Добірка наукової літератури з теми "Fluid-Filled Cellular Polymer Foam"

Rigid low-density plastic foams subjected to mechanical loads typically exhibit a nonlinear deformation stage preceding failure. At moderate strains, when the geometrical nonlinearity is negligible, such foam response is predominantly caused by the nonlinearity of deformation of their principal structural elements—foam struts. Orientational averaging of stresses in foam struts enables estimation of the stresses taken up by foams at a given applied strain. Based on a structural model of highly porous anisotropic cellular plastics filled with clay nanoplatelets and the orientational averaging, a method for calculating their nonlinear deformation is derived in terms of structural parameters of the porous material, the mechanical properties of the monolithic polymer, and filler particles and their spatial orientation. The method is applied to predicting the tensile stress-strain diagrams of organoclay-filled low-density rigid polyurethane foams, and reasonable agreement with experimental data is demonstrated.

Aluminum-based cellular solids are promising lightweight structural materials considering their high specific strength and vibration damping, being potential candidates for future railway vehicles with enhanced riding comfort and low fuel consumption. The filling of these lattices with polymer-based (i.e., polyurethane) foams may further improve the overall vibration/noise-damping without significantly increasing their density. This study explores the dynamic (i.e., frequency response) and acoustic properties of unfilled and polyurethane-filled aluminum cellular solids to characterize their behavior and explore their benefits in terms of vibration and noise-damping. It is shown that polyurethane filling can increase the vibration damping and transmission loss, especially if the infiltration process uses flexible foams. Considering sound reflection, however, it is shown that polyurethane filled samples (0.27–0.30 at 300 Hz) tend to display lower values of sound absorption coefficient relatively to unfilled samples (0.75 at 600 Hz), is this attributed to a reduction in overall porosity, tortuosity and flow resistivity. Foam-filled samples (43–44 dB at 700–1200 Hz) were shown to be more suitable to reduce sound transmission rather than reflection than unfilled samples (21 dB at 700 Hz). It was shown that the morphology of these cellular solids might be optimized depending on the desired application: (i) unfilled aluminum cellular solids are appropriate to mitigate internal noises due to their high sound absorption coefficient; and (ii) PU filled cellular solids are appropriate to prevent exterior noises and vibration damping due to their high transmission loss in a wide range of frequencies and vibration damping.

The effect of polymer structure on both initial and aged thermal conductivity ( K-factor) or thermal resistivity ( R-value) was explored by using a new procedure to estimate the long-term thermal resistance of gas-filled cellular plastics proposed by Norton [1], Edgecombe [2] and Bomberg [3]. This method uses a semi-logarithmic plot of thermal resistivity versus time that produces two distinct stages in the data, thermal drift and plateau with a break point separating the two stages. The plateau stage was fit with a straight line in order to estimate the long-term thermal resistance or K-factor of the foam. This concept was employed on the fourteen CFC-11 blown foams [4] in this study. The effect of me two major types of isocyanates, Specialty TDI (toluene diisocyanate) and PMDI (polymeric diphenylmethane diisocyanate), was isolated and compared. The significance of seven different types of polyol initiators was also evaluated with respect to K-factor and K-factor aging. In the case of the PMDI foams, the data correlated well with the model and the 20-year K-factor predictions appear to be reasonable when compared to the raw data curves. In the case of the TDI foams, however, it was more difficult to find a break point which would define the plateau region in the data. Most of these foams did contain break points, but the break point occurs at a slightly longer time. The 20-year K-factors of these foams could be predicted with reasonable confidence when there was a break point in the resistivity versus log (T) curves.

