Em aplicações que requerem solicitações de impacto, compósitos de matriz polimérica reforçados com fibra de aramida se destacam, principalmente em relação aos metais, devido a propriedades como alta resistência e rigidez específicas, que dão origem a sistemas mais leves e de alta performance. Quando voltados para aplicações de impacto, principalmente a alta velocidade, tais compósitos são, em sua maioria, moldados por compressão ou autoclave, a partir de pré-impregnados. No entanto, tais combinações de processamentos e matéria-prima acarretam em estruturas de elevado custo, tornando a infusão a vácuo uma opção atrativa, além de permitir a obtenção de peças grandes e complexas, dimensionalmente acuradas e partes integradas. Porém, a obtenção de um compósito espesso reforçado por fibra de aramida com elevado desempenho ao impacto por tal método de fabricação ainda é um desafio. Neste contexto, este trabalho aborda o efeito da espessura no processamento por infusão a vácuo de compósitos aramida/epóxi e seu desempenho em aplicações que requerem solicitações de impacto (baixa e alta velocidade) Para isso, foram produzidos compósitos com 5, 8, 13, 18, 23 e 28 camadas de aramida e caracterizados por ultrassom C-scan, microscopia ótica, densidade, teor de constituintes, testes mecânicos (flexão, short beam e indentação quase-estática) e cargas de impacto de baixa e alta velocidade (drop-weight e balístico). Todos os compósitos apresentaram boa homogeneidade na distribuição da matriz ao longo do reforço, com um teor de fibra de ≈60%, e valores de resistência short beam elevados (17,3 - 23,6 MPa). A performance sob impacto (baixa e alta velocidade) foi comparável à de compósitos fabricados por compressão ou autoclave, tendo os compósitos a partir de 18 camadas resistido ao projétil 9 mm Luger FMJ e o de 28 camadas resistido ao projétil .357 Magnum FMJ, podendo ser classificados como nível FB2 e FB3, respectivamente, de acordo com a norma europeia EN 1522. Portanto, o processamento de infusão a vácuo mostrou ser uma alternativa adequada para produzir compósitos espessos de aramida/epóxi (até 12 mm), substituindo rotas de processamento mais caras. / In applications that require impact solicitations, polymer matrix composites reinforced with aramid fiber stand out, especially in relation to metals, due to properties such as high specific strength and stiffness, which give rise to lighter and high-performance systems. When used for impact applications, especially at high speed, such composites are mostly molded by compression or autoclaved, from prepregs. However, such combinations of processing and raw material lead to high cost structures, making vacuum infusion an attractive option, as well as allowing the production of large, complex, dimensionally accurate and integrated parts. Nonetheless, obtaining a thick composite reinforced by aramid fiber with high impact performance by such manufacturing method is still a challenge. In this context, this work addresses the effect of the thickness in the vacuum infusion processing of aramid/epoxy composites and its performance in applications that require impact solicitations (low and high speed) For this, composites with 5, 8, 13, 18, 23 and 28 layers of aramid were produced and characterized by ultrasonic C-scan, optical microscopy, density, constituent content, mechanical tests (flexion, short beam and quasi-static indentation) and low- and high-speed impact loads (drop-weight and ballistic). All composites presented good homogeneity in the matrix scattering along the reinforcement, with a fiber content of ≈ 60%, and high short beam resistance values (17.3 - 23.6 MPa). The performance under impact (low and high speed) was comparable to that of composites processed by compression or autoclave, the composites with 18 layers resisted to the 9 mm Luger FMJ projectile and the one with 28 layers resisted to the .357 Magnum FMJ projectile, being classified as level FB2 and FB3, respectively, according to the European standard EN 1522. In summary, vacuum infusion processing proved to be a suitable alternative to produce thick aramid/epoxy composites (up to 12 mm), replacing more expensive processing routes.

