Increasing worldwide environmental awareness is encouraging scientific research into the development of cheaper, more environmentally friendly and more sustainable construction and packaging materials. Natural fibre reinforced thermoplastic composites are strong, stiff, lightweight and recyclable, and have the potential to meet this need. Industrial hemp fibre is amongst the strongest of the natural fibres available, and possesses a similar specific stiffness to E-glass, but with additional benefits such as low cost and low production energy requirements. The favourable mechanical properties of hemp, however, have yet to be transferred successfully to thermoplastic-matrix composite materials. The aim of this thesis was to achieve a greater understanding of the various parameters that contribute to composite strength and stiffness, and to manipulate these parameters in order to produce an improved hemp fibre reinforced polypropylene composite material. Hemp fibre was alkali treated at elevated temperatures in a small pressure vessel with either a solution of 10wt% NaOH or 5wt% NaOH / 2wt% Na2SO3. Single fibre tensile tests were performed on treated and untreated fibres, and it was found that the NaOH/Na2SO3 treatment produced the strongest and stiffest fibres with a good level of fibre separation. Lignin tests revealed that both alkali treatments were effective in the removal of lignin from hemp fibre, and XRD analysis showed that both alkali treatments resulted in increases in the hemp fibre crystallinity index. TGA and DTA analysis showed that the alkali fibre treatments improved the thermal stability of the treated hemp fibre when compared to the untreated fibre. Alkali treated hemp fibre, polypropylene and a maleic anhydride modified polypropylene (MAPP) coupling agent were compounded in a twin-screw extruder, and injection moulded into composite tensile test specimens. A range of composites with different fibre and MAPP contents were produced and tested. Tensile tests revealed that the optimum composite consisted of polypropylene with 40wt% NaOH/Na2SO3 treated hemp fibre and 4wt% MAPP, and had a tensile strength of 50.5 MPa and a Young's modulus of 5.31 GPa, respectively. The effect of MAPP on the fibre/matrix interface of NaOH/Na2SO3 treated hemp fibre/polypropylene composites was assessed by means of the single fibre fragmentation test. A composite consisting of NaOH/Na2SO3 treated fibres in a matrix of 4wt% MAPP and polypropylene was found to have a critical fibre length of 0.83mm and an interfacial shear strength of 16.1 MPa. The effects of MAPP on the composite fracture mechanisms were evaluated by means of SEM microscopy. TGA and DTA analysis showed that untreated hemp fibre composites and NaOH/Na2SO3 treated hemp fibre composites, each with a matrix of 4% MAPP and polypropylene, were less thermally stable than the polypropylene matrix alone. The Bowyer-Bader model was used to model the strength of an injection moulded composite with a normal fibre length distribution, consisting of 40wt% NaOH/Na2SO3 treated fibre, 4% MAPP and polypropylene. A theoretical composite tensile strength of 149 MPa was obtained from the model, based on the assumption that all the fibres were axially aligned in the composite. Composites with long, axially aligned fibres were produced using a novel solution mixing technique, where the polymer matrix and MAPP coupling agent were dissolved in a solvent and then precipitated inside an aligned fibre mat. Significant improvements in tensile strength and Young's modulus were achieved for solution mixed composites compared to composites produced by means of extrusion and injection moulding. The strongest solution mixed composite had a tensile strength of 84.7 MPa, and consisted of 56wt% NaOH/Na2SO3 treated fibre, 4% MAPP and polypropylene; and the stiffest injection moulded composite had a Young's modulus of 16.0 GPa, and consisted of 63wt% NaOH/Na2SO3 treated fibre, 4% MAPP and polypropylene.

Thesis (M.D.S.)--University of Hong Kong, 1987. / Includes bibliographical references. Also available in print.

