Submitted by FRANCISCO MACIEL MONTICELI null (francisco_monticelli@hotmail.com) on 2017-08-15T16:18:26Z No. of bitstreams: 1 Dissertação Francisco_M_Monticeli.pdf: 22030385 bytes, checksum: 6b57793ae92e8109811a1ce2e8318122 (MD5) / Approved for entry into archive by Monique Sasaki (sayumi_sasaki@hotmail.com) on 2017-08-22T17:27:29Z (GMT) No. of bitstreams: 1 monticeli_fm_me_guara.pdf: 22030385 bytes, checksum: 6b57793ae92e8109811a1ce2e8318122 (MD5) / Made available in DSpace on 2017-08-22T17:27:29Z (GMT). No. of bitstreams: 1 monticeli_fm_me_guara.pdf: 22030385 bytes, checksum: 6b57793ae92e8109811a1ce2e8318122 (MD5) Previous issue date: 2017-07-04 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O compósito híbrido surgiu com o objetivo de reduzir a quantidade de materiais de elevado custo e, ao mesmo tempo, manter as elevadas propriedades mecânicas. Além disso, viu-se a possibilidade de, em se usando reforços diferentes, obter um novo material que evidenciasse as vantagens dos reforços e diminuísse as desvantagens simultaneamente. Um importante fator durante o processamento de compósitos poliméricos para aplicação estrutural é o controle da formação de vazios, pois estes atuam como concentradores de tensão. O objetivo deste trabalho foi produzir compósitos híbridos utilizando diferentes disposições de tecidos de fibra de vidro e carbono, sem perda significativa de propriedades mecânicas. Para a produção do compósito, a pré-forma foi inicialmente caracterizada quanto à impregnação, sendo, para isto desenvolvido um modelo analítico geral que determina o parâmetro de permeabilidade dos compósitos híbridos. O modelo foi validado através de teste de permeabilidade e a qualidade dos laminados (híbridos, e não híbridos) foi certificada pelo processamento dos compósitos e pela quantificação da fração volumétrica de vazios. Este projeto propôs, ainda, a melhoria da análise de vazios pela técnica de porosimetria de Hg com auxílio do planejamento de experimentos. Assim foi possível determinar a fração volumétrica de poros abertos e fechados, a distribuição do diâmetro dos poros e a distância entre os poros dos compósitos, em uma análise conjunta com as técnicas de digestão ácida e microscopia óptica. A pré-forma de carbono apresentou elevada taxa de resistência ao fluxo; por outro lado, observou-se um comportamento oposto para a pré-forma de vidro. Contudo, as pré-formas híbridas apresentaram um efeito híbrido positivo, resultado de uma sinergia que proporcionou um maior valor de permeabilidade. Consequentemente, pode-se conseguir uma otimização do tempo de injeção, considerando uma combinação de tecidos de vidro e carbono equilibrados. O modelo analítico foi capaz de prever o comportamento da frente de fluxo mostrando um valor superestimado de 10%. A técnica de porosimetria de Hg foi validada para análise de poro em compósito avançados com valores próximos obtidos pelas técnicas de digestão ácida e de microscopia óptica. Em função dos resultados obtidos dos valores de diâmetro dos poros, que foi semelhante para todos os compósitos, concluí-se que este ocorre em função do tipo de processo e da resina. Do mesmo modo, a distância e a fração de poros abertos dependem diretamente da quantidade de poros presente no material. Os resultados encontrados indicaram que os compósitos híbridos estudados neste trabalho são materiais promissores para a aplicação aeronáutica, combinando as excelentes propriedades mecânicas da fibra de carbono com a viabilidade do ciclo de injeção da fibra de vidro. Com isso, o laminado híbrido 2 foi o compósito ideal para um processamento com fração de vazios próximo ao uso aeronáutico, resultando em uma redução de custo de matéria prima e tempo de processamento. / Hybrid composite arose with the aim of reducing high cost materials and, at the same time, maintaining mechanical properties suitable for use. In addition, using different reinforcements, a new material could be obtained which would evidence the advantages of the reinforcements and decrease the disadvantages simultaneously. An important factor, during the processing of polymeric composites for structural application, is the voids formation control, since they act as stress concentrators. The aim of this work was to produce hybrid composites using different stacking of glass and carbon fabrics without significant loss of mechanical properties. For the composite manuftacturing, the preform was initially characterized as the impregnation, for which a general analytical model was developed that determines the permeability parameter of the hybrid composites. In addition, the model was validated by conducting permeability test and the quality of several laminates (hybrid, and non-hybrid) was certified by processing them, and voids were quantified thereof. This project also proposed the improvement of voids analysis by the Hg porosimetry technique with the support of design of experimental. Therefore, it was possible to determine the volumetric fraction of open and closed voids, pore diameter distribution and the distance between voids, in an ensemble analysis with acid digestion and optical microscopy. Carbon preform presented high flow resistance; on the other hand, an opposite behavior was observed for the glass preform. The hybrid architecture presented a positive hybrid effect, which means a synergy that provided a higher permeability value. Therefore, optimization in injection time can be achieved, considering a combination of balanced glass and carbon fabrics. The analytical model was enabled to predict the flow front behavior by showing an overestimated value of 10%. The Hg porosimetry technique was validated for advanced composite voids analysis with similar results obtained by acid digestion techniques and optical microscopy. Based on the results obtained from pore diameter values, which were similar for all composites, it was concluded that this occurs as a function of the type of process and the resin. Although, the distance and the open pores fraction depend directly on the amount of pores along the laminate. Hybrid composites have proven to be a promising material in which it combines the excellent mechanical properties of carbon fiber with the viability of the fiberglass injection cycle. With that, hybrid 2 laminate is the ideal composite for a processing with voids fraction close to the aeronautical use requirement with reduction of high-cost material and processing time. / FAPESP: 2015/19967-4

This diploma thesis examines the effect of short fiber reinforcement in particle composite with a polymer matrix and the effect of its structure on the mechanical properties. It studies the refraction toughness depending on the addition of short polyvinylalcohol fibers (PVAL), nanosilica and pulverized polymethylacrylate (PMMA) to a dimethylacrylate matrix. Matrix strengthening was characterised with the help of differential compensation photocalorimetry. The inner structure of the composite and the morphology of fracture were studied using a scanning electron microscope. For the tested samples, the modules of elasticity and toughness were measured, the critical values of stress intensity factor and the energy release rate were determined. The findings suggest that the limit value of short fibers content is 4 vol. %. This content of fibers significantly increases the tenacity of the material but at the same time the uniform distribution of fibers and the ease of preparation of the material decrease. Within the possible applications, the manipulation of this material worsens as well. The fibers content of 2 ± 0.5 vol. % is an acceptable compromise between good treatability, uniform distribution of fibers and the required mechanical properties. During the study of the fracture surfaces of the material, different types of fibers disruption were witnessed (extraction from the matrix, plastic deformation, fibrillation on the surface of the fibers, fracture) depending on the type of used matrix and filling.

