111 research outputs found
Structural integrity assessment of wire arc additively manufactured low carbon steel components for marine applications
In order to increase manufacturing efficiency of large engineering structures, wire arc additive manufacturing (WAAM), that belongs to direct energy deposition (DED) family of additive manufacturing (AM) processes, has been developed. This manufacturing method has significant potential to improve material design and efficiency of structural components, subsequently reducing production cost and lead times. Some industries, such as aerospace and automotive, have already employed WAAM technology into their manufacturing processes. However, insufficient testing data on WAAM components performance for various materials and operational conditions is one of the main barriers to rapid adoption of WAAM technology in the wider range of industrial applications. Particularly, the sensitivity of mechanical and
fatigue properties of WAAM materials to corrosive environment needs to be understood to adopt WAAM technique in marine applications, for instance, in offshore wind structures. Moreover, the WAAM method involves repetitive welding, resulting in high stress concentration between adjacent welded layers and residual stress fields in WAAM components. Since welded joints in offshore constructions are known to be weak points for fatigue failures and crack initiation, it is necessary to conduct the structural integrity assessment
of WAAM built steel components and compare their performance with the currently used wrought materials, to investigate the suitability of the WAAM technique for offshore applications. This thesis investigates the structural integrity of WAAM built ER70S-6 and ER100S-1 steel specimens, defining the hardness, tensile, fracture toughness, fatigue crack growth, uniaxial,
torsion and multiaxial fatigue properties. Aiming to make a contribution for marine applications, corrosion-fatigue crack growth assessment has been also conducted, along with investigation of fracture characteristics of components previously exposed to corrosive environment. Due to heterogeneity of WAAM built components, the results from this study
were analysed with respect to the extraction location and orientation from the WAAM walls. Different load levels were examined for fatigue crack growth tests, confirming the sensitivity of specimen behaviour. The obtained trends were compared with the corresponding recommended lines from the standards and with variety of data sets available in the literature on performance of wrought carbon steels which are widely used in offshore structures, to draw conclusions on suitability of WAAM steel components for the offshore industry. Furthermore, recognising the limitations of the welding based WAAM technique, life enhancement methods were considered, introducing rolling and laser shock peening as post-manufacturing surface
treatments techniques. The efficiency of these methods was analysed by examining the fatigue crack growth and corrosion-fatigue crack growth performance of the treated specimens. The residual stress trends were measured by means of neutron diffraction and X-ray scattering to quantify the introduced changes after surface treatment application. Throughout the research, comprehensive microstructural investigations were conducted, including fractography analysis, evaluating the fracture and fatigue mechanisms, using optical and scanning electron microscope. The conclusions from this research have resulted in several journal publications,
also presented in the thesis, that contribute to the overall understanding of WAAM steel components behaviour and extending the application of WAAM technology to the marine environments in the future.In order to increase manufacturing efficiency of large engineering structures, wire arc additive manufacturing (WAAM), that belongs to direct energy deposition (DED) family of additive manufacturing (AM) processes, has been developed. This manufacturing method has significant potential to improve material design and efficiency of structural components, subsequently reducing production cost and lead times. Some industries, such as aerospace and automotive, have already employed WAAM technology into their manufacturing processes. However, insufficient testing data on WAAM components performance for various materials and operational conditions is one of the main barriers to rapid adoption of WAAM technology in the wider range of industrial applications. Particularly, the sensitivity of mechanical and
fatigue properties of WAAM materials to corrosive environment needs to be understood to adopt WAAM technique in marine applications, for instance, in offshore wind structures. Moreover, the WAAM method involves repetitive welding, resulting in high stress concentration between adjacent welded layers and residual stress fields in WAAM components. Since welded joints in offshore constructions are known to be weak points for fatigue failures and crack initiation, it is necessary to conduct the structural integrity assessment
of WAAM built steel components and compare their performance with the currently used wrought materials, to investigate the suitability of the WAAM technique for offshore applications. This thesis investigates the structural integrity of WAAM built ER70S-6 and ER100S-1 steel specimens, defining the hardness, tensile, fracture toughness, fatigue crack growth, uniaxial,
torsion and multiaxial fatigue properties. Aiming to make a contribution for marine applications, corrosion-fatigue crack growth assessment has been also conducted, along with investigation of fracture characteristics of components previously exposed to corrosive environment. Due to heterogeneity of WAAM built components, the results from this study
were analysed with respect to the extraction location and orientation from the WAAM walls. Different load levels were examined for fatigue crack growth tests, confirming the sensitivity of specimen behaviour. The obtained trends were compared with the corresponding recommended lines from the standards and with variety of data sets available in the literature on performance of wrought carbon steels which are widely used in offshore structures, to draw conclusions on suitability of WAAM steel components for the offshore industry. Furthermore, recognising the limitations of the welding based WAAM technique, life enhancement methods were considered, introducing rolling and laser shock peening as post-manufacturing surface
treatments techniques. The efficiency of these methods was analysed by examining the fatigue crack growth and corrosion-fatigue crack growth performance of the treated specimens. The residual stress trends were measured by means of neutron diffraction and X-ray scattering to quantify the introduced changes after surface treatment application. Throughout the research, comprehensive microstructural investigations were conducted, including fractography analysis, evaluating the fracture and fatigue mechanisms, using optical and scanning electron microscope. The conclusions from this research have resulted in several journal publications,
also presented in the thesis, that contribute to the overall understanding of WAAM steel components behaviour and extending the application of WAAM technology to the marine environments in the future
Religious Commitment as a Predictor of Lower Blood Pressure in High-Risk Pregnancies of Southern Appalachia.
