Materials Engineering - Materiálové inžinierstvo (MEMI)
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OPTIMIZATION OF CAPILLARY ACTION & BRASS CONSUMPTION IN DIP-BRAZING OF ROADSTER BICYCLE FRAMES
Get PDFThis paper describes the requirements of joint clearance between the mating parts, of lugged bicycle frame head, to be brazed by flow of molten filler material (brass) between the micro gap due to capillary action. Tolerance analysis was done to establish the practical requirements of clearances essential to facilitate the assembly of the bicycle frame tubes and mating head lugs. Consumption of brass was computed, by weight measurements, after dip brazing of the lugged joints. Excessive joint clearance between the mating parts was reduced, by cold compaction of the assembled joint on mechanical power press using a press tool. The compacted joints were dip brazed by dipping it partially in the molten brass. Comparison of tensile strength of the brazed joints was done with respect to the strength of parent steel tubes. Brazed samples were sectioned to confirm the flow of brass all along the length of the lugs with improved capillary action. Thickness of the micro layer of the brass between the lug bore and tube outer surface was measured on optical microscope. Reduction in brass consumption due to reduced clearance was estimated volumetrically between the contact area between the lugs and the tubes
ZnO THIN FILMS PREPARED BY ATOMIC LAYER DEPOSITION
Get PDFThe purpose of this paper is present the influence of deposition conditions of nanometric zinc oxide thin films using atomic layer deposition on the mechanical and optical properties. The influence of the deposition temperature and the number of cycles on the transparency and adhesion of the ZnO, thin films was investigated. In addition, the results of chemical and phase composition analysis of the layers and their topography and structure were discussed. As a substrate for the investigated thin films was used glass. For the preparation of ZnO thin films was used ALD method. Selecting this method is justified by the high quality and good properties of the deposited layers
EFFECTS OF CHEMICAL COMPOSITION ON MECHANICAL PROPERTIES OF Al-Mg-Si-Mn BASED ALLOYS
Get PDFEffects of chemical composition and heat treatment on the microstructural and mechanical properties of cast Al-Mg-Si-Mn alloys were investigated. The as-cast and heat treated alloys were investigated by microhardness, macrohardness and tensile stress measurements, scanning and transmission electron microscopy, energy dispersive X-ray analysis and differential scanning calorimetry. It was observed that the mechanical properties depend strongly on composition and addition of excess elements and eutectic phase. Heat treatment leads to the enhancement of all mechanical properties of alloys, which are the result of several mechanisms
Fretting–fatigue behavior of bolted joints using FEM method
Get PDFIn this paper, the fretting damage of a mechanical bolted assembly in three dimensions is studied using a numerical approach. The study consist to analyze the cylindrical coordinates in stress fields and other fretting parameters depending on the angle and radius of the contact areas, and also to determine the position of the initiation and propagation of the crack.The numerical simulation is done in 3D in order to better describe the real behavior in fretting of a bolted joint. According to the simulation results, the tightening torque plays a significant role in the load transfer. The results allowed us to determine the stress that triggers the initiation and crack propagation, and locate the damaged area by fretting
EVALUATION OF WEAR BEHAVIOR OF Al-Si ALLOY USING SiC AS THE REINFORCEMENT
Get PDFThe current study investigates the wear behavior of the SiC particles reinforced Al-Si alloy composites developed using the stir casting process. The results were obtained from the wear tests of the cast Al-Si alloy and prepared SiC reinforcement composites containing 3 % wt and 9 % wt using fine and coarse size SiC particles. The wear test of all the developed composites were done at different testing conditions with varying loads. The analysis of wear traces, as well as the wear debris, was done at every composition but at higher loads. It was observed that the wear resistance was improved with increasing the amount as well as decreasing the size of the SiC particles. However, the wear rate of the composites increases with increasing the applied load. From the microstructural study of specimen after the wear test one can conclude that both adhesive and abrasive wear mechanisms contribute for wear of SiC particle composites
Welding of the tube girder cover made of the C-Mn high strength steel
