Search Results (1 - 25 of 113 Results)

Sort By  
Sort Dir
 
Results per page  

MURUGESAN, SURESHIN SITU PREPARATION AND STRUCTURE - PROPERTY STUDIES OF FILLER PARTICLES IN POLY(DIMETHYLSILOXANE) ELASTOMERS
PhD, University of Cincinnati, 2003, Arts and Sciences : Chemistry
Poly(dimethylsiloxane) (PDMS) is a versatile silicone polymer studied very extensively for various applications. However, because of its mechanical weakness, it is filled with many different filler particles including SiO2, TiO2 and ZrO2. In the present research work, some specialty filler particles were generated by in-situ sol-gel method in PDMS networks. These composites were studied for their structure-property effects in relevance to their transparency, magnetic, electrical and mechanical properties. Structure-property and kinetic studies were performed on TiO2 and ZrO2 filled PDMS composites. Hydrolysis and condensation process was controlled by selecting alkoxides, with longer chain length and bulky side groups (titanium-2-ethyl hexoxide and zirconium butoxide). SAXS, SEM, Instron was used for characterizing these composites. Fe2O3 particles with different shapes and sizes were generated in-situ in PDMS networks using aqueous solutions of FeCl3 and HCl. Non-aqueous method and ferric acetylacetonate [Fe(acac)] however yielded higher amounts of filler. Magnetic and mechanical properties were studied using vibrating sampling magnetometer (VSM) and Instron respectively. Attenuated Total Reflectance (ATR), SEM and EDS. was used to determine the structure, shape and composition of the composite. Polyaniline (PANI) was generated in-situ from monomer aniline, by chemical oxidation in PDMS networks. The effects of temperature, dopant and oxidant were also studied. The structures of the PANIs were studied using ATR. Conductivity was measured using a four-point probe. Conductivity of this composite depends on the degree of oxidation and doping of the generated PANI. A novel approach along with a structure-property study for ZrO2 and TiO2 filled PDMS was performed. A small amount of a stannous compound mixed in alkoxide, dramatically reduced the time for particle generation. The composites were transparent, with ZrO2 filled having higher transparency than TiO2. SAXS data showed a correlation between the particles. Surface of an injection molded microfluidic component made from cyclic olefinic copolymers (COC) was modified in order to change the surface properties applicable to bio-fluidic devices. Plasma treatments and ASG (aerosol gel) coating were used to achieve the surface modifications. Structural changes after the plasma treatments were examined by ATR spectroscopy. Contact angle measurements with water were used as a measure of hydrophobicity.

Committee:

Dr. James E. Mark (Advisor)

Subjects:

Chemistry, Polymer

Keywords:

in situ ; composites poly(dimethylsiloxanes); magnetic composites; conducting composites polyaniline; small angle x-ray scattering analysis of composites

RAJAN, GURU SANKARPREPARATION AND CHARACTERIZATION OF SOME UNUSUAL ELASTOMERIC AND PLASTIC COMPOSITES
PhD, University of Cincinnati, 2002, Arts and Sciences : Chemistry
This work focused on examining the structure – property relationships of filled and unfilled elastomers and plastics. Some of the factors that influence the final properties of these systems are: molecular weight, % isotactic pentad content, shape and structure of the filler particles, surface modification of the filler particles, polymer – filler interaction, particle size, pore size, surface area, etc. The five parts in this dissertation are as follows: Chapter 1: Thermal and mechanical tests of thermoplastic elastomeric polypropylenes (EPP) prepared by the metallocene catalysts showed that they were multiphase, tough elastomeric materials. The moduli and strengths of the unfilled EPPs increased with increase in % isotactic pentad content and increase in molecular weight. Preliminary tests on filled EPPs showed that layered silicates (clays) gave better reinforcement than silica fillers because of the higher aspect ratio of the former. Chapter 2: The mechanical properties of poly (methyl acrylate) composites prepared by using a silane coupling agent designed to suppress the bonding between the silica and the elastomeric matrix were much poorer than those of the corresponding composite having a silane giving strong interfacial bonding, and thus documenting the effects of these interactions on the reinforcement of a typical elastomeric material. Chapter 3: The polystyrene/Vycor blends and pseudo interpenetrating polymer networks (PIPN) did not exhibit any reinforcing ability due to the large particle size of the Vycor filler. The PS/zeolite PIPNs showed reinforcement whereas the PS/zeolite blends did not. The PIPN samples gave larger tensile strength values relative to the corresponding blends. This could possibly be due to increased interfacial interactions in the PIPNs. Chapter 4: Poly(dimethylsiloxane) (PDMS) composites, reinforced by in situ silica precipitation, were prepared by a two – step process. Ultraviolet/visible spectroscopy was used to make quantitative visual observation that the composites were highly transparent. The filler particles gave pronounced increases in mechanical properties of the composites, thus demonstrating excellent reinforcing capabilities. Chapter 5: PDMS composites were prepared using different types of fumed silica. With increase in the surface area (decreasing particle size) and silica loadings, the mechanical properties increased irrespective of the silica used. Incorporating silane coupling agents also increased the tensile properties of the composites.

Committee:

Dr. James E. Mark (Advisor)

Subjects:

Chemistry, Polymer

Keywords:

thermoplastic elastomeric polypropylene; poly(methyl acrylate) composites; polystyrene composites having zeolite or vycor glass; polydimethylsiloxane composites

Myers, Kyle MInvestigation of Novel Precursor Routes for Incorporation of Titanium Alloys and Nano- Sized Features into Ceramic-Metallic Composites Formed via the TCON Process
Master of Science in Chemistry, Youngstown State University, 2012, Department of Chemistry
Fireline TCON Inc. has developed a technology for the creation of alumina/aluminum interpenetrating phase composites via a reactive metal penetration process. TCON composites are created by immersing silica based ceramic precursors into a reactive molten aluminum or aluminum alloyed melt. The molten aluminum metal reacts with the precursor leaving a near net shape alumina ceramic backbone with aluminum filling in the pores in the composite. The resulting composites have unique mechanical properties that are desired for many applications. The mechanical properties of TCON composites can be tuned for specific applications by varying the precursor material, metal composition, and temperature of reaction. Research has shown that the reactive metal penetration process does work with precursors that are not silica based ceramics. Currently Fireline TCON Inc. only works with silica based precursors that leave undesired aluminum-silicon alloys in the metal phase as the transformation takes place. The aluminum-silicon alloys are created from a reduction of the silicon metal cations in the silica based ceramic. The incorporation of titanium into the metal matrix is a more desired result for Fireline. Several titanium based ceramics were transformed using the TCON process to try and incorporate titanium into the metal phase. In addition, specific type materials were transformed in the TCON process in attempt to manifest a nano-sized interpenetrating phase composite. Current technology at Fireline TCON Inc leaves the resulting composites with particle sizes on the micron scale. A nano-scaled titanium-silicon oxide and a β-alumina-type compound, which already has nano-features, were transformed in the TCON process to investigate if a nano-scaled composite would manifest. All of the samples that were transformed were analyzed using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and x-ray diffraction. Fireline TCON Inc decided that one of the precursor materials showed enough promising results that this sample was scaled-up to test bars to be tested for mechanical properties. The mechanical properties of this composite are compared to existing metal ceramic composites.