Em aplicações que requerem solicitações de impacto, compósitos de matriz polimérica reforçados com fibra de aramida se destacam, principalmente em relação aos metais, devido a propriedades como alta resistência e rigidez específicas, que dão origem a sistemas mais leves e de alta performance. Quando voltados para aplicações de impacto, principalmente a alta velocidade, tais compósitos são, em sua maioria, moldados por compressão ou autoclave, a partir de pré-impregnados. No entanto, tais combinações de processamentos e matéria-prima acarretam em estruturas de elevado custo, tornando a infusão a vácuo uma opção atrativa, além de permitir a obtenção de peças grandes e complexas, dimensionalmente acuradas e partes integradas. Porém, a obtenção de um compósito espesso reforçado por fibra de aramida com elevado desempenho ao impacto por tal método de fabricação ainda é um desafio. Neste contexto, este trabalho aborda o efeito da espessura no processamento por infusão a vácuo de compósitos aramida/epóxi e seu desempenho em aplicações que requerem solicitações de impacto (baixa e alta velocidade) Para isso, foram produzidos compósitos com 5, 8, 13, 18, 23 e 28 camadas de aramida e caracterizados por ultrassom C-scan, microscopia ótica, densidade, teor de constituintes, testes mecânicos (flexão, short beam e indentação quase-estática) e cargas de impacto de baixa e alta velocidade (drop-weight e balístico). Todos os compósitos apresentaram boa homogeneidade na distribuição da matriz ao longo do reforço, com um teor de fibra de ≈60%, e valores de resistência short beam elevados (17,3 - 23,6 MPa). A performance sob impacto (baixa e alta velocidade) foi comparável à de compósitos fabricados por compressão ou autoclave, tendo os compósitos a partir de 18 camadas resistido ao projétil 9 mm Luger FMJ e o de 28 camadas resistido ao projétil .357 Magnum FMJ, podendo ser classificados como nível FB2 e FB3, respectivamente, de acordo com a norma europeia EN 1522. Portanto, o processamento de infusão a vácuo mostrou ser uma alternativa adequada para produzir compósitos espessos de aramida/epóxi (até 12 mm), substituindo rotas de processamento mais caras. / In applications that require impact solicitations, polymer matrix composites reinforced with aramid fiber stand out, especially in relation to metals, due to properties such as high specific strength and stiffness, which give rise to lighter and high-performance systems. When used for impact applications, especially at high speed, such composites are mostly molded by compression or autoclaved, from prepregs. However, such combinations of processing and raw material lead to high cost structures, making vacuum infusion an attractive option, as well as allowing the production of large, complex, dimensionally accurate and integrated parts. Nonetheless, obtaining a thick composite reinforced by aramid fiber with high impact performance by such manufacturing method is still a challenge. In this context, this work addresses the effect of the thickness in the vacuum infusion processing of aramid/epoxy composites and its performance in applications that require impact solicitations (low and high speed) For this, composites with 5, 8, 13, 18, 23 and 28 layers of aramid were produced and characterized by ultrasonic C-scan, optical microscopy, density, constituent content, mechanical tests (flexion, short beam and quasi-static indentation) and low- and high-speed impact loads (drop-weight and ballistic). All composites presented good homogeneity in the matrix scattering along the reinforcement, with a fiber content of ≈ 60%, and high short beam resistance values (17.3 - 23.6 MPa). The performance under impact (low and high speed) was comparable to that of composites processed by compression or autoclave, the composites with 18 layers resisted to the 9 mm Luger FMJ projectile and the one with 28 layers resisted to the .357 Magnum FMJ projectile, being classified as level FB2 and FB3, respectively, according to the European standard EN 1522. In summary, vacuum infusion processing proved to be a suitable alternative to produce thick aramid/epoxy composites (up to 12 mm), replacing more expensive processing routes.

