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In additive manufacturing (AM), uneven cooling and thermal deformations deteriorate the quality of manufactured parts. However, the complexity of the non-linear systems, which are required for the modelling of the plasticity phenomena that take place, requires long simulations, a fact that renders them impractical, especially for machine control. In this study, a proof of concept for a numerical-empirical modelling approach of the thermo-mechanical phenomena of the AM process of selective laser melting (SLM) is presented. The dynamic elastic equation is solved in a two-dimensional (2D) space utilizing finite differences (FD); the solution of the coupled dynamic thermal equation is used as input. Movement of the laser heating and melting phase change are also considered. The effects of plasticity in the x-axis of the part are taken into account, utilizing a re-meshing strategy while an empirical bottom boundary condition is used for the encapsulation of the plasticity effects of the z-axis of the part. In this way, the effects of plasticity are taken into account in the proposed thermo-mechanical model, without the need to solve complex non-linear systems. The results of this study have been experimentally validated. more...

Summary In precast technology, the effective design and construction are related to the behaviour of the connections between the structural members in order to cater for all service, environmental and earthquake load conditions. Therefore, the design and detailing of the connections should be undertaken consistently and with awareness of the desired structural response. In the research presented herein, an analytical expression is proposed for the prediction of the resistance of precast pinned connections under shear monotonic and cyclic loading. The proposed formula addresses the case where the failure of the connection occurs with simultaneous flexural failure of the dowel and compression failure of the concrete around the dowel, expected to occur either when (i) adequate concrete cover of the dowels is provided (d > 6 D) or (ii) adequate confining reinforcement (as defined in the article) is foreseen around the dowels in the case of small concrete covers (d more...

In precast technology, the effective design and construction is related to the behaviour of the connections between the structural members in order to cater for all service, environmental and earthquake load conditions. Therefore, the design and detailing of the connections should be undertaken consistently and with awareness of the desired structural response. In the research presented herein an analytical expression is proposed for the prediction of the resistance of precast pinned connections under shear monotonic and cyclic loading. The proposed formula addresses the case where the failure of the connection occurs with simultaneous flexural failure of the dowel and compression failure of the concrete around the dowel, expected to occur either when (a) adequate concrete cover of the dowels is provided (d > 6 D) or (b) adequate confining reinforcement (as defined in the article) is foreseen around the dowels in the case of small concrete covers (d < 6 D). The expression is calibrated against available experimental data and numerical results derived from a nonlinear numerical investigation. Emphasis is given to identifying the effect of several parameters on the horizontal shear resistance of the connection such as: the number and diameter of the dowels; the strength of materials (concrete, grout, steel); the concrete cover of the dowels; the thickness of the elastomeric pad; the type of shear loading (monotonic or cyclic); the pre-existing axial stress in the dowels; and the rotation of the joint. In addition, recommendations for the design of precast pinned beam-to-column connections are given, especially when the connections are utilised in earthquake resistant structures. more...

In precast technology, mostly (but not exclusively), frame structures with pinned beam-to-column connections are preferred, especially in low-rise buildings due to the flexibility, lower cost and more favourable behaviour they provide, especially in the case of large spans and pretensioned interconnected members. However the available literature on the behaviour of pinned connections, especially under seismic loading, can be characterized as poor, even though their use in Europe and elsewhere is rather extended. In the terms of the present research a nonlinear 3D numerical model was developed and calibrated against available experimental data to be used as an effective tool for the analytical prediction of the behaviour of pinned connections, under monotonic and cyclic shear loading. The experimental data were derived from the European FP7 project SAFECAST, Grant Agreement Number 218417. The tests were performed at the Laboratory for Earthquake Engineering of the National Technical University of Athens, Greece. From the numerical results useful information was obtained on component level about: (a) the type of the observed failure mechanism; (b) the amount of dissipated energy; (c) the location of the developed plastic hinges along the steel dowel, and (d) the evolution of stresses and strains along the dowel(s) and in the mass of the surrounding grout. However the numerical model can be further utilized to investigate and quantify the effect of several parameters (that were not experimentally investigated in depth, or were not investigated at all) on the response of pinned connections. more...

The track's ballasted superstructure is a multilayered construction consisting of several constitutive layers. In the slab track for High-Speed Lines, or the embedded track for terminal port stations, a concrete slab replaced the ballast. For the estimation of the increase of the mean value of the static vertical wheel load, a probabilistic approach should generally be adopted in order to cover the statistically desirable safety level. Four calculation methods are cited. An investigation of the change of track stiffness coefficient, both static and dynamic, in Ballasted Track, Transition Zone and Ballastless Track was performed and it is presented. more...

