Physics Procedia最新文献

The manufacturing of large steel structures involves welding thick-section steels. Using hybrid laser welding, it is possible to reduce production costs significantly. However, avoiding solidification cracks in the weld is difficult when welding thick-section steels. In this study, a number of experiments were performed on the hybrid laser welding of 25 mm steel. Different techniques of full penetration and partial penetration welding were discussed. Crack-free welds were obtained using single-pass or two-pass welding techniques. The results of the experiments showed that the joint preparation method and the penetration mode are very important factors in obtaining crack-free welds in welding thick section steels. With the same process parameters applied to hybrid laser welding, partial penetration welds were more susceptible to cracking than full penetration welds. This was partly attributed to a change in the melt flow and, consequently, a different solidification mode that occurred during the full penetration mode welding.

Neutron computed tomography takes more time for a full tomography than X-rays or Synchrotron radiation, because the source intensity is limited. Most neutron imaging detectors have a square field of view, so if tomography of elongated, narrow samples, e.g. fuel rods, sword blades is recorded, much of the detector area is wasted. Using multiple rotation axes, several samples can be placed inside the field of view, and multiple tomographies can be recorded at the same time by later splitting the recorded images into separate tomography data sets. We describe a new multiple-axis setup using four independent miniaturized rotation tables.

To reduce the costs of the fabrication of offshore wind turbine foundations it is necessary to investigate new fabrication technologies. Hybrid laser arc welding is a potentially well-suited process for this because it requires less groove preparation to achieve deep weld penetration and lower heat input, compared to traditional arc welding. A skirt section of a suction bucket in 16 mm steel was used as a case to investigate the hybrid laser-arc welding in order to demonstrate which types of weld and which weld positions are possible. Three types of weld joints were chosen and welded with different welding positions; a butt joint of a bended section, a butt joint of a flat section and a lap joint. Stable welds with sufficient penetration were achieved for the flat welding position of the butt joint of bended section and butt joint of flat section.

According to previous studies the careful argon shielding of the weld is very important in order to achieve a ductile and formable laser weld of Ti-stabilized ferritic stainless steel. In practice it is often difficult to use the root gas shielding of the laser weld. The aim of this study was to determine the sufficient practise of gas shielding in order to achieve the ductile laser weld. According to Erichsen formability results the shielding gas nozzle in the post weld side must be used in order to reach the good formability of the laser weld. The single shielding gas pipe before the weld is not a sufficient method for the gas shielding. There is no need to use root gas in order to achieve a ductile weld. The single shielding gas pipe before the weld can cause a uptake blast in the key hole and further oxidize the weld metal.

In this work the highly effiective light beam diffraction on holographic photonic structure formed in polymer-dispersed liquid crystal (PDLCs) is theoretically described. The ability to manage its diffraction characteristics by the spatially inhomogeneous electric field is also shown.

Within this paper we summarize new approaches for the utilization of neutron beams for imaging purposes. Whereas most of the methods are still based on the radiography mode - however now with higher performance with respect to spatial resolution, dynamic range and linearity (obtained often in short exposure time) - the new aspects of using polarized neutrons, the diffracted neutron signal or grating interferometers are linking towards neutron scattering investigations. Many of the new techniques have already found their user community, while some of them are based on users demands themselves. The further progress in the field depends much on the access to useful beam ports at suitable neutron sources.

We report optical excitation of space-charge and conductivity gratings in wide-bandgap semiconductors. The approach is based on the illumination of semiconductor material with an oscillating interference pattern formed of two light waves, one of which is phase modulated with frequency ω. The non-steady-state photocurrent flowing through the short-circuited semiconductor is the measurable quantity in this technique. The alternating current results from the periodic relative shifts of the photoconductivity and space charge electric field gratings which arise in the volume of the crystal under illumination. The experiments are carried out in β-Ga₂O₃ crystal and the main parameters of the photoinduced carriers are determined.

The objective of this research is to define an optimal innovation policy and funding strategy to improve Additive Manufacturing (AM) capabilities in Finnish companies. To do so, we present an international review of innovation programs in the area of AM. In addition, the study replied upon a survey prepared to evaluate factors for AM implementation. The ultimate goal is to help in the definition of a national policy strategy in the area of AM based on the characteristics of the Finnish industrial ecosystem.

The methodology and data collection method involved defining the taxonomy of Finnish AM industry. The target group of the survey was a population of AM experts, and individuals with knowledge on AM and industrial processes. Overall, the survey revealed that research and innovation activities are well positioned in Finland. In order for future innovation policies to further support developments in the field, we estimated that policy strategies need to generate about 6-8 M€/year in national and EU- funding instruments for AM technology transfer, development, and innovation activities. Efforts should be targeted towards strengthening uses of AM in final production. In fact, only 36% of Finnish respondents declared to use AM for final production, while leading countries in AM use it in average more than 50%. Another area in need of development in Finland is the use of AM high performance materials. Moreover, outsourcing of AM services in Finland is 23 percentage point higher in national and 13 percentage point higher in international outsourcing to service bureaus and suppliers. In this regard, future policies and funding strategies should maintain the created momentum. However, there is a need to acquire high-end research and industrial equipment to stimulate AM integration to the existing production systems. This in the end can trigger the creation of new products, processes and intellectual property, enabling innovation and competitive advantage.

The formation of the periodic structures based on Si-materials by electron beam lithography technique has been studied. We have investigated lithography processes such as designing, exposition, development, etching end others. The developed technique allows forming close-packed arrays of elements and holes in the nanometre range. This can be used to produce two-dimensional photonic crystals (2D PhCs) with emitting micro cavities (missing holes) with lateral size parameters within an accuracy of about 2% in the Si (100) substrate and in silicon-on-insulator structures. Such accuracy is expected to be sufficient for obtaining the cavities-coupling radiation interference from large areas of 2D PhCs.

We present a system capable of performing linear PVD processing by DC ion beam sputtering, suitable for reactive or high-vacuum deposition of dielectrics, metals, or magnetic materials onto conductive, insulating, or magnetic substrates. This equipment can be installed on a single vacuum flange for mounting on a variety of vacuum systems, but linear flow systems are preferred. Our recently developed ion source can generate ribbon ion beams of high current and low divergence over a wide range of energies, but is optimized for about 1 to 5 keV, and high ion currents of up to 1A per meter breadth; breadths of several meters are possible. The current density is an order of magnitude higher than existing systems. Uniformity is intrinsically good and can be controlled in real-time. The ion source and the sputter target are mounted close to each other and to the target; the cross section of the equipment does not change as the equipment is scaled up to large dimensions. The ion beam impinges on the sputter target at the optimum angle and energy, in a field-free region, and in high vacuum. This combination of conditions is unique, and dramatically raises the sputter yield. Free choice of beam energy permits higher thermal efficiency. High vacuum means that the deposited atoms comprising the film retain the full energy of several eV that was produced in the sputtering process. The geometry further permits extremely simple and efficient jetting of reactive gases such as oxygen for the production of oxide films. The single broad-beam source has far higher current density and a far more compact layout than existing ion-beam sputtering systems, and can be installed in linear processing systems in a similar manner to linear magnetrons.