In the case of fracturing of the reservoirs using fracturing fluids, the size of damage to the proppant conductivity caused by treatment fluids is significant, which greatly influence the effective execution of hydraulic fracturing operations. The fracturing fluid should be characterized by the minimum damage to the conductivity of a fracture filled with proppant. A laboratory research procedure has been developed to study the damage effect caused by foamed and non-foamed fracturing fluids in the fractures filled with proppant material. The paper discusses the results for high quality foamed guar-based linear gels, which is an innovative aspect of the work compared to the non-foamed frac described in most of the studies and simulations. The tests were performed for the fracturing fluid based on a linear polymer (HPG—hydroxypropyl guar, in liquid and powder form). The rheology of nitrogen foamed-based fracturing fluids (FF) with a quality of 70% was investigated. The quartz sand and ceramic light proppant LCP proppant was placed between two Ohio sandstone rock slabs and subjected to a given compressive stress of 4000–6000 psi, at a temperature of 60 °C for 5 h. A significant reduction in damage to the quartz proppant was observed for the foamed fluid compared to that damaged by the 7.5 L/m3 natural polymer-based non-foamed linear fluid. The damage was 72.3% for the non-foamed fluid and 31.5% for the 70% foamed fluid, which are superior to the guar gum non-foamed fracturing fluid system. For tests based on a polymer concentration of 4.88 g/L, the damage to the fracture conductivity by the non-foamed fluid was 64.8%, and 26.3% for the foamed fluid. These results lead to the conclusion that foamed fluids could damage the fracture filled with proppant much less during hydraulic fracturing treatment. At the same time, when using foamed fluids, the viscosity coefficient increases a few times compared to the use of non-foamed fluids, which is necessary for proppant carrying capacities and properly conducted stimulation treatment. The research results can be beneficial for optimizing the type and performance of fracturing fluid for hydraulic fracturing in tight gas formations.

The objective of this study was to present a simple and environmentally friendly process combining low pressure (vacuum) and mechanical compression to convert low-density polyethylene (LDPE) foams into low-density foams (76–125 kg/m3) with negative tensile and compressive Poisson’s ratios (NPR). As a first step, four series of recycled LDPE foams (electronics packaging) with starting densities of 16, 21, 30 and 36 kg/m3 were used to determine the effect of different processing conditions including temperature and pressure. Based on the optimized conditions, the tensile and compressive Poisson ratios of the resulting auxetic foams reached −2.89 and −0.66, while the tensile and compressive modulus of the auxetic foams reached 40 kPa and 2.55 kPa, respectively. The foam structure of the samples was characterized via morphological analysis and was related to the mechanical properties before and after the treatment (i.e., foams with positive and negative Poisson’s ratios). The tensile and compressive properties (Young’s modulus, strain energy, energy dissipation and damping capacity) for these auxetic foams were also discussed and were shown to be highly improved. These auxetic foams can be applied in sports and military protective equipment. To the best of our knowledge, there is only one report on vacuum being used for the production of auxetic foams.

The use of lignocellulosic fillers in rigid polyurethane foams (RPUFs) has been receiving great attention due to their good mechanical and insulation properties and the high sustainable appeal of the obtained cellular polymers, although high water uptakes are found in most of these systems. To mitigate this detrimental effect, RPUFs filled with wood flour (2.5% wt) were fabricated with the addition of furfuryl alcohol (FA) to create a polymer grafted with the wood filler. Two concentrations of FA (10 wt% and 15 wt%) were investigated in relation to the wood flour, and the RPUFs were characterized for cell morphology, density, compressive properties, thermal stability, and water uptake. The introduction of wood flour as a filler decreased the cell size and increased the anisotropy index of the RPUFs and, in addition to that, the FA grafting increased these effects even more. In general, there were no significant changes in both mechanical and thermal properties ascribed to the incorporation of the fillers. On the other hand, a reduction of up to 200% in water uptake was ascribed to the FA-treated fillers.

In recent years, microbubble technology has attracted great attention in many application fields including water treatment, food processing, oil recovery, surface cleaning, and therapeutic applications. In this paper, microbubbles (MBs) of air, nitrogen, and argon were applied to produce natural rubber latex foams (NRLFs). The bubbles were generated by flowing the gas through a porous diffuser and latex. The effect of gas source on cellular structure, density, elasticity, indentation hardness, and flammability of the bubbled foams was discussed. Argon MBs offered the latex foams with fine cell diameters and uniform cell size distribution resulting in enhanced elasticity and physical properties of the foams. Indentation hardness index and limiting oxygen index value depended significantly on the gas used. By using the microbubble technique, the future prospects in NRLF production can be expected due to its ability in controllable cellular structure.