No full textThe welding procedure and technology for welding the cover of the tube girder is presented in this paper. The tube cover is made of the C-Mn high-strength steel. The welding has to be performed over the whole perimeter in the V groove. Since the structure in question is a very responsible one (a part of the assembly of the large hadron collider – LHC), the check of the base metal chemical composition and the mechanical properties had to be conducted before actual prescribing of the welding process type and the complete welding technology. Then the weldability of the base metal was estimated, which showed that this particular steel was conditionally weldable with application of preheating. The welding technology was prescribed, based on the previously determined parameters including the welding procedure and the filler metals selection. The prescribed technology was afterwards executed on the selected experimental samples. To verify that the selected technology was adequate, the hardness and the microstructure of all the zones of the welded joints were determined. Analysis of executed experimental welds on chosen samples has confirmed that the welding technology was appropriate and that it could be applied to the real part – the LHC assembly
Effect of tool shape and welding parameters on mechanical properties and microstructure of dissimilar friction stir welded aluminium alloys
Get PDFIn the present experimental study, dissimilar aluminum alloy AA5083 and AA6082 were friction stir welded by varying tool shape, welding speed and rotary speed of the tool in order to investigate the effect of varying tool shape and welding parameters on the mechanical properties as well as microstructure. The friction stir welding (FSW) process parameters have great influence on heat input per unit length of weld. The outcomes of experimental study prove that mechanical properties increases with decreasing welding speed. Furthermore mechanical properties were also found to improve as the rotary speed increases and the same phenomenon was found to happen while using straight cylindrical threaded pin profile tool. The microstructure of the dissimilar joints revealed that at low welding speeds, the improved material mixing was observed. The similar phenomenon was found to happen at higher rotational speeds using straight cylindrical threaded tool.
Experimental and numerical investigation of a simplified exhaust model
Get PDFA simplified experimental equipment was built to investigate heat radiation and free convection around hot exhaust pipe. Temperatures were measured on the surface of the pipe as like as on heat insulating and -reflecting aluminum shield. Special care was taken to the temperature measuring method: result proved that inappropriate fixing of measuring thermocouples lead to an error of up to 30 % in the temperature-increase values. A detailed 1D numerical model was set up and parametrized so as to the calculation results can be fitted to measured temperature values. In this way thermal properties of the surfaces – as emissivities, absorption coefficients and convective heat transfer coefficients – were determined for temperature sweeps and stationary state cases. The used methods are to be further improved for real automotive parts and higher temperatures
Wear resistance of layers hard faced by the high-alloyed filler metal
Get PDFThe objective of this work was to determine the wear resistance of layers hard faced by the high-alloyed filler metal, with or without the austenite inter-layer, on parts that operate at different sliding speeds in conditions without lubrication. The samples were hard faced with the filler metal E 10-UM-60-C with high content of C, Cr and W. Used filler metal belongs into group of alloys aimed for reparatory hard facing of parts damaged by abrasive and erosive wear and it is characterized by high hardness and wear resistance. In experiments, the sliding speed and the normal loading were varied and the wear scar was monitored, based on which the volume of the worn material was calculated analytically. The contact duration time was monitored over the sliding path of 300 mm. The most intensive wear was established for the loading force of 100 N and the sliding speed of 1 m.s-1, though the significant wear was also noticed in conditions of the small loading and speed of 0.25 m.s-1, which was even greater that at larger speeds.
Zirconia / Alumina Composite Foams with Calcium Phosphate Coating
Get PDFIn this study, mechanical properties of calcium phosphate foams were enhanced by zirconia/alumina porous cores prepared by polymer replica technique. This technique was chosen to ensure interconnected pores of optimal size for cell migration and attachment. The porosity of ZA cores (50 – 99%) was controlled by multistep impregnation process, the size of pore windows was 300 – 500 μm. Sintered ZA cores were impregnated by hydroxyapatite or β-tricalcium phosphate slurry to improve bioactivity. The bone like apatite layer was formed on coatings when immersed in a simulated body fluid. Neither of tested materials was cytotoxic. Thus, the composite foam can be potentially used as a permanent substitute of cancellous bone