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Compression resin transfer molding (CRTM) is an effective process for the manufacturing of composite parts with large size and high fiber content. The analysis of the resin flow and stress distributions can only be performed by directly solving the coupled flow/deformation equations, but it is difficult to handle the complicated preform deformation models and geometry models; therefore, the simulation precision and application range are extremely limited. In this paper, an alternative approach is introduced to overcome the above problems, in which the preform deformation and the accompanying resin release during the secondary compaction phase are calculated in an additional element associated with each unit of the discretized model geometry instead of solving the coupled governing equations directly, so the complex compaction models can be adopted. Three simulation examples are presented to demonstrate the accuracy and capability of the above numerical approach on velocity-controlled, force-controlled 3D CRTM processes. [ABSTRACT FROM PUBLISHER]

The vacuum infusion is a process usually applied to manufacture large structures of composite materials, such as wind turbine blades. This work analyzes the macroscopic resin flow through a laminate of fiberglass plies with different orientations, during the filling stage of the vacuum infusion process to manufacture two different pieces. The pressure inside the mold, velocity vectors, and the resin inlet mass flow are studied through a three-dimensional numerical modeling under non-steady conditions validated experimentally. The numerical model simulates each ply of the laminate like an individual porous media and takes into account the stacking sequence of the laminate. The influence of the permeability values of the distribution media and of the fiberglass laminate on the evolution of resin infusion is analyzed. The numerical model reproduces the effects of the stacking sequence and race tracking on the resin flow front. [ABSTRACT FROM AUTHOR]

Studies were carried out on the storage life of Room Temperature (RT)-curable pre-pregs comprising of two varieties of bi-functional epoxy resins (imported resin system and an equivalent grade of indigenous resin system) as matrices and bi-directional glass fabric as reinforcement. The hand-made pre-pregs were stored at sub-ambient temperature (-18°C). The resin flow of pre-preg was determined as a function of storage period. Composite laminates were vacuum molded using the pre-pregs taken out of the deep freezer. The composite specimens were characterized for their thermal (Tg) as well as mechanical properties. The properties obtained were compared with the properties of wet layed-up composites fabricated without the usage of pre-impregnated plies. [ABSTRACT FROM AUTHOR]

The finite element formulation is developed to solve the flow and compaction problems to simulate the resin flow and laminate compaction during the hot-pressing process of fiber-reinforced composite laminates. The numerical flow-compaction model is based on the effective stress formulation, the continuity equations, and Darcy's flow theory. Two methods are used to calculate the variation of the laminate thickness, the simulated results validate the relationship of fiber motion and resin flow velocity. Together with the post-processor software. the visual laminate deforming process is realized through the node moving. The comparison between the predicted and experimental data shows that the program is reliable to predict the laminate thickness and the final fiber volume fraction distribution in the thickness direction. [ABSTRACT FROM AUTHOR]

This paper presents an experimentally validated model to simulate the nonisothermal resin infusion and cure processes in a relatively large and thick composite laminate fabricated using vacuum-assisted resin transfer molding. Compaction effects were accounted for by using a step-wise scheme wherein the panel was divided into three discrete zones along the flow direction, with each zone being assigned different porosities and other material properties. The experimentally observed dynamic evolution of the resin flow front profile due to permeability difference between the high-permeable infusion medium and the glass-fiber preform as well as the heat transfer in the preheated system was captured accurately. Both model predictions and experimental measurements indicate subtle variation in the spatiotemporal distributions of temperature and degrees of resin cure from the infusion stage can result in large differences in the resin cure profile across the laminate, which may cause undesirable residual stresses in large composites. [ABSTRACT FROM AUTHOR]

In the RTM light composite manufacturing process, inorganic fillers are commonly added to the resin to reduce cost and alter the final composite properties, especially rigidity, even though they also adversely affect processability. The aim of this study is to evaluate resin characteristics, reinforcement permeability, and mechanical properties of the composite and analyze the detrimental effects when a variable amount of calcium carbonate (CaCO3) is added to the resin. The addition of calcium carbonate increased the viscosity and gel time of the resin and considerably decreased the permeability of the reinforcement and therefore the expected process productivity. Besides, Barcol hardness, short-beam strength, and elastic modulus increased for higher CaCO3 content, whereas Izod impact, flexural, and tensile strengths decreased. Besides, the coarser CaCO3 filler particles managed to penetrate only partially into the fiber-rich layer of the combination mat used, which comprised of a PP flow media core and glass fibers at the surface. [ABSTRACT FROM PUBLISHER]

We investigate the unsaturated resin flow behavior in a dual scale porosity preform by observing the pressure distribution and the void content. The experimental data show that the pressure profile in the unsaturated flow is nonlinear with positive curvature whereas that in the saturated flow is linear as expected from the classical Darcy's law. To address this issue, the governing equation for mass conservation is modified by introducing a mass sink term. Eventually, it has been found that the discrepancy between the unsaturated and saturated permeability values comes from a misinterpretation of the pressure gradient at the flow front in the unsaturated permeability measurement method and the permeability for a given preform is a unique value regardless of measurement method or flow condition. Based on this investigation, the ratio of unsaturated permeability to saturated permeability is represented as a dimensionless number in terms of void content. [ABSTRACT FROM AUTHOR]