Committee:

Timothy Wagner, Ph.D. (Advisor); Matthias Zeller, Ph.D. (Committee Member); Clovis Linkous, Ph.D. (Committee Member); Virgil Solomon, Ph.D. (Committee Member)

Subjects:

Chemistry; Materials Science

Keywords:

Ceramic-Metallic Composites; Reactive Metal Penetration; Alumina Composites; Spinel Composites

BHARGAVA, SUMEETTEMPERATURE AND GAS SENSING CHARACTERISTICS OF GRAPHITE/POLYMER (PEO) BASED COMPOSITE STRUCTURES
MS, University of Cincinnati, 2006, Engineering : Materials Science
Conductive polymer composites have long been used in sensing applications. Since the demand for such sensors is growing, further research is needed to keep pace and come up with new and improved materials. These materials have percolation structures with sufficient conductor phase dispersed in the polymer insulator matrix. The resistance in these materials can vary with temperature and gas ambience, so as to serve as sensitive sensors, with typically a sharp transition at a particular temperature. This study focused on the use of Poly Ethylene Oxide and graphite flakes. For such plate-like morphologies the conducting paths are formed at low percolation concentrations. The components were blended and hot pressed to pellets. Thermistor and gas sensing data showed sharp change. An inert ceramic additive was used to escalate the thermal stability. Microstructures and other structural features of the samples were observed using Optical microscopy and SEM to establish the structure-property correlation

Committee:

Dr. Relva Buchanan (Advisor)

Subjects:

Engineering, Materials Science

Keywords:

CPC; conductive polymer composites; polymer composites; conductive composites; PEO; temperature sensors; gas sensors; polymer ceramic composite

Joshi, Ninad MilindStudy of the Effect of Unidirectional Carbon Fiber in Hybrid Glass Fiber / Carbon Fiber Sandwich Box Beams
Master of Science (M.S.), University of Dayton, 2013, Materials Engineering
This study investigated the effect of carbon fiber placed in different amount at different location in a square box beam. In total eight designs were selected and three beams were fabricated for each design using hand layup and vacuum bagging technique. The beams were tested using a four point bending test. The stiffness were calculated and compared with all glass fiber beams. The beams were analyzed using finite element method in Abaqus. It was found that the location of the carbon fiber has an effect on the increase in the stiffness of the beam. Beam with 29.6% carbon fiber by volume gave maximum increase in stiffness. The maximum load carried by the beams showed a different trend. It was observed that the maximum load carrying capacity decreased with increase in the amount of carbon fiber. Carbon fiber effectiveness index (ratio of percentage increase in stiffness of beam and volume percent of carbon fiber) was calculated for each design and it was found that the design D3; which has one layer of carbon fiber on the top and bottom face utilized carbon fiber most effectively.

Committee:

Steven Donaldson, PhD (Advisor); Donald Klosterman, PhD (Committee Member); Thomas Whitney, PhD (Committee Member)

Subjects:

Engineering; Materials Science

Keywords:

Composite Beams; box beams; hybrid composites; glass fiber carbon fiber hybrid composites; Hybrid Beams; Finite element analysis of composites using Abaqus; square beams

Gao, XiaodongEffect of Negative Thermal Expansion Material Cubic ZrW2O8 on Polycarbonate Composites
Doctor of Philosophy, University of Toledo, 2015, Chemistry
Research on control of thermal expansion of polymers has attracted significant attention, since polymers exhibit excellent mechanical and electronic properties, but suffer from high thermal expansion due to the thermal motion of their long molecular chains. Such problems can be addressed through formation of composites that contain an inorganic filler material. Filler materials reduce the thermal expansion of polymers through restriction of polymer chain motion. One particular area of interest is the introduction of negative thermal expansion (NTE) materials into polymer composites. The NTE property is expected to have an additional effect on the reduction of the coefficient of thermal expansion (CTE) of the composites. Several papers have demonstrated successful reduction of the CTE of polymer composites using cubic ZrW2O8, however, it is still unclear how much of this effect is caused by the NTE behavior, and how much is due to chain stiffening. To address whether the use of expensive NTE materials is justified, this project is designed to investigate the exact effects of NTE and chain stiffening on the reduction of thermal expansion of polymer composites. This objective was achieved through the preparation and testing of two sets of composites containing isomorphic particles with opposite thermal expansion (ZrW2O8 and ZrW2O7(OH)2¿2H2O), which possess identical chain stiffening effects. The first goal of the project was to synthesize two different particles that have identical morphology but opposite thermal expansion, with cubic ZrW2O8 as the NTE material of choice. The initial idea was to use a-Al2O3 (corundum), which has a known positive CTE value, as the second material. This phase can be obtained through heat treatment of AlOOH at about 1100 °C. The synthesis of AlOOH with controlled morphologies based on choice of synthetic conditions has been reported. Attempts on the synthesis of AlOOH were made through two different routes. Neither of them delivered particles with similar size as cubic ZrW2O8. Additionally, it was found that the heat treatment at high temperature caused sintering of the particles, resulting in the formation of large particles. To circumvent this problem, the precursor of ZrW2O8, ZrW2O7(OH)2¿2H2O, was used as the counterpart for the comparison, since the topotactic transformation between the two phases results in unchanged morphology, giving rod-like shape for both materials. The synthesis of ZrW2O7(OH)2¿2H2O was optimized to prepare particles with small size, high crystallinity, and good resistance to hydration after converting to the cubic NTE phase. The effects of acid concentration and reaction time were explored. The products were examined by powder X-ray diffraction (PXRD) and scanning electron microscopy, and the hydration rates were also estimated based on the PXRD patterns. Final reaction conditions were chosen as 6 M HCl at 230 °C for 7 d. The coefficient of thermal expansion was determined for ZrW2O7(OH)2¿2H2O using Pawley refinements of variable temperature PXRD data, and values of ¿a = 11 × 10-6 ± 1 × 10-6 K-1 and ¿c = 2.6 × 10-6 ± 0.3 × 10-6 K-1, respectively, were found. Rietveld refinements were carried out on PXRD patterns of both types of particles mixed with silicon to estimate their amorphous content. Results indicated that both particles were close to fully crystalline. To improve the interaction between the particles and polymer, surface modification was carried out via in-situ polymerization in the presence of the particles using triphosgene and bisphenol A as monomers. Soxhlet extraction was used to purify the recovered particles. Thermogravimetric analysis was used to determine the surface coverage of the products and the presence of unbound polymer, and the required time for extraction was revealed to be 96 h based on the TGA results. Infrared spectroscopy was also used to examine the modified particles, which confirmed the presence of surface bound oligomers. Optimization of synthetic conditions, including monomers ratio, reaction time and amount of particles, was carried out to obtain the highest possible coverage. It was found that the optimum ratio for the monomers is between 2.2 : 1 and 1.3 : 1. Leveling off was observed for the surface coverage after 21 h of reaction time. Smaller amounts of particles gave higher surface coverages, but resulted in very low quantities of recovered particles due to losses during recovery steps. To recover more particles from a single batch reaction, the particles were subjected to two consecutive modification steps, resulting in both high coverage and high recovered amounts. The precursor particles could be modified under the same optimum conditions found for NTE particles. The interaction between the particles and polymer was found to be improved after the modification. Solution casting was used to prepare the composite films. A custom made glass vessel was created to provide an inert atmosphere with reduced pressure. This can lower the moisture level and increase the evaporation rate of the casting solvent, which can prevent moisture deposition and crystallization of the polymer. The interaction between the two phases was further enhanced through reprecipitation blending. Under optimized conditions, composite films loaded with bth types of particles were prepared with weight loadings ranging from 2 wt% to 25 wt%. Films with loadings above 12 wt% showed agglomeration on optical images. The homogeneity of the particle dispersion within the films was still acceptable based on combustion analysis. Several properties of the composites were measured, including tensile properties, thermal stability, glass transition temperature and coefficient of thermal expansion. All films without agglomeration showed enhance thermal stability. On the other hand, most films with agglomeration exhibited slightly lower thermal stability. Similar trends were seen for the stress and strain at yield for both types of composites. The composites with lower thermal stability showed lower stress and strain at yield than pristine PC films, whereas the rest showed similar values for these two properties. The Young’s modulus of both types of composite films was found to slightly increase with the addition of the filler particles. All composites exhibited similar values as pristine PC. However, the local structure of the two types of the composites was revealed to be different by dynamic mechanical analysis. The films loaded with the precursor particles exhibited earlier softening than pristine PC, while a delay in softening was found for the ones loaded with NTE particles. The coefficient of thermal expansion (CTE) was measured for the film samples at the University of Mulhouse. This instrument produced faulty numbers that required corrections for instrument contributions. The correction for instrument contributions was checked by comparing the corrected values of three selected film samples to values obtained through analysis at West Kentucky University. The composites blended with NTE particles showed consistently lower CTE values than pristine PC and decreased with increased particle loading, whereas the values of the other set of composites showed no clear trends. Overall, considering the errors associated with the CTE values, the difference caused by the NTE behavior of the particles may not be very significant. Additional samples with higher loadings need to be tested to obtain a clearer picture, and data should be collected on well calibrated instruments to reduce errors.

