Hollow glass microspheres have been used extensively in the automotive and marine industries as an additive for reducing weight and saving material costs. They are also added to paints and other materials for their reflective properties. They have shown promise for weight critical applications, but have thus far resulted in materials with low fracture toughness and impact resistance when combined with thermosetting resins in syntactic foam. The advent of commercially available microspheres with a wide range of crushing strengths, densities and adhesive properties has given new impetus to research into syntactic foam with better fracture behaviour. Current research suggests that the beneficial effects on fracture and impact resistance gained by the addition of solid reinforcements such as rubber and ceramic particles are not seen with the addition of hollow glass microspheres. The research presented in this paper has examined the mechanisms for fracture resistance in glass microsphere filled epoxy (GMFE) syntactic foams, as well as determined the effect microsphere crushing strength and adhesion strength has on the material???s fracture toughness. The flexural properties of various GMFE have also been determined. GMFE were manufactured with varying microsphere volume fraction up to 50%, and with variances in microsphere crushing strength and adhesion. The specimens were tested for Mode I fracture toughness in a three point single edge notched bending setup as described in ASTM D5045 as well as a three point flexural setup as described in ASTM D790-3. Fracture surfaces were inspected using scanning electron microscope imaging to identify the fracture mechanisms in the presence of microspheres. Results indicate a positive effect on fracture toughness resulting from new fracture areas created as tails in the wake of the microspheres in the fracture plane. Results also indicate a negative effect on fracture toughness resulting from weak microspheres or from interfacial disbonding at the fracture plane. These two effects combine to show an increase in GMFE fracture toughness as the volume fraction of microspheres is increased to between 10 ??? 20% volume fraction (where the positive effect dominates), with a reduction in fracture toughness as microspheres are added further (where the negative effect dominates).

Hollow glass microspheres have been used extensively in the automotive and marine industries as an additive for reducing weight and saving material costs. They are also added to paints and other materials for their reflective properties. They have shown promise for weight critical applications, but have thus far resulted in materials with low fracture toughness and impact resistance when combined with thermosetting resins in syntactic foam. The advent of commercially available microspheres with a wide range of crushing strengths, densities and adhesive properties has given new impetus to research into syntactic foam with better fracture behaviour. Current research suggests that the beneficial effects on fracture and impact resistance gained by the addition of solid reinforcements such as rubber and ceramic particles are not seen with the addition of hollow glass microspheres. The research presented in this paper has examined the mechanisms for fracture resistance in glass microsphere filled epoxy (GMFE) syntactic foams, as well as determined the effect microsphere crushing strength and adhesion strength has on the material???s fracture toughness. The flexural properties of various GMFE have also been determined. GMFE were manufactured with varying microsphere volume fraction up to 50%, and with variances in microsphere crushing strength and adhesion. The specimens were tested for Mode I fracture toughness in a three point single edge notched bending setup as described in ASTM D5045 as well as a three point flexural setup as described in ASTM D790-3. Fracture surfaces were inspected using scanning electron microscope imaging to identify the fracture mechanisms in the presence of microspheres. Results indicate a positive effect on fracture toughness resulting from new fracture areas created as tails in the wake of the microspheres in the fracture plane. Results also indicate a negative effect on fracture toughness resulting from weak microspheres or from interfacial disbonding at the fracture plane. These two effects combine to show an increase in GMFE fracture toughness as the volume fraction of microspheres is increased to between 10 ??? 20% volume fraction (where the positive effect dominates), with a reduction in fracture toughness as microspheres are added further (where the negative effect dominates).

