. Dislocation nucleation appeared to be very heterogeneous along the Crack front and may be favoured at free surfaces and cleavage edges. Activated slip systems and dislocation arrangements are discussed. It is shown that considerations based on the Crack tip stress field to not suffice to account for the observed slip systems. The ledge Crack mechanism of Zhou and Thomson has probably been observed but cannot be proved to be the main emission mechanism.
Newjin Ho - One of the best experts on this subject based on the ideXlab platform.
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the observation of dislocation reversal in front of Crack Tips of polycrystalline copper after reducing maximum load
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003Co-Authors: H L Huang, Newjin HoAbstract:The loading at a Crack tip varies during fatigue Crack propagation. As a result, overloading causes retardation of Crack propagation, and underloading causes the acceleration of Crack propagation. In addition, reducing the load range by changing either the minimum load or maximum load can cause a reduction or retardation of Crack propagation to occur. Examining a fatigue Cracked specimen made of polycrystalline copper with back scattered electron images (BEI) in a scanning electron microscope (SEM) revealed that (1) the dislocation structures close to the Crack Tips gradually evolved from a cell structure into a new loop patch structure during the Crack retardation period which follows after reducing the maximum load; (2) restoring the Crack propagation rate is a result of re-establishing the cell structure from new loop patches or PSBs; and (3) the evolution of the dislocation structure at the Crack tip due to the maximum loading reduction is affected by residual active slip systems.
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the observation and analysis of the dislocation morphology of fatigue Crack Tips at steady state propagation rates subject to a single peak load
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001Co-Authors: H L Huang, Newjin HoAbstract:Abstract During fatigue Crack propagation there is large interaction effects of the fatigue cycle for different loading amplitudes. Two examples are the retarding effect of overload and the accelerating effect of underload on the Crack propagation. In the former, the result is explained in terms of residual stress effects associated with the overload, and in the latter, the underload partially annihilates the residual stress built up by the positive load. However, at the microstructure level of material under fatigue, the Crack propagation is caused by dislocation action. Assuming this, this paper reports studies of the Crack propagation interaction effect by using microstructural examination of Crack Tips. Observations were made with the Back Electron Images (BEI) of the Scanning Electron Microscope (SEM). The results are: (1) the microstructure of cells close to the Crack Tips formed into vein or loop patch structures upon the overload, so that the Crack propagation was reduced. (2) The region of cells s close to the Crack Tips become enlarged on the underload and the scale of the other microstructure (such as PSB, vein and loop patch) were also enhanced too, so that the Crack propagation was accelerated.
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the study of dislocation structures at fatigue Crack Tips in polycrystalline copper under various Crack propagation rates at stage ii Crack propagation
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2000Co-Authors: H L Huang, Newjin HoAbstract:Abstract The purpose of this study is to investigate the dislocation structures in front of fatigue Crack Tips embedded at various propagation rates in copper. Back electron images with the scanning electron microscope were used for the observation. The results are, at a rate of 10−6 mm per cycle, that the dislocation morphologies are distinguishable and can completely to evolve into various dislocation structures. At a rate of 10−7 mm per cycle, the dislocation morphologies are the same as those of the 10−6 mm per cycle rate, but the ranges of the dislocation structures are too small to be distinguished. Regardless of the plastic strain amplitudes, the average diameter of the dislocation cell in front of the Crack tip is about 0.7 μm. Therefore, once the low-energy dislocation cell was formed, the Crack initiates and/or propagates. At a 10−8 mm per cycle rate, the Crack tip is propagated toward the region of true strain localization. The dislocation structure threshold for propagating the Crack tip is cell with an average diameter of less than 0.7 μm.
Katsuyuki Kida - One of the best experts on this subject based on the ideXlab platform.