The objective of the present study is to improve the pultrusion process by improving the reinforcement wetout, and thus, the quality of the pultruded part in the resin injection pultrusion process. The emphasis here is on one of the processing parameters (pull speed/line speed) with a slot injection tapered chamber by varying the length of the injection chamber. Investigated is the impact of tapering of the walls of the injection chamber on the minimum injection pressure necessary to achieve complete wetout via varying the length of the tapered injection chamber and also the pull speed. This work presents the injection chamber exit pressure, since this is important for chamber design with respect to personnel safety and die/chamber damage. [ABSTRACT FROM PUBLISHER]

This paper presents research being conducted on the use of a combination of fiber optic sensors for process and health monitoring of resin transfer molded (RTM) composite structures. A laboratory scale RTM apparatus has been designed and built with the capability of visually monitoring the resin filling process and embedding fiber optic sensors into the composite. Fiber Bragg gratings (FBG) and etched fiber sensors (EFS) have been multiplexed and embedded in quasi-2-D panels and 3-D hollow semicircular structures using a novel ingress/egress technique for the purpose of both process and structural health monitoring. The objective of this work is to demonstrate the simultaneous usage of FBGs and etched fiber sensors on a single optical fiber for resin flow monitoring and strain monitoring throughout the life of the composite. Three specimens are presented: one quasi-2D panel with two FBGs and three etched fiber sensors, one semicircular tube with two etched fiber sensors and one semicircular tube with two FBGs. Etched fiber sensors have been correlated with visual inspection to detect the presence of resin. Specimens with embedded FBG sensors have been tested in a tensile test machine to characterize the FBGs for strain monitoring. [ABSTRACT FROM AUTHOR]

Manufacturers of lean weight vehicular structures are discovering the advantages of utilizing the high strength to weight ratios found in composite materials. However, traditional closed mold techniques require a long cycle time and relatively expensive tooling. This paper reports on a new technique called Resin Infusion between Double Flexible Tooling (RIDFT). In this innovative process, the resin infusion and resin-fiber wetting are finished between two flexible tools in a two-dimensional flat shape and then the entire wetted reinforcement and flexible tooling is formed into a specified part shape by using a vacuum. This process avoids complex resin flow and mold filling issues and saves mold preparation and fiber stacking time. Using a RIDFT prototype, several components were produced. A larger industrial RIDFT machine was constructed to establish its viability for large component manufacture. An evaluation of production parameters, including infusion pressure, resin temperature, number of fiber layers and hardener content, ascertained their effect on mechanical properties and infusion times for the manufactured parts. The interaction between the hardener and fiber layers were found to directly affect tensile strength. The interaction between hardener and infusion pressure was also shown to affect tensile strength. [ABSTRACT FROM AUTHOR]

To investigate and evaluate the effect of void features on the mechanical performance of composite materials, it is important to be able to manufacture samples with a range of controlled void content. A criterion of less than 2% of porosity is typically acceptable for industry. However, it is important to investigate the effect of void content above and below this range, as voids are typically unevenly distributed in composite parts, and so there are likely to be local void concentrations higher than 2% in some sections of the structures. In this paper, a novel manufacturing process that allows panels with a range of void contents to be manufactured in a controlled manner is introduced. This allowed an investigation of the effect of manufacturing parameters, such as time, pressure and temperature and material systems on the void content and morphology of the voids in specimens produced. [ABSTRACT FROM AUTHOR]

With growing restrictions on the exploitation and trade of current stringed musical instruments fingerboard materials such as ebony and rosewood, for economical and ethical reasons, instrument makers are looking for alternative materials. The present work describes the development of a homogeneous 60% bio-based flax fibre composite material with physical properties similar to commonly used fingerboard woods. As a proof of concept, prototype guitar neck was built using the material, demonstrating its compatibility with existing guitar manufacturing techniques. [ABSTRACT FROM AUTHOR]

Some issues and development in the vacuum-assisted resin transfer molding (VARTM) technique and the use of carbon nanotubes (CNT) as additional reinforcement in laminated composite are discussed in this article. There has been considerable interest in the incorporation of CNT as secondary reinforcement in addition to the primary fiber reinforcement in laminated composites. The use of CNT is apparently able to enhance the out-of-plane material properties by improving interlaminar strength and fracture toughness of laminated composites. The addition of CNT may be done through the VARTM technique, a non-autoclave, relatively low-cost method, frequently used to fabricate parts with complex shapes. This survey shows that while the matrix-dominated interlaminar fracture toughness and shear properties may be improved, the improvement in in-plane fiber-dominated properties is very modest. [ABSTRACT FROM AUTHOR]

A numerical process model was created to simulate unsteady flow through nonhomogeneous unidirectional fibrous media. Permeabilities calculated at the fiber level were applied over small spatial and temporal regions to improve accuracy of macroscopic analysis. Consideration was given to non-ideal aspects of the fiber bed, especially fiber array randomness and fiber bed compressibility. Experimental results indicated that permeant driven fiber compaction had a major influence on flow front advancement. Overall, the process model developed in this work showed marked improvement in predicting flow front locations over a standard bulk property model. [ABSTRACT FROM AUTHOR]

Producing quality pultruded parts requires that complete wet out of the reinforcement fibers is achieved in the injection chamber. The magnitude of the injection pressure is extremely important for achieving good wet out of the fibers. This work focused on the impact of pull speed, resin viscosity, and product thickness on resin fiber wet out in the injection chamber for a polyester resin (mat/roving/mat) composite. Recommended injection pressures for complete wet out are predicted for given sets of processing parameters for polyester/glass fiber (mat/rovings/mat) composites. Flow through porous media (Darcy's law) is employed to model the fiber/resin system of injection pultrusion. The governing equations are solved, by using the finite volume method, to predict the resin pressure, resin velocity field, and resin moving flow front location. The Gutowski (Gutowski, T.G., Morigaki, T. and Cai, Z. (1987). The Consolidation of Laminate Composites, Journal of Composite Materials. 21(7): 172-187) permeability model is used to determine the permeability in the roving layer and the Kozeny-Carman (Carman, P.C. (1939). Flow through Granular Beds, Trans. Int. Chem. Eng., 15: 150-166) model is used to predict the permeability in the mat layers. [ABSTRACT FROM AUTHOR]

