Mechanical characterization of four polymer nanocomposite systems and two pure polymer reference systems was performed. Alumina (Al2O3) and magnetite (Fe3O4) nanoparticles were embedded in poly(methyl methacrylate) (PMMA) and polystyrene (PS) matrices. Mechanical testing techniques utilized include tensile testing, dynamic mechanical analysis (DMA), and nanoindentation. Consistent results from the three techniques proved that these nanocomposite systems exhibit worse mechanical properties than their respective pure polymer systems. The interphase, an interfacial area between the nanoparticle filler and the polymer matrix, was investigated using two approaches to explain the mechanical testing results. The first approach utilized data from thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM) to predict the structure and density of the interphase for the four nanocomposite systems. The second approach analyzed the bonding between the polymer and the nanoparticle surfaces using Fourier Transform Infrared Spectroscopy (FT-IR) to calculate the density of the interphase for the two PMMA-based nanocomposite systems. Results from the two approaches were compared to previous studies. The results indicate that Al2O3 nanoparticles are more reactive with the polymer matrix than are Fe3O4 nanoparticles, but neither have strong interaction with the polymer matrix. The poor interaction leads to low density interphase which results in the poor mechanical properties.

The purpose of thesis aims to investigate the mechanical behavior and properties of a centrally notched hybrid Al alloy/Carbon-Fiber/PEEK(APC-2) laminate at elevated temperature. The high performance hybrid composite laminates of 0.5mm Aluminum alloy sheets sandwiched by APC-2 cross-ply and guasi-isotropic laminates were fabricated. The prepregs of APC-2 were stacked into cross-ply [0/90]s and quasi-isotropic [0/45/90/-45] laminates spread uniformly with nanoparticles SiO2. The sheet surface was treated by chromic acid anodic method to achieve perfectly bonding with matrix PEEK. The modified diaphragm curing process was adopted to fabricate Al/APC-2 hybrid nanocomposite laminates. The panels were cut into the specimens and then drilled an diameter hole in the center with diameters of 1,2,4,6 mm. The MTS 810 material testing machine was used to conduct the tension and fatigue tests. In addition, the MTS 651 environmental chamber was installed to control and keep the specific testing temperatures, such as ,25¢XC(RT), 75¢XC, 100¢XC, 125¢XC and 150¢XC. At first, the nominal stress(£mnom) and stress-strain diagram were obtained due to static tension tests at elevated temperature. The constant stress amplitude tension-tension cyclic tests were carried out by using load-control mode at a sinusoidal loading with frequency of 5Hz and stress ratio R=0.1. The received fatigue data were plotted in normalized S-N curves at variously elevated temperature. For the tensile tests, at the same temperature the nominal stress of cross-ply specimens was higher than that of quasi-isotropic specimens. Comparing with the notched and unnotched of cross-ply specimens, the nominal stress of notched specimens was about 60% to 80% that of unnotched specimens. Besides, as for the notched and unnotched quasi-isotropic specimens, the nominal stress of notched specimens was about 75% to 85% that of unnotched specimens. Then, the fatigue life and stress-cycles (S-N) curves of notched specimens were obtained often tension-tension fatigue tests. In the case of the same loading, notched specimens possess worse fatigue behavior, but in the same normalized stress ratio, the S-N curves of the unnotched were below the notched ones. The fatigue resistance of notched samples decrease as the temperature rising.

