Polymer bead foams are manufactured through a sintering process using foamed polymer beads. It is worth emphasis that the bead foam technology is the only process that can produce 3-dimensionally shaped foam products with ultra-low densities. This unique feature of bead foam process has been attracting enormous attentions from various foam industries. However the conventional bead foam processes still have some limitations associated with manufacturing productivity and safety during the treatment. This thesis deals with novel approaches to innovative and cost-effective manufacturing processes for polystyrene (PS) and polypropylene (PP) bead foam materials, based on thorough understanding of the scientific issues in bead foam technologies. This study also demonstrates the feasibility of new processes by conducting a series of foaming experiments such as batch foaming and continuous extrusion foaming as well as steam chest molding which is a critical common process for all bead foam products. In addition, this study aimed at developing new bead foam processes based on the relationship between the cellular structure and processing/material parameters. When it comes to expandable PS (EPS) bead process, research efforts have been made to eliminate n-pentane which has some disadvantages related to its flammability and low boiling temperature. In addition, the bi-celullar PS foams that feature the superior thermal-insulation property was manufactured through continuous extrusion foaming process. With regard to expanded PP (EPP) bead process, research efforts were focused on the development of cost-effective continuous foaming process in order to resolve the high cost issue of conventional EPP beads. These research strategies were designed on the basis of the comprehension of thermoplastic foaming, steam chest molding process and gas dissolution/diffusion phenomena. The results in the thesis provided considerable introductory and advanced knowledge about the bead foam technologies so that further promising researches can be performed to invent entirely new bead foam materials such as ultrahigh–temperature-durable bead foam products, biodegradable bead foams, other highly functional bead foam products aside from EPS and EPP bead foams.

Estimation of bottomhole pressure during a matrix-acidizing treatment provides the information needed to accurately determine the evolution of skin factor during and after the treatment. It could be a very complicated process, especially when compressible fluids, such as foams, are involved. Existing models for estimating bottomhole pressure during a matrix-acidizing treatment ignore the volume reduction of compressible fluids and its effect on the bottomhole pressure. This research developed a model that uses a unique solution to the mechanical energy balance equation, to calculate the bottomhole pressure from known surface measurements during foamed acid stimulation. The model was used to evaluate two stimulation treatments. Field examples are presented which illustrate the application of the model to optimize stimulation treatments. Properly accounting for the flow behavior and tracking the injected volume of the foam diverter used during the treatment resulted in more reliable and accurate bottomhole pressure profile.

Although the use of compressible drilling fluids is experiencing growth, the flow behavior and stability properties of drilling foams are more complicated than those of conventional fluids. In contrast with conventional mud, the physical properties of foam change along the wellbore. Foam physical and thermal properties are strongly affected by pressure and temperature. Many problems associated with field applications still exist, and a precise characterization of the rheological properties of these complex systems needs to be performed. The accurate determination of the foam properties in circulating wells helps to achieve better estimation of foam rheology and pressure. A computer code is developed to process the data and closely simulate the pressure during drilling a well. The model also offers a detailed discussion of many aspects of foam drilling operations and enables the user to generate many comparative graphs and tables. The effects of some important parameters such as: back-pressure, rate of penetration, cuttings concentration, cuttings size, and formation water influx on pressure, injection rate, and velocity are presented in tabular and graphical form. A discretized heat transfer model is formulated with an energy balance on a control volume in the flowing fluid. The finite difference model (FDM) is used to write the governing heat transfer equations in discretized form. A detailed discussion on the determination of heat transfer coefficients and the solution approach is presented. Additional research is required to analyze the foam heat transfer coefficient and thermal conductivity.