Composite automated placement shows great potential for efficient manufacturing of large aviation components. In order to understand the effect of the contact between the compaction roller and the fiber/tape on the layup quality, it is necessary to study the contact characteristic of the compaction roller and the morphological change of the prepreg under the compaction roller. The contact of the compaction roller is divided into the static and dynamic contact. For the static contact, the contact model is simplified to a roller compaction on an elastic body with curved surfaces, and it is developed based on the elastic contact theory. On the contrary, a dynamic contact model is presented by simplifying the contact areas as idealized rectangular elements with identically sized elements. Due to the compaction roller exerting pressure on the prepreg, the morphology of the prepreg will change with different processing parameters. The deformation model of the prepreg is determined as the resin flows through a porous network of fibers by creep theory. A series of experiments had been conducted to verify feasibility and accuracy of the developed models. Results demonstrate that these models have good precision. [ABSTRACT FROM AUTHOR]

Unidirectional fibre-reinforced composites are increasingly used in the sectors of aerospace, automotive, construction, marine and other technical applications over the decades due to their low weight, high mechanical, thermal properties and high corrosion resistance. As a result, the understanding of mechanisms of their fracture and failure under different loads especially under transverse loading are very important in order to take full advantage of their excellent performance, to optimise production procedures and to develop new materials with higher performance. This paper reviewed the effects of the microstructure of a composite material (including fibre volume, fibre distribution, bonding quality between fibres and matrix and characteristics of matrix) on the performance of fibre-reinforced plastic composites according to mechanics theories and finite element method for microstructure analysis. [ABSTRACT FROM AUTHOR]

There has been a vast growth in manufacturing of fiber reinforced plastics by means of liquid composite molding such as resin transfer molding and vacuum-assisted resin transfer molding processes. In these processes, compression of the porous media and pressure of the injected resin result in in-mold forces that need to be determined. Limited information exists regarding the processing parameters and extent of reinforcing potential natural fibers have in polymer matrices. Current study investigates the effect of different variables such as fiber volume fraction, shive content, fiber size, wax content, and resin viscosity on permeability of five different natural fiber mats. Flax fiber with low-, medium-, and high-shive content as well as hemp and kenaf fiber mats was selected for this study and an original experimental device was setup to measure the permeability of the mentioned fiber mats based on different variables. It was found that increasing fiber volume fraction will result in reduction of permeability of all mats. The presence of shive and larger fiber size increased the permeability. Higher wax content lowered the permeability. These competing factors could be used by manufacturers to produce a mat which had optimum permeability while still maintaining acceptable strength. [ABSTRACT FROM AUTHOR]

Graphene nanoplatelets are two-dimensional carbon structure materials with single or multilayers graphite plane which possesses attractive characteristics. In this study, the environmental aging effect on interlaminar properties of graphene nanoplatelet containing different proportions (0.25, 0.50, 0.75 wt%) reinforced epoxy/carbon fiber (carbon fiber reinforced plastic) composite laminates including interlaminar shear strength and fracture toughness were investigated. The interlaminar properties of graphene nanoplatelets/carbon fiber reinforced plastic composite laminates were improved over that of neat carbon fiber reinforced plastic composite laminates. Experimental results showed that the composite laminates containing graphene nanoplatelets possesses the appreciable improvement. The mechanisms responsible for the interlaminar enhancement were identified by studying the fracture surfaces using field emission scanning electron microscopy. [ABSTRACT FROM AUTHOR]

High injection pressure resin transfer moulding is a variant of resin transfer moulding in which the preform is compressed in a tool and resin is injected into the mould under very high pressure. The high injection pressure (>20 bar) introduces possible fibre washout that translates into manufacturing defects or causes inconsistencies in processing and leads to scatter in mechanical properties of composite parts. A model is presented which quantifies and provides insight into the influence of process variables such as clamping force and injection pressure on fibre washout distance (the one-dimensional model assumes a rigid preform). A generalised one-dimensional stress model for fibre washout is presented for regions that are impregnated with the resin and the regions that are dry. The model shows fibre washout to be significant at the beginning of the injection process. The model allows one to further refine the injection strategy by adjusting injection pressure to account for washout in high injection pressure resin transfer moulding. [ABSTRACT FROM AUTHOR]

A composite material scores over its metallic counter parts in many aspects and can be tailor-made to suit the specific purpose for which it is conceived. However, during functioning the composite is exposed to the severities of the surrounding ambiance and is damaged and degraded by the atmospheric deterrent-reagents like moisture and heat fluctuations. In order to ensure a safe, extended service life-span of the composite material, it is, therefore, pertinent that the behaviour of the material related to its physical, chemical and mechanical characteristics must be analysed and established under different fluctuating ambient conditions. The present report aims at analysing and presenting the degradation/damages caused to the glass-fibre reinforced plastic (GFRP) composites under different ambient conditions and the role played by some inherent factors like the constituent components of the GFRP composites, its pre-existing flaws created during manufacturing/service-life, volume fraction fibres, length and distribution of the fibres in the matrix phase and the curing processes adopted for strengthening and stabilising the matrix structure. [ABSTRACT FROM AUTHOR]

