Papers by Keyword: Cellular Structure

Abstract: Selective laser melting (SLM) can produce Ni-based superalloys with a unique hierarchical structure consisting of micrometer-scale crystallographic lamellar microstructure and nanometer-scale cellular structure under optimized process parameters. This work investigated the effects of input energy density on the morphology of the cells and its influence on the tensile properties of Ni-based superalloy prepared by SLM. We found that the cell spacing decreases with decreasing input energy density. Further investigation of the cells clarified that the boundary of cells is a low angle grain boundary with dislocation cell wall and segregation of certain elements such as Nb and Ti. Moreover, it was demonstrated that the boundary of cells performs as a significant barrier to the griding dislocation. Thus, the cell boundary leads to strong strengthening through the Hall-Petch law.

Abstract: The article is devoted to the problem of raw material base expanding and improving construction and technical properties of porous granular materials. The results of experimental studies of silicate compositions based on liquid glass and technogenic fillers containing burnable or gas-forming components are presented. Influence of molding mixtures’ composition on thermal expansion nature of granular compositions was established. Preference of a filler combined, containing glass cullet, silica clay and mineral additives was revealed. Multicomponent composition of a filler helps to intensify composition’s expansion. Electron microscopy studies of porous silicate granules have confirmed the advantages of combined fillers using. Effectiveness of sodium additive introduction to regulate technological properties of the raw material and the process of pores formation has been proven. Expediency of mechanical activation of a raw mixture to reduce the temperature of expansion and obtain granules with a bulk density of not more than 300 kg/m³ has been determined.

Abstract: It has been presented the study results of the firing process of cellular ceramics from granulated foam glass. The chemical, mineral and granulometric compositions of the raw materials are given. It has been shown the characteristic of ceramic-technological properties of raw materials. The samples were burned from the granulated mixture in the temperature range of 850-1000 ° C. It has been established the change dependence in the physicomechanical properties of cellular ceramic samples on the temperature and firing duration. The results of the study of the macro-and microstructure of cellular ceramics are given. It has been revealed the effect of intensive formation of the pyroplastic phase and the connection between small pores at a temperature of more than 950 ° C. After the enlargement, the cells leave the three-phase ceramic system and it was the increase in the average density of cellular ceramics is 1.4-1.5 times. The influence of a solid glass-ceramic shell along the inner surface of the pores on the decrease in water absorption of cellular ceramics to 6.5-7% is established.

Abstract: One of the most important areas of energy and resource saving in construction is secondary material resources use. In modern construction, the requirements for concrete as one of the main building materials have grown so much that classical compounds are not able to provide the required qualities. Aware of this drawback, there is a tendency to improve and to change the structure and technology of modern concrete production with obtaining better physical and mechanical properties of a new building materials generation. Among the variety of technogenic wastes at the heart of the recycling problem is a significant part of cullet, which is an effective secondary resource in obtaining modern concrete compositions with ecological and economic effects. The physical-mechanical properties of a new high-efficiency thermal insulation material – foam glass concrete are presented. A method for the formation of the lightweight concrete cellular structure is proposed, and the scope of foam glass concrete products and structures is determined.

Abstract: The compression test data are represented for a cellular Ti-6Al-4V titanium alloy, manufactured using laser powder bed fusion on EOSINT 280. The inhomogeneity of deformation was revealed in the form of a barrel of the side surfaces during the test. The problem was simulated by the finite element method for two formulations: the compression of cellular material with friction and without friction. A comparison of the stress-strain state of the two cases was made. The same inhomogeneity of deformation is achieved, both in the experiment and in the analytical solution.

