The relationships between fabrication variables, microstructure and selected properties of carbon bonded magnesia-graphite refractory composite materials have been investigated. A novel optical microscope method of characterizing the morphology of flake graphites was developed and used to determine distributions of length and thickness and average aspect ratios for the four graphite samples used in the study. The compaction behaviour of magnesia alone and in combination with the flake graphites has been studied in some detail and the microstructures of the products elucidated. It is shown that the amount of magnesia of small particle size plays a significant role in determining the graphite-graphite contact area in the structure. An irreversible volume expansion is observed on firing composites, the magnitude of which can be related to the microstructure and the graphite content. A phenolic resin binder restricts this expansion. It is shown that the carbon binder does not bond to the graphite phase and only weakly, if at all, to the magnesia. Consequently the strengths and moduli are low and show only a small variation with graphite type. The effect of adding graphite to carbon-bonded magnesia is to lower the strength slightly, but increasing the graphite content from 20-30% causes a small increase in strength. Increasing the amount of carbon bond from pitch has little effect on strength at levels of 5-15% whereas over the range 5-13% the resin binder has a more pronounced effect. The most significant factor affecting the strength and modulus of fired composites is the amount of silicon or aluminium, added as oxidation inhibitors, which react to form carbide and nitride phases. Finally, a brief study of slag penetration shows that this can be reduced by decreasing the amount of oxide fines in the composite because of the changes in microstructure that, result.

Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, September 1990. / Thesis Advisor(s): Dutta, Indranath ; Mitra, Shantanu. "September 1990." Description based on title screen as viewed on December 21, 2009. DTIC Identifier(s): Fatigue (mechanics), thermal fatigue, metal matrix composites, laminates, bending, ultimate strength, fiber reinforced composites, theses. Author(s) subject terms: Aluminum-graphite composite, bend fatigue, thermal fatigue. Includes bibliographical references (p. 64-65). Also available in print.

Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, June 1990. / Thesis Advisor(s): Wu, Edward M. "June 1990." Description based on signature page as viewed on October 21, 2009. DTIC Identifier(s): Graphite fiber strength testing, graphite fiber statistical evaluation. Author(s) subject terms: Graphite fiber strength testing, graphite fiber statistical evaluation, composite reliability predictions. Includes bibliographical references (p. 78-79). Also available in print.

Includes bibliographical references (p. 115-124).

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Dr. Steve Johnson; Committee Member: Dr. Andrew Makeev; Committee Member: Kyriaki Kalaitzidou. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Energy absorption during complete penetration of thin graphite composites is experimentally shown to be significantly improved by low volume fractions of embedded superelastic shape memory alloy (SMA) fibers. Graphite/Bismaleimide laminates were embedded with 3% and 6% volume fractions of superelastic nitinol fibers. Quasi-static tests were performed on wide clamped-clamped beams to identify progressive damage mechanisms. Low velocity (13.9 ft/s) impact tests, at an impact energy of 31.5 ft-lbs, resulting in complete penetration were also performed on wide clamped-clamped beams. These tests show that only after peak load is there a contribution made by the SMA to the load deflection behavior of the composite. Owing to the SMA's high strength and high strain to failure it remains undamaged after failure of the base composite. The interaction between the base composite and the SMA creates an increase in absorbed energy over the base composite of as much as 41 % in a Graphite/Bismaleimide laminate embedded with a 6% volume fraction of nitinol fibers. C-scans of the hybrids embedded with bi-directional nitinol fibers show a 22% larger delamination areas compared to plain graphite epoxy. The larger delaminations are a result of the nitinol fibers distributing the impact energy to a larger area of the base composite. This interaction between the nitinol and the graphite is one of the reasons for the increases in absorbed energy. Fiber pull-out and strain energy of the nitinol fibers also adds to the increase in absorbed energy. Although damage initiation and peak loads do not seem to be affected by the embedded nitinol fibers, the energy absorption after peak loads is greatly improved. This improvement is a result of increased energy distribution through the SMA to the graphite. The large improvements in energy absorbing capabilities offered by SMA fibers give SMA hybrid material systems promise in applications where penetration resistance is imperative. / Master of Science

Graphite epoxy composites lack effective mechanisms for absorbing local impact energy often resulting in penetration and a structural strength reduction. The effect of adding small amounts of two types of high strain hybrid components on the impact resistance of graphite epoxy composites subjected to projectiles traveling at ballistic velocities (greater than 900 ft/sec) has been studied. The hybrid components tested include superelastic shape memory alloy (SMA), a material having an unusually high stra in to failure (15 - 20%), and a high performance extended chain polyethylene (ECPE) known as Spectra™, a polymer fiber traditionally used in soft and hard body armor applications. 1.2% volume fraction superelastic SMA fiber layer was embedded on the specimens front, middle, and backface to determine the best location for a hybrid component in the graphite composite. From visual observation and energy absorption values, it was concluded that the backface is the most suitable location for a high strain hybrid component. Unlike the front and middle locations, the hybrid component is not restricted from straining by surrounding graphite material. However, no significant increases in energy absorption were found when two perpendicular SMA layers and an SMA-aramid weave configuration were tested on the backface. In all cases, the embedded SMA fibers were pulled through the graphite without straining to their full potential. It is believed that this is due to high strain rate effects coupled with a strain mismatch between the tough SMA and the brittle epoxy resin. However, a significant increase in energy absorption was found by adding ECPE layers to the backface of the composite . With only a 12% increase in total composite mass, a 99% increase in energy absorption was observed. / Master of Science

