3D Digital Volume Correlation of Synchrotron Radiation Laminography images of ductile crack initiation: An initial feasibility study

International audienceA feasibility study of measuring 3D displacement fields in the bulk during ductile crack initiation via combined Synchrotron Radiation Computed Laminography (SRCL) and Digital Volume Correlation (DVC) is performed. In contrast to Tomography, SRCL is a technique that is particularly adapted to obtain in 3D reconstructed volumes of objects that are laterally extended (i.e., in 2 directions) and thin in the third direction, i.e. sheet-like objects. In-situ laminography data of an initiating crack ahead of a machined notch are used with a voxel size of 0.7 μm. The natural contrast of the observed 2XXX Al-alloy caused by intermetallic particles and initial porosity is used to measure displacement fields via a global DVC technique assuming a continuous displacement field. An initial performance study is carried out on data of the same undeformed material but after a substantial shift of the laminography rotation axis with respect to the imaged specimen. Volume correlations between different loading steps provide displacement fields that are qualitatively consistent with the remote loading conditions. Computed strain fields display a strain concentration close to the notch tip

Effect of stress on passivation kinetics and passivation modelling of 304L stainless steel in acidic medium

Stress Corrosion Cracking (SCC) is a typical failure of engineering materials applied in corrosive environments. In light water reactors for example, this results in loss of electrical capacity and related costs of repair and replacement. Film Rupture-dissolution Model explains interganular SCC as a phenomenon resulting from repetitive activation/passivation cycles (Fig.1). Activation takes place mechanically by slip-induced film breakdown which causes excessive material dissolution until it repassivates again. In this study, potentiodynamic cycling experiments serve effectively to perform in-Lab electrochemical simulation of this process. Conventional electrochemical techniques and Inductively Coupled Plasma – Optical Emission Spectroscopy are used to in-situ measure the corrosion transients and dissolution rates. A model was developed proving that stainless steel repassivates according to the High Field Ion Conduction Model in acidic solutions. Having this, quantification of the instantaneous passive film thickness and corrosion susceptibility of the passive film constructed over the surface has been successfully achieved (Fig.2). Quantified results showed that for stressed materials, the time to repassivation is longer, and the constructed passive film, though thicker, is more susceptible to corrosion than passive films developed over non-stressed materials

Crystallography of Stress corrosion cracking of austenitic stainless steel by scanning electron microscope and electron backscatter diffraction

In this study, Stress Corrosion Cracking (SCC) produced for 304L austenitic stainless steel in different concentrations of chloride containing sulfuric acid solutions was analyzed using both Scanning Electron Microscope (SEM), and Electron Backscatter Diffraction (EBSD). X-Ray Diffraction (XRD) was used to analyze the residual-applied stresses before and after cracking. Crack observation using SEM revealed clear traces of successive slipping planes and consequent dissolutions on the facets of the obtained cracks. Moreover, ruptured grains were analyzed for their orientation using EBSD technique. Analysis disclosed two preferential rupture planes; {110}, {111} with percentage of 48% and 37% respectively. After cracking, XRD stress profile analysis showed a gradual stress relaxation through sample’s depth from the applied stress in the bulk of the material to the inherent residual stress attributed to fabrication processes in the zone where the cracks are present

Effect of stress on passivation kinetics and passivation modelling of 304L stainless steel in acidic medium

Stress Corrosion Cracking (SCC) is a typical failure of engineering materials applied in corrosive environments. In light water reactors for example, this results in loss of electrical capacity and related costs of repair and replacement. Film Rupture-dissolution Model explains interganular SCC as a phenomenon resulting from repetitive activation/passivation cycles (Fig.1). Activation takes place mechanically by slip-induced film breakdown which causes excessive material dissolution until it repassivates again. In this study, potentiodynamic cycling experiments serve effectively to perform in-Lab electrochemical simulation of this process. Conventional electrochemical techniques and Inductively Coupled Plasma – Optical Emission Spectroscopy are used to in-situ measure the corrosion transients and dissolution rates. A model was developed proving that stainless steel repassivates according to the High Field Ion Conduction Model in acidic solutions. Having this, quantification of the instantaneous passive film thickness and corrosion susceptibility of the passive film constructed over the surface has been successfully achieved (Fig.2). Quantified results showed that for stressed materials, the time to repassivation is longer, and the constructed passive film, though thicker, is more susceptible to corrosion than passive films developed over non-stressed materials

Crystallography of Stress corrosion cracking of austenitic stainless steel by scanning electron microscope and electron backscatter diffraction