This paper successfully developed a resistance heating method based on carbon fiber thin veil for molding continuous glass fiber reinforced polypropylene composite. Electrical resistance, temperature distribution, and heating response of carbon fiber veil were investigated to evaluate its resistance heating behavior. One layer of carbon fiber veil with about 0.1 mm thickness was sandwiched by prepreg stacks with about 2 mm thickness and composite plate was fabricated through resistance heating and forming process. Void content, glass fiber distribution, and thickness of composite plate were obtained to evaluate forming quality. Flexural test was employed for mechanical assessment. The results shows that carbon fiber veil coupled with copper foil is an effective heating element with uniform temperature distribution and quick heating response, and the processing quality of composite plate is comparable to that using oven heating process. The feasibility of secondary resistance heating of composite plate based on carbon fiber veil was also demonstrated and the results indicate that composite plate containing carbon fiber veil can be molded into composite product using resistance self-heating process. [ABSTRACT FROM AUTHOR]

Autoclave process is widely used in manufacturing processes for thermosetting matrix composite materials. During the process, the non-uniformity of temperature distribution in autoclave may result in non-synchronous curing of composite, which in turn reduces the mechanical properties of composite parts. In order to improve the curing performance, design optimization of autoclave molds has to be performed. In this paper, a finite volume method based numerical model is established to simulate the temperature distribution inside an autoclave and it is verified by known experimental data. Then, a typical mold structure, which is covered with composites and simplified auxiliary materials, is introduced to the numerical model. Moreover, a method which combines the numerical model with the genetic algorithm is presented to optimize design parameters of the substructure of mold with an aim of improving the synchronism of curing. The maximum standard deviation of degree of cure in composite parts is adopted as the objective, while the deformation of the mold under hoisting situation is considered as the constraint. The result shows that the maximum standard deviation of degree of cure in composite parts is improved as much as 17.21%, which indicates that better synchronism of curing is achieved with the presented method. [ABSTRACT FROM AUTHOR]

In this present study, thermally treated flax–polypropylene (PP) based hybrid yarns have been manufactured using DREF-3 spinning method for thermoplastic composite reinforcement. The effect of different process parameters such as core yarn twist level, sheath ratio and thermal treatment temperature on hybrid yarn properties has been studied thoroughly using Box–Behnken design. The DREF-3 spun hybrid yarn for composite reinforcement is optimized based on weavability performance, tensile behaviour and flexural rigidity. Further, degree of resin penetration inside DREF yarn-based unidirectional composite structures and their tensile properties are taken as parameters to judge the quality of composite. It has been observed that increase in sheath ratio, surface treatment temperature and decrease in core twist level resulted in enhancement of weavability of hybrid yarns and also in improvement in resin penetration inside composite structures. [ABSTRACT FROM AUTHOR]

A facile and efficient method was developed to gain accurate prediction of the resin fillet size for self-adhesive prepreg skin to honeycomb core bonding in sandwich composites fabricated by co-curing process. The proposed method mainly contained numerical simulation of the fiber compaction and experimental measurement of the resin fillet. The influences of processing parameters, including pressure applying moment and processing pressure, on the resin fillet size were analyzed and discussed. Some other factors such as skin thickness and initial resin content of prepreg, which are difficult to be investigated using traditional test method, were also researched by means of this method. The obtained results were in good agreement with the experimental data, which indicated the accuracy of this method. These outcomes are greatly helpful to establish and optimize the processing parameters of co-cured honeycomb sandwich composite materials. [ABSTRACT FROM AUTHOR]

The popular analytical and numerical models to residual stresses and distortions in composite structures during curing are reviewed with emphases being placed on the numerical models with viscoelastic, path-dependent, CHILE constitutive laws, and corresponding numerical implementation into finite element analyses in this paper. A simple C-section composite part made of AS4/8552 prepreg, which has been investigated previously, was taken as an example to compare the difference in residual stresses and distortions with analytical model and numerical method with different constitutive laws. This paper mainly focuses on the effects of residual stresses generated at the different stages during curing on the finial distortions of composite structures for different constitutive laws, especially for effects of residual stresses generated in the rubbery stage on the final distortions. The results show that there is insignificant difference in the calculated residual stresses and distortions in C-section composite part induced during curing with different constitutive laws except the CHILE(α) law. [ABSTRACT FROM AUTHOR]

Research in quick Non-Destructive Evaluation methods for field maintenance of aircraft has become a focus of attention due to increase in the use of co-cured skin-stiffened composite structures. When Lamb wave propagates over skin-stiffened structure, the occurrence of multiple modes is unavoidable due to structural features such as stringers and stiffeners, which in turn makes the interpretation of the received wave difficult and limits the defect-detection ability of Lamb waves. Using Finite Element simulations, the propagation of incident S0 Lamb mode in a typical composite T-joint with delamination between the flange and skin (interface) is investigated. Arrival time delays of the out-of-plane mode-converted wave packets are found to be promising indicator for quantitative detection and sizing of the delamination. A novel experimental technique of combining a liquid couplant-free transduction scheme using dry-coupled roller transducer (contact probe) for generating S0 mode and an air-coupled transducer (non-contact probe) as a receiver is proposed. This transduction scheme helps in selectively separating mode-converted wave packets. This investigation also establishes quantitative B-scan imaging method for characterization of delamination in the T-joint. Experimental results show a good agreement with Finite Element predictions. [ABSTRACT FROM AUTHOR]

