Papers by Keyword: Loading

Abstract: Mechanical loading and unloading of silicon is a characteristic feature of grinding and diamond turning processes. Such rapid loading and unloading induces damage and phase transformations. While, indentation tests are often used to study such normal loading and unloading via characteristic events in the force-depth plot, such tests involve only normal loading and lack tangential loading. A better alternative is scratch test, both constant and varying depth ones, involving normal and tangential loading on the scratching tool; this better simulates conditions of machining, or grinding. In this research, the mechanical load/unload behavior response of silicon is studied under scratching conditions by comparing increasing and decreasing depth scratch behaviour. In-situ force responses show that after ductile-brittle transition occurs, higher forces, at a given scratch depth, are required to deform the material during increasing depth scratching for a given depth than in decreasing depth scratch. Large surface and sub-surface damages with the presence of radial, median, and lateral cracks are seen to make the material weaker, ahead of the advancing tool, in decreasing depth scratch. Raman intensity ratio of amorphous silicon (a-Si) to nanocrystalline silicon (nc-Si) shows that high amorphization of silicon occurs during increasing depth scratching than decreasing depth. Using such force-depth plots an attempt is made to compare the normal loads while indenting and scratching. This study can help optimize the processing of silicon by grinding and diamond turning.

Abstract: The paper presents the results of the study of the stress-strain state of polygonal shells of positive and negative curvature with different geometric shape of the plan, taking into account the influence of the prehistory of a high loading level. To derive the resolving equation, equation, a mixed-type equation of the moment theory of shells was used. The calculation of the investigated out according to the moment theory, taking into account the influence of a complex stress state edge effect. The numerical implementation of this solution is carried out in relation to hinged and restrained shells. The bearing capacity of short-term and long-term loaded reinforced concrete polygonal shells was investigated by the method of limiting equilibrium.

Abstract: In this article the use possibility of icosahedron type spatial dot lattices as constructive networks of many-sided domes is considered. The dome triangular panels design with the plywood coverings supported the board edges is accepted. Comparison of results of calculation with the valid work of a triangular Orto-tropic plate at a bend is made. The description of preparation and carrying out static tests of a plywood covering on a cross bend is provided.

Abstract: Microporous aluminum fumarate (A520) is one of the very few metal-organic frameworks (MOFs) that have been promoted to the level of commercial applications and has recently been proven to exhibit a rigid character with an accessible permanent porosity. This study explored the maximum loading amount of A520 for mixed matrix membrane (MMM) preparation by blending it with polyimide (PI) using N-methylpyrrolidone (NMP) as solvent, without compromising the membrane integrity. Scanning electron microscope (SEM) images revealed that MOFs were able to infiltrate the pores and structures of the polymer, improving the interface and mechanical properties of the polymer, as supported by different characterizations like dynamic mechanical analysis (DMA), x-ray diffraction (XRD), and positron annihilation lifetime spectroscopy (PALS). Results showed that MOF loading beyond 10wt% revealed aggregations that compromised the integrity of the membrane.

Abstract: In dry grinding of hard carbon parts, the loading by carbon chips on wheel surface occurs in early grinding process, and the grinding performance of wheel is extremely declined. The deterioration affects the grinding accuracy and efficiency. Therefore, loading is one of the problems that must be resolved for high efficiency and high quality grinding of carbon. Generally, the grinding performance of wheel is recovered by the dressing. However, it’s not suitable from a viewpoint of the wheel life and the production cost because available abrasive grains possessing sharp edges under loading carbon chips on wheel surface are lost by dressing. In this study, we propose the dry ice blasting for removing loading carbon chips on wheel surface. The dry ice particles impact on pressed carbon chips with high pressure and sublimate to carbon dioxide quickly. Therefore, it is little influence on working environment because the dry ice doesn’t remain on wheel surfaces after blasting without the damage. In this report, we carry out the blasting tests of resinoid bond diamond wheel surface without grinding performance by loading carbon chips, and analyzed the effect of nozzle processing speed and nozzle feed pitch on recovering abrasive protrusion. The effective dry ice blasting conditions are investigated for high efficiency removal of loading carbon chips, analyzing the protrusion height of abrasive grains.

Abstract: Cup-wheels are frequently used to grind cermets, a difficult-to-grind material. An investigation was made into the transient geometry of the cup-wheel rim, grit dulling, wheel loading, and wheel self-sharpening with chip thickness. Tests were performed on a saw-tip grinding machine and specific energies, G-ratios and rim geometries were measured. Results showed that, like grinding of tungsten-carbide, loading is prevalent. However, unlike grinding of tungsten-carbide, grit dulling is also prevalent and wheel conditioning is of limited use. Much better results, particularly with respect to surface finish, can be obtained if the wheel is trued to a predetermined geometry. In addition, grinding parameters must be chosen to induce wheel self-sharpening. Practical recommendations are given.

Abstract: Different graft materials and techniques are suggested based on the number of bony walls that remain after the tooth is removed. If the implant can’t be inserted within the bone contours, bone augmentation must be performed, and the graft must be stabilized with a membrane or a thin bone block graft. In the present study, two cases are presented both with small bone defects on the buccal plate. Bone augmentation with autogenous bone graft was performed in one case, respectively titanium implants with zirconia necks were used in the second case. It was demonstrated that titanium implants with zirconia necks are a good choice in some cases where small parts of the buccal plate are missing.

Abstract: The problem of shock deforming of elastic-plastic half-space with large deformation was examined. We have obtained that the deformation state can be changed in two types of simple plastic waves and two types of shock elastic waves in the case of self-similar medium motion. The speeds and characteristics of plastic waves were examined. The numerical solution of boundary value problem was found.

Abstract: The loading of the grinding wheel and adhesion of the workpiece material to the cutting edges of the grinding tool are among the main reasons which limit the process efficiency when grinding ductile materials. The micro topography of the grinding tool changes drastically as a result of loading. Higher grinding forces and temperatures, poorer surface quality and process accuracy are the consequences of the adhesion of the workpiece material to the grinding tool surface. A novel and promising technique to reduce the possibility of loading and adhesion in the grinding process is the infiltrating of the grinding tool. This study describes the results of infiltration of vitrified bonded conventional grinding wheels with graphite in the surface grinding process. The effects of infiltration have been studied for the first time on various grinding wheels with different grain materials, grit sizes, porosity and hardness. Two different types of steel which are very popular in the automobile industry, 100Cr6 and 16MnCr5, were chosen as the workpiece material by the surface grinding experiments. The selected cutting parameters cover a wide range of the practical surface grinding processes which are utilized generally in the industry. It has been experimentally shown that the type of infiltration plays an important role in reducing the loading of the wheel. Better surface quality and longer dressing intervals are the main results of the infiltration of the grinding tools.

Abstract: The given paper is closely connected with the complex proposal relating to the resistance temperature sensor for media temperature. The mentioned proposal is based on the analysis and simulation of loading with the reference to the resistance temperature sensor during the media flow in the pipeline while the heat transfer in solid body and media occurs simultaneously. The simulation of the loading was carried out on the basis of finite element method (FEM) using Cosmos Motion 2.86 program software. During the given investigation, the different media temperatures as well as different velocities or rates of media flow were taken into account.