O objetivo do presente estudo foi de avaliar a influência de soluções de resina com diferentes proporções de monômeros e diferentes concentrações em massa de nanofibras nas propriedades flexurais de compósitos resinosos experimentais reforçados com nanofibras de poliacrilonitrila (PAN). Materiais e métodos: Nanofibras de PAN foram produzidas pelo processo de eletrofiação e caraterizadas por teste de tração e microscopia eletrônica de varredura (MEV). Os compósitos experimentais foram produzidos pela infiltração das mantas de nanofibras com diferentes misturas de BisGMA-TEGDMA (BisGMA/TEGDMA: proporções em % massa de 30/70, 50/50, e 70/30). Foram incorporadas diferentes concentrações em massa de nanofibras (de 0% a 8%). Espécimes em forma de barra foram seccionados a partir de blocos do compósito experimental e armazenados em água na temperatura de 37oC por 24h anteriormente à realização dos testes de flexão de três pontos. Foram avaliados a resistência flexural (RF), o módulo flexural (MF) e o trabalho de fratura (TF). Resultados: Os testes de tração das nanofibras de PAN demonstraram um comportamento anisotrópico das mantas de nanofibras. As propriedades mecânicas exibiram maiores valores na direção perpendicular ao eixo de rotação do coletor metálico utilizado na produção das fibras por eletrofiação. Maiores proporções de BisGMA nas misturas de resina resultaram em maiores valores de RF e MF, o que não ocorreu para os valores de TF. A adição de diferentes concentrações de nanofibras não afetou as propriedades de RF e MF em comparação com o grupo controle (resina pura) (p>0.05). No entanto, a adição das nanofibras promoveu um aumento significante do TF, principalmente para as misturas de resina com maior proporção de TEGDMA (p<0,05). Significância: A inclusão de nanofibras de PAN em resinas de modo a formar compósitos resinosos reforçados por nanofibras não afetou negativamente as propriedades flexurais do material e resultou em um aumento significativo da tenacidade, uma propriedade desejável para um material a ser utilizado para aplicação restauradora. / The present study had the objectives to evaluate the influence of different resin blends concentrations and nanofibers mass ratio on flexural properties of experimental Poliacrylonitrile (PAN) nanofibers reinforced composite. Materials and Methods: Poliacrylonitrile (PAN) nanofibers mats were produced by electrospinning and characterized by tensile testing and scanning electron microscopy (SEM). Experimental resin-fiber composite beams were manufactured by infiltrating PAN nanofiber meshs with varied concentrations of BisGMA-TEGDMA resin blends (BisGMA/TEGDMA: 30/70, 50/50 and 70/30 weight %). The mass ratio of fiber to resin varied from 0% to 8%. Beams were cured and stored in water at 37oC. Flexural strength (FS), flexural modulus (FM) and work of fracture (WF) were evaluated by three-point bending test after 24 hs storage. Results: The tensile properties of the PAN nanofibers indicated an anisotropic behavior being always higher when tested in a direction perpendicular to the rotation of the collector drum. Except for WF, the other flexural properties (FS and FM) were always higher as the ratio of BisGMA to TEGDMA increased in the neat resin beams. The addition of different ratios of PAN fibers did not affect FS and FM of the composite beams as compared to neat resin beams (p>0.05). However, the addition of fibers significantly increased the WF of the composite beams, and this was more evident for the blends with higher TEGDMA ratios (p<0.05). Significance: The inclusion of PAN nanofibers into resin blends did not negatively affect the properties of the composite and resulted in an increase in toughness that is a desirable property for a candidate material for restorative application.