A key component in the quantitative assessment of the risk posed to spacecraft by the micrometeoroid and orbital debris (MMOD) environment is frequently referred to as a ballistic limit equation (BLE). A frequently used BLE for dual-wall configurations (which are commonly used on spacecraft to protect them against the MMOD environment) is the New Non-Optimum, or “NNO”, BLE. In design applications where a BLE is needed for a new structural system that has not yet been tested, but resembles to a fair degree a dual-wall system, it is common practice to equivalence the materials, thicknesses, etc., of the new system to the materials, thicknesses, etc., of a dual-wall system. In this manner, the NNO BLE can be used to estimate the failure / non-failure response characteristics for the new system. One such structural wall system for which a BLE does not yet exist is a dual-wall system that is stuffed with a lightweight polymer-based foam material. In this paper we demonstrate that the NNO BLE, in its original form, frequently over- or under-predicts the response of such a system. However, when the NNO BLE is modified to more properly include the effects of the presence of the foam as well as the actual material properties of the walls and the impacting projectile, there is a marked improvement in its predictive abilities.

Summary Foam is used in the oil industry in a variety of applications, and polymer is sometimes added to increase foam's stability and effectiveness. A variety of surfactant and polymer combinations have been employed to generate polymer-enhanced foam (PEF), typically anionic surfactants and anionic polymers, to reduce their adsorption in reservoir rock. While addition of polymer to bulk foam is known to increase its viscosity and apparent stability, polymer addition to foams for use in porous media has not been as effective. In this pore-level modeling study, we develop an apparent viscosity expression for PEF at fixed bubble size, as a preliminary step to interpret the available laboratory coreflood data. To derive the apparent viscosity, the pressure-drop calculation of Hirasaki and Lawson (1985) for gas bubbles in a circular tube is extended to include the effects of shear-thinning polymer in water, employing the Bretherton's asymptotic matching technique. For polymer rheology, the Ellis model is employed, which predicts a limiting Newtonian viscosity at the low-shear limit and the well-known power-law relation at high shear rates. While the pressure drop caused by foam can be characterized fully with only the capillary number for Newtonian liquid, the shear-thinning liquid requires one additional grouping of the Ellis-model parameters and bubble velocity. The model predicts that the apparent viscosity for PEF shows behavior more shear-thinning than that for polymer-free foam, because the polymer solution being displaced by gas bubbles in pores tends to experience a high shear rate. Foam apparent viscosity scales with gas velocity (Ug) with an exponent [-a/(a+2)], where a, the Ellis-model exponent, is greater than 1 for shear-thinning fluids. With a Newtonian fluid, for which a = 1, foam apparent viscosity is proportional to the (-1/3) power of Ug, as derived by Hirasaki and Lawson. A simplified capillary-bundle model study shows that the thin-film flow around a moving foam bubble is generally in the high-shear, power-law regime. Because the flow of polymer solution in narrower, water-filled tubes is also governed by shear-thinning rheology, it affects foam mobility as revealed by plot of pressure gradient as a function of water and gas superficial velocities. The relation between the rheology of the liquid phase and that of the foam is not simple, however. The apparent rheology of the foam depends on the rheology of the liquid, the trapping and mobilization of gas as a function of pressure gradient, and capillary pressure, which affects the apparent viscosity of the flowing gas even at fixed bubble size. Introduction When a gas such as CO2 or N2 is injected into a mature oil reservoir for improved oil recovery, its sweep efficiency is usually very poor because of gravity segregation, reservoir heterogeneity, and viscous fingering of gas, and foam is employed to improve sweep efficiency with better mobility control (Shi and Rossen 1998; Zeilinger et al. 1996). When oil is produced from a thin oil reservoir overlain with a gas zone, a rapid coning of gas can drastically reduce oil production rate, and foam is used to delay the gas coning (Aarra et al. 1997; Chukwueke et al. 1998; Dalland and Hanssen 1997; Thach et al. 1996). During a well stimulation operation with acid, a selective placement of acid into a low-permeability zone from which oil has not been swept is desired, which can be accomplished with use of foam (Cheng et al. 2002). For environmental remediation of subsurface soil using surfactant, foam is used to improve displacement of contaminant, such as DNAPL, from heterogeneous soil (Mamun et al. 2002).