Extensive literature review inspired a mediational model of the relationship between Religiosity/Spirituality (R/S) and Blood Pressure (BP) tested through secondary analyses of data from the TIPS program. Participants included 205 (92.1% Caucasian; age M=23.72, SD=5.33) pregnant Southern Appalachian women drawn from the region\u27s at-risk pregnancy population. The only variables correlated with BP were women\u27s weight (r=.430, r=.467, p\u3c.01, for diastolic and systolic BP, respectively) and prenatal care use (r=.138, p\u3c.05, with diastolic BP), but not R/S. Multiple regression analyses confirmed participant weight as the only significant independent predictor of BP. Previous findings of health benefits of R/S cannot be assumed to generalize to pregnant women without further study. Limitations of this study and possible explanations for the findings are discussed
Aplicación de matemáticas difusas para elegir intervalos de mantenimiento para vías férreas no públicas
Este artículo analiza la aplicación de las matemáticas difusas para elegir ventanas de tiempo para el mantenimiento de vías férreas no públicas. Las características de diseño de varias estaciones y los puntos de unión de vías férreas no públicas conducen a rutas hostiles en los conductos de la estación. Mover la flota de cambio a través del cuello crea hostilidad hacia la ruta del tren. Para determinar el intervalo de mantenimiento óptimo de vías férreas no públicas, con el objetivo de excluir la hostilidad, es necesario conocer la reserva de rendimiento del elemento del cuello del ferrocarril en una determinada ventana de tiempo. Para localizar la reserva de rendimiento, se propone dividir el día en intervalos de 30 minutos. Esta división permitirá determinar con mayor precisión tanto la reserva de rendimiento del elemento del cuello del ferrocarril como los períodos de servicio de las vías férreas no públicas. La forma más adecuada de calcular la reserva de rendimiento es utilizar números difusos, ya que este método permite tener en cuenta las capacidades desiguales de los valores dentro de los intervalos. Usando el procedimiento de defuzzificación, se asigna un número natural a un número difuso dado. Después de realizar la defuzzificación de la reserva de caudal, los valores obtenidos se pueden utilizar para construir un algoritmo para seleccionar intervalos de servicio para vías férreas no públicas
Shape optimisation of composite corrugated morphing skins
One of the challenging parts of the morphing wing is the anisotropic skin, which must be flexible enough to allow the wing to change its shape and at the same time being stiff enough to withstand the aerodynamic loads. Composite corrugated skins have exceedingly anisotropic behaviour as they are stiff along the corrugation direction but flexible in transverse direction. Hence, elastomeric coated composite corrugated panels have been proposed as a candidate for application in morphing wings. This paper presents the shape optimisation of the corrugation with respect to better performance of the morphing skin and manufacturing constraints. The shape of the skin is optimised by minimising the in-plane stiffness and weight of the skin and maximising its flexural out-of-plane stiffness. The objective functions were obtained from homogenised model that depends on geometric and mechanical properties of the coated corrugated panel by means of finite element method for thin beams. A few methods of optimisation were considered: aggregated and genetic algorithm methods as representative of two major categories of multi-objective solving methods. A number of different approaches are proposed in order to solve the problem, such as corrugated skin with and without elastomer coating. The advantages of the new optimised shape of the corrugated skin over the typical shapes are discussed
Multistage Voting Model with Alternative Elimination
The voting process is formalized as a multistage voting model with successive
alternative elimination. A finite number of agents vote for one of the
alternatives each round subject to their preferences. If the number of votes
given to the alternative is less than a threshold, it gets eliminated from the
game. A special subclass of repeated games that always stop after a finite
number of stages is considered. Threshold updating rule is proposed. A computer
simulation is used to illustrate two properties of these voting games
One or More External Representations: What Is Better for Learning?
