Les principaux enjeux de la fabrication de pièces en matériaux composites (coût, temps de fabrication, performances,...) sont intimement liés aux moyens de mise en oeuvre, principalement les autoclaves; qui engendrent non seulement des coûts très élevés en termes d'installation et d'entretien, mais limitent également les cadences de production à cause de la longueur des cycles. Afin de réduire cette dépendance, des procédés de fabrication hors autoclave ont été envisagés (Quickstep, Roctool, VARTM, VBO...) entrainant par conséquent des modifications dans la conception des matériaux destinés à ces procédés (cinétique, rhéologie, façon dont sont imprégnées les fibres...). Afin de limiter les changements en termes de procédé de fabrication, de matières premières, de produits d'environnement et de conditions de mise en oeuvre, c'est sur le procédé Vacuum Bag Only que porte cette étude. Plusieurs développement de semi-produits ces dernières années ont permis d'augmenter la robustesse de ce procédé de fabrication, palliant ainsi à cette absence de pression externe durant la cuisson en étuve. Il reste toutefois à démontrer la viabilité de ces produits par rapport à leur mise en oeuvre, à comprendre les mécanismes d'extraction de l'air et à estimer les propriétés mécaniques atteignables par rapport à leur équivalent autoclave. / The main issues concerning composite part manufacturing (cost, manufacturing time, mechanical performances, etc.) are closely linked to the means of curing, mainly autoclaves; which do not only generate very high installation and maintenance costs, but also limit production rates because of the length of the cycles. In order to reduce this dependence, non-autoclave manufacturing processes have been envisaged (Quickstep, Roctool, VARTM, VBO ...) therefore leading to modifications in the design of the materials intended for these processes (including kinetics, rheology, fiber impregnation methods). In order to limit the changes in terms of manufacturing process, raw materials, environment products and implementation conditions, this study is based on the Vacuum Bag Only process. Several semi-product developments in recent years have made it possible to increase the robustness of this manufacturing process, thereby overcoming the lack of external pressure during an oven cure. However, the viability of these products in relation to their implementation still needs to be demonstrated, as well as the understanding of the air removal mechanisms and the estimation of the achievable mechanical properties compared to their autoclave counterpart.

Out-of-Autoclave (OoA) processes for manufacturing aerospace-grade parts needs to be better understood to further the development and success of industries that are manufacturing reusable launch vehicles, military and commercial aircraft, and spacecraft. Overcoming the performance limitations associated with OoA, also known as low-pressure prepreg curing, methods (void count, energy absorption, etc.) will help decrease the costs associated with aerospace composite manufacturing and the negative environmental effects correlated with high-pressure composite curing methods. Experimental, theoretical, and numerical approaches are used to explore both low and high-pressure curing cycles and how the two different processes affect final cured parts. Quasi-static uniaxial compression tests on 33mm diameter tubular specimens concluded that the high-pressure curing methods (up to 90 psi) increased the likelihood of a final part with increased stiffness compared to the lower atmospheric-pressure methods (14.7 psi) on an order of 22%. After further extension and deformation past the linear elastic region, tests concluded that although the autoclaved specimens may have been higher-quality parts, the low-pressure-cured specimens performed more efficiently with respect to energy absorption. Considering the specific energy absorption (SEA) and crush force efficiency (CFE) are both on average around 6% higher for the low-pressure specimens, it is concluded that they can perform similarly to the high-pressure specimens and possibly even more efficiently depending on the loading conditions and desired purpose of the structure.

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.

Global competition is pushing the composites industry to advance and become more cost effective. Liquid Composite Molding or LCM is a family of processes that has shown significant promise in its potential to reduce process times and cost while maintaining high levels of part quality. However, the majority of research and information on composite processes have been related to prepreg-autoclave processing which is significantly different than LCM. In order for LCM processes to gain large scale implementation, significant research is required in order to model and simulate the unique nature of the resin infusion process. The purpose of this research is to aid in the development of in situ void measurement and characterization during LCM processing, particularly for carbon fiber composites. This will allow for the gathering of important empirical data for the validation of models and simulations that aid in the understanding of void formation and movement during LCM. For such data to be useful, it needs to include details on the formation, mobility and evolution of the void over time during infusion. This was accomplished by creating a methodology that allowed for in situ images of voids to be captured during the infusion process. A clear mold was used to visually monitor infusions during RTM with UV dye and lighting to enhance contrast. Consecutive images were acquired through the use of macro lens photography. This method proved capable of yielding high quality images of a variety of in situ voids during infusions with carbon fiber composites. This is believed to be the first instance where this was accomplished. A second methodology was then developed for the analysis of the collected images. This was done by using ImageJ software to analyze and process the acquired images in order to identify and characterize the voids. Success was found in quantifying the size and circularity of a wide range of micro and macrovoids in both a satin weave and double bias NCF woven fabrics. To facilitate the burden of collecting large amounts of data, this process was made to be automated. A user generated macro script could be applied to large sets of images for rapid processing and analysis. This automated method was then evaluated against manually processed images to determine its overall effectiveness and accuracy as tool for validating void theory.