Committee:

Cora Lind-Kovacs, Ph.D. (Committee Chair); Maria Coleman, Ph.D. (Committee Member); Jon Kirchhoff, Ph.D. (Committee Member); Terry Bigioni, Ph.D. (Committee Member)

Subjects:

Chemistry

Keywords:

control of thermal expansion; nagetive thermal expansion materials; effect of NTE on CTE control of polymer composites; ZrW2O8; polycarbonate composites

Deshpande, Pranav KishoreInfrared Processed Copper-Tungsten Carbide Composites
MS, University of Cincinnati, 2002, Engineering : Materials Science
The objective of this study is to develop copper matrix composite for electrical contact application. Copper matrix composites with refractory material reinforcement have properties such as high electrical conductivity and high wear and erosion resistance, which make them a preferred candidate for electrical contact application. The approaches for making of these composites have been different not only in the selection of the type, size and shape of the reinforcements but also in the steps involved in its making. This study focuses on the particulate reinforced metal matrix composites produced by using the liquid metal infiltration process. The process consists of the injection and subsequent solidification of liquid copper within the interstitial spaces of a porous tungsten carbide preform. The two critical parameters of this process are temperature and pressure. While the temperature parameter is critical for the viscosity of the liquid metal to be sufficient and the superheat considerations, the pressure parameter plays an important role in forcing the liquid metal into the porous preform. The effect of temperature variation on the microstructure and properties of the composite has been discussed. The infiltration process in this study is without the application of any pressure with the capillary forces providing sufficient pressure drop at the infiltration front. The reliance on the capillary forces brings to fore the wettability aspect of the process. The need of favorable wetting behavior between the constituents cannot be overstated. Copper-tungsten carbide composites were prepared in a very short time using the infrared heating process. The composite produced has a significant increase in the hardness value (360-370 VHN) as compared to copper (170 VHN). The resistivity value of the composite (5.4 x 10 -6Ω-m) is very close to the resistivity value of copper (1.7 x10 –6Ω-m). The density value as close as 97-98% of the theoretical density value has been achieved. The microstructure shows homogeneous distribution of the constituent phases. The study lays foundation for some extensive work on the control of the volume fraction of the constituents and also the predictability of the process.70

Committee:

Ray Y. Lin (Advisor)

Subjects:

Engineering, Materials Science

Keywords:

WC-CU composites; infrared technology; copper and composites

Evarts, Jonathan S.Advanced Processing Techniques For Co-Continuous Ceramic Composites
Master of Science, The Ohio State University, 2008, Materials Science and Engineering
Co-Continuous Ceramic Composites have shown promise to replace traditional materials in high temperature applications due to their combination of strength at elevated temperature, thermal cycling damage tolerance and toughness. Prior work has demonstrated the displacement reaction resulting from immersion of silica precursors into an aluminum bath as an attractive method of creating net-shape alumina-aluminum composites. Here a similar reaction is studied where the bath is predominantly inert copper, however enough aluminum is still present to drive the reaction. Examination of several copper/aluminum ratios shows that an equivalent reaction occurs. However, as the copper fraction rises, reaction kinetics slow, and the microstructure scale decreases, yet the microstructural morphology remains similar. Additionally, the parent metal phase may be replaced with a more refractory material using a Hot Solvent Exchange Reaction. In this reaction both metallic species must be molten, however the processing temperature must be below that of the ceramic phase.

Committee:

Glenn Daehn, PhD (Advisor); James Williams, PhD (Committee Member)

Subjects:

Aerospace Materials; Automotive Materials; Engineering; Materials Science; Metallurgy

Keywords:

ceramic matrix composites; nanocomposite; kinetics, metal matrix composites, aluminum

Li, WeiComposite polymer/graphite/oxide electrode systems for supercapacitors
MS, University of Cincinnati, 2015, Engineering and Applied Science: Materials Science
Supercapacitors are nominally electrochemical double-layer, capacitor devices, fabricated from high specific surface area carbon materials (EDLC’s), or from pseudocapacitive metal oxide systems, or combinations of these. Generally, they can be classified as: electrochemical double-layer capacitors (EDLCs), with carbon as the primary electrode material; as pseudocapacitors, with metal-oxide/polymer composites as the electrode material; or as hybrid capacitors, a combination of both the EDLCs and pseudocapacitive systems [2]. Their charge storage mechanisms are based upon physical charge separation at the electrode surfaces, such that no chemical reactions occur, and no charges are transferred between electrode and electrolyte (EDLC’s), or upon chemical processes such as redox reactions, for pseudocapacitive storage [2]. Although these electrode systems have attained relatively high charge storage capabilities, this performance level is strongly influenced by material composition, structure and properties, in a manner still not fully understood, in particular, for composite polymer/conducting oxide based pseudocapacitive electrode systems. The objective of this research, therefore, was focused on developing an insight into the mechanisms for enhanced charge storage capabilities in these advanced composite electrodes systems. Non-conductive polymer systems such as PEO, SBS, and PVDF were employed as the matrix phase in these studies, with high surface area graphite ~ (115m2/gm), and co-precipitated, heat-synthesized, and pseudocapacitive NiO as the conducting phases in the fabricated composite electrode systems. In this work, the electrode systems were developed as thin/thick film coatings on cleaned SS metal-foil substrates, using spin-coating MOD methodology, and heat treatments in the range of 180 to 300 degree Celsius, guided by the TGA characteristics of the Polymer matrix phase. Addition of graphite to the non-conducting polymers resulted in the development of well-recognized redox characteristics, most notably in PEO, SBS and PPA/AA systems, resulting in significantly enhanced pseudocapacitive charge storage capability, The further incorporation of pseudocapacitive NiO into the polymer/ graphite solutions, resulted in a large additive charge storage effect, and high supercapacitor performance. This work has demonstrated that composite metal oxide/graphite/non-conducting polymer based binder systems, through the percolative principle, can produce high quality, and high storage capacity film electrodes for supercapacitive devices and advancement.