The aims of this thesis are fabrication of Ti/APC-2 hybrid nanocomposite laminates and investigation of their mechanical properties at elevated temperature. The prepregs of APC-2 were stacked into cross-ply [0/90]s and quasi-isotropic [0/45/90/-45] laminates spread uniformly with nanoparticles SiO2. The sheet surface was treated by chromic acid anodic method to achieve perfectly bonding with matrix PEEK. The prepregs were sandwiched with the Ti alloy sheets. The modified diaphragm curing process was adopted to produce Ti/APC-2 hybrid nanocomposite laminates. The nanocomposite laminates were a five-layer composite with two 0.55 mm thick APC-2 layers sandwiched by three 0.5 mm thick Gr.1 titanium alloy sheets. The MTS 810 material testing machine was used to conduct the tension and fatigue tests. In addition, the MTS 651 environmental chamber was installed to control and keep the experimental temperature, such as 25¢XC, 75¢XC, 100¢XC, 125¢XC and 150¢XC. The mechanical proper¬ties, such as ultimate tensile strength, longitudinal stiffness of cross-ply and quasi-isotropic nanocomposite laminates, were obtained from the static tensile test. The stress-strain diagrams were plotted in the corresponding temperature. The constant stress amplitude tension-tension cyclic tests were carried out by using load-control mode at a sinusoidal loading with frequency of 5Hz and stress ratio R=0.1. The received fatigue data were plotted in normalized S-N curves at variously elevated temperature. From the summarized results, some conclusions were made. First, the ultimate strength of Ti/APC-2 nanocomposits was better than Ti/APC-2 composites at room temperature; Second, Both two type nanocomposite laminates¡¦ ultimate strength and S-N curves go downwards as temperature rising, especially at 150¢XC; Third, The fatigue tensile strength of both hybrid composite laminates was the lowest at 150¢XC. Fourth, Ti/APC-2 quasi-isotropic nanocomposite laminates had better fatigue resistance than Ti/APC-2 cross-ply nanocomposite laminates. Finally,The longitudinal stiffness was in good agreement with prediction by using the modified ROM because of the changed curve fitting ranges.

The aims of this thesis to investigate the two step loading of Ti/APC-2 hybrid nanocomposite laminates and their notched effect. Ti/APC-2 laminates were composed of three layers of titanium sheets and two layers of APC-2. Nanoparticles SiO2 were dispersed uniformly on the interfaces of APC-2 with the optimal amount of 1 wt %. Then, APC-2 was stacked according to cross-ply [0/90]s and quasi-isotropic [0/45/90/-45] sequences. The modified diaphragm curing process was adopted to fabricate the hybrid panels for minimal impact of production. The panels were cur into samples and drilled an diameter hole in the center with diameters of 4 or 6 mm. Both tension and fatigue tests were carried out with MTS 810 universal testing machine at room temperature. Also, two-step loading tests include high¡÷low and low¡÷high tests, were conducted. 0.9£mnom is denoted as high load and 0.7£mnom low load for two-step loading spectrum. In both high¡÷low and low¡÷high step loadings the first step is to do cyclic tests at a half life of the corresponding load, and then finish it due to last step load. From the received results, some conclusions were made. First, the ultimate load of notched cross-ply samples was reduced about 50% and the notched quasi-isotropic samples reduced about 30% compared to their unnotched counterparts. Second, the S-N curves are very close for both centrally notched samples of diameters 4 mm and 6 mm in cross-ply and quasi-isotropic samples. Third, quasi-isotropic samples had higher average values of cumulative damage than cross-ply samples. Because of notched effect centrally notched samples of diameters 4 mm had higher average values of cumulative damage than centrally notched samples of diameters 6 mm.

The innovative Al/APC-2 hybrid nanocomposite fiber metal laminates (FMLs) were successfully fabricated. To overcome the usual problem of delamination, the Al alloy 2024-T3 thin sheets were treated by chromic acid anodic (CAA) method to achieve perfectly bonding with matrix PEEK eventually. It was found much better than the previously surface treatment method of CrO3-based chemical etching. A systematic study of hybrid specimens subjected to both static tensile and fatigue tests was conducted at elevated temperatures to obtain their mechanical properties, fatigue lives and failure mechanisms. From the tensile tests, the mechanical properties of Al/APC-2 hybrid cross-ply and quasi-isotropic nanocomposite FLMs at elevated temperatures were received, such as ultimate tensile strength and longitudinal stiffness. Also, the predicted stress-strain curves was proposed and in good agreement with experimental data. The average values of received notched strength were affected significantly by stress concentration and high temperature. The modified point stress criterion (PSC) was used with the varied characteristic length dependent on nature of material and specimen geometry. The predicted notched strengths by the modified PSC model were not only precisely validated, but extended to the application at elevated temperatures. The received fatigue data were plotted in S-N curves at variously elevated temperatures. The predictions of fatigue life curves were also presented and verified. The predicted S-N curves were compared with experimental data and found quite accurate.

