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Compression resin transfer molding using inflatable seals is a new variant of LCM (“Liquid composite molding”) processes, which uses the inflatable seals to compress the fiber reinforcements and drive the resin to impregnate the fabric preform, resulting to fill the entire mold cavity. During resin injection, the preform is relaxed. Consequently, the resin enters easily and quickly into the mold cavity. After, the necessary resin is injected into the mold cavity, the compression stage takes place, in a stepwise manner, by swelling the inflatable seals. The objective of this paper is to present this new process and study the effect of the number of inflatable seals on the filling time.

S-glass-fiber-reinforced plastic layered composites were prepared by the vacuum-assisted resin transfer molding, and their mechanical properties in relation to different layering types were studied. The effects of layering type and off-axis angle on the tensile and flexural strengths of the composites were clarified. In addition, variations in the intelaminar shear strength and bearing strength by bolted joints as functions of off-axis angle were investigated. Results indicated that the tensile and flexural strengths of the S-glass fiber composites with the 0° lamination were more sensitive to the off-axis angle than those with the 0°/90° orthogonal lamination.

The impact behavior and energy absorption of two types of composite tubes, fabricated from carbon fabrics by the resin transfer molding and from carbon prepregs by the lay-up method, were investigated experimentally and numerically. In impact tests, outward-splaying crush caps with different fillet radii were used. Different types of crushing behavior of the tubes were simulated by the finite-element analysis, including a progressive failure function and considering the possibility of delamination. A comparison with experimental results confirmed that, the finite-element analysis was able to well predict the crushing behavior of the composite tubes, showing that the specific energy absorption of the prepreg composite tubes was always about 20% lower than that of the braided ones.

This paper presents a simple and computationally efficient multi-scale procedure to predict the macroscopic temperature dependent coefficient of thermal expansion (CTE) of any linearly thermoelastic material from isothermal mechanical simulations only. The approach relies on Levin’s demonstration that, in analytical homogenization, the effective coefficient of thermal expansion is related to the local coefficient of thermal expansion and the stress concentration tensor. For demonstration purposes, this procedure was applied to a 3D woven composite material. The proposed approach was successfully validated with full thermal simulations.

High Pressure Resin Transfer Molding (HP-RTM) is a new variant of composite Resin Transfer Molding (RTM) process that enables a short cycle time and a high composite strength to weight ratio, thus presents a great potential for fabricating automotive structural parts. Due to the high injection pressure, fiber-tow washout is becoming one of the major defects which impact the properties of composite materials. To predict and mitigate the fiber-tow washout problem, approaches of both experimental process optimization and computational prediction are essential. In this paper, an experimental study of fiber-tow washout is undertaken to determine the flow injection limits beyond which the preform deformation can be observed at various fiber volume fractions. A feasibility map is developed for a specific fabric and resin combination. It provides a means to determine the injection rates and fiber volume fractions to fabricate a quality part with minimal in-plane fiber washout due to the hydrodynamically flow-induced force during the HP-RTM process.

In this study, experimental and numerical investigations were carried out in order to determine the mechanical properties and impact response of hybrid composite laminate. The hybrid composite laminate was formed from plain woven carbon fiber reinforced epoxy (CFRE) and plain woven glass fiber reinforced epoxy (GFRE) fiber using VARTM (vacuum-assisted resin transfer molding) process. The mechanical properties of the hybrid composites were determined using tensile test device with a 1 mm/min loading rate at room temperature. In addition, hybrid composites were subjected to low-velocity impact test under different impact energy levels (10, 20, 30, 40 J) for determining the impact response. Moreover, mechanical properties and impact responses of CFRE and GFRE laminates were also determined to compare to those of hybrid composite (HCGFRE). Microstructure analysis was performed to investigate the damage surfaces of the fiber and matrix in the composite material subjected to impact and tensile forces. In numerical analyses, composite damage model (Mat 54) was utilized in LS-DYNA® explicit finite element program to simulate the impact behavior of CFRE, GFRE and HCGFRE laminates. Consequently, the tensile test results showed that hybrid composite laminate behaved more ductile than carbon composite laminate and it exhibited more brittle behavior than glass composite laminate. Also, it was determined that absorbed energy and impact load capacity of HCGFRE composite laminate are between absorbed energy and impact load capacity of CFRE and GFRE composite laminate. It was determined that numerical results indicate a similar tendency with the experimental results.

This article examines the use of fiber Bragg grating sensors for cure monitoring purposes in resin transfer molding processes. Within a resin transfer molding test series a thermoset epoxy-amine resin system was used in combination with a woven flax fiber reinforcement. Particular attention was paid on the location of the optical fiber sensor and its sensitive Bragg grating element inside the mold cavity. Three different installation approaches were tested and the correlation of the corresponding strain response with the actual cure state of the resin system was investigated at 50°C and 70°C isothermal cure temperature, respectively. We could demonstrate that characteristic, conspicuous strain changes are directly related to the sol–gel conversion of the thermoset polymer, which was analyzed considering different approaches for the gel-point detection based on rheological measurements. With the installation of the sensor inside a controllable, capsuled resin volume, we could achieve the most reliable strain response that provides capabilities to give in-situ information of the cure state beyond the gelation point.