Committee:

Relva Buchanan, Sc.D. (Committee Chair); Mark Schulz, Ph.D. (Committee Member); Donglu Shi, Ph.D. (Committee Member)

Subjects:

Materials Science

Keywords:

Composite electrodes;Polymer composites;Oxide pseudocapacitors;Polymer graphite composites;Supercapacitors;Polymer redox reactions

Nie, ZifengAdvanced Mesomechanical Modeling of Triaxially Braided Composites for Dynamic Impact Analysis with Failure
Doctor of Philosophy, University of Akron, 2014, Civil Engineering
Numerical simulation plays an irreplaceable role in reducing time and cost for the development of aerospace and automotive structures, such as composite fan cases, car roof and body panels etc. However, a practical and computationally-efficient methodology for predicting the performance of large braided composite structures with the response and failure details of constituent level under both static and impact loading has yet to be developed. This study focused on the development of efficient and sophisticated numerical analysis modeling techniques suitable for two-dimensional triaxially braided composite (TDTBC) materials and structures under high speed impact. A new finite element analysis (FEA) based mesomechanical modeling approach for TDTBC was developed independently and demonstrated both stand alone and in the combined multi-scale hybrid FEA as well. This new mesoscale modeling approach is capable of considering the detailed braiding geometry and architecture as well as the mechanical behavior of fiber tows, matrix, and the fiber tow interface, making it feasible to study the details of localized behavior and global response that happen in the complex constituents. Furthermore, it also accounts for the strain-rate effects on both elastic and inelastic behavior and the failure/damage mechanism in the matrix material, which had been long observed in experiments but were neglected for simplicity by researchers. It is capable of simulating inter-laminar and intra-laminar damage and delamination of braided composites subjected to dynamic loading. With high fidelity in both TDTBC architecture and mechanical properties, it is well suited to analyze high speed impact events with improved simulation capability in both accuracy and efficiency. Special attention was paid to the applicability of the method to relatively large scale components or structures. In addition, a novel hybrid multi-scale finite element analysis method, entitled Combined Multiscale Modeling (CMM) approach, has been developed in this comprehensive study in conjunction with dynamic submodeling technique. It was based on the newly developed mesoscale and existing macroscale approaches for modeling the braided composite materials. The CMM hybrid FEA approach enables the full use of the advantages of both the macroscale and the mesoscale approaches, with the mesoscale model or a more detailed macro-scale model to describe the details of local deformation and the macro-scale model or a coarser meso-scale model to capture the global overall response feature of the entire structure. The approach was verified with simple testing specimens and coupon plates, and may be extended to large systems like jet engine containment or automotive body panels. Without directly connecting different portions of the structure modeled with disparate approaches in the same analysis model, the submodeling technique maps the solution of a global model analysis performed for the full structure with less details onto the connecting interface on the portion of the same structure, the submodel, modeled with high fidelity and details. The CMM approach presented here captures the response feature of a triaxially braided composite structure under impact accurately with a much lower computational expense, making it feasible to analyze this type of analysis for exceedingly large structures.

Committee:

Wieslaw Binienda, Dr. (Advisor); Ernian Pan, Dr. (Committee Member); Guo-Xiang Wang, Dr. (Committee Member); Robert Goldberg, Dr. (Committee Member); Qindan Huang, Dr. (Committee Member); Kevin Kreider, Dr. (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Automotive Engineering; Engineering; Mechanical Engineering

Keywords:

Composites; Impact; FEA; Braided Composites; Unit Cell; Textile Composite; Damage; Failure; Explicit Dynamic Analysis; Contact; Meso-mechanical; Multi-scale modeling; Abaqus; T700 E862; Submodeling; Numerical analysis; computer modeling;

Ramunno, Monica V.Preparation and Characterization of Spinel-based Interpenetrating Phase Composites via Transformation of 3-D Printed Precursor Shapes
Master of Science in Chemistry, Youngstown State University, 2016, Department of Chemistry
Interpenetrating phase composites were produced via the reactive metal penetration of ceramic precursor materials. This work was done in collaboration with the TCON division of Fireline, Inc., whose research and development focuses on slip cast silica shapes immersed in molten aluminum. During this process, the silica is transformed into alumina and a network of aluminum channels forms throughout the new ceramic. The interpenetrating nature of these composites yields impressive mechanical and thermal properties, making them valuable materials for ballistic, automotive, and refractory applications. There is new interest, however, in creating composites that contain materials other than alumina as the ceramic phase. The research described in this thesis sought to incorporate magnesium aluminate (MgAl2O4) and aluminum oxynitride (Al3O3N) spinels into IPCs with aluminum. Magnesium titanate and silica in a 2:1 molar ratio was found to produce the MgAl2O4/Al composite when transformed in an aluminum bath containing 5% silicon by weight. SiAlONs were utilized as potential precursors for the Al3O3N/Al materials, though all proved ineffective and the desired IPC was not created. Ceramic precursor shapes for the MgAl2O4/Al composites were created via 3-D printing. The effect this process had on final composite microstructure was investigated using scanning electron microscopy and compressive testing. Furthermore, X-ray diffraction and energy dispersive X-ray spectroscopy were utilized extensively for phase identification and material characterization.

Committee:

Timothy Wagner, PhD (Advisor); Virgil Solomon, PhD (Committee Member); Ruigang Wang, PhD (Committee Member)

Subjects:

Chemistry; Engineering; Materials Science

Keywords:

Interpenetrating phase composites; Magnesium aluminate spinel; Reactive metal penetration; Ceramic matrix composites

Marquina, Edgar AlbertoUse of Dynamic Mechanical Testing, WAXD and SEM Image Analysis to Study the Properties of Polypropylene/Calcium Carbonate Nanocomposites
Master of Science in Polymer Engineering, University of Akron, 2010, Polymer Engineering

Polypropylene (PP) is the most widely used thermoplastic. It has a good combination of physical and chemical properties, reduced cost per volume, great recyclability and good processability. PP nanocomposites have received a lot of attention in the past years because the addition of calcium carbonate nanoparticles to PP is expected to increase its stiffness and impact strength. The low concentration of nanofillers could be a cost effective alternate solution to engineering thermoplastics as long as good dispersion is achieved.

Numerous studies have been made to understand the influence of calcium carbonate (CaCO3) nanoparticles and their properties on the morphology and mechanical properties of the PP/CaCO3 nanocomposites. Some of those studies focused on median particle size and surface treatment of calcium carbonate. Particle size distribution is one of the most important characteristic of fillers. However, not much attention has been paid to studying the particle size distribution of nanoparticles after mixing.

In this work, polypropylene homopolymer composites were prepared using a Brabender internal mixer with CAM rotors (a medium shear-rate blade combining milling, mixing, and shearing forces against the test sample) at 190°C and 60rpm. Different compositions of calcium carbonate with different median particles sizes, including 0.07μm nanoparticles, with and without surface treatment were added to the polypropylene matrix.

SEM image analysis was used to obtain the particle size distribution of calcium carbonate in the polypropylene matrix. The Gamma Variate function was found to fit the particle size distribution of nanoparticles after mixing with a correlation coefficient above 0.99.

