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 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 work aims to manufacture AS-4/PEEK APC-2 nano-composite laminates first. We used the prepreg form of AS-4 Graphite/PEEK laminae to make APC-2 laminates of 2 mm thick with two lay-ups of cross-ply and quasi-isotropic totally 16 plies by a hot press via the modified diaphragm curing. The nano-particles SiO2 with the average diameter of 15¡Ó5 nm were uniformly spread in the specific interfaces of laminate. From mechanical testing it is found that the nanocomposite specimens of spreading 10 plies nanoparticles (3% by wt. of matrix) possesses the highest mechanical properties. we see that in cross-ply specimens the ultimate strength increases 10.91 % and stiffness 6.7 %; while in quasi-isotropic specimens the ultimate strength increases 12.48 % and stiffness 19.93 %. Second, repeat the tensile tests at 50, 75, 100, 125, 150¢J to receive respective stress-strain curve , strength and stiffness. At elevated temperatures the ultimate strength decreases slightly below 75¢J and the elastic modulus reduces slightly below 125¢J, however, both properties degrade highly at 150¢J ( Tg) for two layups generally. Finally, the constant stress amplitude tension-tension cyclic testing was conducted. It is found that both the stress-cycles (S-N) curves are very close below 104 cycles for cross-ply laminates w/wo nanoparticles, and the S-N curve of nano-laminate slightly bent down after 105 cycles. Whilst in quasi-isotropic laminates, the S-N curve of nano-laminate is always slightly below that of APC-2 laminate through the life.

ABSTRACT PEEK matrix reinforced by carbon fibers as one thermoplastic composite material is studied. Thermoplastic composites have the advantages of high specific stiffness and strength, longer fatigue life, good resistance to moisture absorption and high temperature condition. The thesis is aimed to investigate the mechanical properties and fracture mechanism of the centrally notched AS-4/PEEK composite laminates subjected to tension-tension fatigue loading at elevated temperature. We use three common types of laminates, such as cross-ply , quasi-isotropic and angle-ply . After centrally notched, we first obtain the base-line data of mechanical properties by tensile tests at five different temperatures, such as 25¢J¡B75¢J¡B100¢J¡B125¢J¡B150¢J. Then, the fatigue tests are conducted, we receive the fatigue strength and life and establish the stress-life curves. The fatigue characteristics and fracture mechanism of a centrally notched composite laminate at elevated temperature are also recorded and observed. The empirical results can be concluded as follows. At the same temperature, the laminate of cross-ply possesses the largest ultimate strength and fatigue strength, quasi-isotropic the second angle-ply the smallest. As for the elastic modulus, the laminate of cross-ply is larger than that of quasi-isotropic. However, the large strain of angle-ply is within the plastic range that is out of the limit of the study. Thus, a further investigation is needed for angle-ply laminates alone. After centrally notched, the net area is reduced of the specimen, and then the elastic modulus is raised and the ultimate strength and fatigue strength of composite materials are lower. As the temperature increasing, the ultimate strength, fatigue strength and elastic modulus are all decreasing.

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.

Unbonded post-tensioned concrete slabs have been widely used in Canada and the United States since the 1960s, as they allow increased span-to-depth ratios and excellent control of deflections compared to non-prestressed reinforced concrete flexural members. The satisfactory fire performance of unbonded post-tensioned concrete slabs in North America was established by a series of standard fire tests performed in the United States during the 1960s. However, there is a paucity of data on the effect of elevated temperatures on cold-drawn prestressing steel, both in terms of post-fire residual mechanical properties and high-temperature stress relaxation, which can lead to significant prestress loss both during and after a fire. A detailed and comprehensive literature review is presented that provides background on the residual mechanical properties of prestressing steel, as well as on the creep-relaxation behaviour experienced at elevated temperatures under stress. The results of two test series are discussed; the first examining the effects of elevated temperatures on the residual mechanical properties of prestressing steel exposed to elevated temperatures. The second test series examines the irrecoverable and significant loss of prestress force that results from steel relaxation and other thermal effects experienced during heating. A preliminary analytical model is presented, capable of predicting the change in prestress force experienced by a stressed strand under transient heating. The model is then compared with experimental elevated temperature relaxation data. Finally, the analytical model developed and residual mechanical properties obtained through experimentation are used along with a pre-existing finite difference heat transfer model (developed for concrete slabs) to examine the effect of elevated temperature exposure on the residual flexural capacity of a typical unbonded post-tensioned example slab. Several parameters, such as heated length and concrete cover, are examined using the example structure. From this it was observed that, after one hour of exposure to a standard fire (ASTM E119), significant losses in effective prestress and moment capacity occurred even with the appropriate amount of concrete cover. This is a finding which is of the utmost practical importance to engineers engaged in the evaluation of fire damaged unbonded post-tensioned structures. / Thesis (Master, Civil Engineering) -- Queen's University, 2007-12-18 17:15:17.521 / Natural Sciences and Engineering Research Council of Canada, and the Department of Civil Engineering at Queen’s University