Relaxation-compression resin transfer molding under magnetic field is a new variant of VARTM (“vacuum assisted resin transfer molding”) process, which uses a flexible magnetic membrane controlled by a magnetic force, in order to govern the relaxation and compression phases by changing the permeability of the fabric preform. Thus permits to the resin to enter easily into the mold and to increase the resin impregnation velocity and the fiber volume fraction. This innovation is based on the application of the TRIZ theory (“the theory of inventive problem solving”), which allows us to answer to the shortcomings and the conflict links exist inside the VARTM processes. The objective of this paper is to present this new process and to study the effect of the current intensity and the separated gap between the flexible magnetic membrane and solenoid on the permeability of the preform.

Tow bundles inside a quasi-unidirectional non-crimp fabric are maintained by sewing threads that induce variation in the bundles’ shape. Indeed, the sewing threads apply a light clamping force that gives a periodical and sinusoidal shape to the tow’s cross-sectional area. This tow cross-sectional area heterogeneity, as a function of position in the fabric, induces a variation of the permeability values. Consequently, while injecting liquid into the fibrous bed, preform's impregnation is influenced as well as the fabric’s void content. The aim of this paper is to consider the effect of tow cross-sectional area heterogeneity on the quality of the manufactured composite part. It leads to reveal the influence of the fibrous reinforcement’s microstructure on the air bubble creation and compression phenomena, especially in terms of process time and the micro and macro air bubble distribution.

For resin transfer molding in a woven fabric, this study developed a novel framework for optimization by combining a multi-objective genetic algorithm and mold-filling simulation including a void-formation model, which gives us not only the spatial distribution of the mesoscopic and microscopic voids but also the correlations between molding characteristics such as fill time, total amount of void, weld line, and wasted resin. Our experiment observation of one-point radial injection successfully captured the anisotropic distribution of mesoscopic voids, which qualitatively validates the simulated result. As a result of multi-objective optimization for an arrangement of two injection positions, we found the trade-off relations of weld line with the other characteristics, which also have positive correlation with each other. Furthermore, visualization techniques such as self-organizing maps and parallel coordinate maps extracted the design rule of the arrangement. For example, a diagonal gate arrangement with an appropriate distance is required for reducing the both total amount of voids, fill time, and wasted resin; however, the total area of the weld line becomes relatively large. Our framework and the knowledge obtained from this study will enable us to determine the appropriate mold design for resin transfer molding.

In this article, the co-continuous hollow glass microspheres (HGMs)/epoxy resin syntactic foams were prepared by filling the HGM preforms with epoxy resin. The effects of HGM wall thickness and solid loading on the density, open porosity, and morphology of HGM preform and HGM/epoxy resin syntactic foams were studied in detail. The results show that the HGM wall thickness had no effect on the open porosity of HGM preforms. However, the density of preforms increased with the true density of HGMs. The density of HGM/epoxy resin syntactic foams decreased with the contents of HGMs, and the measured density was essentially equal to the theoretical density. The compressive strength decreased with the contents of HGM, regardless of the HGMs wall thickness. However, the variation in compressive modulus was related to the HGMs’ wall thickness. As the HGM solid loading increased, the compressive modulus of composites, prepared using thin-walled HGMs, decreased, while the composites prepared using thick-walled HGMs showed the opposite trend. The co-continuous HGM/epoxy resin syntactic foams possessed low density (0.567–1.002 g/cm3), and excellent compressive strengths (30.32–131.60 MPa). These properties were due to the elimination of matrix pores, and are a type of promising material in deep sea exploration area.

Resin transfer molding and vacuum-assisted resin transfer molding are two of the most commonly used liquid composite molding processes. For resin transfer molding, mold filling simulations can predict the resin flow patterns and location of voids and dry spots which has proven useful in designing the mold and injection locations for composite parts. To simulate vacuum-assisted resin transfer molding, even though coupled models are successful in predicting flow patterns and thickness distribution, the input requires fabric compaction characterization in addition to permeability characterization. Moreover, due to the coupled nature of flow and fabric compaction, the simulation is computationally expensive precluding the possibility to optimize the flow design for reliable production. In this work, we present an alternative approach to characterize and use an “effective” permeability in the resin transfer molding solver to simulate resin flow in vacuum-assisted resin transfer molding. This decoupled method is very efficient and provides reasonable results. The deviations in mold filling times between experiments and simulations for the resin transfer molding process with E-glass CSM and carbon 5HS were 4.7% and 1.0%, respectively, while for the vacuum-assisted resin transfer molding case using “effective permeability value” with E-glass CSM and carbon 5HS fabrics were 11.1% and 12.3%, respectively, which validates the approach presented.

It is generally accepted that matrix pores in the hollow glass microspheres (HGMs)/resin-based composites prepared using stir-casting method (SCM) seriously affect its performance. In this paper, H...