In addition to SEM image analysis, DSC and X-ray diffraction were used to investigate the morphology of the PP nanocomposites and its effect on their tensile and impact properties. Dynamic mechanical testing was also used to study the polymer melt behavior at low frequencies.

The X-Ray diffraction showed three strong α crystalline form peaks and one β crystalline form peak. The intensities of these peaks were used to calculate the k parameter to quantify the β-iPP in the PP composites. Based on this parameter, calcium carbonate nanoparticles seem to be more effective in promoting the formation of β-iPP than microparticles.

The results of the tensile tests showed that the elastic modulus increased up to 30% in comparison with that of neat PP with the addition of 20% of calcium carbonate nanoparticles. Tensile strength was also highest with the addition of 2wt% and 5wt% nanoparticles but the improvement was of only of 5% compared with neat PP. The highest tensile strength and elastic modulus were found with approximately 40% crystallinity.

Impact strength was higher with the addition of calcium carbonate microparticles. However, surface treated nanoparticles at 2wt% and 5wt% compositions and high k proved to increase the impact strength of PP above 40% compared with neat PP. The best combination of mechanical properties was found for PP nanocomposites filled with 2wt% of 0.07μm treated particles and k=0.22.

Committee:

Kyonsuku Min, Dr. (Advisor); Kevin Cavicchi (Committee Chair); Alamgir Karim (Committee Member)

Subjects:

Engineering; Polymers

Keywords:

CaCO3; calcium carbonate; PP composites; particle; POLYPROPYLENE/CALCIUM; composites filled

ATKURI, HARI MUKUNDAMETHODS TO ADJUST THE PHYSICAL PROPERTIES OF LIQUID CRYSTALS AND RELATED DEVICES
PHD, Kent State University, 2012, College of Arts and Sciences / Department of Physics

Liquid crystal devices are possible because of their large optical birefringence and dielectric anisotropy. They have become a part of modern life with the ubiquitous liquid crystal displays dominating the display industry. However, the need to enhance their physical properties is ever increasing and our research tried to provide as much information as possible to fill this void.

In our recent studies, we showed by integrating non-liquid crystalline materials such as specialty particles or well-engineered polymers into a specific liquid crystal host, we could enhance the physical properties of the liquid crystal displays and devices. At the same time, it’s possible to change how we perceive and use various types liquid crystals and related devices. In the dissertation, first, we present our work focusing on producing enhanced LC-polymer composites where we integrated custom-made polymer materials into unmodified 5CB to produce fast switching, high transparent LC-polymer composites.

We developed high transmittance stressed liquid crystals (HTSLC) optimized for their ultra fast operation in the visible and NIR spectral range. The transmittance that is corrected for front and back surface reflections, of the device is more than 95% at 600nm and 99% in the near IR spectral range. The HTSLC produce large phase shifts. For example, an 18-micron thick HTSLC device can produce more than 1-micron phase shift in 1milli second. HTSLC devices have many potential optical applications for display, adaptable lenses and related electro-optic devices.

In the dissertation, as second part, we present our work focusing on enhancing the physical properties of liquid crystals by integrating ferroelectric nano-particles into 5CB, where we achieve minimum of 2deg C and maximum of 4deg C increase in the clearing point of unmodified single component liquid crystal. In addition, we also present how to enhance the dielectric anisotropy and order parameter of the LC and present the results demonstrating it.

Throughout our research, we also present how to produce the particle suspensions or LC-polymer composites or LC-polymer composites and related devices followed by presenting their characteristics and immediate possible applications.

Committee:

John West, L (Advisor); David Allender (Advisor); Qi-Huo Wei (Committee Member); Elizabeth Mann (Committee Member); Alexander Seed (Committee Member)

Subjects:

Chemical Engineering; Chemistry; Engineering; Experiments; Materials Science; Optics; Physics

Keywords:

liquid crystals; high transmittance stressed liquid crystals; HTSLC; ferroelectric nanoparticles; BaTiO3; Sn2P2S6; enhancing LC physical properties; liquid crystal devices; displays; LCD; LC particle composites; LC polymer composites

Boehle, Matthew C.Synthesis and Characterization of a Carbon Nanotube Based Composite Strain Sensor
Master of Science (M.S.), University of Dayton, 2016, Mechanical Engineering
In order to more effectively monitor the health of composite structures, a fuzzy fiber strain sensor was created. The fuzzy fiber is a bundle of glass fibers with carbon nanotubes or nanofibers grown on the surface using a novel chemical vapor deposition process. The nanotube coating makes the fiber bundle conductive while the small conductive path increases sensitivity. The fuzzy fiber sensor can replace conventional metal foil strain gauges in composite applications. The sensor was first characterized by use of a micro-tension test to generate load vs. resistance plots to demonstrate the feasibility of the sensor. The fibers were then cast into epoxy dogbone specimens to enable testing with an extensometer to quantify its strain sensitivity. Sensors were then embedded in carbon fiber prepreg panels. Specimens were prepared to demonstrate their performance in a composite laminate typical of aerospace structures. A multi-axial specimen was constructed to test sensor response to longitudinal, transverse and off-axis loading cases. Cyclic tests were performed to check for hysteresis or non-reversible changes to the sensor. A finite element model was created to compare the experimental results to the expected behavior based on the Poisson effect.

Committee:

Khalid Lafdi (Committee Chair); Thomas Whitney (Committee Member); Vinod Jain (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

carbon nanotube; structural health monitoring; composites; strain sensing; self-sensing composites; CNT strain gage

Hahnlen, Ryan M.Development and Characterization of NiTi Joining Methods and Metal Matrix Composite Transducers with Embedded NiTi by Ultrasonic Consolidation
Master of Science, The Ohio State University, 2009, Mechanical Engineering

Nickel-Titanium (NiTi) is a shape memory alloy that, depending upon composition, can exhibit shape memory or superelastic properties, recovering up to 8% deformation. Utilizing the shape memory effect it is possible to use NiTi as an actuator replacing traditional mechanical systems with a light-weight system using a fewer number of moving parts. In addition to strain recovery, NiTi undergoes significant changes in its material properties, including elastic modulus and electrical resistivity. With these changes in material properties, it is possible to create NiTi based transducers. Currently, NiTi is limited to niche applications due primarily to difficulty in machining and joining NiTi to traditional structural materials.

The goal of this thesis is to develop and characterize consistent methods of creating adaptive structures using NiTi. The research presented consists of two parts; the first deals with the development and characterization of cost-effective methods of joining NiTi and common aluminum and steel alloys. Laser welding, tungsten inert gas welding, and ultrasonic soldering were used to create joints between NiTi and itself, aluminum 2024, O1 tool steel, and 304 stainless steel. Where applicable, joints were subject to mechanical testing and analysis using optical microscopy.

The second part explores the development and characterization of NiTi/Al metal matrix composite transducers constructed using Ultrasonic Additive Manufacturing (UAM), a low temperature solid-state process also referred to as ultrasonic consolidation. An aluminum UAM matrix was first characterized through mechanical testing and analysis using optical microscopy. Using UAM, aluminum matrix composites with embedded NiTi wires were created with up to a 13.4% NiTi cross sectional area ratio. The composites were tested to characterize their stiffness as a function of temperature. A model was also developed using the Brinson constitutive model in order to predict the stiffness and strain sensing properties of current and future UAM NiTi/Al composites.