Two-dimensionally (2D) braided tubular composites have been utilized in a wide range of applications including medical equipment such as braided stents and catheters. Catheters are long flexible tubes used in catheterization procedures, such as angiography and ablations. In this thesis, angiographic catheters were specifically targeted; which are referred as catheters for the remaining of the document. Catheters are typically used with guidewires which provide structural support to the often low rigidity catheters. In some catheterization procedures, it may be beneficial to use a 2D braided catheter for increased control and maneuverability in the body. The 2D braided catheter, if designed properly, may provide all the required rigidities for a successful procedure and decrease the dependency to the guidewire compared to conventional catheters. Hence, use of 2D braided catheters may decrease the procedure time, may provide superior control of the device due to its design, and may also decrease the inherent patient discomfort. A thorough understanding of 2D braided composites is of absolute necessity considering the delicate use of medical equipment, such as catheters, in the human body. The aim of this PhD thesis is to address the shortcomings of the available models in the literature by developing an analytical model geometrically consistent with small braided tubular structures and provide all the necessary tools possible to design a target specific braided catheter. An analytical model that accounts for the effect of diameter of a braided tubular product on the elastic properties, needed for catheter design, was developed. Parametric studies were conducted to highlight the effects of the change in radius on elastic properties of braided composites. Case studies that underline the important geometrical parameters that affect predictions were conducted and findings discussed. Effect of increased undulation length on elastic properties of braided composites was also investigated. The findings were compared to experimental work using three different fiber/matrix system composites. As predicted by the model, a decrease in the properties was observed experimentally; however, this decrease was found to be more important than predicted. Possible reasons for this behavior are discussed in the view of composite materials and geometrical factors. The experimental findings of the open-mesh composites were also used to further validate a regression based model available in the literature. Lower linearity limit values for the regression based model were calculated for longitudinal elastic and shear moduli predictions.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Ian W. Hall, Dept. of Mechanical Engineering. Includes bibliographical references.

This thesis describes the manufacturing, structural analysis and testing of a composite cylinder for space application. This work includes the design and fabrication of a reusable multicomponent mandrel made of aluminum and steel and the manufacturing of a carbon fiber reinforced tube in an epoxy resin matrix. This structure intends to serve as the optical lens housing onboard a spacecraft. In addition, some future work needs to be done before this component is certified. The objective is to determine if the composite meets the stiffness and strength requirements for lens housing. The structural analysis is made by means of a finite element model simulating the true boundary conditions. The testing includes the design of a fixture to allow the composite cylinder to be mounted in one the testing machines at the Department of Aerospace Engineering at Texas A&M University and the preparation for the actual test. The response to the experimental analysis will be compared to the numerical simulation to verify the results.

A composite likelihood is usually constructed by multiplying a collection of lower dimensional marginal or conditional densities. In recent years, composite likelihood methods have received increasing interest for modeling complex data arising from various application areas, where the full likelihood function is analytically unknown or computationally prohibitive due to the structure of dependence, the dimension of data or the presence of nuisance parameters. In this thesis we investigate some theoretical properties of the maximum composite likelihood estimator (MCLE). In particular, we obtain the limit of the MCLE in a general setting, and set out a framework for understanding the notion of robustness in the context of composite likelihood inference. We also study the improvement of the efficiency of a composite likelihood by incorporating additional component likelihoods, or by using component likelihoods with higher dimension. We show through some illustrative examples that such strategies do not always work and may impair the efficiency. We also show that the MCLE of the parameter of interest can be less efficient when the nuisance parameters are known than when they are unknown. In addition to the theoretical study on composite likelihood estimation, we also explore the possibility of using composite likelihood to make predictive inference in computer experiments. The Gaussian process model is widely used to build statistical emulators for computer experiments. However, when the number of trials is large, both estimation and prediction based on a Gaussian process can be computationally intractable due to the dimension of the covariance matrix. To address this problem, we propose prediction methods based on different composite likelihood functions, which do not require the evaluation of the large covariance matrix and hence alleviate the computational burden. Simulation studies show that the blockwise composite likelihood-based predictors perform well and are competitive with the optimal predictor based on the full likelihood.