The application of glass fiber reinforced composites has grown rapidly due to their high strength-to-weight ratio, low cost, and chemical resistance. However, the increasing demand for fiber reinforced composites results in the generation of more composite wastes. Mechanical recycling is a cost-effective and environmentally-friendly recycling method, but the loss in the quality of recycled glass or carbon fiber composite hinders the wide-spread use of this recycling method. It is important to develop novel composite materials with higher recyclability. Thermotropic liquid crystalline polymers (TLCPs) are high-performance engineering thermoplastics, which have comparable mechanical performance to that of glass fiber. The TLCP reinforced composites, called in situ composites, can form the reinforcing TLCP fibrils during processing avoiding the fiber breakage problem. The first part of this dissertation is to study the influence of mechanical recycling on the properties of injection molded TLCP and glass fiber (GF) reinforced polypropylene (PP). The processing temperature of the injection molding process was optimized using a differential scanning calorimeter (DSC) and a rheometer to minimize the thermal degradation of PP. The TLCP and GF reinforced PP materials were mechanically recycled up to three times by repeated injection molding and grinding. The mechanical recycling had almost no influence on the mechanical, thermal, and thermo-mechanical properties of TLCP/PP because of the regeneration of TLCP fibrils during the mold filling process. On the other hand, glass fiber/PP composites decreased 30% in tensile strength and 5% in tensile modulus after three reprocessing cycles. The micro-mechanical modeling demonstrated the deterioration in mechanical properties of GF/PP was mainly attributed to the fiber breakage that occurred during compounding and grinding. The second part of this dissertation is concerned with the development of recyclable and light weight hybrid composites through the use of TLCP and glass fiber. Rheological tests were used to determine the optimal processing temperature of the injection molding process. At this processing temperature, the thermal degradation of matrix material was mitigated and the processability of the hybrid composite was improved. The best formulation of TLCP and glass fiber in the composite was determined giving rise to the generation of a recyclable hybrid composite with low melt viscosity, low mechanical anisotropy, and improved mechanical properties. Finally, TLCP reinforced polyamide composites were utilized in an additive manufacturing application. The method of selecting the processing temperature to blend TLCP and polyamide in the dual extrusion process was devised using rheological analyses to take advantage of the supercooling behavior of TLCP and minimize the thermal degradation of the matrix polymer. The composite filament prepared by dual extrusion was printed and the printing temperature of the composite filament that led to the highest mechanical properties was determined. Although the tensile strength of the TLCP composite was lower than the glass fiber or carbon fiber composites, the tensile modulus of 3D printed 60 wt% TLCP reinforced polyamide was comparable to traditional glass or carbon fiber reinforced composites in 3D printing. / Doctor of Philosophy / The large demand for high performance and light weight composite materials in various industries (e.g., automotive, aerospace, and construction) has resulted in accumulation of composite wastes in the environment. Reuse and recycling of fiber reinforced composites are beneficial from the environmental and economical point of view. However, mechanical recycling deteriorates the quality of traditional fiber reinforced composite (e.g., glass fiber and carbon fiber). There is a need to develop novel composites with greater recyclability and high-performance. Thermotropic liquid crystalline polymers (TLCP) are attractive high performance materials because of their excellent mechanical properties and light weight. The goal of this work is to generate recyclable thermotropic liquid crystalline polymer (TLCP) reinforced composites for use in injection molding and 3D printing. In the first part of this work, a novel recyclable TLCP reinforced composite was generated using the grinding and injection molding. Recycled TLCP composites were as strong as the virgin TLCP composites, and the mechanical properties of TLCP composites were found to be competitive with the glass fiber reinforced counterparts. In the second part, a hybrid TLCP and glass fiber reinforced composite with great recyclability and excellent processability was developed. The processing conditions of injection molding were optimized by rheological tests to mitigate fiber breakage and improve the processability. Finally, a high performance and light weight TLCP reinforced composite filament was generated using the dual extrusion process which allowed the processing of two polymers with different processing temperatures. This composite filament could be directly 3D printed using a benchtop 3D printer. The mechanical properties of 3D printed TLCP composites could rival 3D printed traditional fiber composites but with the potential to have a wider range of processing shapes.