Em aplicações que requerem solicitações de impacto, compósitos de matriz polimérica reforçados com fibra de aramida se destacam, principalmente em relação aos metais, devido a propriedades como alta resistência e rigidez específicas, que dão origem a sistemas mais leves e de alta performance. Quando voltados para aplicações de impacto, principalmente a alta velocidade, tais compósitos são, em sua maioria, moldados por compressão ou autoclave, a partir de pré-impregnados. No entanto, tais combinações de processamentos e matéria-prima acarretam em estruturas de elevado custo, tornando a infusão a vácuo uma opção atrativa, além de permitir a obtenção de peças grandes e complexas, dimensionalmente acuradas e partes integradas. Porém, a obtenção de um compósito espesso reforçado por fibra de aramida com elevado desempenho ao impacto por tal método de fabricação ainda é um desafio. Neste contexto, este trabalho aborda o efeito da espessura no processamento por infusão a vácuo de compósitos aramida/epóxi e seu desempenho em aplicações que requerem solicitações de impacto (baixa e alta velocidade) Para isso, foram produzidos compósitos com 5, 8, 13, 18, 23 e 28 camadas de aramida e caracterizados por ultrassom C-scan, microscopia ótica, densidade, teor de constituintes, testes mecânicos (flexão, short beam e indentação quase-estática) e cargas de impacto de baixa e alta velocidade (drop-weight e balístico). Todos os compósitos apresentaram boa homogeneidade na distribuição da matriz ao longo do reforço, com um teor de fibra de ≈60%, e valores de resistência short beam elevados (17,3 - 23,6 MPa). A performance sob impacto (baixa e alta velocidade) foi comparável à de compósitos fabricados por compressão ou autoclave, tendo os compósitos a partir de 18 camadas resistido ao projétil 9 mm Luger FMJ e o de 28 camadas resistido ao projétil .357 Magnum FMJ, podendo ser classificados como nível FB2 e FB3, respectivamente, de acordo com a norma europeia EN 1522. Portanto, o processamento de infusão a vácuo mostrou ser uma alternativa adequada para produzir compósitos espessos de aramida/epóxi (até 12 mm), substituindo rotas de processamento mais caras. / In applications that require impact solicitations, polymer matrix composites reinforced with aramid fiber stand out, especially in relation to metals, due to properties such as high specific strength and stiffness, which give rise to lighter and high-performance systems. When used for impact applications, especially at high speed, such composites are mostly molded by compression or autoclaved, from prepregs. However, such combinations of processing and raw material lead to high cost structures, making vacuum infusion an attractive option, as well as allowing the production of large, complex, dimensionally accurate and integrated parts. Nonetheless, obtaining a thick composite reinforced by aramid fiber with high impact performance by such manufacturing method is still a challenge. In this context, this work addresses the effect of the thickness in the vacuum infusion processing of aramid/epoxy composites and its performance in applications that require impact solicitations (low and high speed) For this, composites with 5, 8, 13, 18, 23 and 28 layers of aramid were produced and characterized by ultrasonic C-scan, optical microscopy, density, constituent content, mechanical tests (flexion, short beam and quasi-static indentation) and low- and high-speed impact loads (drop-weight and ballistic). All composites presented good homogeneity in the matrix scattering along the reinforcement, with a fiber content of ≈ 60%, and high short beam resistance values (17.3 - 23.6 MPa). The performance under impact (low and high speed) was comparable to that of composites processed by compression or autoclave, the composites with 18 layers resisted to the 9 mm Luger FMJ projectile and the one with 28 layers resisted to the .357 Magnum FMJ projectile, being classified as level FB2 and FB3, respectively, according to the European standard EN 1522. In summary, vacuum infusion processing proved to be a suitable alternative to produce thick aramid/epoxy composites (up to 12 mm), replacing more expensive processing routes.

Within the high-performance composite manufacturing industry, there exists a need to improve the reliability of LCM (Liquid Composite Molding) manufacturing processes in producing composite parts that better approach the quality and consistency of pre-impregnated composite tapes that are cured in autoclaves with cost being a driving factor of this need. One obstacle to that end is the phenomenon of void formation during the LCM infusion processes. The formation of these voids through different mechanisms leads to composite parts with lower mechanical properties and consistency than their pre-impregnated autoclave cure counterparts. The objective of this research is to investigate the different mechanisms through which voids form during LCM processes as well as potential actions that can be taken to reduce the total percent volume of voids that form during the infusion. This research also aims to investigate the correlation of the void content observed at the tool-ply interface compared to the void content through the thickness of composite laminates. Finally, this research investigates the effect that chemical modification of the wettability of carbon fiber fabrics has on void formation during infusions.