Purpose The purpose of this paper is to quantify the environmental footprint and cost and thus compare different manufacturing scenarios associated with the production of aeronautical structural components. Design/methodology/approach A representative helicopter canopy, i.e., canopy of the EUROCOPTER EC Twin Star helicopter described in Pantelakis et al. (2009), has been considered for the carbon footprint (life cycle energy and climate change impact analysis) along with the life cycle costing analysis. Four scenarios – combinations of different manufacturing technologies (autoclave and resin transfer molding (RTM)) and end-of-life treatment scenarios (mechanical recycling and pyrolysis) are considered. Findings Using the models developed the expected environmental and cost benefits by involving the RTM technique have been quantified. The environmental impact was expressed in terms of energy consumption and of Global Warming Potential-100. From an environmental standpoint, processing the canopy using the RTM technique leads to decreased energy demands as compared to autoclaving because of the shorter curing cycles exhibited from this technique and thus the less time needed. As far as the financial viability of both processing scenarios is concerned, the more steps needed for preparing the mold and the need for auxiliary materials increase the material and the labor cost of autoclaving as compared to RTM. Originality/value At the early design stages in aeronautics, a number of disciplines (environmental, financial and mechanical) should be taken into account in order to evaluate alternative scenarios (material, manufacturing, recycling, etc.). In this paper a methodology is developed toward this direction, quantifying the environmental and financial viability of different manufacturing scenarios associated with the production of aeronautical structures.

Applying external pressure on the vacuum bag in heated-Vacuum Assisted Resin Transfer Molding (heated-VARTM) is a new approach for manufacturing high quality composite laminates with minimal voids. The present study focuses on the effects of external pressure and resin flushing on the microstructural features of the laminates, including spatial variation and size distribution of the voids as well as the compaction of fiber tows. The microstructural analysis performed on glass/epoxy composites reveal that external pressure reduces void content and average void size, and leads to more uniform spatial distribution of voids. Significant increase in fiber volume fraction from ∼50% up to ∼62% and a low void content of less than 1% are achieved by applying modest gauge pressure levels up to 138 kPa on laminates with various thicknesses. The increase in fiber volume fraction coupled with low void content improves the flexural properties as much as 20%, while the short-beam shear strength of the laminates remains unchanged due to low void content in all laminates.

Modeling the inhomogeneous microstructures of fibrous tows is important for analyzing the process of resin transfer molding because dual-scale pores in a preform can lead to void formation. This study focused on the development of a microscopic flow analysis method to predict the impregnation of fiber bundles. The moving particle semi-implicit method was adopted to model the microstructure of a fiber bundle explicitly and inter-particle potential force was introduced into the numerical model to take account for the capillary effect. The predicted process of impregnation and void formation agreed with empirical observations. The developed approach was applied to predict the relationship between the modified capillary number and void content to identify the optimal molding conditions to reduce microvoids. The obtained relationship reproduced the trends of a reported experiment, which indicates that the proposed approach will provide information about optimal conditions for minimizing void content.

This study is to investigate the mechanical, hygral, and interfacial strength of continuous bamboo fiber reinforced epoxy composites. The untreated and alkali-treated continuous bamboo fibers were prepared from cutting the nature bamboo culm. The basic characteristics of the bamboo fibers, such as density, equivalent diameter, and tensile properties were experimentally measured. The bamboo fiber reinforced epoxy (BF/EP) composites were fabricated by the resin transfer molding (RTM) process with the resulting fiber volume fraction about 42%. The strength of bamboo fiber was found to decrease with the alkaline treatment. However, alkali-treated bamboo fiber reinforced epoxy composites acquired better tensile strength than those with untreated bamboo fibers. The untreated bamboo fiber was believed to have weak interface with the epoxy resin, which was verified by the subsequent interface strength tests. The size effect of bamboo fibers on the tensile properties of the BF/EP composites were also studied. The results showed that the tensile strength and Young's modulus of the composite increase with the decrease of the bamboo fiber diameter. For the hygrothermal aging test, BF/EP composites are highly sensitive to moisture absorption, and the moisture has a detrimental effect on the mechanical properties of the BF/EP composite.

The aim of this research is the production of epoxy resin composites reinforced by birch, palm, and eucalyptus fibers with resin transfer molding technique and molded fiber production technique combination. The tensile stress of birch, palm, and eucalyptus reinforced epoxy composites were determined as 29.53, 42.24, and 45.28 MPa, respectively. Bending stress of birch, palm and eucalyptus reinforced epoxy composites were found as 58.83, 68.58, and 79.92 MPa, respectively. The birch epoxy composite had 0.105 J impact energy while palm and eucalyptus epoxy composites were determined as 0.130 and 0.124 J, respectively. It is clearly observed that fiber type was very effective on the mechanical properties of composites. The results of studies showed that molded fiber production method had a very promising future for the development of natural fiber reinforced composites. © 2019 Elsevier Ltd

Resin flow correction control with electromagnetic field source, a new variation of the vacuum-assisted resin transfer molding (VARTM) process called electromagnetically induced preform resting (EIPR) for dynamical resin flow controlling is introduced to manipulate the flow front and local permeability to prevent the formation of dry spots. This paper proposes an active and real-time flow control approach that is implemented during the composite laminate infusion. The EIPR process applies an electromagnetic field source to pinch (raise) and vibrate the upper flexible mold to rest the fiber preform and increase the local permeability. Vibration action delivers the fluid through the preform. The EIPR process includes a new and creative upper flexible vacuum bag with embedded elements to lift and create local vibrations via an automated gantry system. The control methodology is performed by tracking the flow front with a real-time correction. System capability is demonstrated with three configurations of preform of different preform permeabilities in each experiment. A low permeability preform is employed in these configurations to disturb the flow pattern and cause an artificial problem or pseudo problem during the filling process. The results indicate that this system fills the mold completely and reduces the filling time without any dry spots and therefore creates no waste material.