The goal of this academic project was to study the effects of different variables on the damage initiation and progression around four bolt holes of a joint in carbon fiber/graphite epoxy composite coupons. The tracked variables included the type of layup, R values, stress levels, and damage mechanisms observed in each specimen. In-situ x-ray of the individual coupons recorded the extent of damage, mostly longitudinal splitting and bearing failure, as a function of the cycle count. The following lay-ups were included: [45/90/-45/02/45/02/-45/0]s, [04/45/03/90/0]s, [±5/65/(±5)2/-65/±5]s, and [±5/65/(±5)2/-65/5/65]s, In particular, the objective was to determine the stress levels at which detectable damage starts developing by applying 50,000 cycles at incremental stress levels. Once damage was initially detected, we typically raised the stress level 2.5 ksi and cycled another 50,000 cycles until damage reached a point where the bolt holes had elongated 10% of the original diameter of 0.25 inches. This type of testing was be continued for several different R ratios and comparisons were be made between the performances of different lay-ups at varying load levels. A finite element model was created in ABAQUS to help understand the stress fields within the laminates.

No description available.

Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: New methods are described for the synthesis of polymer/graphite nanocomposites using the miniemulsion polymerization process. Natural graphite was functionalized by oxidation to produce graphite oxide (GO) nanosheets. Poly(styrene-co-butyl acrylate) (poly(St-co-BA)) nanocomposite latices containing GO nanosheets were successfully synthesized using miniemulsion as a one-step nano-incorporation technique. The approach followed included expanding the GO nanosheets in situ during the miniemulsification step and then polymerizing the monomers in the presence of these expanded nanosheets. Styrene (St) and butyl acrylate (BA) were mixed with GO and then emulsified in the presence of a surfactant and a hydrophobe to afford pre-miniemulsion latex particles. The stable pre-miniemulsions were then polymerized to yield poly(St-co-BA)/GO nanocomposite latices. The polymerization proceeded with relatively high monomer conversion and produced stable nanocomposite latex particles. The nanocomposites exhibited mainly an intercalated morphology, irrespective of the percentage of GO filler loading. The synthesis of exfoliated polymer nanocomposites made with modified GO is described. GO was modified with a surfmer (reactive surfactant), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), which widened the gap between the GO nanosheets and facilitated monomer intercalation between its nanogalleries. The AMPS-modified GO was used for the synthesis of poly(St-co-BA)/GO nanocomposite latices using a similar miniemulsion procedure. The obtained nanocomposites had exfoliated morphologies and the GO nanosheets were largely exfoliated (about 2–5 nm thick) in the resultant films obtained from the synthesized nanocomposite latices. The synthesized nanocomposites had enhanced thermal and mechanical properties compared to pure polymer as a result of the presence of AMPSmodified GO. Furthermore, the nanocomposites made with AMPS-modified GO had better thermal and mechanical properties than the unmodified GO. The mechanical properties of the nanocomposites depended on the AMPS-modified GO loading in the nanocomposites. The synthesis of polystyrene/GO (PS-GO) nanocomposites using the reversible additionfragmentation chain transfer (RAFT) mediated polymerization method is also described. The GO was synthesized and immobilized with a RAFT agent to afford RAFT-functionalized GO nanosheets. The RAFT-immobilized GO was used for the synthesis of PS nanocomposites in a controlled manner using miniemulsion polymerization. The molar mass and dispersity of the PS in the nanocomposites depended on the amount of RAFT-grafted GO in the system, in accordance with the features of the RAFT-mediated polymerization. X-ray diffraction and transmission electron microscopy analyses revealed that the nanocomposites had exfoliated morphology, even at relatively high GO content. The thermal stability and mechanical properties of the PS-GO nanocomposites were better than those of the neat PS polymer. Furthermore, the mechanical properties were dependent on the modified-GO content (i.e., the amount of RAFT-grafted GO). The hydrophobicity and barrier properties of the resulting films prepared from the synthesized poly(St-co-BA)/GO nanocomposite latices to water and water vapor were also investigated. The hydrophobicity of the synthesized nanocomposite films was determined using contact angle measurements. The water permeability was determined by measuring the moisture vapor transmission rate of the films. The GO in the nanocomposites was reduced