As the aerospace industry continues to incorporate composites into its aircraft, there will be a need for alternative solutions to the current autoclaving process. Liquid composite molding (LCM) has proven to be a promising alternative, producing parts at faster rates and reduced costs while retaining aerospace grade quality. The most important factor of LCM is controlling the resin flow throughout the fiber reinforcement during infusion, as incomplete filling of fibers is a major quality issue as it results in dry spots or voids. Void formation occurs at the resin flow front due to competition between viscous forces and capillary pressure. The purpose of this work is to characterize capillary pressure in vacuum infusion, and develop a model that can be incorporated into flow simulation. In all tests performed capillary pressure was always higher for the carbon fiber versus fiberglass samples. This is due to the increased fiber packing associated with the carbon fabric. As the fabric samples were compressed to achieve specific fiber volumes an increase in capillary pressure was observed due to the decrease in porosity. Measured values for capillary pressure in the carbon fabric were ~2 kPa, thus the relative effects of Pcap may become significant in flow modeling under certain slow flow conditions in composite processing.

The subject of this project is to study spun cellulose fibers made by Spinnova Oy inFinland. The fibers are spun using an environmentally friendly spinning process withoutuse of harsh chemicals.The spun filaments and the yarn based on these filaments were characterized and usedas reinforcement in polylactic acid biopolymer (PLA) and in biobased epoxy resin. Acomprehensive mechanical and morphological characterization of the single filamentsand their yarn was conducted. It was found that the single filaments are flat with a largewidth/thickness ratio, they are porous especially on one side and some cellulosemicrofibril orientation is observed on the filament surface. The single filaments are stiffand strong if compared to commercial regenerated cellulose filaments but are difficultto handle as they are very small and extremely light. The yarn showed to have lowermechanical properties but is easier to handle during the process of compositemanufacturing. Unidirectional fiber-reinforced composites were made using theSpinnova-yarn and PLA polymer applying film-stacking processing method. Thecomposite mechanical properties were studied and the results showed that themechanical performance of the PLA was significantly improved. The strength improvedfrom 54 MPa of the neat PLA to 95 MPa and the stiffness from 3.4 to 8.6 GPa withaddition of 22 wt% Spinnova-yarn.The main challenge of the project was handling the single filaments and their yarn todevelop a suitable manufacturing process which allows to exploit the potential of themto obtain a homogeneous fiber “preform” and to achieve good impregnation with the PLA matrix.

Composite materials have traditionally been used in high-end aerospace parts and low-end consumer parts. The reason for this separation in markets is the wide gap in technology between pre-preg materials processed in an autoclave and chop strand fiberglass blown into an open mold. Liquid composite molding has emerged as a bridge between inexpensive tooling and large, technical parts. Processes such as vacuum infusion have made it possible to utilize complex layups of reinforcement materials in an open mold style set-up, creating optimal conditions for composites to penetrate many new markets with rapid innovation. Flow simulation for liquid composite molding is often performed to assist in process optimization, and requires the permeability of the reinforcement to be characterized. For infusion under a flexible membrane, such as vacuum infusion, or for simulation of a part with non-uniform thickness, one must test the permeability at various levels of compaction. This process is time consuming and often relies on interpolation or extrapolation around a few experimental permeability measurements. To accelerate the process of permeability characterization, a small number of methodologies have been previously presented in the literature, in which the permeability may be tested at multiple fiber volume contents in a single test. Some of the methods even measure the permeability over a continuous range of thicknesses, thus requiring no later interpolation of permeability values. A novel method is presented here for the rapid measurement of permeability over a continuous range of fiber volume content, in a single unidirectional vacuum infusion flow experiment. The thickness gradient across the vacuum bag, as well as the fluid pressure at several locations in the mold, were concurrently measured to calculate the fabric compressibility. An analytical flow model, which accounts for the compressibility, is then used by iterating the fitting constant in a permeability model until the predicted flow front progression matches empirical measurement. The method is demonstrated here for two reinforcement materials: 1) a fiberglass unbalanced weave and 2) a carbon bi-ax non-crimped fabric. The standard deviation of calculated permeabilities across the multiple infusion experiments for each material and flow orientation ranged from 12.8% to 29.7%. Validation of these results was performed by comparing the resulting permeability with multiple non-continuous permeability measurement methods.