Fiber-reinforced polymeric (FRP) composites are being considered for structural members in bridge construction as lighter, more durable alternatives to steel and concrete. Extensive testing and analysis of a pultruded, hybrid double web beam (DWB) developed for use in bridge construction has been conducted at Virginia Tech. A primary purpose of this testing is the development of a structural design guide for the DWB, which includes stiffness and strength data. The design manual also includes design allowables determined through a statistical analysis of test data. Static testing of the beams, including failure tests, has been conducted in order to determine such beam properties as bending modulus, shear stiffness, failure mode, and ultimate capacity. Measuring and calculating the shear stiffness has proven to be an area of particular interest and difficulty. Shear stiffness is calculated using Timoshenko beam theory which combines the shear stiffness and shear area together along with a shear correction factor, k, which accounts for the nonuniform distribution of shear stress/strain through the cross-section of a structure. There are several methods for determining shear stiffness, kGA, in the laboratory, including a direct method and a multi-span slope method. Herein lays the difficulty as it has been found that varying methods produces significantly different results. One of the objectives of current research is to determine reasons for the differences in results, to identify which method is most accurate in determining kGA, and also to examine other parameters affecting the determination of kGA that may further aid the understanding of this property. This document will outline the development of the design guide, the philosophy for the selection of allowables and review and discuss the challenges of interpreting laboratory data to develop a complete understanding of shear effects in large FRP structural members. / Master of Science

Esta tese apresenta pela primeira vez a obtenção, a partir de alcoóis, de nanotubos de carbono do tipo cup-stacked nitrogenados sendo esses nanotubos hidrofílicos e semicondutores. Os compósitos híbridos de fibra de carbono/nanotubos de carbono possuem geometria tridimensional nanoestruturada e foram preparados em reator de deposição química de vapor de leito fixo. Neste processo nanotubos de carbono do tipo cup-stacked nitrogenados, de paredes múltiplas organizadas ou helicoidais são crescidos diretamente sobre as fibras de carbono com diferentes graus de grafitização. Os compósitos obtidos foram analisados principalmente por microscopia eletrônica de varredura e de transmissão de alta resolução que mostrou que o grau de grafitização do substrato de carbono tem influência sobre o crescimento. A densidade de NTC diminui com a redução da grafitização das fibras de carbono, o que produz um material com porosidade não observada quando as fibras são bem grafitizadas. O material compósito foi estudado como elemento filtrante, eletrodos de baterias de íons de lítio, emissor de elétrons e como reforço em compósitos de silicone. A constatação da eficiência na filtragem seletiva de uma série de compostos orgânicos voláteis presentes na fumaça do cigarro bem como a preparação de eletrodos de baterias de íons de lítio sem o uso de folhas metálicas de alumínio ou cobre resultaram no deposito de dois pedidos de patente. / This thesis presents for the first time nitrogen-cup-stacked carbon nanotubes with hydrophilic and semiconducting properties synthesized by alcohol precursor. The hybrid carbon fiber/carbon nanotubes composite have three-dimensional geometry and nanostructure. The material was prepared via fixed-bed chemical vapor deposition reactor. In this process nitrogen-cup-stacked, multi-walled or helical carbon nanotubes were synthesized directly onto carbon fibers with different graphitization grade. The composites were analyzed by high resolution scanning and transmission electron microscopy. This characterization showed that the fiber graphitization has influence on the growth. Carbon nanotube density decreases producing a porous composite that was not observed in well-graphitized fibers. The hybrid composite material was studied as a filter, lithium ion battery electrode, electron field emission and as silicone reinforcement. The efficiency to filter several volatile organic compounds present in the mainstream smoke and the development of lithium-ion battery electrodes, aluminum and copper foils free resulted in two patent applications deposit.

This thesis reports on a design study, conducted for an advanced composite helmet shell for helicopter pilots. The helmet shell is expected to provide a level of protection against low velocity impacts with its weight criteria. Therefore, ergonomy, light weight, and the ability to withstand low velocity impact became the main issues for this study. For this purpose, an experimental program has been developed including low velocity impact tests on specimens. The drop height, drop weight, specimen stacking sequences and size were constant parameters. Test specimens were produced using the plate size of 220x220 mm having different thicknesses. Specimen materials were aramid, carbon, and a hybrid form of these two. Thus, the parameters of the study were specimen thickness and the material types. The impact tests are carried out on a specially designed test rig. The design decisions are made in accordance with the results of the experiments. In compliance with the lightweight and manufacturing criteria, the hybrid specimen was selected helmet shell. For the purpose of ergonomy a geometric design was also conducted from headfrom sizes of Turkish Army by using 3D design software. After specifying the composite material, manufactured helmet shell was tested in another test rig according to the ANSI Z90.1.1992. For the requirement of the acceleration level 300g, the helmet shell design was found to be successful at seven different and critical impact points.

Esta tese apresenta pela primeira vez a obtenção, a partir de alcoóis, de nanotubos de carbono do tipo cup-stacked nitrogenados sendo esses nanotubos hidrofílicos e semicondutores. Os compósitos híbridos de fibra de carbono/nanotubos de carbono possuem geometria tridimensional nanoestruturada e foram preparados em reator de deposição química de vapor de leito fixo. Neste processo nanotubos de carbono do tipo cup-stacked nitrogenados, de paredes múltiplas organizadas ou helicoidais são crescidos diretamente sobre as fibras de carbono com diferentes graus de grafitização. Os compósitos obtidos foram analisados principalmente por microscopia eletrônica de varredura e de transmissão de alta resolução que mostrou que o grau de grafitização do substrato de carbono tem influência sobre o crescimento. A densidade de NTC diminui com a redução da grafitização das fibras de carbono, o que produz um material com porosidade não observada quando as fibras são bem grafitizadas. O material compósito foi estudado como elemento filtrante, eletrodos de baterias de íons de lítio, emissor de elétrons e como reforço em compósitos de silicone. A constatação da eficiência na filtragem seletiva de uma série de compostos orgânicos voláteis presentes na fumaça do cigarro bem como a preparação de eletrodos de baterias de íons de lítio sem o uso de folhas metálicas de alumínio ou cobre resultaram no deposito de dois pedidos de patente. / This thesis presents for the first time nitrogen-cup-stacked carbon nanotubes with hydrophilic and semiconducting properties synthesized by alcohol precursor. The hybrid carbon fiber/carbon nanotubes composite have three-dimensional geometry and nanostructure. The material was prepared via fixed-bed chemical vapor deposition reactor. In this process nitrogen-cup-stacked, multi-walled or helical carbon nanotubes were synthesized directly onto carbon fibers with different graphitization grade. The composites were analyzed by high resolution scanning and transmission electron microscopy. This characterization showed that the fiber graphitization has influence on the growth. Carbon nanotube density decreases producing a porous composite that was not observed in well-graphitized fibers. The hybrid composite material was studied as a filter, lithium ion battery electrode, electron field emission and as silicone reinforcement. The efficiency to filter several volatile organic compounds present in the mainstream smoke and the development of lithium-ion battery electrodes, aluminum and copper foils free resulted in two patent applications deposit.