The curing behavior of a fiber-reinforced polymer composite part is interesting for both the industrial and scientific community, for it is related to process optimization, quality upgrade, and material characterization. The study at hand focuses on the potential of temperature measurements as a means to monitor curing; kinetic analysis which conventionally is being done for small neat resin samples in a thermally stable environment (laboratory instruments), is in this study implemented for actual scale composite samples in an environment with significant thermal gradients (manufacturing). To ensure the success of this transition, live temperature data and kinetic parameters derived from DSC of composite samples were used as input to the kinetic equations. Process monitoring with thermocouples that was compared with dielectric constant monitoring and conventional kinetic analysis confirmed the validity of the method. An application with infrared thermography determined the impact of heat insulators within the composite (e.g. delaminations) on the superficial curing degree. [ABSTRACT FROM AUTHOR]

Resin matrix filament wound composite shells are widely applied in the fields of military, aerospace, energy transportation, pressure vessel, and civil engineering. The curing and winding are regarded as the necessary procedures during molding, and they are the key factors affecting the final performance of the composite shells. This paper discusses the application of a new molding process called the heated-mandrel winding process, to take the place of the traditional molding process, which has a two-step procedure. It is proved that the heated-mandrel winding process can not only improve the product quality and production efficiency, but can also reduce the labor cost, without moving the wound shell from the winding machine to the oven. In contrast to the traditional molding process, some properties of the composite formed with the heated-mandrel winding process, including the curing degree and elastic modulus, will be changed because of the heat conduction from the heated mandrel during winding. Therefore, the traditional winding tension system design method is no longer suitable for this new process. Taking the temperature changes into account, this paper uses a theoretical investigation and calculations to suggest a tension system model that describes the relationship between the changeable parameters and the winding tension and to calculate the appropriate tension values for winding, based on the heated-mandrel winding process. The accuracy of the model is verified using an experiment. This paper applies an analytical algorithm based on simple iterative steps to design the tension system. The calculation procedures are simplified, and fewer calculation cycles are required in the analytical algorithm proposed in this paper because it is easier to calculate a few simple linear equations rather than complex nonlinear differential equations under the condition that some initial parameters can be known. As seen during practical application, the model is suitable for a tension system design based on the heated-mandrel winding process and provides further quality improvement in the molding shells. [ABSTRACT FROM PUBLISHER]

Viscose fabric-reinforced unsaturated polyester composites were successfully prepared through vacuum infusion process. Unidirectional viscose fabric was modified by two different organosilane coupling agents and by acetylation treatment. The main objective was to study the influence of fabric treatment on the mechanical and water absorption properties of the composites. Flexural, tensile and impact properties of composites were studied. The results from mechanical testing of composites pointed out that 3-aminopropyltriethoxy silane treatment increased the flexural and impact strengths of the composites with respect to untreated fabric composite. The impact strength of 3-aminopropyltriethoxy silane-treated fabric composites almost doubled compared to the value of untreated fabric composite. Among all the composites under study, those with fabrics treated by 2 vol% 3-aminopropyltriethoxy silane in ethanol/water (95:5) solution exhibited significant improvement in water uptake resistance. An unsaturated polyester gelcoat and topcoat were applied as the outer surface on the composites with untreated fabric. This was done in order to investigate the visual surface appearance and evaluate the gelcoat and topcoat effect on water absorption after accelerated water immersion test. The regenerated cellulose fibre as reinforcement shows high potential to be used as an alternative for natural bast fibres, especially, when toughness of material matters. Chemical treatment of regenerated cellulose fibres could result in improvement in properties of polymer composites, considering that the appropriate treatment method is selected for the corresponding fibre–matrix system. [ABSTRACT FROM PUBLISHER]

The first part of this two-part study introduces an approach for a numerical model of the composite manufacturing method light resin transfer moulding. Discussion of process physics and relevant literature is used to develop a coupled finite element and infusion software simulation of both the structural and flow elements of the method, with the aim of producing an accurate and comprehensive model. This theoretical overview of the model acts as a precursor to the final part of the research where results are presented and verified and a wind energy case-study application will be demonstrated. [ABSTRACT FROM PUBLISHER]

In recent years, a crucial interest has focused on closed mold composites manufacturing technologies. Mainly due to the ability to handle the harmful emissions of hazardous gases and the ability to produce parts with complex geometry. The liquid composite molding term includes a list of manufacturing composite varieties, such as resin transfer molding, vacuum assisted resin transfer molding, compression resin transfer molding. All liquid composite molding varieties involve compressive strain reinforcement before and in many cases during mold filling. The compressive strain reinforcement response is generally considered as non-linear elastic for the modeling. The viscoelastic stress relaxation is thus taken into account. A better understanding of the compressibility phenomenon helps to improve control of implementation process of parts and tooling design. The quality of the parts can also be improved through a better understanding of the stresses acting in composite products. In this paper, we present a detailed review of the most important models that have focused on the compression and relaxation of fiber reinforcements. In the order of succession, we first present the models giving a non-linear elastic behavior for fibrous reinforcements, then the models considering the reinforcements as viscoelastic materials. [ABSTRACT FROM PUBLISHER]

