Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2006. / Liu, Meilin, Committee Member ; Rees, William S., Committee Chair ; McDowell, David, Committee Member ; Moore, Rick, Committee Member ; Muzzy, John, Committee Member.

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published_or_final_version / Dentistry / Master / Master of Dental Surgery

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Seet Wah Cheong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1994. / Includes bibliographical references (leaves 78-81). / Acknowledgement --- p.i / Abstract --- p.ii / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Perturbation approach and Effective Medium Approximation --- p.6 / Chapter 2.1 --- Perturbation method of calculating local fields --- p.6 / Chapter 2.1.1 --- Formalism --- p.7 / Chapter 2.1.2 --- Results of the perturbation calculations of potentials --- p.10 / Chapter 2.2 --- Effective Medium Approximation (EMA) --- p.13 / Chapter 2.2.1 --- Self-consistency conditions --- p.14 / Chapter 2.2.2 --- Results from the self-consistency conditions --- p.14 / Chapter 2.2.3 --- A simplified version of EMA --- p.16 / Chapter 2.3 --- Conclusion --- p.19 / Chapter 3 --- Dilute limit : Enhancement due to surface plasmon resonance --- p.20 / Chapter 3.1 --- Formalism --- p.21 / Chapter 3.2 --- Models and results --- p.25 / Chapter 3.2.1 --- Nonlinear spherical metallic inclusion --- p.25 / Chapter 3.2.2 --- Shell model with nonlinear core --- p.26 / Chapter 3.2.3 --- Shell model with nonlinear shell --- p.28 / Chapter 3.3 --- Conclusion --- p.30 / Chapter 4 --- Numerical calculations of electric potential --- p.32 / Chapter 4.1 --- Formalism --- p.33 / Chapter 4.2 --- Results --- p.41 / Chapter 4.3 --- Symbolic simulations --- p.43 / Chapter 4.3.1 --- Formalism --- p.43 / Chapter 4.3.2 --- Results --- p.45 / Chapter 4.4 --- Conclusion --- p.45 / Chapter 5 --- Local field enhancement in nonlinear composites of multiply coated spherical inclusion --- p.46 / Chapter 5.1 --- Formalism --- p.47 / Chapter 5.2 --- Single spherical inclusion --- p.49 / Chapter 5.3 --- Single shell particle inclusion --- p.50 / Chapter 5.4 --- Nonlinear problem --- p.50 / Chapter 5.5 --- Core field in the single sphere --- p.52 / Chapter 5.6 --- Summary --- p.55 / Chapter 6 --- Optical transition and random resistor network --- p.57 / Chapter 6.1 --- Formalism --- p.58 / Chapter 6.1.1 --- Model --- p.58 / Chapter 6.1.2 --- Solution of the model --- p.60 / Chapter 6.1.3 --- EMA --- p.61 / Chapter 6.1.4 --- Optical transition --- p.62 / Chapter 6.1.5 --- Scaling functions --- p.63 / Chapter 6.2 --- Random resistor network simulation --- p.64 / Chapter 6.2.1 --- One sample frequency dependence --- p.64 / Chapter 6.2.2 --- Sample averages --- p.66 / Chapter 6.3 --- Nonlinear EMA calculations of optical transition --- p.67 / Chapter 6.4 --- Symbolic calculation of conductivities in small h expansion --- p.69 / Chapter 6.4.1 --- Formalism --- p.69 / Chapter 6.4.2 --- Finite size scaling and exponents --- p.71 / Chapter 6.4.3 --- Scaling Function expansion coefficients --- p.74 / Appendix Estimation of surface plasmon resonance frequency --- p.76 / Chapter A.1 --- Single nonlinear metallic sphere --- p.76 / Chapter A.2 --- "Single metallic shell, nonlinear core model" --- p.77 / Bibliography --- p.78 / Figure Caption --- p.82 / List of Tables --- p.91

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.

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

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."