Vacuum bags in conjunction with autoclaves are currently employed to generate the consolidation pressures and temperatures required to manufacture aerospace level composites. As the scale of continuous fiber composite structures increases autoclaving becomes prohibitively expensive or impossible. The objective of this work is to develop flexible magnetic clamping structures to increase the consolidation pressure in conventional vacuum bagging of composite laminates, thereby obviating the need for an autoclave. A ferromagnetic rubber, which consists of rubber filled with iron, is being developed as a conformable and reusable vacuum bag that provides increased consolidation through attractive forces produced by electromagnets. Experiments and finite element modeling indicate that consolidation pressure in the range of 100 kPa can be generated by such a device with realistic power requirements. The effects of the magnetic clamping device process parameters on the consolidation pressure magnitude are modeled and characterized. In addition, a method for the efficient design of the magnetic clamping device is developed.

L’élaboration de composites en cuisson autoclave est un procédé bien maîtrisé maisles cycles de cuisson peuvent être très longs, en particulier dans le cas de préimprégnésaéronautiques. L’objectif de ce travail de thèse est d’étudier la possibilité de diminuer letemps des cycles de polymérisation pour la fabrication de composites stratifiés minces àl’aide d’un procédé de cuisson rapide. Des essais de caractérisation ont permis de définirles grandeurs thermodynamiques du préimprégné carbone/époxy qui a servi de base ànotre étude ainsi que les paramètres du modèle cinétique de la résine. Une simulationnumérique du procédé de cuisson, basée sur une modélisation des couplages desphénomènes chimiques (polymérisation de la résine), thermiques (transferts de chaleuravec prise en compte de l’exothermie de la réaction) et mécaniques (formation decontraintes et déformations résiduelles) induits par le procédé, a été développée dans lebut d’optimiser les cycles de polymérisation. La caractérisation mécanique des matériauxélaborés à partir d’un dispositif de cuisson rapide mis au point au Laboratoire a permis dedémontrer que nous n’avions pas de pertes de caractéristiques par rapport aux piècesélaborées en autoclave. / The autoclave polymerization is the bottleneck of the production flux for largepublic parts, hence the speedy polymerization process emerges to improve the productionratio. The objective is to study the possibility of reducing the cycle time of polymerizationfor the production of thin composite laminates using a fast cure process out-of-autoclave.Specific or standard chemical and mechanical characterization tests had been designed inorder to capture the expected characteristics for the model simulation and validate thesimulation results. According to the values obtained, an analysis based on the finiteelement technique is developed to simulate the speedy curing process of epoxy resincomposite. The analysis relates the cure temperature to the thermal, chemical and physicalprocesses occurring in the thin composite part during cure. Included in the analysis are theeffects such as the heat generation due to exothermic chemical reactions. For a specifiedcure cycle, the model could be used to calculate the temperature distribution, the degree ofcure of the resin inside the composite part as well as predict the residual curing stressesand the strains of the cured composite parts.Keywords :

When laying up dry composite materials and aligning the fibers in the appropriate directions it can be a challenge due to the dryness of the fiber and mold design. Several commercial products are available to help fix plies to molds keeping the proper fiber orientation depending upon mold geometry. Prepreg and wet layups do not have this problem due to the inherent inclusion of a matrix in their manufacturing, dry materials have no added epoxy at the time of layup and are therefore in need of assistance maintain position. The purpose of this research is to determine if Super 77™ or EPON™ 2002 increases or decreases mechanical properties of the neat resin and composite laminates; if the increase or decrease is dependent upon the type of epoxy, and if the amount of applied tackifier can be optimized towards a high or low application quantity to minimize any detrimental effects to mechanical properties. Each tackification agent was applied in high and low concentrations to eight composite panels, with two control panels. The EPON™ was applied manually and set with heat exposure while the Super 77™ was sprayed from an aerosol can. The Super 77™ plies were stacked and pressed by hand while the EPON™ plies were stacked and ironed together to create panels, which were then infused with one of two room temperature infusion epoxies, MVS 610 or INF 114. The panels were then cut to specimen size for testing. Neat resin specimens were cast in silicone molds with high and low concentrations of tackifiers and allowed to cure for 12 hours at room temp, then heated to 60° C for 8 Both Super 77™ and EPON™ 2002 reduced the SBS for both epoxies, but Super 77™ reduced the short beam shear more than EPON™ 2002. The modulus of the neat resin cast specimens with high concentration were between 0 to 20% lower than neat resin with no tackifier; the tensile strength was increased for those specimens with Super 77™ and lower for those with EPON™ 2002. Similarly, the Charpy test resulted in higher values for Super 77™ than for EPON™ 2002. The effects of Super 77™ and EPON™ 2002 are complex and varied depending on application concentration, resin, and tackifier type; but the addition of any tackifier reduces mechanical properties from non-tackified laminates.