جستجوی مقالات مرتبط با کلیدواژه « فوم » در نشریات گروه « فنی و مهندسی »

Hypothesis:

Polymeric foams have fascinating specific properties due to their cellular and porous structure and these properties have attracted much attention in industrial and scientific societies nowadays. The variations in cellular structure of polymeric foams including expansion ratio, cell density, and cell size may affect their final properties. For this reason, it seems necessary to study the effect of process parameters on the cellular structure of polymeric foams. On the other hand, the rotational molding method is developing rapidly compared to other processing methods due to its ability to fabricate large complex hollow parts Different process parameters can affect the structural properties of polymeric foams Utilizing nucleation agents as a material parameter improves the structural properties of polymeric foams significantly in different processing methods.

The effect of adding two types of nucleating agents including talc microparticles and clay nanoparticles in different sizes on the structural properties of polyethylene foams made by rotational molding process was investigated Azodicarbonamide was used as the chemical blowing agent. Talc microparticles (1% by weight) and clay nanoparticles were added to polyethylene and foamed using rotational molding process. Cell density, cell size, and expansion ratio were investigated as structural properties.

The findings revealed that the effect of talc microparticles on increasing cell density and decreasing cell size was more significant than the effect of clay nanoparticles. Cell density of polyethylene foam was improved by 96% and 89% by adding 1% (by weight) of talc microparticles and clay nanoparticles, respectively. A 20% and 17.5% decrease in the cell size of polyethylene foam was also observed with the addition of 1% (by weight) of talc microparticles and clay nanoparticles respectively.

In this research, the energy absorption capacity of hollow and filled foam thick-wall aluminum tubes under axial loading with a variety of damage models has been investigated empirically and numerically. Experiments to determine the mechanical properties of the specimens and to apply compressive loads on them were performed using a Zwick servohydraulic testing machine. Numerical simulations were performed using the Abaqus finite element software and the results were compared with the results of the experiments. In numerical analysis, three damage models, Johnson-Cook, Gurson-Tvergaard-Needleman (GTN) and modified Rousselier were used. Eventually it turned out that the modified Rousselier model has the least error. The Johnson-Cook damage model is available in Abaqus software but the Gurson-Tvergaard-Needleman and the modified Rousselier damage models were created through programming in Abaqus software. Also, in this research, the effect of thickness and foam injection on the energy absorption capacity of aluminum pipes was investigated and it becomes clear that increasing the thickness of absorber increases the absorbed energy and ultimate crushing force.

In this paper, the impact behavior of polyurethane foam-based composites reinforced with warp-knitted spacer fabric is investigated, experimentally. For this purpose, warp-knitted spacer fabric with different structures such as two different thickness, small and large mesh sizes and position of the meshes facing each other and not facing each other were produced. Then composite samples were fabricated using warp-knitted spacer fabrics as reinforcement, and polyurethane foam as matrix. The physical properties of samples like weight per unit area and fiber volume fraction of composite were measured. The failure energy of prepared samples was measured during quasi-static impact test, and finally low velocity impact with an initial energy of 5 J was carried out on composite samples. The results showed that the impact energy of samples is increased at least tripled by using the reinforcement. The maximum energy absorption is 2.858 J which is related to the samples reinforced with fabric with large mesh, high thickness and not facing of the meshes relative to each other. Generally, the energy absorption on average has been increased 21.2% by increasing the thickness, 9.5% by increasing the size of the meshes from small to big, and 47.3% by changing the position of the meshes from facing to non-facing.