In this study, Stress Corrosion Cracking (SCC) produced for 304L austenitic stainless steel in different concentrations of chloride containing sulfuric acid solutions was analyzed using both Scanning Electron Microscope (SEM), and Electron Backscatter Diffraction (EBSD). X-Ray Diffraction (XRD) was used to analyze the residual-applied stresses before and after cracking. Crack observation using SEM revealed clear traces of successive slipping planes and consequent dissolutions on the facets of the obtained cracks. Moreover, ruptured grains were analyzed for their orientation using EBSD technique. Analysis disclosed two preferential rupture planes; {110}, {111} with percentage of 48% and 37% respectively. After cracking, XRD stress profile analysis showed a gradual stress relaxation through sample’s depth from the applied stress in the bulk of the material to the inherent residual stress attributed to fabrication processes in the zone where the cracks are present

Burnout among surgeons before and during the SARS-CoV-2 pandemic: an international survey

Background: SARS-CoV-2 pandemic has had many significant impacts within the surgical realm, and surgeons have been obligated to reconsider almost every aspect of daily clinical practice. Methods: This is a cross-sectional study reported in compliance with the CHERRIES guidelines and conducted through an online platform from June 14th to July 15th, 2020. The primary outcome was the burden of burnout during the pandemic indicated by the validated Shirom-Melamed Burnout Measure. Results: Nine hundred fifty-four surgeons completed the survey. The median length of practice was 10 years; 78.2% included were male with a median age of 37 years old, 39.5% were consultants, 68.9% were general surgeons, and 55.7% were affiliated with an academic institution. Overall, there was a significant increase in the mean burnout score during the pandemic; longer years of practice and older age were significantly associated with less burnout. There were significant reductions in the median number of outpatient visits, operated cases, on-call hours, emergency visits, and research work, so, 48.2% of respondents felt that the training resources were insufficient. The majority (81.3%) of respondents reported that their hospitals were included in the management of COVID-19, 66.5% felt their roles had been minimized; 41% were asked to assist in non-surgical medical practices, and 37.6% of respondents were included in COVID-19 management. Conclusions: There was a significant burnout among trainees. Almost all aspects of clinical and research activities were affected with a significant reduction in the volume of research, outpatient clinic visits, surgical procedures, on-call hours, and emergency cases hindering the training. Trial registration: The study was registered on clicaltrials.gov "NCT04433286" on 16/06/2020

Degradation of 304L stainless steel in acidic solutions : Influence of stress on passivation kinetics, and cracking crystallography and mechanics.

Une approche expérimentale mettant en œuvre des techniques électrochimiques et mécaniques a été utilisée pour étudier la corrosion sous contrainte (CSC) de l’acier inoxydable 304L dans des électrolytes acides (0,5-5 M H2SO4) avec et sans chlorure. La CSC a été réalisée dans le but d’étudier les aspects cristallographique et cinétique de la rupture. La microscopie électronique à balayage a dévoilé, d’une part, des traces successives au niveau des plans de glissement sur les facettes de la fissure, et d’autre part une vitesse non-linéaire de la fissuration. Une méthode a été proposée pour accéder à la cristallographie de fissuration en utilisant la diffraction d'électrons rétrodiffusés (EBSD). Il a été démontré que les ruptures préférentielles s’effectuent au niveau des plans {111} pour ¾ du temps et des plans {110} le reste du temps. Ces résultats soutiennent les modèles récents de la CSC, tels que la plasticité localisée rehaussée par la corrosion. Les profils d’évolution de la contrainte appliquée/résiduelles ont été déterminés par diffraction des rayons X avant et après CSC. Ces analyses serviront à développer un modèle de rupture micro-mécanique. Lors des essais potentiodynamiques optimisés de corrosion, les taux de dissolution élémentaires et le courant total ont été mesurés en combinant une cellule d'écoulement électrochimique et l'analyse des produits de corrosion par spectroscopie d'émission atomique à plasma à couplage inductif. Ces résultats ont été utilisés, pour séparer la partie de courant consacré à la formation de la couche passive du courant total. Le modèle de conduction ionique sous tension élevée a été mis à jour pour calculer le taux de passivation et l'épaisseur de la couche passive. Les contraintes dans le matériau expliquent une différence mesurable de la cinétique de croissance du film passif et de son épaisseur.: A multidisciplinary experimental approach of electrochemical and mechanical techniques was employed to study the corrosion of different stress states of 304L stainless steel in acidic electrolytes (0.5-5 M H2SO4) with and without chloride additives. Stress corrosion cracking (SCC) conditions were applied to evidence cracking crystallographical and propagation aspects. Scanning electron microscopy of SCC revealed clear traces of successive slipping planes and consequent dissolutions on the crack facets, and nonlinear crack propagation kinetics. A method was proposed to access cracking crystallography using electron back scattered diffraction. It demonstrated {111} and {110} preferential cracking planes in proportion of about 75% and 25% respectively, which supports recent SCC models such as corrosion enhanced localized plasticity. The profiles of (applied/residual) stress evolution measured by X-ray diffraction before and after SCC were used as an introduction to develop a micro-mechanical cracking model. During optimized potentiodynamic corrosion tests, elemental dissolution rates and total current transients were measured by combining electrochemical flow cell and downstream solution analysis by inductively coupled plasma atomic emission spectroscopy. The results were used to separate the current portion spent on passive film formation from the total current. The high field ion conduction model was upgraded to calculate the constructed passive film thickness and passivation rate. The applied stress caused a measurable difference in passive film growth kinetics and its thickness