In the modern-day society, there are an increasing number of explosions, either by accidental explosions or by terrorist attacks on civilian and military infrastructure. In view of the increased threat to infrastructure and lives of people from explosions, there is an urgent need to precisely predict the blast loads resulting from detonation of high explosives, accurately assess the structural responses to blast loads and develop effective blast mitigation technologies and materials which require extensive field testing. One of the most effective methods for protection against blast waves is the use of fluid-filled cellular material as a protective cover on the structure that needs to be systematically evaluated by field testing and numerical simulations. Since blast experiments on real life structures are costly and time consuming, numerical simulation can be used as an alternative to the field experiments, provided they are validated with relevant experimental data. The main goals of this research are: 1. Field experimental investigation of the response of clamped mild steel plates to close range spherical air blast loads and examination of the effect of standoff distance on the structural response. 2. Development of numerical models for predicting the response of structures to close range air blast loads and validation of the numerical models using the field experimental data. 3. To demonstrate and assess the potential of blast mitigation technology using fluid-filled cellular polymer foam. In order to achieve the first objective, a series of close-range blast experiments on mild-steel plates have been conducted at different scaled distances by varying the standoff distance and the mass of explosive charge. The plates deformed into conical or spherical-dome shapes, depending on the severity of blast wave and the permanent deformation profiles and the midpoint deflections of the plates were measured after each blast event. The air-blast pressure and the dynamic strains in the plates were also measured in some of the experiments. Towards achieving the second objective, fluid-structure coupled numerical models for the field air blast experiments are developed using the commercial finite element hydrocode LS-DYNA to simulate the detonation of high explosive in air, blast wave interaction with the structure and the plastic deformations of the plate structures. With the physically consistent coupled numerical models and the material constitutive data evolved in the present research, a good agreement between the air-blast experimental data and the numerical predictions has been achieved. Further, a numerical procedure validated with experimental data is proposed to estimate the total impulse imparted to the structure under air blast loads. In addition, an empirical relation is formulated from the field experimental data to predict the midpoint deflections of the plates subjected to close range spherical explosions in air. Additional numerical simulations are performed with ANSYS-AUTODYN and ConWep codes and the results are compared with LS-DYNA ALE simulation results and the field air-blast experimental data to assess their relative performance in predicting the structural response to close-range air blast loads. The third goal is addressed by conducting a series of air blast experiments, on steel plates covered with cellular polymer foam filled with water, at different scaled distances to vary the intensity of blast load. Further, the effect of foam thickness on blast mitigation is investigated by varying the water-filled foam thickness from 50 mm to 100 mm.The blast mitigation is quantified by the reduction in the plate midpoint deflection and the change in the deformation profiles of the plates by comparing the experimental data on plates tested with and without the water-filled foam protection.The experiments indicate that the blast protection offered by water-filled polymer foam depends on the intensity of the blast load and the thickness of the foam protection. It is found from the experimental data that with 50 mm as well as 100 mm thick water-filled foam protection, there is a reduction in plate midpoint deflection up to 49%. It is further observed that with 50 mm thick protective cover, depending on the intensity of the blast load, there is enhancement of damage to the structure in some of the experiments.Numerical simulations of the blast-protection experiments with fluid-filled foam indicate that the momentum transfer from the blast wave to the foam and water is the principal mechanism of blast protective action by fluid (water)-filled foam, that results in energy dissipation as increase in kinetic energy of water present in the foam, work done in expelling the water from the foam and atomization of water into fine droplets, increase in strain energy of the foam and energy expenditure in disintegrating and dispersing the foam.

Abstract Passenger vehicles are constantly being redesigned to maximize occupant safety in the event of a collision. Changes and improvements to automobiles have resulted in a significant amount of energy absorption capability through the vehicle chassis. Axial crushing members are often deployed in vehicle front end and side chassis structures and are designed to absorb a maximum amount of energy before complete deformation. These structures experience a series of progressive folding during axial deformation resulting in moderate and relatively constant force throughout the crushing behavior. To increase the performance of these structures, different cross-sectional shapes and core materials have been investigated. The present study investigates the addition of graded cellular core structure with zones of crushable foam and fluid inserts within the cell voids. The addition of crushable foam material aimed to provide stability to the crushing behavior of the structure. The incompressible nature of the fluid insert provided sections of increased structural strength and a more global crushing response. The finite element approach was conducted using ABAQUS dynamic environment and the square crush tubes were subjected to dynamic axial crushing. Foam and fluid addition provided additional energy absorption while creating a more global deformation response.