Purpose: To determine microleakage and microtensile bond strength (µTBS) of composite restorations bonded with self-adhesive resin-cements. Methods: Six groups of molars were assigned to cements: RelyX-Unicem, Breeze, Monocem, PanaviaF-2.0, Filtek-LS, and Scotch-Bond-Multipurpose (adhesive). For microleakage, Class II preparations were made. Cements were applied onto all cavity walls. Preparations were restored, specimens themocycled and then immersed in red dye. Dye penetration was assessed according to 5-point scale. For µTBS test, 6 mm composite buildups were made over tooth surfaces. Rectangular rods were cut and subjected to tensile force. Mean µTBS and SDs were calculated. Results: RelyX-Unicem and Breeze showed low microleakage, however, they had lower µTBS values. Filtek-LS showed the least microleakage and the highest µTBS with dentin. Conclusion: RelyX-Unicem, Breeze and Filtek-LS will improve marginal seal when used in subgingival Class II composite restorations.

As explicit finite element codes improve and advanced material models become available, such tools find more widespread application in many industries. This thesis reports the research study of the low velocity impact simulation on carbon reinforced polymer epoxy composite tube using nonlinear explicit finite element software LS-Dyna. Validation of the experimental results is done with the proposed finite element model in LS-Dyna. A finite element model is implemented on quadratic stress based global failure progressive damage formulation to model the response and damage progression through carbon epoxy tube. Belytschko-Tsay shell quadrilateral shell element is used to model the eight layer unidirectional lamina’s composite cylinder with [30/-30/90/90/30/-30/90/90] lay up configuration. Also parametric studies were done to find their effects on the low velocity impact damage process. Comparisons of the finite element simulations to the experimental data include degradation, as well as the time history responses. Results indicate that the general shapes of the force versus time curve histories are correlate well with the experimental test data results. Parametric study results are also co related with the results in the published literature and papers and good agreement was found between the simulation results and the published data. Parameters such as impactor velocity, lay-up configurations, boundary conditions on composite tube, and different impactor velocity were considered which affect the impact damage process. Thus this study work demonstrates the accuracy and effectiveness of finite element simulation of low velocity impact test on composite cylinder with LS-Dyna and predicting good simulation results with published data for various parameters. / Thesis (M.S.)--Wichita State University, Dept. of Mechanical Engineering. / "May 2006."

Purpose: To determine microleakage and microtensile bond strength (µTBS) of composite restorations bonded with self-adhesive resin-cements. Methods: Six groups of molars were assigned to cements: RelyX-Unicem, Breeze, Monocem, PanaviaF-2.0, Filtek-LS, and Scotch-Bond-Multipurpose (adhesive). For microleakage, Class II preparations were made. Cements were applied onto all cavity walls. Preparations were restored, specimens themocycled and then immersed in red dye. Dye penetration was assessed according to 5-point scale. For µTBS test, 6 mm composite buildups were made over tooth surfaces. Rectangular rods were cut and subjected to tensile force. Mean µTBS and SDs were calculated. Results: RelyX-Unicem and Breeze showed low microleakage, however, they had lower µTBS values. Filtek-LS showed the least microleakage and the highest µTBS with dentin. Conclusion: RelyX-Unicem, Breeze and Filtek-LS will improve marginal seal when used in subgingival Class II composite restorations.

To design a bolted joint, the transition bearing stress and maximumbearing stress have to be regarded. Transition bearing stress is thebearing stress where bearing failure begins and maximum bearing stressis where the joint goes to total failure. A method for studying rotationin a bolted joint has been developed using an optical instrument calledDigital Speckle Photography, DSP, which is a non-contact extensometerusing digital cameras, together with a load frame. The data from DSPsystem is transformed and analyzed to get rotations for different partsof the joint. Thinner joints give higher values on transition bearingstress, higher maximum bearing stress and higher maximum bolt rotation,than thicker joints. Bolt torque has a big impact and higher torquegives the same positive results as thinner joints. Increased secondarybending makes the joint more resistant to bearing failure, whichincreases the transition bearing failure stress, maximum bearing failurestress and maximum bolt rotation. There is a relationship between thecurve slope in a bearing stress versus bolt rotation figure and thetransition bearing stress. If the joint has a lower value on boltrotation, in comparison with other joints, at the same bearing stress,this will lead to a higher transition bearing stress.