This work aims at modeling the homogenized behavior of a polymer matrix composite reinforced with three dimensional (3D) woven fabric. The effective warp and weft tows’ properties were determined by numerical homogenization with Abaqus considering elastic fibers, a viscoelastic matrix and periodic boundary conditions. The temperature- and cure-dependent linearly viscoelastic model previously developed by the authors for this particular polymer matrix was implemented into a subroutine using a differential strategy. A second homogenization procedure was carried out to obtain the mesoscopic structure homogenized behavior. Moreover, rectangular composite plates were manufactured by Resin Transfer Molding (RTM) and isothermal creep tests were carried out to study the material’s viscoelastic behavior at high temperatures below the resin’s glass transition temperature. Experimental results were compared to the temperature-dependent homogenized linearly viscoelastic model predictions. This model is a step forward for the accurate prediction of the residual stresses developed during the manufacturing of structural parts made out of 3D woven interlock composites.

It is shown that the fabrication of large glass-fiber reinforced plastic parts by means of transfer molding technologies makes it possible to solve technical problems that cannot be solved by using other materials. The development of accessible technologies and equipment for efficient recycling of such parts will make glass-fiber reinforced plastic a sixth technological paradigm material.

In an RTM process the mold contains three constituents including fibres, a resin and a gas. Due to its similarity to a porous medium, the process can be modeled within the Theory of Porous Media (TPM), where the simulation of the moving resin front generates an inherent difficulty: In widely used approaches for mold filling simulations, that are element/control volume methods (Bruschke and Advani, 1990) and Level set methods (Soukane and Trochu, 2006), the moving resin front is either approximated roughly, such that an interface thickness of multiple finite elements arises, or respectively by a sharp interface with zero-thickness which requires a special numerical treatment. The present study intends to close this gap. To this end, we outline regularizations of the sharp interface such that the above mentioned difficulties can be overcome with a regularized sharp interface theory as a branch of phase-field models which go back to the classical Ginzburg-Landau equation. In this way, the sharp discontinuities between different phases, i.e. resin and gas, are approximated by smooth transitions of suitable order parameters, of which one is the resin fraction. Thus, the sharp interface topology as well as the surface energy of the interface are smeared out over a region proportional to a chosen regularization length scale. As an additional advantage, the phase-field method facilitates a thermodynamic treatment of phase interfaces rendering it more physically consistent in combination with the TPM, which also works within a thermodynamically sound framework. To this end, a coupled finite-element strategy is presented accounting for both, a Ginzburg-Landau- and Cahn-Hilliard-type regularization scheme for the interface. Two boundary value problems are formulated in the context of the TPM. They consider a multiphase-system, represented by deformable fibres interacting with the resin saturating the pores, that is coupled to one of both regularization schemes. Accordingly, two numerical examples demonstrate the capabilities of both regularized formulations by simulations of an RTM process.

Composite materials are becoming the most useful material for aircraft structures. Their main advantage is connected to the possibility of deeply reducing weight and costs by maintaining high performances in terms of strength and security. The second major advantage in using this them depends on the possibility they could be proper designed to guarantee services they are made to. Many ways to combine them lead to the necessity of planning experimental tests in order to evaluate the real both elastic and plastic mechanical properties and to compare their variability as function of the fiber type, matrix type and manufacturing technology involved for realizing them. In this paper, a comparison between two innovative Carbon Fiber Reinforced Plastic materials was done. They differ, one from each other, for the matrix type (PEEK and BENZOXAZINE) and for the manufacturing process used to assemble the matrix with the reinforcement (Compression Molding and Resin Transfer Molding). On the other hand, the resin percentage weight content of both materials is maintained constant for all the tests: it is 42% for PEEK matrix and 64% for BENZOXAZINE matrix. The aim of the work is to critically analyze the results in order to get useful information for choosing the best one intended for designing and making the back section of fuselage of a regional aircraft. The component will consist of a front portion with structural aims (zoom phase) and a back part able to withstand to elevated temperatures.

The manufacturing of fiber composite materials involves a set of complex, interconnected processes that span across multiple physics and scales. The characterization of uncertainty in composite manufacturing predictions is a challenging task that involves high-dimensional, multiscale, multiphysics stochastic models. We demonstrate the use of a basis adaptation scheme within a polynomial chaos representation that permits the incorporation of a large number of stochastic variables in the analysis. We use the proposed PCE-based workflow to analyze the interplay of uncertainty through all the fiber composite manufacturing stages that comprise the Resin Transfer Molding (RTM) process. The proposed framework is centered on an integrated assessment of uncertainty in composite structures using probabilistic surrogate models for predefined QoI.