Committee:

Marcelo Dapino, PhD (Advisor); Somnath Ghosh, PhD (Committee Member)

Subjects:

Engineering; Mechanical Engineering

Keywords:

Ultrasonic Additive Manufacturing; Ultrasonic Consolidation; Shape Memory Alloy; NiTi; Metal Matrix Composites; Active Composites; Laser Welding; Ultrasonic Soldering

Kerkar, Awdhoot VasantInvestigation of steric stabilization as a route for colloidal processing of silicon carbide/silicon nitride composites
Doctor of Philosophy, Case Western Reserve University, 1990, Chemical Engineering
The final strength, uniformity, and quality of ceramic components depend on their green microstructure. One key issue is the control of the number, size and distribution of particle agglomerates and voids in the green microstructure. Colloidal engineering strategies which attempt to control the strength of the interaction between the solids when in their processing fluids may provide an effective means to improve the green body microstructure. The application of steric stabilization, a colloidal engineering strategy, for the enhanced processing of SiC/Si3N4 composites, is investigated. Steric stabilization involves adsorption of polymers onto the powders from the processing medium. The system under investigation consists of silicon powder to be processed in nonaqueous media such as benzene and trichloroethylene. Poly(methyl methacrylate), poly(styrene), and their copolymer adsorbed onto silicon powder are used as stabilizing agents. The goal of the present work was to provide an in depth understanding of the phenomenon of steric stabilization as applied to the processing of ceramic powders and fibers. Also, the various functional roles played by the adsorbed polymers during green processing are demonstrated. It has been found that steric stabilization leads to elimination of inter-particle agglomeration of silicon powder. As a result, improved control over the particle size distribution and particle packing in nonaqueous slips is possible. Adsorbed polymers offer great processing flexibility as they can be used reversibly as dispersants and flocculants. The use of steric stabilization during pressure casting yielded compacts with higher packing densities and controlled microstructures. The adsorbed polymers also exhibited excellent binder characteristics as reflected by the improvement in the green strength of the compacts. The effect of steric stabilization on subsequent reaction bonding of Si to Si3N4 was studied. Also, the role of polymers in improving the wetting characteristics of the SiC fibers with the stabilized silicon slip were studied qualitatively. These results reported herein can be used as guidelines for infiltration of SiC fiber arrays with Si slips to obtain green composites via pressure casting. The green composites were also subsequently nitrided to yield SiC fiber-reinforced/reaction bonded silicon nitride (RBSN) composites

Committee:

Donald Feke (Advisor)

Subjects:

Engineering, Chemical

Keywords:

Steric stabilization; Colloidal engineering; Silicon carbide/silicon nitride composites

Rozak, Gary AlanEffects of processing on the properties of aluminum and magnesium matrix composites
Doctor of Philosophy, Case Western Reserve University, 1993, Materials Science and Engineering
A356 aluminum and AZ91 magnesium alloys were reinforced with SiC p and cast prior to hot deformation processing. Tensile properties and microstructural features were quantified for the composites heat treated to a T6 condition for each of the processing conditions. The aluminum composite material was supplied by the Dural Composites Corporation in ingot form with a 20 vol.% reinforcement level. The magnesium composites were processed at a 20 vol.% level with subliquidus stir mixing prior to casting. The molten composites were squeeze cast under 140 MPa of pressure. Additionally, the aluminum composite was sand cast and the magnesium composite was both sand and permanent mold cast. The A356 composite was hot worked via swaging to reductions of 33 to 95%; the AZ91 composite was hot extruded at a 92% reduction. The unreinforced alloys of these matrices were similarly processed and examined. The combination of squeeze casting and hot deformation with 95% reduction for the aluminum composite and 92% reduction for the magnesium composite significantly improved the ductility. This improvement was accompanied by an increase in tensile strength of the aluminum alloy and in both the tensile and yield strength for the magnesium alloy. The best properties obtai ned were as follows for the A356-T6 composite: 279 MPa yield strength, 339 MPa tensile strength and 8.1% tensile elongation; and for the AZ91D-T6 composite: 310 MPa yield strength, 432 MPa tensile strength and 3.5% elongation attained. The particulate composite demonstrated an improvement in the modulus of elasticity. The A356 exhibited an increase from 65 to 100 GPa; while the AZ91D was increased from 42 to 70 GPa. Lower ductility resulted from the presence of the SiC p but the final ductilities exceeded those of published results. These composites offer good properties as space structural materials with improvements over the unreinforced alloy. Improvements in specific stiffness were realized with the addition of 20 vol.% SiC p. The coefficient of thermal expansion was decreased for the AZ91D alloy by the presence of the SiC p in the composite. Exposure of these materials to a low earth orbit space environment did not produce any measurable degradation.

Committee:

John Lewandowski (Advisor)

Keywords:

Effects processing properties aluminum magnesium matrix composites

Iyer, SubramanianStructure Property Relationships in Polymer Blends and Composites. Part I - Polymer/POSS Composites Part II - Poly(ethylene terepthalate) ionomer/Polyamide 6 Blends Part III - Elastomer/Boron Nitride Composites
Doctor of Philosophy, Case Western Reserve University, 2006, Macromolecular Science
Multiphase polymer systems are an increasingly important technical area of polymer science. By definition, a multiphase system is one that has two or more distinct phases. From the standpoint of commercial applications and developments, polymer blending represents one of the easiest ways to achieve properties not available in individual materials. This work discusses the structure property relationships in polymer certain blends and composites. Polymer/polyhedral oligomeric silsesquioxanes (POSS®) blends and copolymers have gained significant attention in the last decade due the unique properties of the inorganic-organic hybrid structure of POSS. The majority of the research in polymer/POSS has been in the form of copolymers and thermosets. The criteria for the reinforcement of polymers using POSS as a filler material is not been discussed in literature. Part I of the thesis will highlight the effect of blending POSS with different polymers and discuss the rules for reinforcement of polymers when using POSS as a filler material. Part II of the thesis will discuss the structure property relationships in poly(ethylene terephthalate) ionomer/polyamide 6 blends. Part III will discuss the control of coefficient of thermal expansion of elastomers using boron nitride as a filler material.

Committee:

David Schiraldi (Advisor)

Keywords:

Polymers; Blends; Composites; Nanocomposites; Boron Nitride; Elastomers; Polyhedral Oligomeric Silsesquioxanes

Anyaogu, Kelechi ChigbooStabilized Metal Nanoparticle-Polymer Composites: Preparation, Characterization and Potential Applications
Doctor of Philosophy (Ph.D.), Bowling Green State University, 2008, Photochemical Sciences
Metal nanoparticle-polymer composites have created a new generation of materials that exhibit unique electrical, optical, or mechanical properties making them attractive for applications in areas like optics, photoimaging and patterning, sensor design, catalysis, and as antimicrobial coatings. The present thesis describes the synthesis, characterization, and incorporation of stabilized metal nanoparticles like those of copper, gold, and silver into a polymer matrix as well as their potential applications.Biofouling has been a worldwide problem for seagoing vessels and other structures exposed to the aquatic environment. Its prevention remains a major challenge and there is a need to develop antifouling systems that exhibit active durability, are easily affordable and eco-friendly. The first part of the thesis demonstrates the antifouling potential of copolymerizable acrylic-functionalized copper (Cu) nanoparticles (NPs). The Cu NPs can be chemically integrated to a polymer backbone, providing a tighter control of the leaching of the metals from the matrix. Biological experiments show that the newly synthesized composites exhibit antimicrobial activity similar to that of conventional copper-based biocides present in most antibacterial and marine antifouling coatings. Therefore, these materials may have value for the development of antibacterial paints and coatings for household materials, hospital and food storage equipment, as well as to reduce biofouling on ships. In addition, a novel photochemical route for incorporation of stabilized metal nanoparticles into a polymer matrix without the use of conventional photoinitiators is illustrated. Charge separated states of 5-mercapto-2,2'-bithiophene (BTSH) functionalized metal NPs generated upon exposure to UV light are active intermediates that can cause polymerization of an acrylic monomer. Electron microscopy data reveal uniform distribution of the NPs within the polymer matrix. These composites may also find useful application as conductive polymeric nanomaterials. Furthermore, the cure performance of light emitting diodes (LEDs) is compared to that of conventional light sources in the UV light cured acrylate formulations. Polymerization rates and properties of the resulting coatings indicate that UV LEDs can be good alternatives to conventional light sources for a variety of applications.