The goals of this work were to synthesize high performance perovskite based thin film solid oxide fuel cell (TF-SOFC) cathodes by pulsed laser deposition (PLD), to study the structural, electrical and electrochemical properties of these cathodes and to establish structure-property relations for these cathodes in order to further improve their properties and design new structures. Nanostructured cathode thin films with vertically-aligned nanopores (VANP) were processed using PLD. These VANP structures enhance the oxygen-gas phase diffusivity, thus improve the overall TF-SOFC performance. La0.5Sr0.5CoO3 (LSCO) and La0.4Sr0.6Co0.8Fe0.2O3 (LSCFO) were deposited on various substrates (YSZ, Si and pressed Ce0.9Gd0.1O1.95 (CGO) disks). Microstructures and properties of the nanostructured cathodes were characterized by transmission electron microscope (TEM), high resolution TEM (HRTEM), scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS) measurements. A thin layer of vertically-aligned nanocomposite (VAN) structure was deposited in between the CGO electrolyte and the thin film LSCO cathode layer for TF-SOFCs. The VAN structure consists of the electrolyte and the cathode materials in the composition of (CGO) 0.5 (LSCO) 0.5. The self-assembled VAN nanostructures contain highly ordered alternating vertical columns formed through a one-step thin film deposition using a PLD technique. These VAN structures significantly increase the interface area between the electrolyte and the cathode as well as the area of active triple phase boundary (TPB), thus improving the overall TF-SOFC performance at low temperatures, as low as 400oC, demonstrated by EIS measurements. In addition, the binary VAN interlayer could act as the transition layer that improves the adhesion and relieves the thermal stress and lattice strain between the cathode and the electrolyte. The microstructural properties and growth mechanisms of CGO thin film prepared by PLD technique were investigated. Thin film CGO electrolytes with different grain sizes and crystal structures were prepared on single crystal YSZ substrates under different deposition conditions. The effect of the deposition conditions such as substrate temperature and laser ablation energy on the microstructural properties of these films are examined using XRD, TEM, SEM, and optical microscope. CGO thin film deposited above 500 ºC starts to show epitaxial growth on YSZ substrates. The present study suggests that substrate temperature significantly influences the microstructure of the films especially film grain size.

Vertically aligned nanocomposite (VAN) thin films have recently stimulated significant research interest to achieve better material functionality or multifunctionalities. In VAN thin films, both phases grow epitaxially in parallel on given substrates and form a unique nano-checkerboard structure. Multiple strains, including the vertical strain which along the vertical interface and the substrate induced strain which along the film and substrate interface, exist in VAN thin films. The competition of these strains gives a promise to tune the material lattice structure and future more the nanocomposite film physical properties. Those two phases in the VAN thin films are selected based on their growth kinetics, thermodynamic stability and epitaxial growth ability on given substrates. In the present work, we investigated unique epitaxial two-phase VAN (BiFeO3)x:(Sm2O3)1-x and (La0.7Sr0.3MnO3)x:(Mn3O4)1-x thin film systems by pulsed laser deposition. These VAN thin films exhibit a highly ordered vertical columnar structure with good epitaxial quality. The strain of the two phases can be tuned by deposition parameters, e.g. deposition frequency and film composition. Their strain tunability is found to be related directly to the systematic variation of the column widths and domain structures. Their physical properties, such as dielectric loss and ferromagnetisms can be tuned systematically by this variation. The growth morphology, microstructure and material functionalities of VAN thin films can be varied by modifying the phase ratio, substrate orientation or deposition conditions. Systematic study has been done on growing (SrTiO3)0.5:(MgO)0.5 VAN thin films on SrTiO3 and MgO substrates, respectively. The variation of column width demonstrates the substrate induced strain plays another important role in the VAN thin film growth. The VAN thin films also hold promise in achieving porous thin films with ordered nanopores by thermal treatment. We selected (BiFeO3)0.5:(Sm2O3)0.5 VAN thin films as a template and get uniformly distributed bi-layered nanopores. Controllable porosity can be achieved by adjusting the microstructure of VAN (BiFeO3):(Sm2O3) thin films and the annealing parameters. In situ heating experiments within a transmission electron microscope column provide direct observations into the phases transformation, evaporation and structure reconstruction during the annealing. Systematic study in this dissertation demonstrate that the vertically aligned nanocomposite microstructure is a brand new architecture in thin films and an exciting approach that promises tunable material functionalities as well as novel nanostructures.

