The manufacturing of complex aerospace carbon epoxy components remains dominated by processes involving prepreg cured in autoclaves. This manufacturing route is expensive, not only because prepreg precursor materials have short shelf lives and require refrigerated storage, but also because large autoclaves carry very high operating costs and are in very intensive usage, with limited worldwide availability. Vacuum Assisted Resin Transfer Moulding (VARTM) is an interesting alternative for the manufacturing of near net-shape components as it reduces the costs related to material storage and removes the need for autoclave cure. The production of parts with complex geometry using VARTM is highly influenced by the kinetics of resin flow into preforms upon infusion, and on optimization of the infusion system for speed, consistency and robustness. In this work, the permeability of carbon fibre textile stacks and of equivalent glass fibre stacks was probed in manufacturing replicate trials, with the aim of bettering the production process. Trials were conducted using a substitute silicon oil infused through glass fibre and carbon preforms to enable capture of the evolving flow fronts on camera. The trials covered the effects of preform geometry, port and vent location, and stitching on resin flow. Tooling necessary for conducting the trials was designed and built. The timing of operations was determined in order to optimise the manufacturing process.

Polymer matrix composites (PMC's) perform well under many loading conditions and situations. Exposure of PMC's to fire is a concern due to their inherent material degradation at elevated temperatures. The elevated temperature response of PMC's to combined thermal and mechanical loads are especially of concern. PMC thermal and mechanical properties undergo transformations at elevated temperatures. Some of these effects are reversible if the maximum temperatures are lower than approximately 200C. The stiffness is significantly reduced at elevated temperatures but if the applied temperature is under the thermal degradation temperature of the matrix, the stiffness should be recoverable upon cooling. Some effects like the endothermic decomposition of the matrix are not reversible effects. This study focuses on reversible properties in the temperature range from room temperature to about 200C. Thermally these effects alter the thermal conductivity and specific heat. Reversible elastic effects considered are the off axis stiffness reductions as functions of temperatures. Thermal profile predictions were conducted using a finite difference code that included convection and radiation effects on the front and back faces of the composite. These predictions were shown to be in good agreement with experimental data. A modified classic laminate analysis (CLT) was implemented to predict the failure times of the composites under combined thermal and mechanical loading. The Budiansky-Fleck micro-buckling analysis technique was used as the failure function of the [0] surface plies. A finite element analysis (FEA) analysis was also performed and showed good agreement with the experimental data. / Master of Science

