The territorial administrative structure of the Czech Republic has been reformed by Act No. 51/2020 Sb. This change implements an integrated system of local administrative units for the performance ...of the state administration on different levels based on local units defined as micro-regions. The new arrangement respects the existing boarders of territorial self-governing units while provides an abolishment of the old system of administrative regions based on Act No. 36/1960 Sb.
The skeletonization of binary images is a common task in many image processing and machine learning applications. Some of these applications require very fast image processing. We propose novel ...techniques for efficient 2D and 3D thinning of binary images using GPU processors. The algorithms use bit-encoded binary images to process multiple points simultaneously in each thread. The simpleness of a point is determined based on Boolean algebra using only bitwise logical operators. This avoids computationally expensive decoding and encoding steps and allows for additional parallelization. The 2D algorithm is evaluated using a data set of handwritten characters images. It required an average computation time of 3.53 ns for 32
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32 pixels and 0.25 ms for 1024
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1024 pixels. This is 52–18,380 times faster than a multi-threaded border-parallel algorithm. The 3D algorithm was evaluated based on clinical images of the human vasculature and required computation times of 0.27 ms for 128
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128
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128 voxels and 20.32 ms for 512
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512
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512 voxels, which is 32–46 times faster than the compared border-sequential algorithm using the same GPU processor. The proposed techniques enable efficient real-time 2D and 3D skeletonization of binary images, which could improve the performance of many existing machine learning applications.
We studied the microstructural evolution of the low stacking fault energy α-brass alloy CuZn15 during accumulative roll bonding (ARB). Most notably, the typical brass-type texture was clearly ...observed after four ARB passes (approx. 93.8% total thickness reduction), before significant shear localization set in. This observation contradicts the widely accepted idea that shear band formation is a necessary prerequisite for the development of the brass type texture, indicating that the two phenomena, shear banding and development of the brass texture, are only correlated in ARB, and that their order of appearance can be switched depending on experimental parameters.
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We use a nanoindenter with a Berkovich tip to study local mechanical properties of two polycrystalline intermetallics with a B2 crystal structure, NiAl and NiTi. We use orientation imaging scanning ...electron microscopy to select a relevant number of grains with appropriate sizes and surface normals parallel to 〈001〉, 〈101〉 and 〈111〉. As a striking new result, we find a strong crystallographic orientation dependence for NiTi. This anisotropy is less pronounced in the case of NiAl. For NiTi, the indentation force required to impose a specific indentation depth is highest for indentation experiments performed in the 〈001〉 direction and lowest along the 〈111〉 direction. We consider transmission electron microscopy results from cross-sections below the indents and use molecular dynamics simulations and resolved shear stress calculations to discuss how this difference can be accounted for in terms of elementary deformation and transformation processes, related to dislocation plasticity (NiAl and NiTi), and in terms of the stress-induced formation and growth of martensite (NiTi). Our results show that the crystallographic anisotropy during nanoindentation of NiTi is governed by the orientation dependence of the martensitic transformation; dislocation plasticity appears to be less important.
Tube hydroforming is a well-established process in industry for producing complex shaped parts with closed cross section geometry and high geometrical accuracy. Hot-metal gas forming (HMGF) extends ...the conventional tube hydroforming process by a complex thermo-mechanical approach and thus potentially enables the complex processing of tubes from the relatively new class of quenching & partitioning-steels (Q&P steels). To prove the feasibility of an integrated Q&P treatment in the HMGF process, a simple demonstrator geometry is considered in the present study. The applied forming pressure is limited to 70 MPa, resulting in incomplete forming of the parts in the corner areas. The resulting, locally varying contact situation between workpiece and die allows the investigation of different cooling rates and their influence on local microstructural changes and on the corresponding mechanical properties. A numerical finite element simulation is used to estimate local cooling rates in three different areas of the tube (maximum cooling rates between 60 and 280 K/s), which are then correlated with hardness measurements and typical microstructural features. The hardness distribution is inhomogeneous over the cross section of the part (varies about 150 HV), with a minimum in the areas without die contact during quenching. Ferritic areas are observed in these regions due to the significantly lower cooling rates. Tensile tests show that the stress-strain behavior after the shortest partitioning time of 10 min is not only better from an energy efficiency point of view, but also provides both high strength (Rm =2050 MPa) and high ultimate strain (19.7 %), while longer partitioning times result in inferior properties. Thus, the present study shows that the Q&P treatment can be integrated into the HMGF process, but the local cooling rates must be taken into account as they strongly influence the final mechanical properties of the workpiece.
