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.

Standard neutron imaging procedures are based on the “shadow” of the transmitted radiation, attenuated by the sample material. Under certain conditions significant deviations from pure transmission can be found in the form of enhancement or depression at the edges of the samples. These effects can limit the quantification process in the related regions. Otherwise, an enhancement and improvement of visibility can be achieved e.g. in defect analysis. In systematic studies we investigated the dependency of these effects on the specific material (mainly for common metals), such as the sample-to-detector distance, the beam collimation, the material thickness and the neutron energy. The beam lines ICON and BOA at PSI and ANTARES at TU München were used for these experiments due to their capability for neutron imaging with highest possible spatial resolution (6.5 to 13.5 micro-meter pixel size, respectively) and their cold beam spectrum. Next to the experimental data we used a McStas tool for the description of refraction and reflection features at edges for comparison. Even if minor contributions by coherent in-line propagation phase contrast are underlined, the major effect can be described by refraction of the neutrons at the sample-void interface. Ways to suppress and to magnify the edge effects can be derived from these findings.

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.

Spare parts for products that are at the end of their life cycles, but still under warranty, are logistically difficult because they are commonly not stored in the central warehouse. These uncommon spare parts occupy valuable space in smaller inventories and take a long time to be transported to the point of need, thus delaying the repair process. This paper proposes that storing the spare parts on a server and producing them with additive manufacturing (AM) on demand can shorten the repair cycle by simplifying the logistics. Introducing AM in the repair supply chain lowers the number of products that need to be reimbursed to the customer due to lengthy repairs, improves the repair statistics of the repair shops, and reduces the number of items that are held in stock. For this paper, the functionality of the concept was verified by reverse engineering a memory cover of a portable computer and laser sintering it from polyamide 12. The additively manufactured component fit well and the computer operated normally after the replacement. The current spare part supply chain model and models with AM machinery located at the repair shop, the centralized spare part provider, and the original equipment manufacturer were provided. The durations of the repair process in the models were compared by simulating two scenarios with the Monte Carlo method. As the biggest improvement, the model with the AM machine in the repair shop reduced the duration of the repair process from 14 days to three days. The result points to the conclusion that placing the machine as close to the need as possible is the best option, if there is enough demand. The spare parts currently compatible with AM are plastic components without strict surface roughness requirements, but more spare parts will become compatible with the development of AM.

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.

The spatial-dependent lattice spacing and microstructure of an α-iron plate with two notches was measured during tensile tests using a pulsed neutron transmission method to ascertain changes depending on the load. Changes in microstructural parameters such as macrostrain, microstrain, crystallite size and texture are interesting during the transition from the elastic to plastic deformation region, especially over a relatively wide field of view to see propagation of the change. The method has the capability to show changes in the position-dependence of microstructural information simultaneously over a wide area in the bulk material. Transmission spectra around the Bragg-edge regions of the neutron total cross section of α-iron were obtained, and the microstructural parameters, {110} plane spacing and its distribution, texture coefficient and crystallite size were analyzed. The spatial-dependent distributions (images) of these parameters show sample shape effects including strain concentration around the notches and the effect of dislocations being multiplied during the plastic deformation. The spatial dependence of the microstructural parameters visualized herein provides useful information for evaluating the inhomogeneous progress of deformation of the bulk engineering material.

Pulsed neutron transmission spectroscopy was applied to clarify a phase change phenomena of lead-bismuth eutectics (LBE). The melting and solidification behaviors of the LBE should be well understood to enhance the safety of an LBE-cooled accelerator driven system. In this study, the heating experiments were performed using a rectangular test section and LBE phase change process was visualized by the energy-resolved pulsed neutron imaging at BL22 RADEN facility in J-PARC and the solid/liquid interface was identified from the radiograph and Bragg edge information. The transient location of the interface was compared with measured temperature profiles and it would be useful to evaluate the LBE thermal properties.

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.

Nanotubular titanium oxide coatings with different morphology and dimensional parameters are formed by anodic oxidation under different voltage and time modes in fluorine aqueous-nonaqueous electrolytes containing glycerin as well as several surface-active agents (SAA). Their morphological peculiarities are examined and qualitative and quantitative analysis of obtained types of ordering is carried out, geometric configuration entropy are calculated on the base of analysis SEM images and theory of self-organization.

A vision and spectroscopic system for estimation of the joint gap width in autogenous laser beam butt welding is presented. Variations in joint gap width can introduce imperfections in the butt joint seam, which in turn influence fatigue life and structural integrity. The aim of the monitoring approach explored here is to acquire sufficiently robust process data to be used to guide post inspection activities and/or to enable feedback control for a decreased process variability. The dual-sensing approach includes a calibrated CMOS camera and a miniature spectrometer integrated with a laser beam tool. The camera system includes LED illumination and matching optical filters and captures images of the area in front of the melt pool in order to estimate the joint gap width from the information in the image. The intensity of different spectral lines acquired by the spectrometer has been investigated and the correlation between the intensity of representative lines and the joint gap width has been studied. Welding experiments have been conducted using a 6 kW fiber laser. Results from both systems are promising, the camera system is able to give good estimations of the joint gap width, and good correlations between the signal from the spectrometer and the joint gap width have been found. However, developments of the camera setup and vision algorithm can further improve the joint gap estimations and more experimental work is needed in order to evaluate the robustness of the systems.