Etude expérimentale et numérique des défauts de bouclage et de glissement lors de la mise en forme de composites structuraux à base de fibres synthétiques et végétales

Les composites à renforts fibreux sont très prisés dans les industries de pointe comme l’aéronautique ou l’automobile du fait de leur rapport propriété mécanique/masse supérieur à celui des métaux. Leur mise en forme complexe présente de forts enjeux scientifiques, notamment pour les composites à renforts tissés. En effet, les renforts tissés sont sujets à l’apparition de défauts lors de leur mise en forme sur géométries complexes à double courbure. Certains de ces défauts ont déjà fait l’objet de plusieurs études alors que d’autres, comme les défauts de bouclage et de glissement des mèches, n’ont pour le moment pas encore été totalement explorés. À l’heure actuelle, les codes de simulations ne peuvent pas prédire précisément l’apparition et le développement des défauts de bouclage et de glissement des mèches lors de la mise en forme des renforts tissés. L’une des raisons est le manque de connaissances sur l’origine et la cinématique de développement de ces défauts. Ce travail de thèse propose d’apporter plus de compréhension sur ces défauts par une approche expérimentale et numérique. Concernant le défaut de bouclage, l’influence des tensions dans les réseaux de mèches, de la nature du renfort, de l’armure du renfort et des dimensions des mèches ont été étudiés. Pour le défaut de glissement, l’influence du type de renfort, des tensions dans les mèches, de l’armure du renfort et de l’orientation des mèches dans le renfort ont été explorés. Ces résultats ouvrent des perspectives concernant l’amélioration de la qualité des pièces composites

Utilization of Ammonia Hydroxide /Diesel Fuel Blends in Partially Premixed Charge Compression Ignition (PPCCI) Engine: A Technical Review

Almost 50% of new car registrations in Europe at the turn of the century were diesel. However, reports of harmful NOx emissions have been corroborated by diesel emissions scandals, which have sent the diesel engine market into a tailspin and raised concerns about the diesel engine\u27s long-term viability. Developing of diesel cars with low NOx emissions has been announced by major automakers. Modern posttreatment systems can be installed, and they will result in decreased NOx emissions for heavy-duty, marine, or power production applications. Despite attempts to lower NOx emissions, the automobile, marine, and power generation industries must decarbonize if we are to reach greenhouse gas emission objectives and prevent global warming. Using fuels with low carbon, like ammonia, can help decarbonize a diesel engine. Using ammonia as a fuel for diesel engines is discussed at length in this work. To drastically lower carbon emissions, Ammonia could be burned when mixed with diesel or another low-temperature fuel in a dual-fuel system. Creating advanced injection technologies can improve overall emissions while also improving performance. However, due to the coupling of nitrogen to the fuel, dual fuel combustion of ammonia currently has relatively large emissions of ammonia and nitrogen oxides. As a result, post-processing mechanisms need to be put in place. With the introduction of modern combustion systems like HCCI, PCCI, and RCCI systems, ammonia is currently only a practical alternative in specific applications including maritime, power generating, and maybe heavy duty

Impact of Utilizing a Diesel/Ammonia Hydroxide Dual Fuel on Diesel Engines Performance and Emissions Characteristics

The problem of global warming and environmentally polluting emissions has become the call of the times. To solve this problem, the trend to change or share new types of fuel has become a new way to solve this problem. One of the most promising types of fuel in the future is ammonia, as it is a carbon-free fuel, unlike traditional fossil fuels. Because of the danger of using ammonia as a gas, it was safer to use ammonia as a liquid. In this study, ammonia hydroxide was used as a proportion with diesel fuel in a PCCI diesel engine. The diesel engine is a single-cylinder, four-stroke engine. Ammonia hydroxide fuel with a ratio of 33% ammonia-water by volume was used with diesel fuel. The experiment was carried out with ammonia hydroxide ratios of 2.5%, 5%, 7.5%, and 10%, respectively. The results of emissions, thermal efficiency (BTE), fuel consumption (BSFC) and exhaust temperatures were compared. It was concluded that using ammonia hydroxide ratios to diesel led to an increase in thermal efficiency by 23.5% compared to diesel only by 20.5%, and fuel consumption was also reduced. 391.083g/Kw.h compared to diesel is only 455.56 g/Kw.h. As a result of the presence of ammonia hydroxide, exhaust temperatures are lower than when using diesel only. Therefore, this study discusses with practical experience the effect of using ammonia hydroxide with diesel on the performance and efficiency of the engine and fuel emissions characteristics