Efficient drilling cuttings transport is one of the most important parameters affecting drilling rate of wells. Foam has a great potential to reduce drilling problems compared to conventional well drilling fluids due to its unique properties such as low density and high viscosity. Proper description of foam behavior enables us to improve the performance of foam for hole- cleaning. In this paper, cuttings transport using foam was studied using a computational fluid dynamics approach. In this study the Eulerian multi-phase model was used to describe cuttings-fluid mixture flow. Foam rheology was expressed by the non-Newtonian power law model. Effects of foam quality and injection velocity, cuttings size, pipe eccentricity and rotational speed of drillpipes were studied. Modeling results were also compared with experimental data. Results showed that increase of foam quality improved hole-cleaning operation mainly due to the enhanced foam viscosity. Increase of foam injection velocity led to a reduction in in-situ cuttings concentration. This was due to the foam capability to destruct stationary cuttings bed. Accordingly, as foam injection velocity increased from 3 to 5 ft/s, cuttings concentration decreased by 1.3 times. Also, an increase in the size of the cuttings caused a poor well cleaning. It was found that pipe eccentricity resulted in the accumulation of cuttings in the wellbore annulus. But, increase of the drillpipe rotational speed provided a better hole-cleaning, so that by increasing the rotational speed to 40 RPM, cuttings concentration decreased by 1.8 and 1.4 times in concentric and eccentric pipe, respectively.

Foam packaging involves long-term storage and protection of a variety of foods against physical, chemical and biological agents. Polymer foams are safe and recommended for many applications due to their very light weight, high versatility, durability, mold resistance and good appearance. This has led to high production and consumption of these materials, and due to the non-biodegradability of these materials, they have caused a lot of environmental concerns. Therefore, significant efforts have been made to develop environmentally friendly alternatives, especially in the case of starch foams. Because starch is a cheap, available, abundant, renewable and biodegradable biopolymer. These properties make starch the most important biopolymer for the development of biodegradable films, but the starch itself is relatively weak and water-sensitive. To improve the thermal and mechanical properties, moldability, water impermeability and other properties of starch-based foams, many approaches such as chemical modification of starch, combination with various biodegradable polymers, combination with natural fibers and the addition of nano-fillers are proposed.

The purpose of this study was to investigate the effect of high alumina cement and Sintering temperature on microstructure, physical and mechanical properties of foamed alumina insulation bricks. The Slurry samples  were prepared containing 75wt% of alumina and 25% wt of deionised water containing 1%, 3%, 5%, 7% wt% high Alumina cement and 2% wt% foam. Then samples were poured into metal molds. After drying the samples, they were sintered at 1510° C for 3 h. The Samples containing 7% wt cement were also sintered at 1600,1650° C for 3. The results showed that alumina slurry containing 2% foam and 7% high alumina cement additives at 1s-1 shear velocity had a viscosity equal to 3 Pa.s, which decreased with increasing shear velocity to 100 s-1and its decreased to 0.3 Pa.s. The samples showed a total density between 63.6 and 87.6  g/cm3, a total porosity between 59 and75%, a flexural strength between 6.6 and 6.8 Mpa and the average size of the spherical porosity between 8.5 and 11µm depending on the amount of cement and the baking temperature. phase investigations show that the peaks formed at the temperature of 1510° C correspond to the corundum and calcium aluminate phase)CaO.6Al2O3).

In this research, the structure and mechanical properties of polyethylene (PE)/ethylene-vinyl acetate copolymer (EVA)/nanoclay microcellular foams obtained through extrusion physical foaming by using carbon dioxide were investigated. The effect of PE/EVA concentration, organically-modified nanoclay and temperature profile on the properties were evaluated. The foaming process of these systems has significant complexity due to the occurrence of two concurrent phase transitions including upper critical solution temperature (UCST) phase behavior of PE/EVA blends and gas phase transition in the cell nucleation and growth process. Owing to the UCST phase behavior of PE/EVA mixtures, an increment in the process temperature profile has a profound impact on the morphology and mechanical properties of the foams and results in higher miscibility of the polymeric constituents of the blends and nanocomposites. Moreover, the nanoclay compatibilization mechanism leads to better miscibility of the polymeric phases. At higher temperature profile, lighter foams with higher cell density are obtained. Increasing the EVA content in the blends improves the nanoclay dispersion state and as a result, causes an improvement in the foam structure. By increasing the temperature profile and adding nanoclay, the elastic modulus of the foams improves and worsens respectively, due to the better PE/EVA miscibility state and nanoparticle influential role in the bubble formation.