Fiber-reinforced composites play an important role in enabling the industrial composites industry including automotive, pressure vessels etc. to meet ever increasingly aggressive fuel efficiency requirements. Modeling and analysis is often employed in composite development as a tool to achieve faster and more cost-effective solutions to both product and process designs. Thermal conductivity measurements play a critical role in enhancing the fidelity of these models, especially in scenarios involving non-isothermal processing. Accurate characterizations of anisotropic thermal conductivities that are typical of dry fibrous preforms are especially challenging because of their highly porous and complex structures. In this article, an inverse approach is developed to estimate the anisotropic thermal conductivities of a dry preform made of biaxial [0°/90°] stitched glass-fiber mats based on the measurements of thermal conductivities of cured epoxy-matrix composites. This method is found to not only yield more accurate results than direct preform measurements but also provide the capability to characterize preforms in multiple directions rather than only through-thickness direction. The estimated thermal conductivities are used in preform heating simulation that is validated against experiments. [ABSTRACT FROM AUTHOR]

In this investigation, the effect of fiber volume fraction on the energy absorption capacity of fiber-reinforced composite materials was studied using dynamic mechanical analysis measurements. Laminates were fabricated with and without vacuum bag using plain weave E-glass fabric and three types of polymer matrix: epoxy, polyester, and vinyl ester. The higher energy absorption displayed by samples processed under vacuum was related to the shorter distance between adjacent fibers which produces stresses of higher magnitude in the matrix, thus promoting higher energy dissipation. However, when the energy dissipation is divided by the material density, the higher material density of vacuum processed laminates offsets the effects of increased loss modulus at higher fiber volume fraction. [ABSTRACT FROM PUBLISHER]

The structure of T-stiffened skins molded integrally by co-curing or co-bonding is widely used in aircraft industry nowadays. Ongoing research focuses on the study of the compaction of simple structure composite components and the analysis of mechanical properties of T-stiffened skins. In this article, using carbon fiber/bismaleimide prepregs, T-stiffened skins were integrally fabricated by different tool assembly schemes in autoclave. The influence of tool assembly schemes and integral molding technologies on the compaction of T-stiffened skins was discussed in detail. A method of self-designing solid pressure testing was introduced to measure the pressure distribution upon T-stiffeners during cure process. The compaction of T-stiffeners was studied quantitatively by thickness distribution and analyzed qualitatively by pressure transferring. The experimental results showed that the pressure distribution in T-stiffeners was significantly influenced by tool assembly schemes and tool radii, which directly affected the compaction of T-stiffeners. The optimum assembly of rigid tool and triangle flexible tool with appropriate stiffness was adopted. In comparisons of co-curing and co-bonding, little difference of compaction in web and flange of T-stiffeners were found except higher thickness in corner section for co-curing. [ABSTRACT FROM AUTHOR]

The aim of this study was to carry out RTM experiments to determine in-plane permeability of glass mats, non-woven polypropylene flow media (PP) and hybrids (glass + PP), with different stacking sequences, and to compare these with various sisal mats and hybrids (glass + sisal). RTM composites were also molded. Permeability decreased for higher fiber content and, for the same fiber volume content, the permeability of the sisal mats was much higher than that of glass mats and also higher than that of the PP non-woven core, often used as an infiltration medium. Besides, a tendency of increasing permeability with sisal fiber length (up to 30 mm) was noticed. The use of the sisal mat as a flow medium increased the permeability of the hybrid reinforcement and slightly improved the mechanical properties of the composite. Hence, the sisal mat may be indicated in engineering applications as a substitute for commercial flow media, widely used in the process called RTM light. [ABSTRACT FROM AUTHOR]

Based on statistical analysis, considerable defect information obtained by nondestructive identification (NDI) techniques for composite components, different type defects which often form in autoclave molding of composites were summarized, and the effect rules of complex structure in composite components on manufacturing defects were also revealed. Combined with statistical results and defect micrographs, the strong correlation between geometric characteristics (for instance, thickness, gradient of thickness variation, curvature radius) in composite components and controllability of manufacturing defects was discussed in detail. It was found that delamination, pore, void, and rich resin were the four main defects in autoclave molding, and that the ratio of defect appearance was remarkably influenced by complex structure of composite components. Especially, geometric characteristics of composite components had a significant influence on the defect type and defect ratio. For example, too thin or too thick components, too small radius and abrupt change of thickness in components would obviously increase the ratio of defect production. Thickness, curvature radius, and gradient of thickness variation would probably lead to the defects of delamination and void, and gradient of thickness variation would also result in rich resin around the overlap region of long fiber and short fiber in the thickness transition zone. [ABSTRACT FROM AUTHOR]

This work assessed the viability of co-infusing a thermoset resin and liquid coating formulations for the in-mold coating of composite components manufactured by the resin infusion between double tooling (RIDFT) process. Material trade studies conducted to resolve the compatibility issues of the separation layer and coating material were successful. The modifications of the RIDFT--IMC assembly succeeded in eliminating the risk of premature fiber wetting during coating material infusion. Experiments were conducted to determine the best manufacturing conditions for production of a viable RIDFT--IMC component. The results indicate that reducing the coating exposure to heat yielded in improved surface characteristics. Microstructural examination further confirmed that the coating did not infiltrate the fiber--resin interface. [ABSTRACT FROM AUTHOR]