A novel low-melting, low-viscosity, one-part bismaleimide resin based on m-xylylene bismaleimide has been developed and examined for application in vacuum-assisted resin infusion. The resin is a fully formulated system comprising a ternary eutectic BMI mixture blended with bis-( o-propenylphenoxy)benzophenone and 2,2'-bis(3-allyl-4-hydroxyphenyl)propane as co-monomers. The resin offers enhanced properties for melt processing techniques. The formulation strategy and chemistry is presented and discussed in detail. For resin infusion and/or resin transfer molding technologies, the melt processing temperature of the resin is in the range of 90–110℃. Processing data of the uncured and mechanical properties of cured neat resin are provided. The resin shows a Tgof 285℃ when post-cured at 250℃ for 6 h. Finally, a 400 × 500 mm2carbon fabric laminate was successfully molded for demonstration by a VARI process. The microscopic study reveals no voids and no laminate surface imperfections. The VARI processing details are presented and discussed.

The low-velocity impact behavior of polyester glass fiber composite laminates has been investigated under different clamping conditions, by wetting the specimens surface with fluids having different densities. Unidirectional composite laminates, based on polymer resin and fibers of naval interest, with different thicknesses have been manufactured by resin transfer molding process in order to have a high control of the final properties and a high fiber volume fraction. Impact tests in air have been, first, performed up to penetration on all manufactured composites having four different thicknesses to get information on the material impact behavior. The effect of the clamping conditions and the interaction of the laminates with two fluids different in density, i.e., water and paraffin oil, have been investigated, then, only on the thickest laminates that showed a lower tendency to impact damage. In particular, the impact tests have been performed by impacting the front surface of the sample and by wetting the back surface of the composite samples under unclamped and clamped conditions, replicating the boundary constraints suggested by ASTM D7136 Standard for the conventional impact tests. Experimental results showed a lower initial rigidity, higher absorbed energy and deflection for specimens exposed to liquids with respect to those exposed to air, confirming the need of taking into account the fluid interaction in the case of marine composite applications.

Lately, natural fibers have been gaining consideration in development of composites due to its biodegradability, availability and low-cost compared to synthetic fibers. Natural fibers are renewable sources, biodegradable, environmentally friendly and effortless in machinery. In this paper, the manufacturing of production for natural fiber reinforced polymer composite (NFRC) will be reviewed. These including injection molding, resin transfer molding (RTM), pultrusion, sheet molding compound (SMC) and compression molding processing technique. Injection molding and compression molding are mostly used in industry. This is due to the machines give a good finishing surface of the products and low cost.

The objective of this study is to investigate a novel methodology for the in situ light resin transfer molding manufacturing of sandwich panels in which the poly(ethylene terephthalate) foam core is reinforced by transverse polymeric pins used to improve both flatwise compressive and flexural strength of the foam. The foam cores were pre-drilled, and these holes were later filled with resin during the light resin transfer molding production of the panels. Five types of samples were evaluated: control (core without pins) and reinforced cores with variable pin diameters and distances. Both experimental and numerical results are presented, and good agreement between them was achieved. Pin diameters below 3 mm lead to failure by local buckling, whereas diameters larger than 4 mm showed manufacturing issues related to the incomplete formation of pins.

International audience; The objective of this paper is to develop a global modelling approach, that simulates both the resin transfer molding (RTM) manufacturing and the prediction of the effective thermal conductivity (ETC) of a carbon–cpoxy (CE) laminated composite reinforced with particles. This numerical approach is based on two main stages. First, a numerical simulation of the suspension flow and the filtration of the charges during the RTM process. A method, for simulating the flow of a resin, loaded with particles in suspension through a fibrous medium, considering its double porosity scale, has been proposed. It is based on the description of the flow by Stokes–Darcy coupling, filtration phenomenon and particle dynamics. Secondly, the ETC of the composite thus produced is evaluated using a numerical homogenisation technique, considering the spherical particles inserted into the carbon–epoxy laminated composite. These obtained results have shown that, the incorporation of particles in the laminated composite leads to a significant increase in their effective thermal conductivity, which depends on their thermal conductivity. Finally, a simple linear thermal model has been proposed to predict the effective thermal conductivity of the composite carbon–epoxy–particles, as a function of that of the base composite carbon–epoxy and that of the particles.

This paper is concerned with the improvement of a tensile test method and the material properties of carbon fiber reinforced polymer manufactured by resin transfer molding considering stacking sequences at various strain rates for auto-body. Auto-body structure experiences the strain rates up to several hundreds per second during car crash. In order to apply the carbon fiber reinforced polymer panel into auto-body structures, it is critical to acquire the material properties of carbon fiber reinforced polymer at various strain rates considering stacking sequences. The tensile test method is improved for acceptable test results. Test specimens are modified for high-speed tensile tests of carbon fiber reinforced polymer in order to achieve designated strain rates and eliminate the effect from unfavorable conditions of inhomogeneity of deformation. Various types of grip tab materials are employed for acceptable failure modes. Tensile tests have been carried out with non-crimp fabric made by 50K high strength carbon fiber (NCF) and woven fabric made by a 2/2 twill pattern of 3K high strength carbon fiber (TWILL) with different stacking sequences of 0° and 90° unidirectional cases as well as [0°/90°] and [45°/−45°] symmetric cases. Digital image correlation method and force equilibrium grid method are adopted for strain and stress measurement of a carbon fiber reinforced polymer specimen during a tensile test. The material properties acquired indicate that the carbon fiber has little rate dependency, while the epoxy matrix has remarkable rate hardening at strain rates from 0.001 s−1to 100 s−1.

