Papers by Keyword: Bulk

Abstract: In this work, we investigate the static electrical parameters of 1200 V 4H-SiC power diodes with various designs and architectures (Schottky, PiN, and JBS with hexagonal or stripes anode), fabricated on two types of 150 mm substrates (single crystal 4H-SiC reference and 3C-poly silicon carbide based substrates: SmartSiC^TM). I(V) measurements are carried out in both reverse and forward modes to assess the impact of designs and substrates. Non-destructive avalanche mode is reached with similar performance (leakage, V_AV) observed for both substrates (due to identical drift layers and device structures). All diode designs on SmartSiC^TM exhibit a larger current conduction and less resistance in the ohmic regime (compared to bulk), whatever the temperature (up to 200°C). Partitioning model is also proposed for evaluating the substrate contribution on the measured specific resistance and on the observed SmartSiC^TM gains.

Abstract: The work refers to the modern method of stabilizing unstable, water-saturated creeping slopes, with the combination of bulk piles and gabions. The application of the method makes it possible to ensure the stability of the slope by means of bulk piles, passing through weak soils, building semi-massive gabion walls on the piles with a stepped front edge. Bulk piles and gabions are used in modern construction for strengthening the slopes of river banks, in the preparation of protective structures to stand the rockfall, avalanche floods, in the construction of bridges, hydraulic and other facilities. The novelty of the proposed method is the stabilization and watering of the slopes organized without the construction of reinforced concrete retaining walls and land-based systems. It provides strength in depth and minimizing hydrostatic pressure.

Abstract: Free standing 3C-SiC wafers with a dimeter of 50 mm and a thickness of ca. 0.8 mm have been grown on a regular base using 3C-SiC CVD seed transfer from Si wafers to a poly-SiC-carrier and a sublimation epitaxy configuration. Up to the thickness of almost 1 mm, stable growth conditions of the cubic polytype have been achieved. The high supersaturation was kept stable by the proper design of the hot zone that enables a high axial temperature gradient at the growth interface. The Sirich gas phase was realized by the application of a Tantalum getter that was integrated into the graphitebased growth cell. Furthermore, an adaption of the growth setup allowed the growth of 3C material with a diameter of 95 mm and bulk material up to 3 mm on 25 mm diameter. Computer simulations were used to determine the supersaturation of the growth setup for different source-to-seed distances. The minimum supersaturation necessary for stable growth of cubic SiC was found to be higher 0.1 for seed already containing the required 3C polytype.

Abstract: In metallic glasses plastic deformation occurs via the creation and the propagation of a softened region in the shear bands. Some of the high strength metallic glasses (as Zr-based metallic alloys) exhibit complex shear band topography and the final failure respects the allocation of the shear bands. We studied the differences in the fracture surfaces of Zr-and Mg-based amorphous alloys. Ductile behaviour of the shear bands in Zr-based amorphous alloy tends to the dimple creation during the failure. On the fracture surfaces the vein pattern morphology manifestations were present. Conchoidal fracture was typical for Mg-based amorphous glass. Two different surface morphologies, plumes and rib marks ornament the fracture surfaces.

Abstract: The paper is focused on microstructure characterisation of five bulk metastable β-type Ti-based alloys, with improved mechanical properties, composed of non-toxic (bio inert) elements like: Nb, Ta, Cr, Zr, Ag, and In. These types of alloys designed in this study, are expected to have also higher corrosion resistance in biological media and good performance such as lower Young’s modulus of elasticity, greater strength, good workability, also in as cast state. However, high strength as well as low Young’s modulus is required for the implants subjected to cyclic loading under complicated stress conditions. Thus, the major aim is decreasing the Young’s modulus and increasing the tenacity of these alloys.

Abstract: The work analyzes application perspectives of Ti-based alloy VT6 (Ti-6Al-4V) with an ultrafine-grained structure with different grain sizes as structural material to produce high-load machine parts. The paper considers technological factors for ensuring quality of parts with account of assumed conditions of their exploitation, differently directed change of mechanical properties with reduction of an average grain size and choice of surface hardening technique.

Abstract: The pressure on the wagon body is generated for stochastic vibration of train or vehicle. The value and variation of this dynamic pressure are great significance in the study of the fatigue strength of the wagon body. This paper reviews the various influencing factors of the pressure distribution and also summarizes its simulation and prediction method based on the sufficiently literature reading.

Abstract: Dense mesoporous alumina bulks were successfully synthesized by a hydrothermal hot-pressing (HHP) method for mesoporous alumina powders prepared as starting material with a high BET surface area and narrow pore size distribution. As a result, mesoporous alumina HHP bulks had high density with uniformity pore size distribution and a high specific surface area. Their microstructural features for dense mesoporous alumina bulks were observed by SEM. The characterization of mesopores was examined.

Abstract: The main limitation of bulk metallic glasses for their application as structural materials is the large brittleness under the external loading. We analyzed the failure characteristics of Co₄₃Fe₂₀Ta_5.5B_31.5 (at.%) bulk metallic glass deformed in a compression at the room temperature and a low strain rate. Under loading the amorphous structure can store high elastic energy. During the failure this energy is released and the alloy breaks into small particles or powder exhibiting a fragmentation mode. The nanoscale fracture surface morphology respects the micromechanisms of failure of the amorphous structure. The fracture surface consists of a smooth mirror cleavage zone and a river pattern zone with the nanosized dimples arranged in lines respecting the periodic corrugation zones oriented perpendicular to the crack propagation direction.

Abstract: This Finite element method is one of the most advanced calculating methods for approximation of accurate solutions to engineering problems. Optimization of grabs quay cranes is necessary because most port operators use this type of equipment for loading and unloading bulk cargo. Initial research methods applied in this study are based on observations and surveys conducted on Bocşa 16 t - 32 m mobile quay cranes of MinMetal S.A. Constanta port operator. Modeling and analysis for grabs structure optimization was made with FEMAP and NX NASTRAN - version 10.3.1 applications, which use the finite element method and finite element analysis. After calculations and analysis, the following optimizations resulted:-to increase the grabs closing force (in order to minimize the loss of cargo between jaws and to increase digging force) the lower beam weight must be reduced.-to reduce the amount of cargo drained from the grabs jaws at loading, rubber jaws barriers can be fixed or bars can be welded at grabs jaws.- if cargo has high granulation, in order to reduce grabs weight the plate of the jaw can be cropped.-cups supporting tie rods could be replaced by hydraulic cylinders.The greatest tension is located in the cups supportive arms and in the area where cups are attached to arms. Shafts tensions are larger than the grabs metal structure and are located in shafts-arms contact areas, ie support bearings. In these areas, an optimization can be made by installing ball bearings to reduce friction. The largest deformations occur in the middle area of the arms. To increase safety in operation it is necessary to change the material of the four arms supporting cups, given that deformation of 89.7 mm (~ 9 cm) combined with external factors and / or shock loads can lead to permanent deformation or even material breaks. After changing the material, the model showed that the deformations in the middle area of the arms are substantially reduced, at only 4 mm. In the contact area of the upper arms with the two bars of the upper beam, hazardous tensions may be minimized if there are inserted bearings.