In this study, a comprehensive continuum dual-scale model has been developed for LCM processes for woven fiber reinforcements. This model incorporates the main flow mechanisms involved, including mass exchange between dual-scale porosities, micro-diffusion within fiber tows between neighboring repeating unit cells (RUCs), and the capillary effect within fiber tows. Macroand micro-flows are simulated at the same numerical scale. A sink and a source term are introduced into the two different scaled flows to couple them together. An unsaturated flow model is adopted to describe micro-diffusion within fiber tows between neighboring RUCs. The physics of the sink/ source term is modelled according to the impregnation of tows within a RUC. Two models developed in soil physics have been adopted to evaluate the capillary effect and the partially saturated permeability within fiber tows. A finite element method is employed to solve the governing equations, and a simple implicit time integration method is suggested. A 1D RTM example has been modeled. The modeling results indicate that all of the three main mechanisms have significant influences on the LCM processes, but the mass exchange between the dual porosities plays a dominate role, particularly under high injection rates. [ABSTRACT FROM AUTHOR]

This paper quantifies the elastic behavior and failure response of discontinuous carbon fiber/ epoxy laminates produced by compression molding of randomly oriented preimpregnated unidirectional tape. Flat plates have been successfully molded using manually prepared prepreg charges, and showed a satisfactory degree of randomization. Complex relationships between reinforcement aspect ratio and tensile, compressive, and flexural moduli and strengths are observed. For this particular material system, failure is a matrix-dominated event, with little or no fiber breakage, and it promotes relatively high variation in the measured properties. The high-volume carbon fiber content, combined with an aerospace-qualified epoxy resin, opens up opportunities for more aircraft parts to be made of composite materials, particularly for stiffness-critical components where discontinuous fibers offer performance similar to the continuous quasi-isotropic value. [ABSTRACT FROM AUTHOR]

Composites of woven sisal in polyester matrix using three different weave architectures: (plain, twill, and matt) were prepared using a resin transfer molding technique with special reference to the effect of resin viscosity, applied pressure, weave architecture, and fiber surface modification. More than the applied pressure, the resin viscosity, and fiber surface modification, the weave architecture was found to have maximum influence on the ultimate composite properties. The resin permeability, which is related to fiber wetting, was found to be dependent on the weave architecture and the fiber surface morphology. Sisal fibers in woven form, with a fiber volume of 32%, were found to improve the properties of polyester tremendously, irrespective of the resin used and the injection pressure. The maximum improvement in tensile strength was observed for resin with a viscosity of 420 cps. While the tensile strength showed a 32% improvement, the tensile modulus showed a 100% improvement by reinforcing fabrics with the weave architecture with maximum fibers in the loading direction, for the same resin. The flexural strength gave an improvement of 19% while the flexural modulus gave a 55% improvement. Fabrics with maximum fibers in the loading direction (matt weave) proved to be the best reinforcement to impart maximum properties. Finally, the fracture surfaces were examined by scanning electron microscopy to get an insight into fiber/matrix interactions. [ABSTRACT FROM AUTHOR]

In this study, the effects of the cutout and the lay-up configuration on the buckling behavior and the damage tolerance of the stiffened carbon/epoxy panels manufactured by the resin transfer molding (RTM) are evaluated. The samples are manufactured using the RTM technique. The tensile test specimens are also prepared similarly to characterize the behavior of the material. Finite element analysis (FEA) of the panel samples is carried out and the comparisons are made among the results. The effects of the cutout and the lay-up configuration on the results are discussed. [ABSTRACT FROM AUTHOR]

The structural characterization of hybrid fiber reinforced polymer (FRP) autoclaved aerated concrete (AAC) panels is examined in this study. The structural system is based on the concept of a sandwich construction with strong and stiff FRP composite skins bonded to an inner AAC panel. The FRP composite material is made of carbon reinforcing fabrics embedded in an epoxy resin matrix. The carbon fiber reinforced polymer (CFRP) reinforcement is applied on the top and bottom faces of the AAC panel, and several innovative processing techniques are used including the hand lay-up as well as the vacuum assisted resin transfer molding (VARTM). The main focus of the research is to combine the AAC with the FRP face sheets into a synergetic system, which would be consistent with the recent interest in high performance and zero maintenance of civil infrastructures. This combination, being lightweight in nature, has the potential to be used for speedy panelized construction purposes, for disaster mitigation, and to prevent labor-intensive construction. The CFRP has been used with regular concrete before and has shown phenomenal reinforcing capabilities. The AAC, on the other hand, is a cellular concrete and is very light to work with, in comparison to normal concrete. It is also structurally very brittle in nature and has much lower flexural as well as compressive strengths than normal weight concrete. An experimental protocol based on a four point bending test is used to characterize the stiffness, ductility, and strength response of the hybrid FRP AAC sandwich panels. Since there are no previous research data available on the hybrid CFRP-AAC panels and the bonding characteristics of AAC with FRP are unknown, a set of basic tests are also initiated including the bonding test on AAC samples wrapped with CFRP. To understand and optimize the flexural/shear behavior of the hybrid CFRP-AAC sandwich panels, several innovative reinforcing schemes with CFRP skin are used, as elaborated in this article. In addition, both continuous and discrete AAC blocks are used to fabricate AAC panels. Results from the experiments emphasize the need for a complementary test program where the best reinforcing scheme from the study would be duplicated in future tests on structural elements of the typical sizes including beams, floors, lintels, etc. [ABSTRACT FROM AUTHOR]

As composite materials gain wider acceptance within the transportation industry, it is pertinent to investigate the available coating processes with a view to reducing emissions and associated costs. This work aims to develop a methodology for in-mold coating components manufactured using the resin infusion between double flexible tooling (RIDFT) process. RIDFT is a neoteric two-stage manufacturing process that involves (1) infusion of resin between two flexible silicone membranes until thorough wetting of the fibers is achieved and (2) vacuum forming, where the membranes are pulled over a one-sided mold. The viability of in-mold coating RIDFTed components is investigated. This work-in-process reports on successes and challenges presented during the co-infusion of a polyurethane enamel paint (DuPont Imron 5000) and a vinyl ester resin (Derakane 470-45). Methodologies for achieving co-infusion are investigated. It has been found that co-infusion is achievable with the use of an appropriate separation layer. [ABSTRACT FROM AUTHOR]