O objetivo do presente estudo foi de avaliar a influência de soluções de resina com diferentes proporções de monômeros e diferentes concentrações em massa de nanofibras nas propriedades flexurais de compósitos resinosos experimentais reforçados com nanofibras de poliacrilonitrila (PAN). Materiais e métodos: Nanofibras de PAN foram produzidas pelo processo de eletrofiação e caraterizadas por teste de tração e microscopia eletrônica de varredura (MEV). Os compósitos experimentais foram produzidos pela infiltração das mantas de nanofibras com diferentes misturas de BisGMA-TEGDMA (BisGMA/TEGDMA: proporções em % massa de 30/70, 50/50, e 70/30). Foram incorporadas diferentes concentrações em massa de nanofibras (de 0% a 8%). Espécimes em forma de barra foram seccionados a partir de blocos do compósito experimental e armazenados em água na temperatura de 37oC por 24h anteriormente à realização dos testes de flexão de três pontos. Foram avaliados a resistência flexural (RF), o módulo flexural (MF) e o trabalho de fratura (TF). Resultados: Os testes de tração das nanofibras de PAN demonstraram um comportamento anisotrópico das mantas de nanofibras. As propriedades mecânicas exibiram maiores valores na direção perpendicular ao eixo de rotação do coletor metálico utilizado na produção das fibras por eletrofiação. Maiores proporções de BisGMA nas misturas de resina resultaram em maiores valores de RF e MF, o que não ocorreu para os valores de TF. A adição de diferentes concentrações de nanofibras não afetou as propriedades de RF e MF em comparação com o grupo controle (resina pura) (p>0.05). No entanto, a adição das nanofibras promoveu um aumento significante do TF, principalmente para as misturas de resina com maior proporção de TEGDMA (p<0,05). Significância: A inclusão de nanofibras de PAN em resinas de modo a formar compósitos resinosos reforçados por nanofibras não afetou negativamente as propriedades flexurais do material e resultou em um aumento significativo da tenacidade, uma propriedade desejável para um material a ser utilizado para aplicação restauradora. / The present study had the objectives to evaluate the influence of different resin blends concentrations and nanofibers mass ratio on flexural properties of experimental Poliacrylonitrile (PAN) nanofibers reinforced composite. Materials and Methods: Poliacrylonitrile (PAN) nanofibers mats were produced by electrospinning and characterized by tensile testing and scanning electron microscopy (SEM). Experimental resin-fiber composite beams were manufactured by infiltrating PAN nanofiber meshs with varied concentrations of BisGMA-TEGDMA resin blends (BisGMA/TEGDMA: 30/70, 50/50 and 70/30 weight %). The mass ratio of fiber to resin varied from 0% to 8%. Beams were cured and stored in water at 37oC. Flexural strength (FS), flexural modulus (FM) and work of fracture (WF) were evaluated by three-point bending test after 24 hs storage. Results: The tensile properties of the PAN nanofibers indicated an anisotropic behavior being always higher when tested in a direction perpendicular to the rotation of the collector drum. Except for WF, the other flexural properties (FS and FM) were always higher as the ratio of BisGMA to TEGDMA increased in the neat resin beams. The addition of different ratios of PAN fibers did not affect FS and FM of the composite beams as compared to neat resin beams (p>0.05). However, the addition of fibers significantly increased the WF of the composite beams, and this was more evident for the blends with higher TEGDMA ratios (p<0.05). Significance: The inclusion of PAN nanofibers into resin blends did not negatively affect the properties of the composite and resulted in an increase in toughness that is a desirable property for a candidate material for restorative application.

This research was conducted to characterize the flexural and tensile characteristics of thin, very high-strength, discontinuously reinforced concrete panels developed by the U.S. Army Engineer Research and Development Center. Panels were produced from a unique blend of cementitous material and fiberglass reinforcing fibers, achieving compressive strength and fracture toughness levels that far exceeded that of typical concrete.The research program included third-point flexural experiments, novel direct tension experiments, implementation of micromechanically based analytical models, and development of finite element numerical models. The experimental, analytical, and numerical efforts were used conjunctively to determine parameters such as elastic modulus, first-crack strength, post-crack modulus and fiber/matrix interfacial bond strength. Furthermore, analytical and numerical models implemented in the work showed potential for use as design tools in future engineered material improvements.