Severe plastic deformation techniques can produce ultrafine-grained aluminum alloys with high strength and ductility, but further processing often requires costly and/or time-consuming machining. In ...this study, we investigate the potential of an alternative processing route that operates below recrystallization temperature and that can produce fine-grained materials. Cast billets of the age hardening aluminum alloy AA6060 were solution annealed and then extruded at room temperature or at 170°C (which corresponds to the aging temperature of the alloy, and allows for simultaneous forming and aging). The materials were then subjected to an aging treatment. Electron microscopy and mechanical testing were performed to characterize the resulting microstructural features and mechanical properties. Both extruded profiles exhibit similar, strongly graded microstructures with submicron-sized grains in the highly deformed surface layers, and a mixture of coarse and fine grains in the center regions. Despite different processing routes (i.e., cold vs. warm extrusion), both materials are characterized by similar mechanical properties in terms of maximum hardness, strength and ductility; these results are discussed in the light of the relevant microstructural deformation and precipitation mechanisms.
After reporting on the ability of micro-EDM to significantly alter the transformation behaviour of Nitinol whereby increasing discharge energy reduces thermal hysteresis and results in a three-peak ...reverse phase transformation on heating, this study helps to further characterize the Nitinol micro-EDM process. This is by closely varying discharge energy so as to establish the boundary conditions for the three peak transformation behaviour as well as establish the influence of arcing on the mechanical properties of Nitinol. Samples machined using micro-EDM and jet-ECM are analysed using differential scanning calorimetry as well as tensile testing with five loading and unloading cycles after which the samples are loaded till failure. Moreover, discharge pulses are used to analyse arcing. From the results, it is not only possible to conclusively identify and establish arcing as the main phenomenon behind the three peak transformation behaviour, but also that the thermal damage caused by arcing results in a high residual strain, reduced elongation to failure, loss of machining accuracy and a reduction in upper and lower plateau stresses. It is also evident that if the discharge energy is carefully controlled to avoid arcing, it can be increased over a significant range (from ≈3.4 μJ to ≈130.2 μJ in this study) without significantly altering the phase transformation behaviour of Nitinol, which is very closely linked with its shape memory and superelasticity.
Simple shear tests are widely used for material characterization especially for sheet metals to achieve large deformations without plastic instability. This work describes three different shear tests ...for sheet metals in order to enhance the knowledge of the material behavior under shear conditions. The test setups are different in terms of the specimen geometry and the fixtures. A shear test setup as proposed by Miyauchi, according to the ASTM standard sample, as well as an in-plane torsion test are compared in this study. A detailed analysis of the experimental strain distribution measured by digital image correlation is discussed for each test. Finite element simulations are carried out to evaluate the effect of specimen geometries on the stress distributions in the shear zones. The experimental macroscopic flow stress vs. strain behavior shows no significant influence of the specimen geometry when similar strain measurements and evaluation schemes are used. Minor differences in terms of the stress distribution in the shear zone can be detected in the numerical results. This work attempts to give a unique overview and a detailed study of the most commonly used shear tests for sheet metal characterization. It also provides information on the applicability of each test for the observation of the material behavior under shear stress with a view to material modeling for finite element simulations.
The production of high quality powder metallurgical NiTi alloys with elevated phase transformation temperatures is challenging. During processing, an unavoidable pickup of impurity elements ...(especially oxygen and carbon) results in a decrease of phase transition temperatures and in the formation of brittle secondary phases. We introduce a processing route including melting, gas atomization and hot isostatic pressing for binary NiTi shape memory alloys which minimizes these problems. We demonstrate that the microstructure of the Ti-rich NiTi alloy contains precipitates of Ti
2Ni type which can be exploited to dissolve oxygen picked up during later process stages. In this study, three powder fractions with different grain sizes and impurity contents were subjected to hot isostatic pressing. The evolution of microstructures and material properties was studied by chemical analysis, microscopy, differential scanning calorimetry, and mechanical testing. Exploiting the solubility of oxygen in Ti
2Ni, the processing route presented in the present paper succeeds in producing powder metallurgical NiTi shape memory alloys with good structural and functional properties.
► AZ31 processed by ECAP and/or bi-directional rolling at 523 and 573K. ► ECAP increases texture-induced softening and ductility. ► Bi-directional rolling and water quenching enhances strength. ► ...Interrelation of microstructures, crystallographic textures and mechanical properties. ► Novel route leads to yield strength of 345MPa and elongation to failure of 13.9%.
In this study the hexagonal close packed magnesium alloy AZ31 is deformed plastically by equal-channel angular pressing (ECAP) at 523K, bi-directional rolling (BR) at 573K, and by combinations of these processes. The evolution of microstructures, crystallographic textures and of the mechanical properties is investigated systematically as a function of the processing method, the amount of accumulated strain or the ECAP processing route (strain path). Both BR and ECAP enforce a crystallographic reorientation, with an alignment of (0002) basal planes parallel to the direction of shear deformation. This results in significant changes of the strongly texture-dependent mechanical properties. In combined processing, ECAP is applied as a method to increase texture-induced softening and ductility, whereas BR followed by water quenching is used as a method to induce strengthening by work hardening. The aim of tailoring materials and microstructures that are strong, but still ductile, and that can consume a moderate amount of plastic work during deformation, is best met by a combination of ECAP and subsequent BR. The corresponding yield strength of 345MPa and elongation to failure of 13.9% demonstrate the considerable potential of the novel processing routes presented here for the first time.
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