Resin infusion of composite parts has continually been reaching to achieve laminate quality equal to, or exceeding, the quality produced with prepreg in an autoclave. In order for this to occur, developers must understand the key process variables that go in to producing a laminate with minimal void content. The purpose of this research is to continue efforts in understanding 1) the effect of process conditions on the resultant void content, with a focus on resin infusion flow rate, 2) applying statistical metrics to the formation, location and size of voids formed, and 3) correlate these metrics with the local mechanical properties of the composite laminate. The variation in dispersion and formation of micro-voids and macro-voids varied greatly between the rates of flow the infusion occurred, especially in the non-crimp carbon fiber samples. Higher flow rates led to lower volumes of micro-voids in the beginning section of the carbon fiber laminates with macro-voids being introduced approximately half-way through infusion. This was determined to have occurred decreasing pressure gradient as the flow front moved away from the inlet. This variation in void content per location on the laminate was more evident in the carbon fiber samples than the fiberglass samples. Micro-voids follow void formation modeling especially when coupled with a pressure threshold model. Macro-void formation was also demonstrated to correlate strongly to void formation models when united with void mobility theories and pressure thresholds. There is a quick decrease in mechanical properties after the first 1-2% of voids signaling strength is mostly sensitive to the first 0-2% void content. A slight decrease in SBS was noticed in fiberglass laminates, A-F as v0 increased but not as drastically as represented in the NCF laminates, G and H. The lower clarity in the exponential trend could be due to the lack of samples with v0 greater than 0% but less than 1%. Strength is not well correlated to void content above 2% and could possibly be related to void morphololgy.

Out-of-autoclave manufacturing processes for composite materials are increasing in importance for aerospace and automotive industries. Vacuum Infusion processes are leading the push to move out of the autoclave. An understanding of the various process parameters associated with resin infusion is necessary to produce quality product. Variance in compaction, resin, and vacuum pressures are studied, concentrating on developing a compaction pressure profile as it relates to fiber volume fraction. The purpose of this research is twofold: (1) to show and quantify the existence of a resin pressure gradient in compression testing using rigid tooling, and (2) to use measured test data to validate and improve resin flow simulation models. One-dimensional compression tests revealed a pressure gradient across the diameter of the compression tool. The pressure gradient follows trends consistent with Darcy's Law. Compression tests revealed fabric hysteresis during compaction as shown in previous studies. Fiber compaction pressure was found to not be directly equal to compressive forces of the Instron when resin is present in the system. The relationship between Instron, resin and compaction pressures is defined. The compression study was used to validate previously developed flow simulation models. Resin pressures are critical to developing an accurate two-dimensional radial flow simulation for low permeability fabrics. It is feasible to determine final fiber volume fraction at a given compaction pressure.

Hybrid composites play a key role in sustainable development. For many years, carbon fibres in an epoxy matrix have been an attractive option for many structural applications because of their higher specific mechanical properties mostly. However, recycling and sustainability are some of the composite shortcomings; and in that context, natural fibres have gained popularity.  The present study aimed to design and manufacture short carbon/flax hybrid composites. Two different arrangements were chosen: random and layers configuration. Resin Transfer Moulding (RTM) was used to fabricate these hybrid composites. Mechanical tests and optical microscopy technique were conducted to understand the effect of the interaction of these two different reinforcements. Mechanical tests showed a remarkable difference between the hybrid configurations under flexural loadings. Furthermore, outstanding property values were observed in the hybrid configurations compared to single fibre composites. The resultant materials have seemed an attractive combination of fibres with a remarkable balance between mechanical performance and eco-friendliness.