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

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.

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.

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.

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.

Sandwich panels due to high strength to weight ratio and energy absorption properties, are widely used in various industries including aerospace industries, marine and automotive industries. Analysis of ballistic resistance of sandwich panels is mainly numerical and experimental, and there are a few analytical models in this field due to mathematical complexities. Hoo Fatt et al. have studied analytically high velocity impact on sandwich panels with composite skins and foam core. Because of the widespread use of sandwich panels with metal face-sheets and foam core in aerospace industry, by modifying the analytical method provided by Hoo Fatt et al. the ballistic resistance of the foam core sandwich panels with metal surfaces impacted by high velocity cylindrical projectile is analytically investigated in this paper. Two types of panels with polymeric and metallic foam cores and aluminum surfaces have been used to assess the accuracy of the analytical method. Results show that the proposed analytical method can predict the residual velocity of the projectiles impacted at high velocities on the foam and metallic core panels with different relative densities of the core.

This paper presents the experimental study on vibration characteristics of polymeric nanocomposites containing 1 weight percentage of mesoporous silica (MCM-41)، Hydroxy Apatite (HA)، the composite of MCM-41 and HA (MH) and carbon nanotube (CNT) as a fillers. Experimental results show that damping ratio and natural frequency increase in the neat PP، CNT/ PP، HA/ PP، MCM-41/ PP nanocomposites and MH/ PP hybrid nanocomposite specimens، respectively. In order to introduce the effect of foam agent in the vibration absorbing properties، foam agent is added to CNT/ PP and MH/ PP nanocomposits. The results show that foamed specimens have more damping capacity and lower natural frequency than unfoamed specimens. The maximum value of increasing the damping ratio and natural frequency of the MH/ PP hybrid nanocomposite than neat PP is 55. 02 % and 34. 05%، respectively. So، MH/ PP hybrid nanocomposite that is studied in this paper for the first time، can remove the reduction of unwanted vibrations of structures problems.

In this paper, a new analytical model has been presented for energy absorption of aluminum-foam sandwich panels under ballistic impact. The panels consist of foam core sandwiched between two aluminum skins. In analytical model two types of sticker including cylindrical projectile with flat and hemispherical ended have been considered. It is supposed that aluminum skins failure by mean resistive pressure. Also foam absorbed a partial of projectile energy by crushing. Energy absorption of aluminum-foam sandwich panel is 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 have good agreement with experimental results. Also the effects of projectile mass and diameter in energy absorption of sandwich panel has been investigated.