Biocomposites made from biodegradable polymer as matrix and natural fiber as reinforcement are certainly environmentally friendly materials. Both constituent materials are fully biodegradable and do not leave any noxious components on Earth. The natural fibers have been used as reinforcement due to their advantages compared to glass fibers such as low cost, high specific strength and modulus, low density, renewability and biodegradability. Major aims of this work were to produce natural fibers and/or nanoparticles with polyethylene (PE), polypropylene (PP) and polylactide (PLA), poly(hydroxybutyrate-co-hydroxyvalerate)(PHBV) matrices and determine their structure-property relationships. Following abstracts of the present research work are manifold: BINARY COMPOSITES Polylactide (PLA)/flax mat composites The polylactide (PLA)/flax mat and modified PLA/flax mat composites were produced by hot press technique. Two additives of non-regulated wax/ethylene acrylate copolymer/butyl acrylate and acrylic were used as modifier for PLA. The dispersion of the flax mat in the composites was studied by scanning electron microscopy (SEM). The PLA composites were subjected to instrumented falling weight impact test. The mechanical and thermal properties of the composites were determined in tensile test, thermogravimetric analysis (TGA) and dynamic-mechanical thermal analysis (DMTA), respectively. It was found that the PLA based composites increased the impact resistance. The tensile strength value of modified PLA/flax mat composite decreased slightly compared to the PLA. The elongation at break data indicated that an improvement in ductility of modified PLA and its composites. Moreover, addition of thermal modifier enhanced thermal resistance below processing temperature of PLA and had a marginal effect on the glass transition temperature of PLA. The storage modulus master curves were constructed by applying the time-temperature superposition (TTS) principle. The principle of linear viscoelastic material was fairly applicable to convert from the modulus to the creep compliance for all systems studied. Polylactide (PLA)/woven flax textiles composites The polylactide (PLA)/woven flax textiles 2x2 twill and 4x4 hopsack composites were produced by interval hot press technique. Two weave styles of flax used to reinforce in PLA. The dispersion of the flax composite structures in the composites was inspected in scanning electron microscopy (SEM). The PLA composites were subjected to instrumented falling weight impact test. The mechanical properties (tensile, stiffness and strength) of the composites were determined in tensile and dynamic-mechanical thermal analysis (DMTA) tests, respectively. SEM observed that the interfacial gaps around pulled-out fibers were improved when produced by the interval hot press. It was also found that the both styles of flax composites increased the impact resistance compared to the neat PLA. The tensile strength and stiffness value of PLA/flax composites were markedly higher than that of the neat PLA and reflect the effects of composite structures. The calculated storage creep compliance was constructed by applying the time-temperature superposition (TTS) principle. The calculated creep response of these flax composites was much lower than that of the neat PLA. Polyethylene and polypropylene/nano-silicon dioxide/flax composites Composites composed of polylactide (PLA), modified PLA and woven flax fiber textiles (Flax weave style of 2x2 twill and 4x4 hopsack) were produced by hot press technique. Two structurally different additives used to modify PLA. The dispersion of the flax composite structures in the composites was studied by scanning electron microscopy (SEM) and computed microtomography system (µCT). The PLA composites were subjected to water absorption and instrumented falling weight impact tests. The thermomechanical and creep properties of the composites were determined in thermogravimetric analysis (TGA), dynamic-mechanical thermal analysis (DMTA)and short-time creep tests, respectively. It was found that the modified PLA and its composite increased the impact resistance compared to the unmodified PLA. Incorporation of flax decreased resistance to thermal degradation and increased water uptake. The impact energy and stiffness value of PLA/flax composites was markedly higher than that of PLA but reflect the effects of composite structures and flax content. The storage modulus master curves were constructed by applying the time-temperature superposition (TTS) principle. From the master curve data, the effect of modified PLA on the storage modulus was more pronounced in the low frequencies range. Polylactide (PLA)/woven flax fiber textiles/boehmite alumina (BA) composites The textile biocomposites made from woven and non-woven flax fibre reinforced poly(butylene adipate-co-terephthalate) (PBAT) were prepared by compression moulding using film stacking method. The mechanical properties (such as tensile strength and stiffness, flexural strength and modulus, and impact strength) of textile biocomposites were determined in tensile, flexural and impact tests, respectively. The PBAT-based composites were subjected to water absorption. The comparison of the mechanical properties was made between pure PBAT and textile composites. The influence of flax weave styles on the mechanical properties was also evaluated. The results showed that the strength of the textile biocomposites was increased according to weave types of fibers, especially in the stiffness was significantly increased with the higher densification of the fibers. The 4x4-plain woven fibers (4-yard-wrap and 4-yard-weft weave direction) reinforced biocomposite indicated the highest strength and stiffness compared to the other textile biocomposites and pure PBAT. This was considered to be as the result of the character of weave style of 4x4-plain woven fibers. The aminopropyltriethoxysilane affected the mechanical properties and water absorption of the resulting composites laminates due to the surface compatibility between flax fiber and PBAT. HYBRID COMPOSITES Polyethylene/nanoparticle, natural and animal composites Binary and ternary composites composed of high-density polyethylene (HDPE), boehmite alumina (BA) and different kinds of natural-, animal fibers, like flax, sponge