Thesis advisor: Elida V. LaskiUse of base-10 decomposition strategy for addition in first grade is related to mathematics advantage in the later years (Geary et al., 2013), yet we know little about the strategy’s prevalence among first graders or factors contributing to its use. The present study sought to bridge this gap by testing 87 first graders in the greater Boston area. The results confirmed previous findings that showed that in the last 10 years first graders in the US have increased in frequency of base-10 decomposition. Children who had better knowledge of basic number facts used it more frequently, particularly on problems with smaller addends. Further, the study tested whether an instructional intervention would be effective in increasing reliance on base-10 decomposition. 61 of the original participants were selected to take part in an experimental intervention that taught them to execute the strategy while relying on external representations – sometimes known as manipulatives. Informed by two lines of research, the present study tested the hypothesis that the efficacy of the intervention may depend on whether one or multiple external representations are used for instruction. The results showed a dramatic increase in first graders’ mental base-10 decomposition use as a result of the intervention. Children grew in their use of the strategy at the same rates across genders, levels of basic arithmetic fluency, and working memory. Overall, the results showed that relying on multiple representations during instruction appears more beneficial to strategy use on mental arithmetic, but this benefit may be conditional on how well the children have mastered and abstracted the strategy. Implications to classroom interventions aimed to increase the use of advanced arithmetic strategies are discussed.Thesis (PhD) — Boston College, 2016.Submitted to: Boston College. Lynch School of Education.Discipline: Counseling, Developmental and Educational Psychology
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Abnormal reward prediction error signalling in antipsychotic naïve individuals with first episode psychosis or clinical risk for psychosis
Ongoing research suggests preliminary, though not entirely consistent, evidence of neural abnormalities in signalling prediction errors in schizophrenia. Supporting theories suggest mechanistic links between the disruption of these processes and the generation of psychotic symptoms. However, it is unknown at what stage in psychosis these impairments in prediction error signalling develop. One major confound in prior studies is the use of medicated patients with strongly varying disease durations. Our study aims to investigate the involvement of the meso-cortico-striatal circuitry during reward prediction error signalling in earliest stages of psychosis. We studied patients with first episode psychosis (FEP) and help-seeking individuals at-risk for psychosis due to subthreshold prodromal psychotic symptoms. Patients with either FEP (n=14), or at-risk for developing psychosis (n=30), and healthy volunteers (n=39) performed a reinforcement learning task during fMRI scanning. ANOVA revealed significant (p<0.05 family-wise error corrected) prediction error signalling differences between groups in the dopaminergic midbrain and right middle frontal gyrus (dorsolateral prefrontal cortex, DLPFC). FEP patients showed disrupted reward prediction error signalling compared to controls in both regions. At-risk patients showed intermediate activation in the midbrain that significantly differed from controls and from FEP patients, but DLPFC activation that did not differ from controls. Our study confirms that FEP patients have abnormal meso-cortical signalling of reward prediction errors, whilst reward prediction error dysfunction in the at-risk patients appears to show a more nuanced pattern of activation with a degree of midbrain impairment but preserved cortical function
Investment attractiveness of small innovational business under the conditions of globalization and integration
Purpose – The purpose of the article is to study the problems and perspectives of increase of investment attractiveness of small innovational business under the conditions of globalization and integration. Design/methodology/approach – With the help of corresponding methods of conduct of scientific research, the work performs comparative analysis of approaches to determination of small innovational business and SWOT analysis of attraction of investments into development of small innovational business under the conditions of globalization and integration. Findings – The authors determine peculiarities of functioning and development of small innovational business under the conditions of globalization and integration and determine problems and perspectives of attraction of investments into development of small innovational business under the conditions of globalization and integration. Originality/value – The most important item of scientific novelty of this work is the proprietary mechanism of increase of investment attractiveness of small innovational business under the conditions of globalization and integration.peer-reviewe
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