Remote welding provides new possibilities for highly productive and flexible joining of metal structures, especially in the automotive industry. This study presents an experimental investigation on the behavior of the lap welds’ geometrical characteristics with respect to the laser beam inclination. Two remote welding systems (RWSs) have been utilized: a large field RWS with a CO2 laser and a small field RWS with an Nd:YAG laser. The materials investigated include steels (noncoated, zinc-coated, and stainless) and an Al alloy. Conclusions are drawn related to the behavior of the process mechanism under different laser beam inclinations, useful for the industrial application of the process and for further research in the field. more...

A theoretical and experimental investigation of the limitations of the pulsed laser drilling process is presented in this study. A theoretical model has been developed for simulating the process of drilling with medium irradiance laser beams. It takes into account the required time for reaching melting temperature as well as the melting and the subsequent removal of a volume of material during each laser pulse. The model estimates for a specific laser beam power, a maximum drill depth. The pulsing frequency of the laser beam has no effect on the maximum drill depth. A 1.8 kW CO 2 laser has been used for the experimental verification of the theoretical predictions and the fine tuning of the model. more...

In this study, a theoretical approach of the remote welding process has been developed and discussed. The study obtains numerically the melting boundaries of different heat source angles, based on an analytical calculation of the keyhole depth. The approach considers the dominant process parameters of the laser power, the welding speed and the inclination of the laser beam on the workpiece surface. The geometrical particularities of the beam spot, due to the different inclination of the laser beam upon the processing plane, have also been considered in a previous study of the authors. The theoretical results present good agreement when compared with experimental data obtained from a remote welding system (RWS) on lap welding of AISI 304 stainless steel, thin sheets. more...

Remote welding opens new possibilities for the highly productive and qualitative joining of metal structures, especially in the automotive industry. This work first summarises the different types of remote welding systems (RWSs) based primarily on the different features of the laser beam scanning systems that RWSs implement. A generalised two-mirror scanning system is geometrically analyzed in order to evaluate the irradiated laser intensity on the workpiece as it changes due to the inclinations with which the laser beam impinges to the processing plane. The study discusses the limitations that a two-mirror scanning system enforces in remote welding, and sets the foundation for further theoretical and experimental investigation of this process. more...

Um projeto estrutural adequado é fundamental para que a satisfação dos requisitos fundamentais de uma estrutura sejam alcançados sob a ação de um sismo. Como é bem conhecido, o projeto de uma estrutura inclui três fases distintas, nomeadamente a conceção estrutural, a análise (cálculo de efeitos das ações, tendo também em consideração a ação sísmica) e o dimensionamento – verificação. A experiência baseada na história da engenharia sísmica e a experiência recente sobre o comportamento das estruturas de betão armado mostrou que, apesar da enorme evolução dos meios informáticos, a satisfação dos requisitos fundamentais do projeto sísmico não pode ser alcançada diretamente por meio de cálculos, tendo-se verificado que a observância de alguns conceitos básicos de projeto é mais importante. Este capítulo enfatizará a grande importância da primeira etapa do projeto, a chamada, conceção estrutural. Ou seja, cada análise tem que ser feita de acordo com uma conceção estrutural pré-concebida; várias decisões deverão ser tomadas a priori, antes de qualquer procedimento analítico, como por exemplo, minimizar incertezas relacionadas com a resposta sísmica da estrutura. publishersversion published more...

Laser beams can be used in many industrial applications including machining whereby it constitutes an alternative to traditional material removal techniques and can be used to process a variety of materials including metals, ceramics, glass, plastics, and composites. Laser machining is characterized by a number of advantages such as absence of tool wear, tool breakage, chatter, machine deflection and mechanically induced material damage, phenomena which are usually associated with traditional machining processes. However, as with all manufacturing processes, optimum operating parameters have to be determined. These include the laser power, the spot size of the focused laser beam, etc. In order to arrive at a set of optimum setting variables, either experiments can be conducted and optimum conditions can be found based on the results, or a process model can be created and evaluated for the selection of setting variables, which will optimize the desired performance measures. Analytical and numerical modeling have contributed to the understanding of laser processing, but there are still many questions to be answered. This paper attempts to give an overview of laser machining modeling and experimentation techniques, elucidating recent developments and research trends. more...