The laminated joints used in this work were adhesive joints constructed using two dry carbon fiber halves. Some improvements were introduced to the joints to enhance their bending strength performance: stitching of the two halves together by fiber bundles and inserting extra carbon fiber covers in the joint connection. We studied three adhesive joints: a conventional basic and two improved laminated joints. All joint specimens were fabricated using a vacuum-assisted resin transfer molding (VARTM) process. The joints were evaluated with a bending test, and were compared to the bending strength of a jointless carbon fiber reinforced plastic (CFRP) laminate. Two acoustic emission (AE) sensors were placed on the specimen to monitor the fracture progresses during the test. The improved laminated joints, stitched and multiple-cover overlapped joints, showed enhanced bending strength and joint efficiency. The improvement depended significantly on the number of carbon fiber layers. The maximum increase was 24% for the stitched laminated joint of 5 layers and 58% for the multiple-overlapped joint of 6 layers, respectively. Such high joint efficiency was due to the effect of the carbon fiber reinforcement on the joints, by which many carbon fibers supported the strength in advance of reaching the maximum load point, as confirmed by AE measurement analysis.

A drastically growing requirement of electronic packages with an increasing level of complexity poses newer challenges for the competitive manufacturing industry. Coupled with harsher operating conditions, these challenges affirm the need for encapsulated board-level (2nd level) packages. To reduce thermo-mechanical loads induced on the electronic components during operating cycles, a conformal type of encapsulation is gaining preference over conventional glob-tops or resin casting types. The availability of technology, the ease of automation, and the uncomplicated storage of raw material intensifies the implementation of thermoset injection molding for the encapsulation process of board-level packages. Reliability case studies of such encapsulated electronic components as a part of board-level packages become, thereupon, necessary. This paper presents the reliability study of exemplary electronic components, surface-mounted on printed circuit boards (PCBs), encapsulated by the means of thermoset injection molding, and subjected to cyclic thermal loading. The characteristic lifetime of the electronic components is statistically calculated after assessing the probability plots and presented consequently. A few points of conclusion are summarized, and the future scope is discussed at the end.

The high-pressure resin transfer molding (HP-RTM) process has potential applicability to the mass production of lightweight vehicles made of carbon fiber-reinforced plastic in the automotive indust...

Manufacturing defects are an issue of composite manufacturing processes. Local clamping is proposed to prevent fiber washout during high pressure resin transfer molding of non-crimp fabrics. At the clamping regions the material is compacted by through-the-thickness compression. The current work investigates the mechanical performance of such regions under static and fatigue loading. Two typical manufacturing defects are intrinsic to the compacted regions: fiber undulation and resin starved/dry spots. In component tests the thereby generated damage is monitored using 3D digital image correlation and the complete processes of damage initiation and propagation are analyzed. Static and low cycle fatigue failure are dominated by fiber undulation at the edges of the compacted region, triggering matrix damage and delaminations. High cycle fatigue is dominated by decreasing fiber matrix adhesion within the compacted region, leading to longitudinal splitting and progressive fiber failure. Identification of damage initiation is supported by numerical finite element simulations.

Zinc oxide nanorod (ZnO NR)-grown woven carbon fiber/polyamide 6 composites were fabricated using hydrothermal synthesis and thermoplastic resin transfer molding. The in-situ polymerization of e-caprolactam, which exhibits extremely low viscosity and high reaction speed, enabled excellent penetration of the resin into the densely grown ZnO forest on the carbon fibers. This further increased the mechanical interlocking and chemical interaction between the fiber and resin, leading to enhanced interfacial bonding. By increasing the number of oxygen functional groups and the surface roughness of the fiber surfaces through an atmospheric plasma treatment, the ZnO NRs were observed to grow even with very low growth-solution concentrations (20 mM), fewer seed cycles (4), and a short hydrothermal treatment time (4 h). By using the plasma-treated carbon fibers for ZnO NR growth, the impact resistance and in-plane shear strength were enhanced by up to 72 and 50%, respectively, as compared to carbon fiber composites without ZnO NRs, while the use of ZnO precursors and growth time was minimized.

Current manufacturing processes using resin transfer molding or low-pressure prepreg curing may result in different defects and interfacial properties. The effect of autoclave pressure on the delamination behavior of T800/X850 composite laminates is explored. Cohesive zone model was used to model the delamination of unidirectional composite laminates under short-beam bending. Composites with various interlaminar properties were manufactured using autoclave under cure pressure from 0 MPa to 0.6 MPa. Cohesive zone model was validated using the material parameters of the composite cured under 0.6 MPa. The effect of cohesive zone model parameters including cohesive strength, mode I fracture toughness ([Formula: see text]), and mode II fracture toughness ([Formula: see text]) on the delamination behavior and load–displacement response was investigated. Parametric study shows that interlaminar cohesive strength and mode II fracture toughness dominated the initiation of yield and post-yield region, respectively. The correlation between autoclave pressure and mode II fracture toughness was predicted, which is mainly affected by void content.

