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

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

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

Directions of realization of the economic potential of biotechnologies at the municipal level

The article examines the current state and trends of development of the municipal district due to the introduction of new biotechnology. The authors have identified the main measures contributing to the socio-economic development of this industry and improving the quality of services provided in the study area