to its original form (i.e., graphite), and the barrier properties of the obtained nanocomposite films were determined and compared to films containing the unmodified GO (as-prepared GO). Results showed that reduction of GO had a significant impact on the water affinity of the resultant films prepared from the synthesized nanocomposite latices. The presence of reduced-GO (RGO) instead of unmodified GO in the miniemulsion formulation significantly improved the hydrophobicity and barrier properties of the final films to water. However, the barrier properties of the nanocomposites were unaffected by the amount of RGO in the nanocomposites. / AFRIKAANSE OPSOMMING: Nuwe metodes is beskryf vir die sintese van polimeer/grafiet nanosamestellings deur gebruik te maak van die miniemulsie polimerisasieproses. Natuurlike grafiet is gefunksionaliseer dmv oksidasie om grafietoksied (GO) nanovelle te vorm. Polistireen-ko-butielakrilaat (poli[St-ko- BA]) nanosamestellinglatekse wat GO nanovelle bevat is suksesvol gesintetiseer deur gebruik te maak van miniemulsie polimerisasie as ‘n een-stap nano-insluitingstegniek. Die benadering wat gevolg is het die uitbreiding van die GO nanovelle, in situ, gedurende die miniemulsifiseringstap behels, gevolg deur die polimerisasie van die monomere in die teenwoordigheid van hierdie uitgebreide nanovelle. Stireen (St) en butielakrilaat (BA) is met GO gemeng en daarna emulgeer in die teenwoordigheid van ‘n seepmiddel (surfactant) en ‘n hidrofoob om pre-miniemulsielateksdeeltjies te lewer. Die stabiele pre-miniemulsies is gepolimeriseer om poli(St-ko-BA)/GO nanosamestellinglatekse te vorm. Die polimerisasie het met redelike hoë monomeeromskakeling verloop en het stabiele nanosamestellinglateksdeeltjies gelewer. Hierdie nanosamestellings het hoofsaaklik geïnterkaleerde morfologie, onafhanklik van die persentasie GO vullers, getoon. Die sintese van afgeskilferde polimeernanosamestellings berei met gewysigde GO is beskryf. GO is gewysig met ‘n ‘surfmer’ (reaktiewe seepmiddel), 2-akrielamido-2-metiel-1- propaansulfoonsuur (AMPS), wat die gapings tussen die GO nanovelle vergroot het en die monomeer interkalering tusssen sy nanogange fasiliteer. Die AMPS-gewysigde GO is gebruik vir die sintese van poli(St-ko-BA)/GO nanosamestellinglatekse deur gebruik te maak van ‘n soortgelyke miniemulsie prosedure. Die nanosamestelling sό verkry het ‘n afgeskilferde morfologie getoon en die GO nanovelle was grootendeels afgeskilfer (ongeveer 2–5 nm dik) in die films wat berei is van die gesintetiseerde nanosamestellinglatekse. Laasgenoemde het verhoogde termiese en meganiese eienskappe gehad in vergelyking met die suiwer polimeer, as gevolg van die teenwoordigheid van die AMPS-gewysigde-GO. Die meganiese eienskappe van die nanosamestellings hang af van persentasie AMPS-gewysigde GO vullers in die nanosamestellings. Die sintese van PSt/GO nanosamestellings dmv die omkeerbare-addisie-fragmentasieoordrag- (OAFO-, Eng. RAFT-) bemiddelde polimerisasie metode is ook beskryf. Die GO is berei en geïmmobiliseer met ‘n RAFT verbinding om GO nanovelle met RAFT funksionaliteit te lewer. Die RAFT-geïmmobiliseerde GO is gebruik vir die sintese van PSt nanosamestellings in ‘n gekontrolleerde manier mbv miniemulsie polimerisasie. Die molêre massa en dispersie van die PSt in die nanosamestellings hang af van die hoeveelheid RAFTgeënte GO in die sisteem, in ooreenstmming met die kenmerke van RAFT-bemiddelde polimerisasie. X-straaldiffraksie en transmissie-elektronmikroskopie analises het bewys dat die nanosamestellings, selfs by relatiewe hoë GO inhoud, ‘n afgeskilferde morfologie gehad het. Die termiese stabiliteit en meganiese eienskappe van die PSt-GO nanosamestellings was beter as dié van die suiwer PSt polimeer. Verder was die meganiese eienskappe afhanklik van die gewysigde-GO-inhoud (dws, die hoeveelheid RAFT-geënte-GO). Die hidrofobisiteit en spereienskappe van die films berei vanaf die gesintetiseerde poli(St-ko- BA)/GO nanosamestellinglatekse teenoor water en waterdamp is ook ondersoek. Die hidrofobisiteit is ondersoek deur gebruik te maak van kontakhoekmeting. Die waterdeurlaatbaarheid is bepaal deur die waterdampoordragtempo van die films te bepaal. Die GO in die nanosamestellings is gereduseer tot sy eenvoudigste vorm (grafiet) en die spereienskappe van die nanosamestellingfilms is bepaal en vergelyk met die films wat die ongewysigde GO bevat het. Resultate het getoon dat reduksie van GO ‘n groot invloed gehad het op die wateraffiniteit van die films wat berei is vanaf die gesintetiseerde nanosamestellinglatekse. Die teenwoordigheid van die gereduseerde-GO (RGO) in plaas van die onveranderde GO in die miniemulsie formulasie het die hidrofobisiteit en spereienskappe van die finale films, teenoor water, baie verbeter. Die spereienskappe van die nanosamestellings is egter nie beïnvloed deur die hoeveelheid RGO in die nanosamestellings nie.