The flexibility of processing PA6-based discontinuous carbon fiber panels using vacuum-assisted resin transfer molding was studied. The ease of incorporating various reinforcements namely baseline, tow in the center of preform, fabric in the center of preform and fabric on the outside as skin was investigated. Mechanical characterization was conducted on all the variations made. There was an average increase of about 3%, 20% and 47% in the tensile properties of tow in the center, fabric in the center and fabric on the outside as skin, respectively, as compared to the baseline. A similar increase in properties was noticed in its flexural and impact strength. The data showed a correlation between the mechanical properties and the total surface area of additional reinforcements used. As the surface area of the reinforcement increased, the mechanical properties increased as well. It also showed that reinforcements on the surface of the preform as a skin performed the best. DMA analysis showed the effect of reinforcement on the storage modulus and tan delta across temperatures ranging from 30°C to 150°C. SEM analysis showed that the fibers and the additional reinforcements were coated with PA6 which translated into consistent mechanical performance.

The application of Fiber Reinforced Thermoplastics (FRTP) is expected to reduce the weight of automobiles. The press and injection hybrid molding method was developed to mold FRTP with high strength and high stiffness by giving complicated shapes such as ribs and bosses to the outer shell structure of FRTP with continuous fiber. However, as this method uses high-cost FRTP laminated sheets, it is necessary to develop a low-cost FRTP manufacturing process. In this study, we aim at the development of Melted Thermoplastic-Resin Transfer Molding (MT-RTM) to mold FRTP with complicated shape at low cost by injecting melted short fiber reinforced thermoplastics into dry fabric. The effects of press condition on the mechanical properties of GFRTP molded by MT-RTM were clarified by bending tests. GFRTP molded at high mold temperature and high closing speed showed high mechanical properties because of good impregnation of injection resin into continuous fabric in the outer shell structure.

This study investigated the effect of moisture absorption on the mechanical performance of polyurethane sandwich composites. The core material was a closed cell polyurethane foam. Face sheets were made of E-glass/polyurethane composite laminates. Vacuum-assisted resin transfer molding process was used to manufacture specimens for testing. The foam core, laminates, and sandwich composites were submerged in salt water for prolonged periods of time. Mechanical property degradation due to moisture absorption for each constituent was evaluated. Compression test was performed on the foam core samples. Laminates were evaluated by three-point bending tests. The interfacial bond strength in the sandwich structure was evaluated by double cantilever beam mode-I interfacial fracture test. The testing results revealed that the effect of salt water exposure on the compressive properties of the foam core is insignificant. The flexural modulus of polyurethane laminates degraded 8.9% and flexural strength degraded 13.0% after 166 days in 50% salinity salt water at 34°C conditioning. The interfacial fracture toughness of polyurethane sandwich composites degraded 22.4% after 166 days in 50% salinity salt water at 34°C conditioning.

Transverse compaction and geometric conformation of fiber reinforcements have a significant importance in the production of complex dry fiber preforms for the resin transfer molding (RTM) process. This work investigates for the first time the planar compaction and preforming of two reinforcements made from aligned flax yarns held together by a thin layer of short kraft pulp or flax fibers. Planar compaction tests have been carried out in order to evaluate the influence of temperature, pressure, humidity and number of layers of reinforcement on the creep percentage, thickness recovery and permanent deformation of reinforcements. Next, the effect of process parameters on the quality of a complex 3D preform was evaluated. It appears that temperature, pressure and humidity increase the permanent deformation while the number of layers acts inversely. In addition, hot and wet made preforms have better dimensional stability (dimensions and geometry) than preforms obtained under other conditions.

High-speed molding of continuous carbon fiber-reinforced composites was carried out by thermoplastic resin transfer molding using a very-low-viscosity thermoplastic monomer. After dispersing 0.1 wt.% of various nanomaterials in e-caprolactam, a monomer of anionic polymerized polyamide 6 (A-PA6), the processing temperature and catalyst-activator contents were optimized based on the polymerization induction time required for resin injection in the mold. Additionally, the dispersion stability, solidification time, monomer conversion, crystallinity and mechanical properties of the composites were evaluated. Higher dispersion stability of the nanomaterials in A-PA6 resulted in a significantly shortened process cycle time – on the order of seconds –and higher crystallinity in the composite. In addition, carbon fibers treated with atmospheric plasma were used to increase the rate of resin impregnation into fibers. These factors not only increased composite fabrication productivity but also enhanced its mechanical properties.

In this study, a simplified cost effective simulation-based methodology is proposed to assist manufacturing engineers in the design and development phase of the resin transfer molding process. Race-tracking is unavoidable in the resin transfer molding and can lead to entrapment of air pockets, which results in parts being discarded as scrap. A purely numerical methodology is presented to distinguish between the critical and non-critical race-tracking scenarios, that will guide the design and production engineers plan an efficient and effective manufacturing strategy. The detection methodology is based on computing the pressure evolution with time during the injection process. The novelty relies on the superimposition of the computed pressure gradient maps that reveals unsuspected common features in the numerous race-tracking cases investigated in the various geometries of increasing complexity considered. The pressure sensors are meant to detect and evaluate different race-tracking scenarios and their level of criticality. The minimum number and locations of pressure sensors arise directly from the highest pressure gradient zones for simple geometries. Sensors placement guidelines are introduced for a simple rectangular shape, then this information is used to qualitatively apply the guidelines to parts of more complex shapes. A general rule that all parts, no matter how complex, can be considered as a combination of simpler ones is presented. Furthermore, a new failure criterion is proposed based on the flow patterns that highlights the likely flow patterns to entrap voids.