Cellular beams (CBs) have become increasingly popular in the UK and other countries over the recent years. However, the research into the behaviour of these beams has not advanced at the same rate. There is still no robust codified guidance available to design cellular beams and cellular composite beams at ambient and elevated temperatures. Meanwhile, numerical simulation approaches, such as Finite Element (FE) analysis, have enabled the researchers to advance their investigations into various behavioural aspects of these beams. In this research, the developed numerical models using the ABAQUS package were able to predict, to a high accuracy, the failure mode and failure load (temperature) of CBs and cellular composite beams at ambient and elevated temperatures.Within the investigations on cellular beams, it was found that predicting the correct failure mode by FE models can be extremely sensitive to the maximum load increment allowed in the software (for elastic-perfectly plastic stress-strain relationship for steel material) and also to the applied boundary conditions. In particular, slight changes in the boundary conditions applied to the top flange of the beam, can change the failure mode from web post buckling to Vierendeel mechanism. The buckling resistance of the web post of cellular composite beams was found to be sensitive to the amplitude of web imperfections at ambient temperature. However, the ultimate resistance of these beams was not affected by the amplitude of web imperfections at elevated temperature. This suggests that the 'Strut' model used in current design method to estimate the buckling resistance of the web post is not reasonable at elevated temperature and needs to be modified. The failure of cellular composite beams under a uniform distributed load (UDL) and at elevated temperatures, was governed by distorsional buckling before the development of web post buckling. Adding full-height web stiffeners to the beam in such cases improved their loading resistance at ambient temperature by up to 15% and prevented the occurrence of distorsional buckling at elevated temperature. Increasing the end-restraints decreased the deflections of CBs which are governed by catenary action at elevated temperature. However, this also critically promoted the occurrence of web post buckling which could be due to the P-∆ effects and instabilities resulting from the restrained expansion of the beam.Asymmetric beams showed a higher sensitivity and vulnerability to the magnitude of the load ratio than symmetric sections. This suggests a more prudent approach for the fire design of asymmetric beams as opposed to symmetric beams.

Paper and paperboard are the major constituents found in US landfills. Typically paper consists of 79% to 98% of lignocellulose which is considered to be the most abundant source of natural carbon on earth. Lignocellulose decomposition depends on the association of biodegradable cellulose and hemicellulose with lignin. Lignin is a recalcitrant material which hinders cellulose degradation in conventional landfills. Because of this property of lignin cellulose to lignin ratio (C/L) is a common landfill stabilization parameter. Refuse degradation in landfills is a microbiological process and is highly dependent on temperature, moisture, and pH. Bioreactor landfills are designed to enhance biodegradation of refuse by providing favorable conditions for microorganisms. Effect of elevated temperature and moisture on possibility of lignin degradation is studied in this work. Synthetic and newspaper lignin were preheated and then inoculated with anaerobically digested sludge. Newspaper in distilled water exposed to 95°C for 48 hours released 8 times more of solubilized lignin then non preheated newspaper. Moreover lignin monomers were detected as a result of 95°C pretreatment indicating the positive effect of high temperature on the providing lignin in more bioavailable form for microbes. Digested sludge inocula was found to be capable of lignin monomers degradation as well as low but significant mineralization of synthetic lignin with approximately 6% of carbon originated from lignin mineralized into methane and carbon dioxide. An exponentially increasing trend for lignin monomers solubilization as a function of temperature was observed for three types of substrate, synthetic lignin, cardboard, and newspaper with the highest rate of solubilization for newspaper. Results of this study suggest that some lignin degradation can occur at conditions typical for bioreactor landfills. / Master of Science