Small scale tests can be conducted using Lab-on-a-chip devices with very tiny amount of fluids. In the case that the fluid is in the gas phase, it should be carried inside a bubble. In this paper, this type of bubbles is generated with certain size in a flow focusing microfluidic device. Microfluidic device can be manufactured by SOFT LITHOGRAPHY. when the bubble density is high enough in a channel, they come in to contact, and they flow in the form of crystal foam. the flow of the foams in the channel depends on the liquid flow rate and inlet gas pressure. This shall determine dynamic behaviors of the flow such as super-stability. Two types of foam including wet and dry foams are generated in flow focusing device. At certain pressure of 600 to 700 (mbar), the foam behavior is switched to non-linear behavior in which the shape of bubble is changed in period of time. At specific flow rate of 0.1 and 0.2 (ml/hr), it is observed that bubbles are generated in one raw and some others are in two within channel which are called hex-one and hex-two. The effects of increasing the flow rate at constant pressure (which reduces the size of the bubble from dry foam to wet foam) and the effects of increasing the pressure in the constant flow rate (which increases the size of the bubble from wet foam to dry foam) are investigated.

Consumers now have stronger affinity towards eco-friendly products instead of plastics. Eco-friendly packaging is made of recyclable or renewable materials which are sustainable and safe for not only individuals but also the environment. Mushroom- based packaging is one of the eco-friendly materials that have received considerable attention, recently. Mycelium is a fast growing vegetative part of a fungus which latches onto whatever around it like any low value organic matter to create a super-dense network of threads. Once growing in the mold to reach the desired density and shape, the material is dehydrated and heat treated, to stop further growth. Supplementary processes such as compression and laser cutting may also be used to achieve the required shape and structure. The result is a heat and fire-resistant, biodegradable and low cost material that has similar properties like synthetic foam plastics. There is no spore or allergen concern as the mycelium is not fully grown to produce fertile bodies. This paper reviews the current status of technology for production of mycelium based material and its applications as a sustainable alternative for polystyrene.

In this research, the behavior of conical and hemispherical shells, made of steel and aluminum, respectively, subject to impact loading has been investigated using experimental and numerical methods. The energy absorption capacity of these adsorbers has been calculated and the effect of foam injection on the collapse behavior and energy absorption capacity of aluminum hemispherical shells has been determined. The effect of geometrical parameters on the collapse behavior and adsorption capacity of steel conical adsorbers has also been investigated. Numerical simulations have been performed using the Abaqus finite element software and the results have been compared with the results of the experiments. In Numerical analysis, three damage models, Johnson-Cook, GTN, and modified Rousselier have been used. The Johnson-Cook damage model is available in Abaqus software but the GTN and the modified Rousselier damage models have been created through programming in Abaqus software. The results show that the modified Rousselier damage model is more accurate than the other damage models. Also, in this research, the effect of thickness of conical shells on their efficiency has been investigated and it becomes clear that increasing the thickness of absorber increases efficiency. In addition, foam injection does not a positive effect on the hemispherical absorber performance.

Naturally fractured reservoir account for 20% of world's oil reserves, in these reservoirs conductivity is mostly in the fracture network while the oil is mostly in the matrix and after primary recovery most of oil remains in the reservoir. Most of secondary or tertiary recovery methods such as water injection or gas injection are not efficient in fractured reservoirs. One of the remedy methods to control and improve volumetric sweep efficiency is foam injection. Foam in porous media is a dispersed gaseous phase within a continuous aqueous phase comprised mainly of thin films known as lamellae. The lamellae are stabilized by adsorption of surfactant at the gas/liquid interfaces. In the paper, experiments were performed to study the pertinent oil displacement mechanisms during gas and foam injection in a transparent fractured porous medium. Transparent material such as glass was used to construct micro models and to study various aspects of fluid displacement at pore scale. By using micro models, the displacement of the fluids can be observed and investigated in terms of micro-geometry and physical characteristics of the presented liquids, gases and solids. The classification of foams in based on their bubble size and gas fraction. The strength of foam is measured by the magnitude of the pressure drop that is generated along the medium. To create a large pressure drop very strong foams, and therefore very small bubbles, are required. Low productivity of gas injection in fractured reservoir leads to use foam instead of gas in order to increase resistance of fracture corridor against the injected fluid and to better control to mobility of gas.