This research is concerned with the modeling and failure analysis of closed cell foam with various scales of microstructure that is disordered due to defects. This foam material is used for the forward bipod closeout on the space shuttle external tank. Three dimensional finite element simulations of closed cell foams with various microstructures are performed to study the influence of the geometric character of the microstructure (eg. defect size and distribution) on the stiffness and failure behavior of the foam. First, regularly arrayed cells are modeled for a reference to compare with the disordered microstructure. For studying the effect of cellular microstructure, a discrete model is developed where in every edge and face of each cell are modeled. Two types of defects, point defects (void) and area defects (knot), are indicated from the examination of BX250 and BX265 polyurethane foams. However, this research is focused on the point defect. Analyzing a material with such complex microstructure is especially challenging in terms of computation power as well as required modeling techniques. A finite element model consisting of only beam and shell elements was developed. Certain complications that arise from using beam and shell elements were resolved using novel techniques. Stiffness predictions from the model agreed with data from the literature for a wide range of relative densities. Parametric studies were performed to examine the effect of different properties, such as relative densities and edge fraction, on the effective stiffness, Von Mises stress, and buckling stress. The thickness of the face plays an important role in the behavior of the foam material. Linear buckling and postbuckling analyses were performed to understand the effect of local buckling on the effective properties of the foam and stress concentrations. A distorted multicell model was developed to analyze the effect of point defects on the foam behavior. In particular, two geometric parameters, the defect size and the defect density (or the distance between two defects) were varied to find their effect on the stress concentrations and the effective stiffness of the foam. It is seen that the discrete model that accounts for the foam microstructure reveals much more about the foam behavior than a homogenous model.

Thesis (M.S. in Combat Systems Technology)--Naval Postgraduate School, December 2009. / Thesis Advisor: Hixson, Robert S. Second Reader: Sinibaldi, Jose O. "December 2009." Description based on title screen as viewed on January 26, 2010. Author(s) subject terms: Ceramic, composite armor, Dyneema, orthotropic materials, penetration resistance, porous foams. Includes bibliographical references (p. 89-90). Also available in print.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Foamed cement is widely used in the oil and gas industry to provide zonal isolation. Foamed cement provides various advantages vs. pure cement. The primary purpose of foamed cement is to reduce the density of the cement mixture. Consequently, foamed cement can be used in weak formations were reduced exerted hydrostatic pressure is needed to prevent/control cement circulation loss into the formation. However, Due to gas compressibility, foamed cement’s gas injection rate has to be constantly adjusted in order to create a constant density slurry through the height of the cement column. Furthermore, foamed cement’s properties include higher ductility, constant pressure exertion to the formation during cement transition time (gelling) and lower thermal conductivity. The ability of solid silica nanoparticles to generate stable gas/water foams was researched for foamed cement applications. Solid nanoparticles have been shown to permanently stabilize foams by assembling into layers at the gas/water interface. A potential decrease in compressibility of the gas phase by the presence of these armoring bubble layers was investigated. Enhancement of cement’s splitting tensile strength and compressive strength by silica nanoparticles was also investigated. The addition of uncoated silica nanoparticles at various concentrations did not appear to enhance neither cement’s splitting tensile or compressive strength. In most tests with varying silica nanoparticles concentrations, the samples with nanoparticles exhibited a slightly reduced splitting tensile and compressive strength. The exception being the compressive strength of the samples mixed with the highest nanoparticle concentration tested. However, the strength improvement was small vs. its pure cement counterpart. An apparatus to test the compressibility of nanoparticle stabilized foams was built for this research. The functionality of the apparatus was validated using various test fluids. The validation process allowed for the establishment of a compressibility benchmark to compare the compressibility of nanoparticle stabilized foams. A vital conclusion of this process was that generating the particle stabilized foams under pressure would allow for greater discernment between the existence of the armored bubble effect and gas dissolution into the water phase. A type of nanoparticle was identified as having the capacity to generate long term stable foams without the need of surfactant. Partially hydrophobic surface treated silica nanoparticles were utilized to generate gas/water foams under pressure and subsequently their compressibility was measured. The compressibility of these foams did not appear to show the armored bubble effect behaving as an equivalent ideal gas + water mixture. An additional surfactant and particle stabilized foam recipe was tested and displayed the same results. It was concluded that either the particle layers were not fully forming in the foam or in the case they were forming; either foam geometry was not conductive to the distribution of forces or they likely had limited rigidity and buckled when compressed. If the latter was true, the apparatus was not sensible enough to measure the limited rigidity. / text

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