Comparative study of tow buckling defect during preforming of structural composites based on vegetal fibers

During the complex shape forming of composite fibrous reinforcement, the planar bending of roving tows results in an out-of-plane deflection, along with a rotation on its central axis. The need to accurately follow and quantify the mechanism of formation of such defect has led us to consider two 3D imaging techniques, of which, have been tested and compared in this work

Impact of Utilizing a Diesel/Ammonia Hydroxide Dual Fuel on Diesel Engines Performance and Emissions Characteristics

The problem of global warming and environmentally polluting emissions has become the call of the times. To solve this problem, the trend to change or share new types of fuel has become a new way to solve this problem. One of the most promising types of fuel in the future is ammonia, as it is a carbon-free fuel, unlike traditional fossil fuels. Because of the danger of using ammonia as a gas, it was safer to use ammonia as a liquid. In this study, ammonia hydroxide was used as a proportion with diesel fuel in a PCCI diesel engine. The diesel engine is a single-cylinder, four-stroke engine. Ammonia hydroxide fuel with a ratio of 33% ammonia-water by volume was used with diesel fuel. The experiment was carried out with ammonia hydroxide ratios of 2.5%, 5%, 7.5%, and 10%, respectively. The results of emissions, thermal efficiency (BTE), fuel consumption (BSFC) and exhaust temperatures were compared. It was concluded that using ammonia hydroxide ratios to diesel led to an increase in thermal efficiency by 23.5% compared to diesel only by 20.5%, and fuel consumption was also reduced. 391.083g/Kw.h compared to diesel is only 455.56 g/Kw.h. As a result of the presence of ammonia hydroxide, exhaust temperatures are lower than when using diesel only. Therefore, this study discusses with practical experience the effect of using ammonia hydroxide with diesel on the performance and efficiency of the engine and fuel emissions characteristics

Experimental, analytical and numerical investigation to prevent the tow buckling defect during fabric forming

We investigate the causes, kinematic and possible ways to prevent the tow-buckling defect during the complex shape-forming of a dry woven reinforcement. Macro-scale compression leads to wrinkles; we focus on a meso- scale phenomenon generated by a non-uniform axial compression of the tow due to in-plane bending. An ex- perimental study is presented, followed by an efficient method to predict the onset of the tow-buckling defect. This investigation is based on the combination of an experimentally validated analytical approach, with a macro- scale simulation of the forming process for a single fabric layer. A particular focus is given to the resulting tow curvatures that allows us to predict the zones of high tow buckling probability. The relatively simple numerical approach based on Lagrange assumptions does not take into account tow slippage. However, for most cases, where buckles appear before slippage, this approach alleviates the compulsory need for an expensive meso-scale representation

Study of the tow buckling defect during the complex shape forming of synthetic and vegetal fibre reinforced structural composites

Fibrous reinforcements for structural composites manufacturing need to undergo in certain cases a complex shape forming process during which multiple defects could appear. These defects, such as tow buckling and tow sliding may reduce the integrity of the final part. The onset of these defects depends on the initial loading conditions, the shape of the preform and the characteristics of the textile material. While mechanisms behind the formation and development of both defects are yet to be fully understood. We focused, in this work, on investigating the buckling defect. In order to do so, we used optical field measurement techniques to monitor the kinematics of the defect appearance and predict it via an adapted analytical model of the defect appearance

Experimental investigation of vegetal and synthetic fabrics cohesion in order to prevent the tow sliding defect via frictional and pull-out test

The tow-sliding defect also referred to as gapping that appears during complex shaping of woven reinforcements is due to a loss of cohesion in the fabric. The cohesion of the fabric tends to keep the tows from sliding under tension. This cohesion depends on the frictional behavior of the tows mainly. Other factors such as the weave of the fabric, the tensions and shear state of the fabric during forming play an important role as well. An analysis of the frictional behaviors of the tows coupled to out of plane pull-out tests to determine the influence the aforementioned parameters on the cohesion of the reinforcements was then carried out. It was showed that the cohesion of the fabric, limiting the risk of appearance of tow sliding defect, can be improved by increasing the transverse tow tension in low shear region, and by the in-plane shear itself in highly sheared zones

Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis

BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London

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