Conducting polypyrrole (PPy) nanoparticles were synthesized via microemulsion polymerization system. The characterization of PPy nanoparticles was done by Fourier transform infrared spectrometer (FTIR) and scanning electron microscope (SEM). Nanocomposites were prepared by melt-mixing of polypyrrole with polypropylene (PP) and processed with injection molding. The amount of PPy in nanocomposites varied in the range of 1-20% by weight. The effect of PPy nanoparticles on mechanical, electrical properties and thermal stability of nanocomposites were investigated. Tensile test has revealed that increasing amount of PPy increased the strength and the stiffness of the nanocomposite while limiting the elongation of PP. Thermal gravimetric analysis has showed that incorporation of PPy nanoparticles has improved the thermal stability of the nanocomposites. Four probe conductivity measurement has exhibited that increasing amount of PPy nanoparticles increases the conductivity of nonconductive PP up to 2,4.10-4 Scm-1. In order to improve the dispersion of PPy in PP, sodium dodecylsulphate was used as dispersant. The same techniques were used to characterize nanocomposites containing 2% by weight dispersant. Composites prepared with dispersant have exhibited improvement in some mechanical and thermal properties and involved smaller dimension PPy nanoparticles.

The aim of this study was to improve the mechanical properties &ldquo / Moplen&rdquo / EP300L which is a heterophase copolymer. Polymer blends and nanocomposites were prepared by melt compounding method in a twin screw extruder. Nanofil&reg / 5 (N5) and Nanofil&reg / 8(N8) were used as the organoclays, and maleic anhydride grafted polypropylene (M) was used as the compatibilizer. The effects of additive concentrations and types of organoclays on the morphology, mechanical and thermal properties were investigated. Organoclay loading over 2 wt% prevented the intercalation mechanism resulting in large aggregates of clay, thus the material properties became poor even in the presence of compatibilizer. Compatibilizer addition improved the intercalation ability of the polymer, however a substantial increase in mechanical properties was not obtained up to 6 wt % loading of the compatibilizer. XRD analysis revealed that intercalated structures were formed with the addition of compatibilizer and organoclay. The nanocomposites that were prepared with N5 type organoclay showed delaminated structures at 6 wt % compatibilizer loading. v Nanofill &reg / 5 exhibited the highest improvements in mechanical properties, since the degree of organoclay dispersion was better in Nanofill &reg / 5 containing nanocomposites in comparison to Nanofill &reg / 8 containing ones. The DSC analysis indicated a insignificant reduction in the melting temperature of the ternary nanocomposites.

The thesis is to fabricate Al/APC-2 hybrid nanocomposite laminates and investigate their mechanical properties at elevated temperature. The prepregs of Carbon /PEEK were stacked into cross-ply [0/90]s and quasi-isotropic [0/45/90/-45] laminates spread uniformly with nanoparticles SiO2. The sheet surface was treated by chromic acid anodic method to achieve perfectly bonding with matrix PEEK. The prepregs were sandwiched with the Al alloy sheets. The modified diaphragm curing process was adopted to produce Al/APC-2 hybrid nanocomposite laminates. The hybrid nanocomposite laminates were a five-layer composite with two 0.55 mm thick Carbon/PEEK layers sandwiched by three 0.5 mm thick 2024-T3 Aluminum alloy sheets. The MTS 810 material testing machine was used to conduct the tension and fatigue tests. In addition, the MTS 651 environmental chamber was installed to control and keep the specific testing temperature, which was room temperature, 75¢XC, 100¢XC, 125¢XC and 150¢XC. The mechanical proper¬ties, such as ultimate tensile strength and longitudinal stiffness of hybrid cross-ply and quasi-isotropic nanocomposite laminates, were obtained from the static tensile test, and the stress-strain diagrams were plotted in the corresponding temperature. The constant stress amplitude tension-tension cyclic tests were carried out by using load-control mode at a sinusoidal loading with frequency of 5Hz and stress ratio R=0.1. The received fatigue data were plotted in normalized S-N curves at variously elevated temperature. In order to observe the failure mechanism of samples, the scanning electron microscope was used. From the summarized results, some conclusions were made. First, the slope changed at strain=0.1% in the stress-strain diagram, and led to a noticeable error between the experimental data and ones calculated according to Rule of Mixtures. Second, the Al/APC-2 cross-ply nanocomposite laminates were less resistant to fatigue than quasi-isotropic. Third, the ultimate tensile strength of both hybrid composite laminates was the lowest at 150¢XC. Fourth, the Al/APC-2 quasi-isotropic nanocomposite laminates were more resistant to the temperature effect. Finally, The mechanical proper¬ties were better for the surface treated by chromic acid anodic method than chemical etching.