Committee:

Douglas C. Neckers, PhD (Advisor); George S. Bullerjahn, PhD (Committee Co-Chair); Robert Micheal McKay, PhD (Committee Member); Deanne L. Snavely, PhD (Committee Member); Thomas H. Kinstle, PhD (Committee Member)

Subjects:

Chemistry; Materials Science; Polymers

Keywords:

Metal Nanoparticle; Polymer Composites; Acrylic monomers; Antimicrobial Activity

Radhakrishnan, VikramCohesive zone modeling of the interface in linear and nonlinear carbon nano-composites
MS, University of Cincinnati, 2008, Engineering : Mechanical Engineering
The interface of a carbon nano-composite plays a large role in determining the effective response of the composite, since it is the medium through which load transfer occurs. It is necessary to understand how the variation of interfacial properties affects the overall behavior of the composite. In this work, the interface of a uniaxially reinforced composite representative volume element (RVE) is modeled using the cohesive zone modeling (CZM) approach. A three parameter bilinear traction separation relationship is used to characterize the interface and the effect of variation of these parameters on the response of the composite is studied. Uniaxial tension and compression tests are simulated using a finite element model to study the response of the composite with varying constituent properties. The matrix is modeled as a linearly elastic material initially and as a hyperelastic material subsequently. The importance of each interfacial parameter on the effective behavior of the composite is investigated. Failure at the interface and its effect on the response of the composite is studied, and the load sharing within the composite when external load is applied is observed.

Committee:

Kumar Vemaganti, PhD (Committee Chair); Ronald Huston, PhD (Committee Member); Yijun Liu, PhD (Committee Member)

Subjects:

Engineering; Mechanical Engineering

Keywords:

carbon nano-composites; cohesive zone modeling (CZM); interface; finite element analysis

Pulikollu, Rajasekhar VenkataNano-Coatings on Carbon Structures for Interfacial Modification
Doctor of Philosophy (PhD), Wright State University, 2005, Engineering PhD
Pulikollu, Rajasekhar Venkata. Ph.D., Department of Mechanical and Materials Engineering, Wright State University, 2005. Nano-coatings on Carbon Structures for Interfacial Modification. Surface modification of materials is a rapidly growing field as structures become smaller, more integrated and complex. It opens up the possibility of combining the optimum bulk properties of a material with optimized surface properties such as enhanced bonding, corrosion resistance, reactivity, stress transfer, and thermal, optical or electrical behavior. Therefore, surface functionalization or modification can be an enabling step in a wide variety of modern applications. In this dissertation several surface modification approaches on carbon foam and carbon nano-fibers will be discussed. These are recently developed sp 2 graphitic carbon based structures that have significant potential in aerospace, automotive and thermal applications. Influence of surface modification on composite formation and properties have also been investigated. Two types of property changes have been investigated: one for enhancing the surface reactivity and another for surface inertness. Characterization techniques such as X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), Contact Angle Measurement, Scanning Electron Microscope (SEM), Transmission Electron Microscope(TEM), and mechanical testing are used in this study to find out the influence of these coatings on surface composition, chemistry, and morphology. Mechanical testing has been performed on composites and stand-alone foam to study the influence of surface modification on physical and mechanical properties of the composite materials. The effectiveness of these coatings on metallic/graphite interface has also been investigated for metal-matrix composite related applications. Additionally, the influence of plasmacoatings on nucleation and growth of nanotubes on larger carbon structures (to produce multiscale, multifunctional materials) have also been studied. It is seen that the liquid phase activation treatment introduces oxygen functional groups on the surface, but may cause severe enough degradation that damages the ligaments and cell walls of carbon foam. This results in higher elastic modulus but lower strength. So, to get any benefit from such approaches the optimization window may be very narrow and marginal in controllability. An alternative solution would be to synthesize ultra thin film coatings without etching the surfaces. It is observed that plasma assisted coatings having thickness in the range of few nanometers (4-5nm) are completely covering the graphite substrates. The coating surface, chemistry, and morphology information is based upon XPS and AFM studies on pyrolytic graphite substrate. Two types of plasma surface modification techniques have been attempted: one is to make the surface more reactive for structural components and the other is to make the surface more inert for stand-alone structures. In order to achieve these goals, plasma assisted oxide and fluorocarbon coatings are studied in detail. The synthesized oxide and fluorocarbon coating chemistries are comparable to conventional silica (SiO2) and polytetrafluoroethylene (PTFE, –CF2-). It is seen that the fluorocarbon coatings provide moisture resistance to graphitic foam by making the surface inert at the nanometer scale. On the other hand, plasma assisted oxidecoating is a feasible and effective means of improving the wettability and dispersion of foam and nanofibers in organic polymer matrix material. Surface analysis as well as microstructural studies and mechanical tests have shown encouraging results. The interface reactions between graphite (coated and uncoated) and epoxy have also been studied in detail. Nano-scale plasma coatings have also been applied for metal matrix composites and semiconductor related applications. The fluorocarbon coating promotes delamination/exfoliation of the metal on graphite, hence may be used for patterning or lithography. Oxide coatings seem to enhance the adhesion and metallic diffusion between graphite and metal, hence can be used for the development of metalmatrix composites. Additionally, oxide coating seems to enhance the length and density of nanotubes synthesized on carbon structures, desired for the design of advanced nano-composites.

Committee:

Sharmila Mukhopadhyay (Advisor)

Subjects:

Engineering, Materials Science

Keywords:

Nano-coatings; carbon foam; nanofibers; nanotubes; surface modification of materials; plasma-assisted oxide coatings; plasma-assisted fluorocarbon coatings; interfacial bonding; carbon-core polymer and metal matrix composites; metallization.

Yurcho, Anthony M.Microstructural Investigation of Al/Al-Fe alloy-Al2O3 Interpenetrating Phase Composites Produced by Reactive Metal Penetration
Master of Science in Engineering, Youngstown State University, 2011, Department of Civil/Environmental and Chemical Engineering

Aluminum-Al2O3 and Al alloy-Al2O3 based ceramic-metallic interpenetrating phase composites (IPC's) possess unique physical and mechanical properties that are desirable for a number of potential applications. Fireline TCON, Inc. (FTi) of Youngstown, OH produces such ceramic-metallic IPC's using a reactive metal penetration (RMP) process. The RMP process allows other materials and alloying metals to be added to the composite in order to tailor its final properties. Currently, TCON® IPC's are being marketed as refractory materials for handling high temperature molten metals. However, it is desired to expand the applications of ceramic-metallic IPC's to markets such as automotive brake rotors and military vehicle and body armor.