This article presents a robust resin transfer molding (RTM) process window of a phenylethynyl terminated imide (PETI) oligomer with melt viscosity lower than 1 Pa s over 15 min and 10 Pa s for 2 h at 280°C. Curing occurs rapidly only above 350°C. Curing should be over 30 min at 370°C. Molding optimization reduces the melt viscosity. The oligomer is heated rapidly from 265 to 280°C for the minimum viscosity being lower. The melt is further heated for easier flow in injection and early permeation. The mechanical properties of the prepared composite remain almost constant up to 280°C, facilitating the fabrication of large, complex, high-quality aerospace parts. [ABSTRACT FROM AUTHOR]

A multiaxial loading on a laminate, combined with numerical optimization is utilized to determine the five elastic constants for a transversely isotropic composite material in this study. A special in-plane loader, capable of any combination of in-plane displacements plus a rotation is utilized for the testing portion. A corresponding finite element analysis model is created and numerical optimization is utilized to obtain the optimum engineering elastic constants. By utilizing only one test specimen geometry, the resources for determining the constitutive properties can be significantly reduced in terms of time and money, and more precise properties over a wider loading range are gained with this procedure. [ABSTRACT FROM AUTHOR]

In the present work, the transverse thermal conductivity of a composite material is determined by inverse analysis of the heat conduction phenomenon. Knowing the evolution of boundary conditions in time, i.e., the bottom and top surface temperatures of a specific sample, the thermal conductivity can be deduced from transient temperature measurements at three given positions through the thickness of the part. Starting from an initial estimate of thermal conductivity, the inverse method begins by solving the direct problem, i.e., the heat equation. The solution gives the transient temperature field everywhere in the composite sample. Calculated temperatures are then compared with transient experimental measurements based on a criterion evaluating the integral in time of the square of the distance between the measured and predicted temperatures. Conductivity is modified iteratively so as to minimize this criterion until the desired accuracy is achieved. The inverse methodology is tested in this article for a composite part made out of unsaturated polyester resin and unidirectional glass fibers. A special multifunctional mold was designed to produce the composite test plates by the Resin Transfer Molding Process (RTM) and at the same time, measure the transverse thermal conductivity as a function of time and resin degree of polymerization. The mold has an adjustable cavity depth to accommodate various experimental configurations and allows easy testing of a series of different fiber volume contents. It is equipped with controlled heating and cooling devices. Numerical simulations were performed to determine the dimensions of the mold and to optimize the positions of temperature and pressure sensors. [ABSTRACT FROM AUTHOR]

In-mold coating is desired by the composites industry since it eliminates the current paint process, which is not only laborious and time consuming, but expensive and presents safety issues. This work set out to investigate a means of implementing an in-mold coating scheme that would result in near class-A finish of composite component parts manufactured by the Resin Infusion between Double Flexible Tooling (RIDFT) process. RIDFT is a novel two-stage process, which incorporates resin infusion and wetting with vacuum forming. The flow front of the infused resin is two-dimensional and avoids flow complexities prevalent in the three-dimensional flow seen in other liquid composite molding techniques. It employs a one-sided mold, which provides obvious cost benefits when compared with resin transfer molding. This paper describes the preliminary results of in-mold coating assessment studies made using thermoformable paint films. A room temperature-cured vinyl ester resin is used and the paint film is an Avery Dennison Avloy film. [ABSTRACT FROM AUTHOR]

The use of piezoelectric ceramic materials for structural actuation is a fairly well-developed practice that has found use in a wide variety of applications. However, just as advanced composites offer many benefits over traditional engineering materials for structural design, actuators that utilize the active properties of piezoelectric fibers can improve upon many of the limitations encountered with monolithic piezoceramic devices used to control structural dynamics. This paper discusses the Macro Fiber Composite (MFC) actuator, which utilizes piezoceramic fibers, for example, lead zirconate titanate (PZT), embedded in an epoxy matrix for structural actuation. An overview of the MFC assembly process is presented, followed by a cure kinetics model that describes the behavior of the thermosetting epoxy matrix. This empirical model is seen to agree closely with the experimental data. [ABSTRACT FROM AUTHOR]

This paper discusses the experimental study on the response of affordable plain and satin weave carbon/epoxy composite laminates subjected to high strain rate compression loading using a modified Compression Split Hopkinson's Pressure Bar (SHPB). 37 layer laminates were manufactured using aerospace grade woven fabrics with SC-15 epoxy resin system utilizing Vacuum Assisted Resin Infusion Molding (VARIM) approach. Samples were subjected to high strain rate compression loading at five different strain rates ranging from 17/s to 817/s in the in-plane as well as through-the-thickness directions using a modified SHPB that facilitates controlled single pulse loading of the sample. High strain rate response was compared with that of static compression. Optical microscopy was used to characterize the failure mechanisms. Resets of the study indicate considerable increase in dynamic compression peak stress as compared to static loading, whereas the strain at peak stress was lower by 35-65%. Samples loaded through-the-thickness exhibit higher peak stresses as compared to those loaded in the in-plane direction. [ABSTRACT FROM AUTHOR]