Hip and knee replacements are a common solution for patients whom have experienced loss in knee cartilage or have fractured their bones due to the weakening of the bone from osteoporosis. The number of bone replacements continues to rise as the number of ACL and meniscus repair surgeries increases. These surgeries accelerate the loss of cartilage especially at the knee. Current materials in use are nickel-cobalt alloys, titanium, and high-density polyethylene. These replacements have a lifespan of 10-20 years with a 10% risk of rejection from the body. Rejection can be caused by metal leeching into the bloodstream, growth of bacteria on the surface of the material, and the weakening of bone at the interface due to a large difference in young’s modulus between the replacement material and bone. Additionally, today’s bone replacement does not replicate the porous structure of bone to allow for the growth of bone cells. This research expands on a potential new material for bone replacement, poly(ether ether ketone) or PEEK. PEEK is a polymer that can be introduced to the body without rejection, and has been used as a material for spinal fusions and partial skull replacements. Additionally, not being a metal, PEEK avoids the risk of the introduction of metals into the bloodstream and weakening of surrounding bone due to its young’s modulus being lower than bone. However, traditional processing methods of injection or compression molding require high heat for melt resulting in a restriction of the structure and narrowing additives to inorganics. We introduce a unique solvent casting process with the use of chlorophenol dissolving PEEK at 150 °C. The process varies average pore sizes and allows for the introduction of organic and inorganic additives, cellulose nanocrystals and hydroxyapatite, to change the mechanical properties as well as provide a foundation for bone cell growth. We analyze the properties of the PEEK and PEEK composites through SEM imaging, thermal analysis, and mechanical testing. SEM imaging displays pore sizes in the nanometer ranges which are too small for cellular growth but small enough for mineralization. Thermogravimetric analysis confirms a proper distribution of additives within the PEEK. From differential scanning calorimetry, residual solvent remains from the processing. For mechanical testing, the additives’ significance on the PEEK composites could not be determined. However, evidence points towards higher drying temperatures, for solvent removal, increasing the modulus and yield strength of the PEEK and PEEK composites. Future research should be conducted to increase the pore size to allow for cell growth as well as cell culture studies to look at the degree of cell growth on the samples. Also, experiments should be performed to fully remove solvents and the understand the effect of drying temperatures on the PEEK composites’ structure and properties. / MS / Hip and knee replacements are a common solution for patients whom have experienced loss in knee cartilage or have fractured their bones. According to the American Joint Replacement Registry, close to 400,000 total hip and knee replacement procedures were conducted in 2016 with an 100% increase from the previous year. The number of bone replacements continues to rise as the number of knee ligament and meniscus repair surgeries increases. These repairs accelerate the loss of cartilage at the knee due to an imbalance within the joint. At extreme conditions of ligament and meniscus damage, a total bone replacement is needed. These replacements remove all ligaments and rely on the replacement material to provide stability in all directions. Because of the lack of ligaments, movement is restricted to bending motions. Current materials to replace bone are metals such as titanium or polymers such as polyethylene. These replacements have an estimated lifespan of 10-20 years with a 10% risk of rejection from the body. Rejection can be caused by metal leeching into the bloodstream, growth of bacteria on the surface of the material, and the weakening of bone at the interface. Additionally, today’s bone replacement does not replicate the porous structure of bone to allow for the growth of bone cells. This research expands on a potential new material, with a new process method, for bone replacement, poly(ether ether ketone) or PEEK. PEEK is a polymer that can be introduced to the body without rejection, and has been used as a material for spinal fusions and partial skull replacements. Additionally, not being a metal, PEEK avoids the risk of the introduction of metals into the bloodstream and weakening of surrounding bone. However, traditional melt processing methods restrict the structure and composition of PEEK. We introduce a solvent casting process that avoids melting the PEEK at high temperatures. The process alters the structure of PEEK, thus moving towards mimicking the structure of bone. To replicate bone further and increase strength, hydroxyapatite and cellulose nanocrystals are added to develop nanocomposites. Imaging shows the introduction of pores into PEEK depending on the drying conditions. These pores are too small for cell growth but small enough for the mineralization of bone. Thermal analysis exhibits a distribution of the additives with no alteration of the PEEK’s thermal stability from the process. From mechanical tests, the PEEK composites are weaker than that of bone. Future research should be conducted to increase the pore size to allow for cell growth as well as cell culture studies to look at the degree of cell growth on the samples.

No description available.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 212-220). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains xiii, 183 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 180-183).

Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (leaves [150]-154).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 93-96). Also available via the Internet.

A numerical method is developed to determine the dynamic behavior of delamination and transverse cracks in multilayered plates. The plate is subjected to a time dependent antiplane shear stress field which is acting on the plate surfaces. The interaction of waves diffracted at the crack tip with those reflected at the plate boundaries and transmitted at the material interface makes the problem very complicated, so analytical study of this problem cannot be carried out with our present state of knowledge; hence the problem is solved numerically. The finite element equations are obtained by variational calculus applied in the frequency domain. Thus time intregration schemes are avoided, but time dependent response can still be obtained after inverting the frequency dependent response spectra numerically by Fast Fourier Transform (FFT) routine. Another advantage of the frequency domain analysis is that the resonance frequency can be easily detected from the sharp peaks of the response spectra. The numerical difficulty associated with the singular behavior of the stress field near the crack tip has been avoided by using quarter point elements. The numerical results obtained from this investigation are compared with analytical results to verify the accuracy of the method.

Thesis (Ph. D.)--Ohio State University, 2009. / Title from first page of PDF file. Includes vita. Includes bibliographical references (p. 160-166).