In this dissertation, three types of microfabricated solid-state sensors had been designed and developed on silicon wafers, aiming to detect hydrogen gas at elevated temperatures. Based on the material properties and sensing mechanisms, they were operated at 140°C, 500°C, and 300°C. The MOS-capacitor device working at 140°C utilized nickel instead of the widely-used expensive palladium, and the performance remained excellent. For very-high temperature sensing (500°C), the conductivity of the thermally oxidized TiO2 thin film based on the anodic aluminum oxide (AAO) substrate changed 25 times in response to 5 ppm H2 and the response transient times were just a few seconds. For medium-high temperatures (~300°C), very high sensitivity (over 100 times’ increment of current for H2 concentration at 10 ppm) was obtained through the reversible reduction of the Schottky barrier height between the Pt electrodes and the SnO2 nano-clusters. Fabrication approaches of these devices included standard silicon wafer processing, thin film deposition, and photolithography. Materials characterization methods, such as scanning electron microscopy (SEM), atomic force microscopy (AFM), surface profilometry, ellipsometry, and X-ray diffractometry (XRD), were involved in order to investigate the fabricated nano-sized structures. Selectivities of the sensors to gases other than H2 (CO and CH4) were also studied. The first chapter reviews and evaluates the detection methodologies and sensing materials in the current research area of H2 sensors and the devices presented this Ph.D. research were designed with regard to the evaluations.

The thesis comprises the two parts in each chapter: the first part focuses on the development and characterization of polyimide (PI) based composite coatings on a steel substrate. In order to improve the tribological performance of polyimide coatings, the fillers i.e. multi-walled carbon nanotubes (MWCNTs) and Graphene (GP) were added into PI and conducted friction test at elevated temperatures ranging from room temperature (RT) to 200°C. Also, the influence of fillers (MWCNTs and GP) materials into PI coatings surface, mechanical and tribological properties of polyimide composites coatings are measured. The addition of MWCNTs and GP reduces the friction coefficient as well as wear volume at elevated temperatures 50°C, 100°C and sometimes at 150°C. These temperatures play a vital role to form a lubrication layer in the contact interfaces at certain load and operating conditions. In these cases, three weight percentage (3wt%) of MWCNTs and GP into polyimide composites showed low friction and high wear-resistant as compared to other PI composites. Besides, by adding these two fillers into pure PI improved the mechanical properties such as micro-hardness and nanoindentation. The scanning electron microscope (SEM) was used to observe the wear mechanism of the composite coatings worn surfaces. The consequences expose that the fatigue wear mechanisms were predominant in the worn surfaces. Moreover, the thermal study of the polyimide composite coatings was conducted using thermal gravimetric (TG) to analyze the behavior of composite coatings at high temperatures. The results showed that the PI coatings with MWCNTs and GP have high thermal stability at 60% sample residue. In the second part-an epoxy coatings with filler materials e.g. hexagonal boron nitride (h-BN) and expanded graphite (EG) were made and conducted their tribological i.e. friction coefficient and wear performance. Also the perfect mixing ratio 4:1 (80 wt% base epoxy matrix and 20 wt% curing agent) was determined on the basis of stoichiometric ratio to cure the epoxy accurately. Therefore, seven samples with a various weight percentage (wt%) were prepared i.e. pure epoxy, epoxy with 5wt%, 10wt%, 15wt% of h-BN and EG. All the prepared samples ran at two different loading 2 N and 4 N conditions with 5 Hz frequency, 300 rpm and 30 minutes duration. The epoxy with h-BN showed low friction as compared to EG where EG has better wear-resistant behavior than h-BN.