Amorphous steel slag was blended with different concentrations of waste glass (20, 40, 50, 60, 70 wt.%) and SiC to obtain a composite. According to Hot Stage Microscopy images, slag-glass composite contractions started at 1050 ºC. scanning electron microscope micrographs of slag-SiC (foaming agent) composite revealed tunnel-like porosities of 500 to 1000 microns. Gaseous products of carbide decomposition led to the formation of these tunnel-like porosities. By adding up to 50 wt. % of waste glass to this composite and sintering at 1200 ° C, the size of cavities decreased by 10 times and achieved 50 microns to form spherical cavities. By increasing glass content, the total porosity of slag-glass-SiC increased to 80 wt.% followed by a decrease in the strength to 3.2 MPa. Having an overall density of 0.8 g/cm3, the slag-glass composite could be classified as a porous foam material. Pseudo Waltonite phase was also detected in this composite after sintering.

To reduce the damage caused by sudden collisions, energy absorbers are used. Energy absorbers, with their large deformation and folding, cause a large amount of collision energy to be absorbed, thus preventing damage to critical components. In the present research, the effect of geometric parameters of bi-tubular conical tubes and effect under axial loading on energy absorption is investigated by experimental and numerical methods. Then, the effect of foam is also studied to absorb more energy. In the experimental section, firstly, conical tubes made of aluminum with empty and filled with polyurethane foam were prepared, and then the samples are experimentally tested and the displacement-force diagram is obtained in each test. In the numerical section, the simulation of the axial deformation phenomenon of the thin-walled conical tubes is carried out with the ABAQUS software. The comparison of experimental and numerical results show that the proposed model is a suitable method for studying its collapse and amount of energy absorbed in the energy absorber system. Finally, the effect of the main system parameters, such as difference of inner and outer tube diameter, tube length, wall thickness, type of tube material, and the filling of foam, is studied on the energy absorption in thin-walled bi-tubular conical tubes absorber using numerical methods.

Energy absorbing systems are used in many engineering structures, especially in moving machines, to prevent or to reduce impact induced damages. The aim of this study is to survey deformation and energy absorption of sandwich structures consisted of two concentric aluminum tubes with EVA polymer foam between them. Two loading methods have been used; quasi-static loading and impact loading. Deformation mode, energy absorption and mean crush force were investigated as mechanical behavior parameters. Moreover, the effects of changes in tubes length and foam density on these parameters have been studied. For parametric study, finite element simulations carried out using LS-Dyna software. Results of the study show that using foam increases energy absorption; the higher the foam density the greater the energy absorption and mean crush force. Furthermore, comparison of folding mechanism between foam-filled structures and empty ones shows that using foam does not affect the folding mode.

In this research, through carrying out experimental tests and finite element simulation, the crushing method of empty and foam-filled thin-walled structures under the influence of axial, Quasi-static loading has been compared. In experimental study, the conical samples are made through spinning method. These samples are compressed between two rigid plates under quasi-static loading conditions, and then the collapse mechanism, the crushing force fluctuations and absorbed energy are calculated. Simulation of tested specimens has been executed by ABAQUS software in 3- dimensional models and through explicit method. The comparison of numerical and experimental results showed that the present model provides an appropriate procedure to determine the collapse mechanism and load-compression curve. The validated finite element model was then used for the parametric studies, in order to determine the effect of the empty and filler tube geometry parameters (i.e. semi-apical angle, foam density, wall thickness) and loading parameters (i.e. impact mass and impact velocity) on the energy absorption and factor crushing load ) .(

Foam injection for the purpose of Enhanced Oil Recovery (EOR) process is one of the approaches of chemical EOR. In this method, in addition to using the surfactant, other chemical additives are used to achieve ultralow IFT which result in mobilizing the residual oil of the primary and secondary recovery stage. Foam generation causes to achieve the mobility ratio of less than 1, and then the foam generation improves volumetric sweep efficiency. In foam flooding, foam stability is one of the determining parameters for increasing oil recovery. Generating the most stable foam is one of the subjects of the recent researches on this kind of EOR process in stand point of selection of type and concentration of chemicals. In this study, effects of salinity, surfactant concentration, and the type and the concentration of co-solvent were investigated on foam stability. Optimized stability was gained in different co-solvents. This optimum was used in flooding process to investigate its effect on oil recovery. Butyric acid and 1-butanol were two used co-solvent. The most stable foam was resulted from the samples which utilized butyric acid as co-solvent. Maximum oil recovery of 44% of OOIP has observed in solution with 1-butanol as co-solvent, which is not displaced by water flooding. Moreover, observing the maximum oil recovery validates the efficacy of this technique.