gourd (SG), palm and pig hair (PH) were produced by hot press technique. Aqueous BA suspensions were sprayed on the HDPE/flax mat to prepare nanoparticle/natural fiber reinforced ternary polymer composites followed by drying. The dispersion of the natural-, animal fibers and BA particles in the composites was studied by scanning electron microscopy (SEM) and discussed. The thermomechanical and stress relaxation properties of the composites were determined in thermogravimetric analysis (TGA), dynamic-mechanical thermal analysis (DMTA) and short-time stress relaxation tests (performed at various temperatures), respectively. The HDPE based composites were subjected to water absorption and instrumented falling weight impact tests. It was found that the all composites systems increased the stiffness, stress relaxation and reduced the impact toughness. The stress relaxation modulus of natural-, animal fiber composites were higher compared to that of the neat HDPE. This modulus increased greatly with in corporation of BA. The relaxation master curves were constructed by applying the time-temperature superposition (TTS) principle. The inverse of Findley power law could fairly applicable to describe the relaxation modulus vs. time traces for all systems studied. Incorporation of BA particles enhanced the thermal resistance which started to degrade at higher temperature compared to the HDPE/flax mat composite. The HDPE/flax mat/BA composite could reduce the water uptake. Polyethylene/Flax/SiO2 Composites Composites composed of high-density polyethylene (HDPE), woven flax fiber textiles (Flax weave style of 2x2 twill and 4x4 hopsack) and silicon dioxide (SiO2) were produced by hot press with nano spraying technique. The SiO2 slurries were sprayed by a hand onto the both surface of the woven flax fiber. The HDPE /woven flax fibers composites with and without used nano-spraying technique were produced by hot pressing in a laboratory press. The dispersion of SiO2 particles and flax in the composites was studied by scanning electron microscopy (SEM). The related HDPE based composites were subjected to instrumented falling weight impact test. The thermal resistance, stiffness and tensile strength properties of the composites were determined in thermogravimetric analysis (TGA), dynamic-mechanical thermal analysis (DMTA) and tensile tests, respectively. It was found that the impact energy and stiffness value of HDPE/flax composites was markedly higher than that of HDPE but reflect the effects of composite structures and flax content. Incorporation of SiO2 particles enhanced resistance to thermal degradation. It was established that the linear viscoelastic material principle are fairly applicable to convert from the modulus to the creep compliance results. Un- and Modified Polylactide (PLA) /woven Flax Fiber composites Hybrid composites composed of polypropylene (PP) or high-density polyethylene (HDPE), different flax fibers (unidirectional-, biaxial and twill2x2) and silicon dioxide (SiO2) were produced by hot press technique. The ternary polymer composite was effectively fabricated by spraying SiO2 solvents onto the surface of flax fiber. The dispersion of SiO2 particles and flax in the composites was studied by scanning electron microscopy (SEM). The related PP and HDPE based composites were subjected to instrumented falling weight impact test. The thermal and mechanical properties of the composites were determined by thermogravimetric analysis (TGA), dynamic-mechanical thermal analysis (DMTA), creep and stress relaxation tests, respectively. It was found that thermal decomposition temperature of the PP or HDPE/flax composites increased by the addition of SiO2 particles. The impact energy, stiffness, creep resistance and relaxation modulus value of all flax composites increased markedly compared to the PP and HDPE matrix. Time–temperature superposition (TTS) was applied to estimate the creep and relaxation modulus of the composites as a function of time in the form of a master curve. The activation energies for the all PP and HDPE composites systems studied were also calculated by using the Arrhenius equation. The generalized Maxwell model was fairly applicable to the stress relaxation results. Polylactide (PLA)/woven flax fiber textiles/boehmite alumina (BA) composites Composites composed of polylactide (PLA), woven flax fiber textiles (weave style of 2x2 twill and 4x4 hopsack) and boehmite alumina (BA) were produced by hot press. The spraying technique served for the pre-dispersion of the alumina nanoparticles. The aqueous alumina slurry was produced by mixing the water with water dispersible alumina. The dispersion of the flax structures and alumina particles in the composites was studied by scanning electron microscopy (SEM). The PLA composites were subjected to water absorption and instrumented falling weight impact tests. The creep and thermomechanical properties of the composites were determined in short-time creep tests (performed at various temperatures), thermogravimetric analysis (TGA) and dynamic-mechanical thermal analysis (DMTA), respectively. It was found that the incorporation of alumina particles reduced the water uptake compared to the PLA/flax blends. The impact energy and stiffness value of PLA/flax blends was markedly higher than that of PLA but reflected the effects of composite structures. Incorporation of alumina particles enhanced storage modulus and the creep resistance compared to the PLA/flax blends but slightly incremented thermal resistance at high temperature. No clear trend in the flax weave style- effect was found in the thermal behaviour. The creep master curves were constructed by applying the time-temperature superposition (TTS) principle. The Findley power law could satisfactorily describe the creep compliance vs. time traces for all systems studied. Poly(hydroxybutyrate-co-hydroxyvalerate)/sisal natural fiber/clay composites Poly(hydroxybutyrate-co-hydroxyvalerate)(PHBV) biocomposites different sisal containing with the fiber length of 0.25 and 5 mm, and addition of clay particles were prepared by hot compression technique. Silane (Bis(triethoxysilylpropyl)tetrasulfide) treatment has been used to modify in order to enhance the properties of related hybrid composites. The all composites were subject to water absorption test. The mechanical properties of hybrid composites such as tensile stiffness and strength, toughness and hardness determined in tensile, impact and hardness tests, respectively. It was found that tensile strength, stiffness and impact strength of long sisal fiber improved with increasing fiber content. Hardness of short sisal fiber improved with increasing fiber content. Treated Silane of long fibers at 20 wt.