Dégradation de l’acier inoxydable soumis à la contrainte : L’influence des contraintes sur la cinétique de passivation, et la cristallographie de la fissuration dans des milieux acides

: A multidisciplinary experimental approach of electrochemical and mechanical techniques was employed to study the corrosion of different stress states of 304L stainless steel in acidic electrolytes (0.5-5 M H2SO4) with and without chloride additives. Stress corrosion cracking (SCC) conditions were applied to evidence cracking crystallographical and propagation aspects. Scanning electron microscopy of SCC revealed clear traces of successive slipping planes and consequent dissolutions on the crack facets, and nonlinear crack propagation kinetics. A method was proposed to access cracking crystallography using electron back scattered diffraction. It demonstrated {111} and {110} preferential cracking planes in proportion of about 75% and 25% respectively, which supports recent SCC models such as corrosion enhanced localized plasticity. The profiles of (applied/residual) stress evolution measured by X-ray diffraction before and after SCC were used as an introduction to develop a micro-mechanical cracking model. During optimized potentiodynamic corrosion tests, elemental dissolution rates and total current transients were measured by combining electrochemical flow cell and downstream solution analysis by inductively coupled plasma atomic emission spectroscopy. The results were used to separate the current portion spent on passive film formation from the total current. The high field ion conduction model was upgraded to calculate the constructed passive film thickness and passivation rate. The applied stress caused a measurable difference in passive film growth kinetics and its thickness.Une approche expérimentale mettant en œuvre des techniques électrochimiques et mécaniques a été utilisée pour étudier la corrosion sous contrainte (CSC) de l’acier inoxydable 304L dans des électrolytes acides (0,5-5 M H2SO4) avec et sans chlorure. La CSC a été réalisée dans le but d’étudier les aspects cristallographique et cinétique de la rupture. La microscopie électronique à balayage a dévoilé, d’une part, des traces successives au niveau des plans de glissement sur les facettes de la fissure, et d’autre part une vitesse non-linéaire de la fissuration. Une méthode a été proposée pour accéder à la cristallographie de fissuration en utilisant la diffraction d'électrons rétrodiffusés (EBSD). Il a été démontré que les ruptures préférentielles s’effectuent au niveau des plans {111} pour ¾ du temps et des plans {110} le reste du temps. Ces résultats soutiennent les modèles récents de la CSC, tels que la plasticité localisée rehaussée par la corrosion. Les profils d’évolution de la contrainte appliquée/résiduelles ont été déterminés par diffraction des rayons X avant et après CSC. Ces analyses serviront à développer un modèle de rupture micro-mécanique. Lors des essais potentiodynamiques optimisés de corrosion, les taux de dissolution élémentaires et le courant total ont été mesurés en combinant une cellule d'écoulement électrochimique et l'analyse des produits de corrosion par spectroscopie d'émission atomique à plasma à couplage inductif. Ces résultats ont été utilisés, pour séparer la partie de courant consacré à la formation de la couche passive du courant total. Le modèle de conduction ionique sous tension élevée a été mis à jour pour calculer le taux de passivation et l'épaisseur de la couche passive. Les contraintes dans le matériau expliquent une différence mesurable de la cinétique de croissance du film passif et de son épaisseur

Experimental hydraulic fracturing of Berea sandstone under triaxial stress state

In this work, a newly designed experimental setup is used to perform in-lab fracking under controlled triaxial loading on cylindrical cores of Berea sandstone. Fracking tests are conducted at 10 MPa confining pressure, with vertical compressive loading, as well as two horizontal stresses that simulate reservoir triaxial stress state. Multiple injection scenarios are tested to investigate the effect of the pore fluid injection conditions on the fracking and failure mechanisms. In-situ micro-seismic monitoring via eight acoustic emissions sensors is used for logging the fracking events evolution with time. Post-experimental characterization included computational tomography (CT) scanning to characterize the resulting fracture patterns