The term of 3D laser processing has been used so far to describe a group of different three-dimensional laser processing concepts. At each of these concepts the 3D aspect refers to a different manipulation of one or more laser beams, as to process and/or produce three-dimensional geometries by performing material removal, welding or heat treating. The most important concepts are focused mainly in laser machining and laser welding processes by incorporating one or two laser beams simultaneously. This paper overviews a number of these concepts that have been developed in research or industrial level, along with their advantages, drawbacks and fields of application. more...

This study presents an environmental analysis of a number of cutting and joining processes taking place during the ship hull repair. These processes include oxy-acetylene cutting, plasma arc cutting, shielded metal arc welding, flux core arc welding and submerged arc welding. The processes are modelled in terms of their environmental impact. The environmental-related inputs and outputs of each process are elaborated with a life cycle assessment tool. The impact on various aspects, such as human health, resource depletion etc., is assessed by the 'environmental priority strategy (EPS)' and the 'Eco-Indicator 99' impact assessment methods. Based on the results, a benchmarking of the cutting and welding processes is performed, in terms of their environmental impact. more...

This article briefly summarises experiments, including very recent work, at the NTU in Athens, on the connections of large precast reinforced concrete panels when subjected to monotonic, repetitive-dynamic and cyclic shearing actions. Conclusions as to the seismic behaviour of such connections are also presented. For monotonic loading, a theoretical model for predicting ultimate bearing capacity of the connections is shown schematically, accompanied by a design formula. The relevant behaviour under repetitive-dynamic loading is represented by a 'fatigue curve'. For rational seismic design of the connections, experimental data show cyclic-strain reactions, such as shear-force response, shear-stiffness degradation, hysteretic damping, ultimate (static) bearing capacity and residual strength. These lead to a proposed approximate behavioural model for possible use in computer analyses of composite walls, and to design values (together with degradation factors) for estimating the bearing capacity of v... more...

Serum haptoglobin phenotypes were studied in 100 Greek patients suffering from duodenal ulcer by vertical starch gel electrophoresis. A sample of 2026 healthy subjects served as control. No statistically significant differences were found in Hp phenotypes and gene frequencies between patients and healthy controls. more...

Measurement of serum lipids in 75 patients on regular haemodialysis showed that they had a higher mean serum triglyceride level than normal subjects. Cholesterol levels were not significantly different. Amongst haemodialysis patients men had higher serum triglycerides than women and women had higher cholesterol levels than men, a situation analogous to that found in normal subjects. In men, serum triglycerides correlated with percent body fat and treatment with Sustanon 250(R) intramuscularly weekly caused a significant rise. more...

The electrophoretic patterns of serum proteins, glucoproteins and Iipo proteins were determined in acute infectious diseases (viral hepatitis, mumps, diphtheria, measles, pertussis and chickenpox) in infants and children. In respect to proteins a constant diminution of albumin and a slight elevation of α- and γ-globulin fractions was found in all the investigated diseases. The lowest values for albumin and the highest for γ-globulin were found in viral hepatitis. In lipoproteins a decrease of the α-and an increase of the β-fraction was noticed in all the cases, the changes being more prominent in viral hepatitis. As for the glucoproteins, the following patterns could be distinguished. A pattern characterized mainly by a marked decrease of the carbohydrates bound to albumin with a marked increase of the γ-glucoprotein fraction was found in viral hepatitis and pertussis. A second pattern, having as the main finding an elevation of α2-glucoprotein, was found in mumps, measles and chickenpox. Diphtheria did not exhibit any constant glucoprotein change. © 1966 S. Karger AG, Basel. more...

A family with hereditary methemoglobinemia due to DPNH-methemoglobin reductase deficiency is reported. Genetic studies indicate that this defect is inherited as an autosomal recessive trait. Homozygotes had cyanosis, methemoglobinemia and a very low erythrocyte DPNH-methemoglobin reductase activity. Heterozygotes had no cyanosis, no methemoglobinemia (with the exception of one individual who had slight elevation of methemoglobin) and the DPNH-methemoglobin reductase activity was a little lower than normal. Spectroscopic and electrophoretic studies of hemolyzates demonstrated normal adult hemoglobin. G-6-PD and GSSG reductase activities were within normal limits. © 1967 S. Karger AG, Basel. more...

Nanomanufacturing encompasses processes aimed at building nanoscale structures, devices and systems in one, two or three dimensions. Nanomanufacturing involves both bottom-up and top-down approaches. This paper reviews and discusses some critical issues of nanomanufacturing from the cost, production rate, quality and flexibility point of view. more...