% loading was found to enhance the tensile strength fiber by 10% and impact strength by 750% as compared to the neat PHBV. Note that this feature was also confirmed by the appearance of a scanning electron microscopy. Moreover, the hardness and water resistance of the PHBV/sisal composites increased by the addition of clay particles. The diffusion coefficient for the PHBV and hybrid composites systems studied were also calculated. / Bioverbundwerkstoffe aus biologisch abbaubarem Polymer als Matrix und Naturfasern als Verstärkung sind ohne weiteres umweltfreundliche Materialien. Beide Bestandsmaterialien sind vollständig biologisch abbaubar und hinterlassen keine schädlichen Bestandteile auf der Erde zurück. Die als Verstärkung verwendeten Naturfasern wurden aufgrund ihrer Vorteile gegenüber Glasfasern, wie z.B. geringe Kosten, hohe spezifische Festigkeit und Steifigkeit, geringe Dichte, Erneuerbarkeit und Kompostierbarkeit ausgesucht. Der Hauptfokus dieser Arbeit lag darin Naturfasern und/oder Nanopartikel mit Polyethylen (PE), Polypropylen (PP) und Polylactid (PLA) herzustellen, sowie Poly-Hydroxybutyrat-Co-Hydroxyvalerat (PHBV) Matrizen und deren Struktur-Eigenschaft-Verhältnis zu bestimmen. Die folgenden Kurzfassungen der vorliegenden Forschungsarbeit sind vielfältig: BINÄRE VERBUNDWERKSTOFFE Polylactid (PLA)/ Flachsmatten-Verbundwerkstoffe Die Polylactid (PLA)/Flachsmatte und modifizierte PLA/Flachsmatten-Verbundwerkstoffe wurden im Pressverfahren hergestellt. Als Modifikator für das PLA wurden zwei nicht regulierte Wachs/Ethylen-Acrylat-Copolymer/Butyl-Acrylat und Acryl Additive verwendet. Die Verteilung der Flachsmatte in den Verbundwerkstoffen wurde mit dem Rasterelektronenmikroskop (SEM) untersucht. Die PLA-Verbundwerkstoffe wurden dem instrumentalisierten Fallgewichtsschlagzähigkeitstest unterzogen. Die mechanischen und thermischen Eigenschaften der Verbundwerkstoffe wurden im Zugversuch, der thermogravimetrische Analyse (TGA) und der dynamisch mechanischen Thermoanalyse (DMTA) jeweils bestimmt. Es zeigte sich, dass die PLA/Flachsmatten-basierten Verbundwerkstoffe eine erhöhte Schlagzähigkeit aufwiesen. Die Zähigkeitswerte der modifizierten PLA/Flachsmatten-Verbundwerkstoffe waren leicht verringert im Vergleich zum PLA. Die Bruchdehnungswerte zeigten eine Verbesserung der Verformbarkeit des modifizierten PLAs und dessen Verbundwerkstoffe. Nach Zugabe eines Wärme-Modifikators verbesserte sich der Wärmewiderstand auf unter Verarbeitungstemperatur des PLA und hatte nur einen unwesentlichen Einfluss auf die Glasübergangstemperatur des PLA. Die Hauptkurve des Speichermoduls wurde mit der Zeit-Temperatur-Überlagerung (TTS) aufgestellt. Auf alle untersuchten Systeme konnte das dafür gut geeignete Prinzip der linear viskoelastischen Werkstoffe angewendet werden um die Steifigkeit in die Kriechneigung umzuwandeln. Polylactid (PLA)/Flachstextilgewebe-Verbundwerkstoffe Die Polylactid (PLA)/Flachstextilgewebe 2x2 Körper und 4x4 Gewebe mit Leinwandbindung-Verbundwerkstoffe wurden im Intervall-Pressverfahren hergestellt. Das PLA wurde mit zwei Flachsgewebeformen verstärkt. Die Verteilung der Flachs-Verbundwerkstoffstrukturen in den Verbundwerkstoffen wurde mit dem Rasterelektronenmikroskop (SEM) untersucht. Die PLA Verbundwerkstoffe wurden dem instrumentalisierten Fallgewichtsschlagzähigkeitstest unterzogen. Die mechanischen Eigenschaften (Zugfestigkeit, Steifigkeit und Festigkeit) der jeweiligen Verbundwerkstoffe wurden in Zugversuchen und dynamisch mechanischen Thermoanalysen (DMTA) bestimmt. Das Rasterelektronenmikroskop zeigte auf, das der Grenzflächenzwischenraum von rausgezogenen Fasern sich durch das Herstellen im Intervall-Pressverfahren verbessert hat. Auch zeigte sich, dass beide Arten der Flachs-Verbundwerkstoffe die Schlagzähigkeit der Verbundwerkstoffe erhöht im Vergleich zum puren PLA. Die Zugfestigkeit- und Steifigkeitswerte der PLA/Flachs-Verbundwerkstoffe waren deutlich höher als die der puren PLA und spiegeln die Effekte von Verbundwerkstoffstrukturen wieder. Die berechnete Kriechneigung im Speichermodul wurde durch die Anwendung des Zeit-Temperatur-Überlagerung (TTS) Prinzips aufgestellt. Die errechnete Kriechgeschwindigkeit der Flachs-Verbundwerkstoffe war wesentlich geringer als im puren PLA. Polyethylen und Polypropylen/Nanosilikon Dioxid/Flachs-Verbundwerkstoffe Verbundwerkstoffe hergestellt aus Polylactid (PLA), modifiziertem PLA und Flachsfasertextilgewebe (Flachsgewebeform von 2x2 Körper und 4x4 Gewebe mit Leinwandbindung) wurden im Pressverfahren hergestellt. Zwei strukturell unterschiedliche Additive wurden verwendet um das PLA zu modifizieren. Die Verteilung der Flachs-Verbundwerkstoffstruktur wurde unter dem Rasterelektronenmikroskop (SEM) und dem computergestütztes Computer-Tomography-System (µCT) untersucht. Die PLA Verbundwerkstoffe wurden dem Wasseraufnahme- und instrumentalisierten Fallgewichtsschlagzähigkeitstest unterzogen. Die Kriech- und thermomechanischen Eigenschaften der respektiven Verbundwerkstoffe wurden in der thermogravimetrischen Analyse (TGA), der dynamisch mechanischen Thermoanalyse (DMTA) und dem Kurzzeit-Kriechversuch bestimmt. Das modifizierte PLA und dessen Verbundwerkstoffe zeigten eine Erhöhung der Schlagzähigkeit im Vergleich zum unmodifizierten PLA. Die Einbindung von Flachs verringerte den Widerstand gegenüber thermischer Degradierung und erhöhte die Wasseraufnahme. Die Schlagenergie- und Steifigkeitswerte der PLA/Flachs-Verbundwerkstoffe war deutlich höher als die der PLA aber spiegelt die Effekte von Verbundwerkstoffstrukturen mit Flachsinhalt wieder. Die Hauptkurve des Speichermoduls wurde mit dem Zeit-Temperatur-Überlagerung (TTS) Prinzip aufgestellt. Das Datenmaterial der Hauptkurve zeigte den Effekt des modifizierten PLAs auf dem Speichermodul deutlich ausgeprägter im Bereich der Niederfrequenz. Polylactide (PLA)/Flachfasertextilgewebe/Böhmit Aluminumoxid (BA)-Verbundwerkstoffe