Preparation of thermoplastics composites using engineering thermoplastics and plant fibers or fillers is a technical challenge because the processing temperature of the thermoplastics is generally above the temperature of degradation of plant fibers of fillers. There have been numerous attempts for processing high melting point engineering thermoplastics like Nylon-6 with plant natural fibers and fillers. Low temperature processing methods, fiber modification or addition of additives which drops polymer melting point are some of proposed solutions for this problem. The objective of this thesis was to develop a formulation using wheat straw (WS) as a reinforcing fiber for Nylon-6. The concentration of WS was 15 wt-%. The thermoplastic composites were prepared by mixing grinded wheat straw and Nylon-6 using a laboratory scale twin-screw extruder; follow by preparation of samples using injection moulding. The strategy investigated in this thesis was utilization of additives to lower the melting point or to decrease the viscosity of Nylon-6. Lithium chloride salt (LiCl) and N-Butyl benzene Sulfon amide plasticizer (N-BBSA) were used as process additives to decrease melting point and to reduce the processing temperature and time. The addition of the wheat straw (15 wt-%) to the Nylon-6 increased modulus by 26.9 % but decreased the strength by 9.9 %. Effect of different level of these two additives on mechanical, thermal, physical properties and processability of the composite runs were studied. Addition of 4 wt-% LiCl was found to decrease the melting point from 222 °C to 191 °C, to increase modulus by 14 % in comparison to Nylon-6/wheat straw (15 wt-%). However, it decreased the processability and strength by 12.7 %. Plasticizer was investigated to easing processability and decreasing the degradation by reducing the residence time in the extruder, it does not affect the melting point of Nylon-6. The addition of 4 wt-% of plasticizer (N-BBSA) increased modulus and strength only by 2.6 % and 3 %, respectively, in comparison to Nylon-6/wheat straw (15 wt-%) composites. The results of mechanical properties were used as a benchmark for comparisons among samples with different formulations (levels of additives) to find out levels of LiCl and N-BBSA for the best mechanical properties. It was found that samples with 2 wt-% LiCl and 2 wt-% of N-BBSA had 29.3 % higher tensile modulus than neat Nylon-6, while its strength was almost same as neat Nylon-6 and 6.3 % higher than Nylon-6/WS (15 wt-%). These results were used to correlate the mechanical properties as a function of percentage of salt and plasticizer in the formulation. Differential scanning calorimetry (DSC) was used to evaluate the percentage of crystallinity and the melting point of the thermoplastic phase and thermal gravimetric analysis (TGA) was used to measure the thermal stability of different formulation. The kinetics of crystallization and degradation were evaluated using results from DSC and TGA, respectively. The activation energy for thermal degradation and the percentage of crystallinity of the thermoplastic composites were correlated to mechanical properties using linear regression. It was found that fiber degradation had a significant effect on strength but the effects of percentage of crystallinity on composites strength were insignificant. On the other hand, the percentage of crystallinity affects stiffness and impact strength. The ductility was a function of both crystallinity and thermal stability.

Preparation of thermoplastics composites using engineering thermoplastics and plant fibers or fillers is a technical challenge because the processing temperature of the thermoplastics is generally above the temperature of degradation of plant fibers of fillers. There have been numerous attempts for processing high melting point engineering thermoplastics like Nylon-6 with plant natural fibers and fillers. Low temperature processing methods, fiber modification or addition of additives which drops polymer melting point are some of proposed solutions for this problem. The objective of this thesis was to develop a formulation using wheat straw (WS) as a reinforcing fiber for Nylon-6. The concentration of WS was 15 wt-%. The thermoplastic composites were prepared by mixing grinded wheat straw and Nylon-6 using a laboratory scale twin-screw extruder; follow by preparation of samples using injection moulding. The strategy investigated in this thesis was utilization of additives to lower the melting point or to decrease the viscosity of Nylon-6. Lithium chloride salt (LiCl) and N-Butyl benzene Sulfon amide plasticizer (N-BBSA) were used as process additives to decrease melting point and to reduce the processing temperature and time. The addition of the wheat straw (15 wt-%) to the Nylon-6 increased modulus by 26.9 % but decreased the strength by 9.9 %. Effect of different level of these two additives on mechanical, thermal, physical properties and processability of the composite runs were studied. Addition of 4 wt-% LiCl was found to decrease the melting point from 222 °C to 191 °C, to increase modulus by 14 % in comparison to Nylon-6/wheat straw (15 wt-%). However, it decreased the processability and strength by 12.7 %. Plasticizer was investigated to easing processability and decreasing the degradation by reducing the residence time in the extruder, it does not affect the melting point of Nylon-6. The addition of 4 wt-% of plasticizer (N-BBSA) increased modulus and strength only by 2.6 % and 3 %, respectively, in comparison to Nylon-6/wheat straw (15 wt-%) composites. The results of mechanical properties were used as a benchmark for comparisons among samples with different formulations (levels of additives) to find out levels of LiCl and N-BBSA for the best mechanical properties. It was found that samples with 2 wt-% LiCl and 2 wt-% of N-BBSA had 29.3 % higher tensile modulus than neat Nylon-6, while its strength was almost same as neat Nylon-6 and 6.3 % higher than Nylon-6/WS (15 wt-%). These results were used to correlate the mechanical properties as a function of percentage of salt and plasticizer in the formulation. Differential scanning calorimetry (DSC) was used to evaluate the percentage of crystallinity and the melting point of the thermoplastic phase and thermal gravimetric analysis (TGA) was used to measure the thermal stability of different formulation. The kinetics of crystallization and degradation were evaluated using results from DSC and TGA, respectively. The activation energy for thermal degradation and the percentage of crystallinity of the thermoplastic composites were correlated to mechanical properties using linear regression. It was found that fiber degradation had a significant effect on strength but the effects of percentage of crystallinity on composites strength were insignificant. On the other hand, the percentage of crystallinity affects stiffness and impact strength. The ductility was a function of both crystallinity and thermal stability.