Abstract: Metal foams are a cellular structure that has a solid matrix made of metal and has pores in their structure. Metal foams offer excellent combination of properties which led researchers interested in investigation in recent years. Closed-cell stainless steel (SS316L) foams for biomedical application were prepared by space holder method and the physical and morphological properties of SS316L foams were studied. Stainless steel (SS316L) powders as metallic material, polyethylene glycol (PEG) as a binder and Urea as a space holder material were mixed homogenously to avoid the particle wrecked. This mixture was compacted using uniaxial pressing machine and pressurized to 8 tons to formed the green body. By using tube furnace, the SS316L foams was two-stage sintered, the first phase at 600°C for 2 hours to decompose the urea, and the second phase at 1000°C, 1100°C, and 1200°C respectively to sinter the steel. The porosity and density test was carried out by applying Archimedean principles, while morphological observation was done by using Field Emission Scanning Electron (FESEM). The samples with 40wt.% SS316L composition and sintered at temperature of 1100°C, leads to porosities of about 44.539% and show the potential as the best metal foams.

Abstract: The growing demand for advanced manufacturing processes calls for reduction in manufacturing cost and manufacturing time. Fused Deposition Modelling (FDM) is one of the rapidly developing rapid Prototyping (RP) process. In this work an effort has made to make FDM process cost effective by replacing solid model with shelled model in-filled with user-defined parametric cellular structures. This approach helps in keeping a balance between material usages, build time and mechanical properties. The proposed method is implemented on a few specimens and results signify that 20-30% expensive build material as well as build time can be saved by this approach. The whole algorithm is based on .STL format, and is coded in MATLAB providing a versatile and widely acceptable platform.

Abstract: The recent introduction of selective laser melting (SLM) for the processing of medical grade cobalt chromium (CoCr) alloy has led to a complex shape fabrication of porous custom CoCr alloy implants with controlled porosity to meet the requirements of the anatomy and functions at the region of implantation. This paper discusses finite element (FE) analysis and mechanical characterization of porous medical grade CoCr alloy in cubical structures with volume based porosity ranging between 60% and 80% produced using SLM rapid manufacturing process. Analysis by FE is considered beneficial to predict the effective mechanical properties of the porous structures manufactured by SLM due to minimization of the need for expensive and time consuming physical testing. Cellular structures modelling for fabrication with Direct Metal Laser Sintering machine were designed to vary between 60% and 80% to study the effect of structural variation on mechanical properties of the cellular porous structure. ANSYS 14.0 FE modelling software was used to predict the effective elastic modulus of the samples and comparisons were made with the experimental data. FE results show that with the material properties in the functions of porosities, minimum mesh size of 0.2 mm for triangular shape mesh and boundary as well as load conditions as applied in this study, agreement in equivalent stress, strain and deformation with the experimental results can be achieved to some extent. The technique for FE in this study can be used to investigate stress distribution in three dimensional model of real bone.

Abstract: We consider the problem of a density-graded cellular rod in a temperature gradient field axially subjected to a mass impact. Two-dimensional cell-based finite element models and one-dimensional shock models are employed to explore the mechanisms of deformation and wave propagation. The yield stress distribution in a cellular specimen depends on both the density gradient field and the temperature gradient field. The stress distribution and the yield stress distribution are analyzed. For the increasing yield stress along the impact direction, one shock front propagates from the proximal end to the distal end of the specimen. For the decreasing yield stress along the impact direction, two shock fronts propagate in opposite directions and the one close to the proximal end ceases at a particular time. The predicted stresses of the extended shock models are compared well with the numerical results.

Abstract: In the present work has been carried out the treatment of silumin by high-intensity electron beam with different density of the input energy. The structure and phase composition of surface layer have been studied by the methods of X-ray diffraction and electron microscopy both scanning and diffraction transmission. The mechanisms are responsible for improvement of properties of modified material have been revealed. It has been shown that electron beam treatment of silumin is accompanied by the formation of multilayer submicro-and nanocrystalline structure and result in increasing the microhardness of the surface layer (towards the core) is ~ 3.5 times, the Young's modulus in a ~ 1.4 times, the ultimate bending strength (in ~ 1.2 times) and tensile strength (in ~ 1.4 times), the bending plastic limit (in ~ 1.2 times) and tensile (in ~ 1.8 times).