Die textilen Bioverbundwerkstoffe wurden aus flachsfaserverstärkten Poly(Butylen Adipat-Co-Terephtalat) (PBAT) Gewebe und Vlies im Formpressverfahren mit der Folien-Stapelmethode hergestellt. Die mechanischen Eigenschaften (wie Zugfestigkeit und Steifigkeit, Biegefestigkeit, Steifigkeit und Schlagzähigkeit) der jeweiligen textilen Bioverbundwerkstoffe wurde in Zug-, Biege-, und Schlagtests ermittelt. Die PBAT basierten Verbundwerkstoffe wurden dem Wasseraufnahmetest unterzogen. Der Vergleich der mechanischen Eigenschaften wurde zwischen reinem PBAT und textilen Verbundwerkstoffen durchgeführt. Der Einfluss der Flachsgewebeformen auf die mechanischen Eigenschaften wurde ebenfalls untersucht. Die Ergebnisse zeigten das die Festigkeit der textilen Bioverbundwerkstoffe mit der Webart der Fasern anstieg, signifikant in Bezug auf die Steifigkeit bei einer erhöhten Verdichtung der Fasern. Die 4x4 flachfasergewebten (4-Schussfaden-Windung und 4-Kettfaden-Windung) verstärkten Bioverbundwerkstoffe zeigten die höchste Festigkeit und Steifigkeit im Vergleich zu den anderen textilen Bioverbundwerkstoffen und dem puren PBAT. Dieses Resultat wurde der Beschaffenheit der 4x4-flachfasergewebten Webart zugewiesen. Das Aminopropyltriethoxysilan beeinträchtigte die mechanischen Eigenschaften und Wasseraufnahme der entstandenen Verbundlaminate durch Oberflächenkompatibilität zwischen der Flachsfaser und dem PBAT. HYBRIDE VERBUNDWERKSTOFFE Polyethylen/Nanopartikel, natürliche und tierische Verbundwerkstoffe Binäre und ternäre Verbundwerkstoffe, bestehend aus hoch dichtem Polyethylen (HDPE), Böhmit Aluminumoxid (BA) und verschiedenen natürlichen und tierischen Fasern wie Flachs, Schwammgurke (SG), Palmfaser und Schweinehaar (PH), wurden im Pressverfahren hergestellt. Vorbereitend wurden wasserhaltige BA-Suspensionen auf die HDPE/Flachsmatte gesprüht um nanopartikel/naturfaserverstärkte ternäre Polymer-Verbundwerkstoffe nach dem Trocknen zu erhalten. Die Verteilung der Natur-,Tierfasern und der BA-Partikel in den Verbundwerkstoffen wurde unter dem Rasterelektronenmikroskop untersucht und diskutiert. Die thermomechanischen und Spannungsrelaxation-Eigenschaften der jeweiligen Verbundwerkstoffe wurden in der thermogravimetrischen Analyse (TGA), der dynamisch mechanischen Thermoanalyse (DMTA) und dem Kurzzeit-Stressrelaxationstest (bei unterschiedlichen Temperaturen durchgeführt) bestimmt. Die HDPE-basierten Verbundwerkstoffe wurden Wasseraufnahme- und instrumentalisierten Fallgewichtsschlagzähigkeitstests unterzogen. Es wurde festgestellt, dass alle Verbundwerkstoffsysteme eine Erhöhung der Steifigkeit und Spannungsrelaxation und eine Verminderung der Kerbschlagzähigkeit aufzeigten. Die Spannungsrelaxations-Steifigkeit von Naturfaser-, Tierfaserverbundwerkstoffen war größer im Vergleich zu reinem HDPE. Diese Steifigkeit steig deutlich an mit der Einbindung von BA. Die Hauptkurven der Relaxation wurden mit dem Zeit-Temperatur-Überlagerung (TTS) Prinzip aufgestellt. Die Umkehrung des Findley Potenzgesetzes konnte gut für die Beschreibung der Relaxations-Steifigkeit vs. Zeitüberwachung in allen untersuchten Systemen angewendet werden. Die Einbindung der BA-Partikel erhöhte den Wärmewiderstand, welcher bei höherer Temperatur zu sinken begann im Vergleich zu HDPE/Flachsmatten-Verbundwerkstoff. Der HDPE/Flachsmatte/BA-Verbundwerkstoff konnte die Wasseraufnahme verringern. Polyethylen/Flachs/SiO Verbundwerkstoffe Verbundwerkstoffe bestehend aus hoch dichtem Polyethylen (HDPE), Flachsfasertextilgewebe (Flachsgewebeform 2x2 Körper und 4x4 Gewebe mit Leinwandbindung) und Siliziumdioxid (SiO2) wurden im Pressverfahren mit Nanospritztechnik hergestellt. Die SiO2 Schlämme wurden auf beide Oberflächen des Flachsfasergewebes per Hand gesprüht. Die HDPE/ Flachsfasergewebe-Verbundwerkstoffe wurden in einer Laborpresse im Pressverfahren mit und ohne Nanospritztechnik hergestellt. Die Verteilung der SiO2-Partikel und des Flachs in den Verbundwerkstoffen wurde unter dem Rasterelektronenmikroskop (SEM) untersucht. Die ähnlichen HDPE-basierten Verbundwerkstoffe wurden dem instrumentalisierten Fallgewichtsschlagzähigkeitstest unterzogen. Der Wärmewiderstand, Steifigkeit- und Zugfestigkeit-Eigenschaften der jeweiligen Verbundwerkstoffe wurden in thermogravimetrischen Analysen (TGA), dynamisch mechanischen Thermoanalysen (DMTA) und Zugversuchen bestimmt. Es zeigte sich, dass die Aufprallenergie und Steifigkeitswerte der HDPE/Flachs-Verbundwerkstoffe deutlich höher als die des HDPE waren aber die Effekte von Verbundwerkstoffen mit Flachsinhalt widerspiegeln. Die Einbindung von SiO2-Partikeln erhöhte den Widerstand von thermischer Degradierung. Es wurde bestimmt, das das Prinzip der linear viskoelastischen Werkstoffe gut anwendbar auf die Umwandlung der Steifigkeit zu Kriechneigungsergebnissen ist. Modifizierte und nicht modifizierte Polylactid (PLA)/Flachsfasergewebe-Verbundwerkstoffe Hybride Verbundwerkstoffe aus Polypropylen (PP) oder hoch-dichtem Polyethylen (HDPE), verschiedenen Flachsfasern (unidirektional, biaxial und 2x2 Körper) und Siliziumdioxid (SiO2) wurden im Pressverfahren hergestellt. Der ternäre Polymer-Verbundwerkstoff wurde wirkungsvoll durch das Aufbringen von SiO2 Lösemitteln auf die Oberfläche der Flachsfaser hergestellt. Die Verteilung der SiO2-Partikel und des Flachs in den Verbundwerkstoffen wurde unter dem Rasterelektronenmikroskop (SEM) untersucht. Die ähnlichen PP- und HDPE-basierten Verbundwerkstoffe wurden dem instrumentalisierten Fallgewichtsschlagzähigkeitstest unterzogen. Die thermischen und mechanischen Eigenschaften der respektiven Verbundwerkstoffe wurde in thermogravimetrischen Analysen (TGA), dynamisch mechanischen Thermoanalysen (DMTA), Kriech- und Spannungsrelaxations-Tests bestimmt. Es zeigte sich, dass die thermische Zersetzungstemperatur der PP oder HDPE/Flachs-Verbundwerkstoffe durch das Auftragen der SiO2-Partikel ansteigt. Die Aufprallenergie-, Steifigkeit-, Kriechbeständigkeit- und Relaxation-Steifigkeitn-Werte aller Flachs-Verbundwerkstoffe stiegen deutlich an im Vergleich zur PP und HDPE Matrix. Die Zeit-Temperatur-Überlagerung (TTS) wurde angewandt um die Kriech- und Relaxation-Steifigkeit für die Verbundwerkstoffe als Funktion der Zeit in Form einer Hauptkurve zu schätzen. Die Aktivierungsenergien aller untersuchten PP und HDPE-Verbundwerkstoffsysteme