The sensitivity of piezoelectric/polymer composite materials is inversely proportional to their dielectric permittivity. Introducing a cellular structure into these composites can decrease the permittivity while enhancing their mechanical flexibility. Foaming of highly filled polymer composites is however challenging. Polymers filled with high content of dense additives such as lead zirconate titanate (PZT) exhibit significantly decreased physical foaming ability. This can be attributed to difficulty in gas diffusion, decreased fraction of the matrix available, the reduced number of nucleated cells and the difficulty in cell growth. Here, both CO2 foaming and Expancel foaming were examined as potential methods to fabricate low-density thermoplastic polyurethane (TPU)/ PZT composite foams. While composites containing up to only 10vol.% PZT could be foamed using CO2, Expancel foaming could successfully yield highly-expanded composite foams containing up to 40vol.% (80wt.%) PZT. Dispersed Expancel particles in TPU/PZT composites acted as the blowing agent, activated by subjecting the samples to high temperatures using a hot press. Using Expancel, foams with expansion ratios of up to 9 were achieved. However, expansion ratios of greater than 4 were not of interest due to their poor structural integrity. The density of solid samples ranged from 1.8 to 3.3 g.cm−3 and dropped by a maximum of 80%, even for the highest PZT content, at an expansion ratio of 4. As the expansion increased, the dielectric permittivity of both CO2-foamed and Expancel-foamed TPU/PZT composites decreased significantly (up to 7.5 times), while the dielectric loss and electrical conductivity were affected only slightly. This combination of properties is suitable for high-sensitivity and flexible piezoelectric applications.

A metal foam filled microchannel cooling device for polymer-electrolyte-membrane fuel cell (PEFC) and flow batteries was investigated experimentally and numerically in this study. Nickel foam was selected due to its high conductivity, large surface area, low density and low cost. The properties of the nickel foam were determined analytically and experimentally. Experiments were conducted to obtain pressure drop at various Reynolds numbers for metal foams of varying porosities. The experimental data was used to provide inputs for the numerical model. A modeling approach for flow in a metal foam filled channel was validated with the available data. The validated model was then used to analyze the heat transfer and fluid flow characteristics of the metal foam microchannel. Two different locations of the cooling device with respect to the PEF C stack were investigated. The thermal resistance and pressure drop change with Reynolds number are presented. Significant temperature drop was observed with the metal foam microchannel design. The modeling results can be used to guide the direction of future experiments.

As the field of Tissue Engineering advances to its ultimate goal of engineering a fully functional organ, there’s an increase need for enabling technologies and integrated system. Important roles in scaffold guided tissue engineering are the fabrication of extra-cellular matrices (ECM) that have the capabilities to maintain cell growth, cell attachment, and ability to form new tissues. Three-dimensional scaffolds often address multiple mechanical, biological and geometrical design constraints. With advances of technologies in the recent decades, Computer Aided Tissue Engineering (CATE) has much development in solid freeform fabrication (SFF) process, which includes but not limited to the fabrication of tissue scaffolds with precision control. Drexel University patented Precision Extrusion Deposition (PED) device uses computer aided motion and extrusion to precisely fabricate the internal and external architecture, porosity, pore size, and interconnectivity within the scaffold. The high printing resolution, precision, and controllability of the PED allows for closer mimicry of tissues and organs. Literatures have shown that some cells prefer scaffolds built from stiff material; stiff materials typically have a high melting point. Biopolymers with high melting points are difficult to manipulate to fabricate 3D scaffold. With the use of the PED and an integrated Assisting Cooling (AC) device; high melting points of biopolymer should no longer limit the fabrication of 3D scaffold. The AC device is mounted at the nozzle of the PED where the heat from the material delivery chamber of the PED has no influence on the AC fluid temperature. The AC has four cooling points, located north, south, east, and west; this allows for cooling in each direction of motion on a XY plane. AC uses but not limited to nitrogen, compressed air, and water to cool polymer filaments as it is extruded from the PED and builds scaffolds. Scaffolds fabricated from high melting point polymers that use this new integrated component to the PED should illustrate good mechanical properties, structural integrity, and precision of pore sizes and interconnectivity.