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changes in magnetic field intensities around fatigue Crack Tips of medium carbon low alloy steel s45c jis
International Journal of Fatigue, 2013Co-Authors: Katsuyuki Kida, Edson Costa Santos, Takashi Honda, Megumi Uryu, Justyna Rozwadowska, Kenichi SaruwatariAbstract:Abstract Damage of machine components occur when Cracks form and continue to grow to a size large enough to cause fracture. In order to understand the Crack propagation phenomena, non-destructive evaluation methods that can be correlated to measurements around the fatigue Crack Tips are necessary. In the present work, we developed a scanning Hall probe microscope (SHPM) equipped with a three-dimensional sensor and observed magnetic fields around fatigue Cracks at room temperature in air while they were growing. In order to study the relation between plastic deformations and magnetic flux densities, both as-received non-heat-treated and heat-treated (quenched and tempered) specimens were used. Medium carbon low alloy steel specimens (S45C, JIS) were used in the experiments. The area around the Crack tip was magnetized and the changes in the area were observed. The changes in magnetic fields in soft and hard specimens with the same intensity factors were compared. A strong correlation between the changes in the magnet fields and plastic deformation areas was found.
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changes in magnetic flux density around fatigue Crack Tips of carbon tool steels
Proceedings of SPIE the International Society for Optical Engineering, 2009Co-Authors: Takashi Honda, Katsuyuki Kida, Edson Costa Santos, Hirotaka TanabeAbstract:Fatigue failure of steel occurs when small Cracks form in a component and then continue to grow to a size large enough to cause failure. In order to understand the strength of steel components it is important to find the Cracks which eventually grow to cause failures. However, at present, it is not easy to distinguish, in the early stages of growth, the Cracks which will grow fast and cause failure. We hypothesized that it may be possible to distinguish them by comparing changes in the magnetic flux density around the Tips of those Cracks that grew large enough to cause failure. In order to measure these changes in magnetic flux density, we developed a scanning Hall probe microscope and observed the fatigue Cracks growing from artificial slits in carbon tool steels (JIS SKS93). We also compared the changes in magnetic flux density around Crack Tips which grew under different loads and found that there is a strong correlation between the magnetic flux density, Crack growth and stress intensity factors. In order to understand this relation, we measured the changes in the magnetic flux density and residual tensile stress by using an X-ray system, and found that the magnetic flux density changes not only in the plastic deformation area but also in the area of elastic stress field with increased stress.
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three dimensional observations of magnetic flux density around fatigue Crack Tips of bearing steels
Proceedings of SPIE the International Society for Optical Engineering, 2009Co-Authors: Katsuyuki Kida, Edson Costa Santos, Takashi Honda, Hirotaka TanabeAbstract:Fatigue failure of steel occurs when small Cracks form in a component and then continue to grow to a size large enough to cause failure. In order to understand the strength of steel components it is important to find these Cracks. However, at present, it is not easy to distinguish the Cracks that will grow fast and cause failure. We developed a three-dimensional scanning Hall probe microscope (3D-SHPM) and observed fatigue Cracks at room temperature while they were growing. Four-point-bending fatigue tests were carried out using pre-Cracked specimens (JIS-SUJ2, bearing steel). We observed the two-dimensional magnetic flux density distributions around the Crack Tips and found that there is a strong correlation between the changes in the magnetic flux densities and the Crack growth. In order to understand this, we looked into all the three components of the magnetic flux densities, and found that they shape an arched bridge around a Crack. We also found that the magnetic flux density moves in front of the Crack tip along the Crack growth direction.
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changes in magnetic flux density around fatigue Crack Tips
Fatigue & Fracture of Engineering Materials & Structures, 2009Co-Authors: Katsuyuki Kida, Hirotaka Tanabe, H OkanoAbstract:Fatigue failure of steel occurs when small Cracks form in a component and then continue to grow to a size large enough to cause failure. In order to understand the strength of steel components, it is important to find the Cracks, which eventually grow to cause failures. However, at present, it is not easy to distinguish, in the early stages of growth, the Cracks that will grow fast and cause failure. We hypothesized that it may be possible to distinguish them by comparing changes in the magnetic flux density around the Tips of those Cracks that grew to failure. In order to measure these changes in magnetic flux density, we developed a scanning Hall probe microscope and observed the fatigue Cracks growing from artificial slits in soft bearing steels. Note that we did not magnetize the specimens artificially but succeeded to measure the changes in magnetic flux density during the fatigue tests. We also compared the changes in magnetic flux density around Crack Tips, which grew under different loads, and found that there is a strong correlation between the magnetic flux density, Crack growth and stress intensity factors. In order to understand this, we looked into the relation between stress field, residual strain and magnetic flux density, and concluded that the changes in magnetic flux density are caused not only by the residual strain occurring around the Crack Tips but also by the increase in the elastic stress.