wurden mit der Arrhenius Gleichung errechnet. Das generalisierte Maxwell Model war gut auf die Spannungsrelaxationsergebnisse anwendbar. Polylactide (PLA)/Flachsfasertextilgewebe/Böhmit Aluminiumoxid (BA)-Verbundwerkstoffe Verbundwerkstoffe bestehend aus Polylactid (PLA), Flachfasertextilgewebe (Gewebeform 2x2 Körper und 4x4 Gewebe mit Leinwandbindung) und Böhmit Aluminium (BA) wurden im Pressverfahren hergestellt. Für die Vordispergierung der Aluminiumoxid-Nanopartikel wurde die Spritztechnik angewendet. Die wasserhaltigen Aluminiumoxid-Schlämme wurden durch das Vermischen von Wasser mit wasserdispergierbarem Aluminiumoxid hergestellt. Die Verteilung der Flachsstrukturen und Aluminiumoxid-Partikeln in den Verbundwerkstoffen wurde mit einem Rasterelektronenmikroskop (SEM) untersucht. Die PLA-Verbundwerkstoffe wurden Wasseraufnahme- und instrumentalisierten Fallgewichtsschlagzähigkeitstests unterzogen. Die Kriech- und thermomechanischen Eigenschaften der jeweiligen Verbundwerkstoffe wurden in Kurzzeit-Kriechversuchen (bei unterschiedlichen Temperaturen durchgeführt), thermogravimetrischen Analysen (TGA) und dynamisch mechanischen Thermoanalysen (DMTA) bestimmt. Es zeigte sich, dass das Einbringen der Aluminiumoxid-Partikel die Wasseraufnahme im Vergleich zu PLA/Flachs-Gemischen reduziert. Die Aufprallenergie- und Steifigkeitswerte der PLA/Flachs-Gemische waren signifikant höher als die des PLA aber spiegelten die Effekte von Verbundwerkstoffstrukturen wieder. Das Einbringen von Aluminiumoxid-Partikeln verbesserte die Lagerungs-Steifigkeit und die Kriechbeständigkeit im Vergleich zu PLA/Flachs-Gemischen, erhöhte allerdings leicht den Wärmewiderstand bei hohen Temperaturen. Kein klarer Trend in der Flachswebart konnte dem Temperaturverhalten zugeordnet werden. Die Kriech-Hauptkurven wurden mit dem Zeit-Temperatur-Überlagerung (TTS) Prinzip aufgestellt. Das Findley Potenzgesetz konnte zufriedenstellend die Kriechneigung vs. Zeitüberwachung für alle untersuchten Systeme beschreiben. Poly(Hydroxybutyrat-Co-Hydroxyvalerat)/Natursisalfaser/Ton-Verbundwerkstoffe Poly(Hydroxybutyrat-Co-Hydroxyvalerat) (PHBV) Bioverbundwerkstoffe die Sisalfasern in Längen von 0,25 und 5 mm und Ton-Partikeln enthalten wurden im Heißpressverfahren hergestellt. Die Silan (Bis(Trithoxysilylpropyl)Tetrasulfide) Behandlung wurde für die Modifizierung verwendet um die Eigenschaften von ähnlichen hybriden Verbundwerkstoffen zu verbessern. Alle Verbundwerkstoffe wurden dem Wasseraufnahmetest unterzogen. Die mechanischen Eigenschaften der jeweiligen hybriden Verbundwerkstoffe wie Zugsteifigkeit und Festigkeit, Zähigkeit und Härte wurden in Zugversuchen, Schlagtests und Härteprüfungen bestimmt. Es zeigte sich, dass die Zugfestigkeit, Steifigkeit und Schlagzähigkeit von langen Sisalfasern sich mit der Erhöhung des Fasergehalts verbessert. Behandeltes Silan von langen Fasern mit 20 wt.% Belastung zeigte eine Verbesserung der Faser-Zugfestigkeit um 10% und Schlagzähigkeit von 750% im Vergleich zu reinem PHBV. Diese Besonderheit wurde auch von einem Rasterelektronenmikroskop bestätigt. Weiterhin ist die Härte und Wasserbeständigkeit in PHBV/Sisal-Verbundwerkstoffen durch das Einbringen von Ton-Partikeln angestiegen. Die Diffusionskoeffizienten für die untersuchten PHBV- und hybriden Verbundwerkstoffsysteme wurden auch errechnet.

In this work, the effect of adding short deformable polyvinylalcohol fibers into dimethacrylate resins on mechanical properties of composite materials was investigated. Furthermore, micro- or nano-fillers were added into the matrix. The effect of filler/short fibers combination on mechanical properties of so-called hybrid composites was studied. Composites were characterized by differential compensation photocalorimetry (DPC), termogravimetric (TGA) and dynamic mechanical (DMA) analysis. The fracture surfaces were examined using scanning electron (SEM) and confocal laser (CLSM) microscopy. Elastic modulus and strength, the critical value of stress intensity factor and strain energy release rate and the viscoelastic properties of composite materials were measured. The mechanical properties of composite materials are affected not only by the type of filler/reinforcement, but also by properties of the matrix. These properties also depend on the way of network formation during photo-initiated polymerization. For this reason, heat of polymerization, degree of conversion and the maximum polymerization rate of mixture of dimethacrylate monomers were determined.

Fiber reinforced polymeric (FRP) composite materials are beginning to find use in construction and infrastructure applications. Composite members may potentially provide more durable replacements for steel and concrete in primary and secondary bridge structures, but the experience with composites in these applications is minimal. Recently, however, a number of groups in the United States have constructed short-span traffic bridges utilizing FRP members. These demonstration cases will facilitate the development of design guidelines and durability data for FRP materials. The Tom's Creek Bridge rehabilitation is one such project that utilizes a hybrid FRP composite beam in an actual field application. This thesis details much of the experimental work conducted in conjunction with the Tom's Creek Bridge rehabilitation. All of the composite beams used in the rehabilitation were first proof tested in four-point bending. A mock-up of the bridge was then constructed in the laboratory using the actual FRP beams and timber decking. The mock-up was tested in several static loading schemes to evaluate the bridge response under HS20 loading. The lab testing indicated a deflection criterion of nearly L/200; the actual field structure was stiffer at L/450. This was attributed to the difference in boundary conditions for the girders and timber panels. Finally, the bridge response was verified with an analytical model that treats the bridge structure as a wood beam resting upon discrete elastic springs. The model permits both bending and torsional stiffness in the composite beams, as well as shear deformation. A parametric study was conducted utilizing this model and a mechanics of laminated beam theory to provide recommendations for alternate bridge designs and modified composite beam designs. / Master of Science