In EPB-TBM tunneling, a positive face control during tunnel excavation is delivered and the tunnel face is supported by pressure from the mass of remolded soil within the cutterhead chamber. EPB TBMs operate more eectively when the soil immediately ahead of the cutterhead and in the chamber forms a plastic plug, which ensures face support. The target properties for extracting soil in an EPB TBM can best be described as a soil matrix exhibiting a soft workable plastic consistency. The behavior of excavated soil from mixing up to extraction depends mainly on the property called workability of conditioned soil. Workability in simple terms can be de- ned as the ease with which the excavated soil can be mixed with additives, compressed in pressure chamber, owed freely from the face and finally extracted from screw conveyor. Furthermore, the workability is an indicator for the plasticity of the support media, comparable to the consistency of cohesive grounds and thus a criterion for the applicability of EPB tunneling. The factors which effect the workability of conditioned soil are water content, fine grain, foam injection ratio (FIR). In this study, effecting 10 and 20 percentage of water content and FIR on workability of conditioned soil for EPBTBM tunneling is assessed with laboratory slump test. The 66 laboratory trials of soil-foam-mixtures were made to investigate the in uence of the mentioned parameters on workability of conditioned soil. To analyze the available data using statistical methods, relationships between mentioned parameters and slump test results were investigated. Results of analyzes show that there are a quantitative relation between water content and the workability for the application of EPB shields. The present study clearly showed that the decrease of water content and FIR became stronger with the decrease of the slump of conditioned soil. Finally, in this study, a new empirical chart, for assessment of and workability of conditioned soil is suggested.

The aim of this work is to study stability and mobility of modified nanoparticle-stabilized foam. Adding oppositely charged surfactant to the hydrophilic silica nanoparticle leads to variation in the hydrophobicity of nanoparticles. Surfactant’s adsorption on the nanoparticle’s surface is compared with different mixtures by a new criterion which is calculated by measuring conductivity. The adsorption criterion in domain of surfactant concentration has a maximum close to 1 CMC where nanoparticle reaches to maximum hydrophobicity. NPS-stabilized CO2 foam formed with simultaneous injection of CO2 and foam agent dispersion through a glass bead pack at reservoir pressure. Nanoparticle alone is not surface active. By adding appropriate surfactant concentration to nanoparticle dispersion¡ it becomes surface active. The complementary study of both pressure behaviour and morphology of foam using foam’s dynamic characterization apparatus¡ shown in the domain of surfactant concentration¡ apparent viscosity of the foam has a maximum about 6.034 cp which is consistent with the maximum adsorption criterion. Also¡ adding nanoparticle to the solution of surfactant forms more uniform¡ and the smaller foams and the apparent viscosity increase significantly. Increasing at a CO2 injection rate will also increase the size of the bubbles and reduce the apparent viscosity which means an increase in mobility.

In this paper, a new analytical model has been presented for energy absorption calculation of aluminum-foam sandwich panels under high velocity impact. The panels consist of foam core sandwiched between two aluminum skins. In analytical model, cylindrical rigid projectile with flat ended has been considered. In the quasi-static loading, by using the springs-mass model, energy absorption of aluminum skins with considering difference energy absorption mechanisms has been calculated. Also foam absorbed a partial of projectile energy by crushing. Energy absorption of aluminum-foam sandwich panel was calculated and energy balancing equation has been employed for determination the ballistic limit and residual velocity of projectiles. The results of ballistic limit and residual velocity computed by new model presented good agreement with experimental and numerical results. Also the effects of foam density, projectile mass and diameter in energy absorption of sandwich panel has been investigated.