In order to tailor ceramic-metallic IPC's to different applications, a more thorough understanding of their microstructures and how they are affected by additions is necessary. In this study, the microstructural properties of two IPC's produced by the TCON RMP process were investigated. The materials include Al-Al2O3 and an Al-Fe alloy-Al2O3 ceramic-metallic IPCs. Analysis was performed using optical microscopy (OM), scanning electron microscopy (SEM), scanning/transmission electron microscopy (S/TEM), energy dispersive spectroscopy (EDS), focused ion beam (FIB), X-ray diffraction (XRD), and Vickers hardness testing. The results can be used to correlate the microstructure properties to the materials' physical performance. This information is valuable for developing IPC's modified for specific applications.

Committee:

Virgil C. Solomon, PhD (Committee Chair); Douglas M. Price, PhD (Committee Member); Matthias Zeller, PhD (Committee Member); Timothy R. Wagner, PhD (Committee Member)

Subjects:

Materials Science

Keywords:

interpenetrating phase composites; reactive metal penetration; Al2O3; ceramic metallic; aluminum-alumina; IPC; IPC's

Wolcott, Paul JosephToward Load Bearing Reconfigurable Radio Frequency Antenna Devices Using Ultrasonic Additive Manufacturing
Master of Science, The Ohio State University, 2012, Mechanical Engineering

Ultrasonic additive manufacturing (UAM) is a low temperature, solid-state manufacturing process that enables the creation of layered solid metal structures with designed anisotropies and embedded materials. As a low temperature process, UAM enables the creation of composites using smart materials or other components that would otherwise be destroyed in fusion-type processes. The process uses ultrasonic energy to bond metallic foils to one another under an applied load through a scrubbing action at the foil interface. This scrubbing action creates the nascent surfaces necessary for solid state bonding. To be able to take full advantage of the UAM process, the mechanical properties of composites made therein must be fully characterized. In this study, scanning electron microscopy is utilized to investigate the bonding behavior at the foil interface of samples tested in tension. Findings show a relationship between the amount of ductile fracture and the strength of UAM samples. In addition, fatigue testing was conducted on UAM Al samples to determine their lifetime under cyclic loading conditions. The results indicate a flat S-N behavior between the loading and number of cycles to failure. This indicates that lifetime prediction of UAM samples is difficult at this time due to the inconsistent bonding at the interface. It is theorized that the unbonded areas at the interfaces grow into one another and eventually lead to fast fracture.

Along with the developments made in understanding UAM mechanical properties, the design and manufacture of reconfigurable antennas was conducted with an eventual goal of developing a structural reconfigurable antenna using UAM. The reconfigurable antenna design concept uses shape memory alloy switches to electrically connect to an antenna structure to create discrete shifts in the antenna natural frequency. Using this design concept, three sets of shape memory alloy switches were made to connect with three different antenna structures. The first switch proved the concept of reconfiguration with a monopole antenna, yielding a frequency shift of 85 MHz. The second switch design used smaller dimensions to work in conjunction with a microstrip line, an antenna-like device. With this switch, the transmission of a radio frequency signal was tested to confirm the operation of the switches in both the on and off positions. This setup showed that the metallization of the antenna could effectively change the natural frequency while maintaining significant signal strength. A final set of switches was made for implementation into a planar antenna structure. The planar antenna was designed and constructed with free segments within the structure where switches are connected create reconfiguration. This antenna provides tunable frequency shifts from 2.43 GHz with no switches connected to 2.25 GHz when both switches are connected while maintaining a high gain and repeatable radiation pattern.

Committee:

Marcelo Dapino, Ph.D. (Advisor); S. Suresh Babu, Ph.D. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Ultrasonic Additive Manufacturing; Ultrasonic consolidation; Metal matrix composites; Fatigue; Reconfigurable antennas; Smart materials

AMINJIKARAI, SRINIVASA BABUA STRAIN RATE DEPENDENT 3D MICROMECHANICAL MODEL FOR FINITE ELEMENT SIMULATIONS OF PLAIN WEAVE COMPOSITE STRUCTURES
MS, University of Cincinnati, 2003, Engineering : Aerospace Engineering
A 3D micromechanical model has been developed for Plain Weave Composites (PWC) and implemented in the explicit finite element software DYNA3D. The model accounts for the strain rate dependency, inherent material nonlinearity, and progressive failure of constituents of PWC. The micromechanical equations have been obtained for a Representative Volume Cell (RVC) which is assumed to represent the behavior of a PWC lamina. The model implemented in DYNA3D can be used for the simulation of the mechanical behavior of PWC structures under various loads such as multi-axial and impact. The yarns were assumed to be transversely isotropic till initial failure. A viscoplastic constitutive model was used for the resin constituent as it was the primary reason for the rate dependency of PWC. The nonlinear behavior in shear was modeled by updating the shear moduli of the constituents based on their current stress state. Progressive failure was modeled by defining a set of maximum strain criteria for detecting failure in constituents and degrading the properties depending on the failure mode. The implemented model was validated in different loading conditions by comparing its prediction with experimental results available in the literature. Good correlation was observed between the predicted and the experimental results.

Committee:

Dr. Ala Tabiei (Advisor)

Keywords:

plain weave composites; material model; micromechanical; strain rate dependent; constitutive model

BOY, SERPILRETROFIT OF EXISTING REINFORCED CONCRETE BRIDGES WITH FIBER REINFORCED POLYMER COMPOSITES
MS, University of Cincinnati, 2004, Engineering : Civil Engineering
Fiber-Reinforced Polymer (FRP) plates and fabrics have emerged as viable systems for retrofitting of existing reinforced concrete members with insufficient capacity. The results from previous research, conducted predominately on newly cast laboratory specimens, have been used to develop design guidelines. Detailed testing and evaluation of aged members retrofitted with FRP systems are very limited. This research is conducted to fill this gap. A 45-year old, three-span reinforced concrete slab bridge with insufficient capacity was retrofitted with 76.2 and 127-mm wide CFRP plates, 102-mm wide bonded CFRP plates with mechanical anchors at the ends, and bonded CFRP fabrics. Using four systems in one bridge provided an opportunity to evaluate field installation issues, and long-term performance of each system under identical traffic and environmental conditions. Through controlled truckload tests, the response of the bridge before retrofitting, shortly after retrofitting, and after one year of service was measured. The FRP system's stiffness was small in comparison to the stiffness of the bridge deck, therefore the measured deflections did not noticeably change after retrofitting. The measured strains suggest participation of the FRP systems, and more importantly the strength of the retrofitted bridge was increased. Detailed three-dimensional finite element models of the original and retrofitted bridge was developed and calibrated based on the measured deflections. Those models were used to calculate the rating factors and the corresponding load limits, which increased by 22% after retrofitting. In view of the increased capacity and performance of the bridge, load limits were removed and normal traffic was resumed.

Committee:

Dr. Bahram Shahrooz (Advisor)

Keywords:

Fiber Reinforced Polymer Composites; FRP; Retrofitting; Reinforced Concrete; Bridge; Installation; Design; Rating Factor; Load Rating; Moving Load Analysis; Normalization; ACI-440; AASHTO

Next Page