جستجوی مقالات مرتبط با کلیدواژه « porosity » در نشریات گروه « مکانیک »

It is not possible to fabricate the complex geometry of coherent cooling channels with conventional machining methods, so channels can be created in the mold using additive manufacturing processes such as selective laser melting. Parts created by selective laser melting always have porosity, and the amount of porosity depends on process parameters. On the other hand, the ability to make porous materials with a selective laser melting process has made these materials with features such as lower density and better heat transfer in the aerospace industry, automobile, medical uses and heat exchangers to be the attention of researchers and according to Porosity Percentage, in addition to directly affecting mechanical properties, also affects heat transfer. In this research, the effect of porosity on heat transfer in the mold was investigated. First, the model and mold were designed, in order to investigate the effect of porosity, four simulation models with volume porosity percentage of 0, 10, 20 and 30% were performed and analyzed in the software. The analysis of the results shows that the increase in the percentage of porosity in the mold causes a faster increase in temperature in the mold, also with the increase in the percentage of porosity in the mold, the speed of temperature decrease in the mold increases. And the cooling of the part happens faster. Examining the results of the maximum thermal gradient of the non-porous material compared to the material with 30% porosity shows a 21% increase in the thermal gradient in the porous material

Many parameters,including scanning strategy,speed,power,etc,have an impact on the mechanical and physical properties of the parts made by the selective laser melting process.Correct and optimal selection of these parameters prevents defects such as porosity,incomplete fusion gaps and cracks in the parts of the manufacturing process.Despite all the advantages of the selective laser melting process,the creation of defects directly affects the mechanical properties and fatigue resistance of the parts negatively. In this research,the impact of zero,45,and90degree build orientations,the effect of changing the size of the parts on mechanical properties such as tensile and shear strength,fracture strain,and the number of defects investigated.The built parts were subjected to tensile and shear tests,and the fracture area was examined using SEM and the existing defects identified.The tensile test results showed that larger samples have higher tensile strength than smaller samples.Moreover,higher tensile strength and lower fracture strain were observed in samples made in zerodegree orientation.The results of the shear test also showed that the strength of the shear stress for the small and large samples made in all orientations is almost the same,and the highest shear strain of failure is related to the samples made in the orientation of 45degrees independent of the dimensions.The SEM results also showed that the amount and distribution of spherical holes and fusion gaps in large samples made at90degrees is more than in samples made at 0and45degrees

Exposure of the TBCs layers to high temperatures for a long time causes sintering in the ceramic layer, resulting in changes in the porosity. Since the thermal conductivity of air in the porosity of the layers is much lower than the ceramic material in the coating, a decrease or increase in the percentage of porosity will end up with changes in the conductivity of the layer, which subsequently affect the overall efficiency. In this study, a TBC was first applied to the prepared samples from Inconel738 turbine blades. The samples were subjected to an aging process in the furnace for a specified time. The porosity changes in the ceramic layer of the coating during the aging process were investigated using image processing of the SEM images. The porosity of the images obtained from SEM and thermal conductivity in different porosities were determined by OOF2 and ImageJ software, respectively. To validate the numerical results, temperature distribution on the thermal barrier coatings is obtained by the analytical solution of the Fourier equation. According to the analysis performed on the SEM images gathered from the samples during different aging hours, it is observed that by increasing the aging hours during 48 hours, the percentage of porosity of the whole ceramic layer decreased by 8%. According to the results, by decreasing porosity in the ceramic layer, an increase in thermal conductivity has been observed, followed by an increase in the substrate's temperature and a decrease in the overall performance over time.