Les éco-composites s'imposent progressivement comme une alternative à certains matériaux classiques. L'utilisation de fibres végétales en guise de renfort permet en effet d'améliorer les performances environnementales de ces matériaux ainsi que leurs propriétés spécifiques élevées. Dans ce contexte, cette étude propose d'élaborer un éco-composite sandwich dont les peaux sont constituées d'une résine thermoplastique innovante associée à des fibres de lin et à une âme en balsa. Tout d'abord, les comportements statiques de la résine et de l'âme sont analysés. Par la suite, le composite renforcé de fibres de lin constituant les peaux du sandwich est étudié. Les caractéristiques élastiques principales du pli UD en contraintes planes sont déterminées. De plus, une analyse des mécanismes d'endommagement est effectuée au moyen de la technique d'émission acoustique. Le comportement des poutres sandwiches sollicitées en flexion est ensuite étudié. Une attention particulière est portée à la compréhension des modes de rupture et à l'influence des variations locales des propriétés mécaniques de l'âme. Par ailleurs, certaines propriétés dynamiques de cette structure sont explorées, notamment son comportement en fatigue et sa réponse à l'impact afin de discuter de sa durabilité. Enfin, une étude expérimentale du comportement vibratoire des poutres composites et sandwiches est réalisée. Le rôle des différents constituants dans l'amortissement global des vibrations est discuté au moyen d'une modélisation par élément finis. L'ensemble des propriétés déterminées sont comparées à celles des matériaux non bio-sourcés, afin de situer ses performances. / Bio-based composites appear to be very promising alternatives to traditional composites. The use of natural fibres as reinforcement reduces the environmental impact of these materials and their specific properties are significantly increased. In this context, this work focuses on the manufacturing and the mechanical characterization of a bio-based sandwich structure. The skins are made of an innovative thermoplastic resin associated with flax fibres. The core is made of balsa wood. First, quasi-static analyses are performed on the different components. Then, the tensile properties of the composite skins are studied. Moreover, the main damage mechanisms are identified and described by means of the acoustic emission technique. Next, the flexural behavior of the whole sandwich structure is studied. Particular attention is paid to the detection and prediction of the main fracture modes. Moreover, the statistical spreads of the material properties of the balsa core are taken into account. In addition, cyclic fatigue and impact tests are performed to investigate the behavior of this structure under dynamic loads, and to discuss whether or not this material could be suitable for potential semi-structural applications. Finally, experimental analyses of the vibration behavior of composite and sandwich beams are performed. The contributions of the different components to the global damping properties of the sandwich structure are analyzed by means of a finite elements model. This work also compares the properties of this bio-based sandwich to those of traditional materials, in order to benchmark its mechanical performances with a view to further industrial usage.

The purpose of the work is the determination of flexural properties for thebiocomposite Durapulp. The study includes laborative tests on Durapulp andreference materials, commonly used in the building sector. Stiffness and strength of Durapulp show that it has the potential as a replacement for conventional wood-based materials.

No description available.