Various morphologies of α-MnO2 nanostructures were synthesized on the surface of woven Kevlar fiber (WKF) by hydrothermal method under different reaction conditions. Reduced graphene oxide-polyaniline nanofiber (RGO-PANI) arrays were synthesized by an in situ dilute polymerization technique and then dispersed within polyester (PES) resin. High-performance composites based on α-MnO2-grown WKF and RGO-PANI array-dispersed PES were fabricated with effective microwave-absorbing and mechanical properties by vacuum-assisted resin transfer molding (VARTM). WKF/MnO2 nanofibers/PES/PANI-RGO (2%) composites showed superior electromagnetic parameters in the frequency range of 1–18 GHz. The reflection loss (RL) of WKF/MnO2 nanofibers/PES/PANI-RGO (2.0%) was −36.5 dB at an absorbing frequency of 11.8 GHz, which has not been reported before. A higher tensile strength (160.12%), modulus (104.43%), and absorbed impact energy (207%) were observed for α-MnO2 nanofibers, compared with other morphologies of α-MnO2-incorporated WKF composites and the properties were enhanced with an increased percentage of PANI-RGO.

The epoxy nanocomposites with Fe3O4 modified graphene oxide (Fe3O4/GO) were used to influence the micro-cracks resistance of carbon fiber reinforced epoxy (CF/EP) laminate at 77 K. Fe3O4/GO with good paramagnetic properties were prepared by co-precipitation method and used to modify epoxy for cryogenic applications. Fe3O4/GO modified CF/EP laminates were also prepared through vacuum-assisted resin transfer molding (VARTM). The results show that the Fe3O4/GO can effectively improve the mechanical properties of epoxy (EP) matrix at 77 K and reduce the coefficient of thermal expansion (CTE) of EP matrix. It also can obviously improve the micro-cracks resistance of CF/EP composites at 77 K. Compared to neat EP, the CTE of Fe3O4/GO modified EP composite is decreased 51.6%. Compared to CF/EP composite, the micro-cracks density of Fe3O4/GO modified CF/EP composite at 77 K is decreased 60.0%.

The main objective of this work was an experimental investigation making it possible to monitor, as well as achieve a deeper understanding of, the structural evolution of polyamide-6 as a thermoplastic-based composite matrix. Polyamide-6 from anionic ring-opening polymerization (AROP) of e-caprolactam was chosen as a model matrix. Throughout this work, various formulations of PA with anionic polymerization from caprolactam were studied depending on different activator/catalyst pairs, concentrations and combinations. Moreover, chemorheological properties were first determined ex-situ by rheology coupled with FTIR and microdielectrometry. The extent of the reaction conversion was thus obtained and subsequently modeled. The formed PA6 matrix materials were fully characterized in terms of their viscosimetric properties and molar masses. In a second step, a hybrid extrusion resin transfer molding machine (T-ERTM) with an instrumented mold was designed for the in-situ monitoring. Thereby, specific dielectric sensors were used to follow the different processing steps for the manufacturing of complex and continuous glass fiber-reinforced parts. Furthermore, the reaction kinetics in competition with the crystallization were probed and quantified as a function of the processing parameters (mold temperature, times given for impregnation, time for demolding etc.). Calibration curves were obtained in which the ionic conductivity was correlated to the change of viscosity determined previously from ex-situ measurements. Indeed, a processing window was proposed for each PA6 system to ensure a good preform impregnation. Interestingly, the apparent conversion calculated from the online dielectric measurements corroborated the ex-situ values obtained from chemorheological studies. The viscosity and conversion evolution were then tracked in the mold. Based on the present findings and for the optimal formulation, a Time-Temperature-Transformation (TTT)-equivalent diagram was established from online measurements and related to the reactive processing to get a better handle on the PA6-based composite.

We present the development of a high-performance flame-retardant vinyl ester (FR-VE)/flax fabric (FF) biocomposite through a hybrid approach using vacuum-assisted resin transfer molding. FF was modified to form FR fibers (mFF) using surface treatment with varying amounts (5–20%) of ammonium polyphosphate (APP), and the FR-VE/mFF composites were fabricated by including flame retardants such as chitosan (CS), APP, and modified CS (NCSAPP). The optimized mFF (15% APP) exhibited enhanced thermal stability (38 wt% residue at 700 °C) and it achieved a V0 rank in the UL 94 test. In addition, the dual effects, i.e., the effects modification of the reinforcement and inclusion of the FRs into the matrix, improved the properties of the FR-VE/mFF composites, providing them with high thermal resistance (28 wt% residue at 700 °C), and fire resistance (V0 rank in the UL 94 test), and self-extinguishing characteristics with a suppressed peak heat release rate (69%), total heat release, and smoke production rate.

Liquid composite molding (LCM) simulations for processes such as resin transfer molding (RTM) and vacuum assisted resin transfer molding (VARTM) face serious challenges while modelling resin flow through dual scale fabrics such as bi-directional (BD) (stitched or woven) fabrics and triaxial fabrics as it requires characterization of two permeability values: inter-tow gap or bulk permeability and tow permeability. Conventional experimental methodologies can characterize the inter-tow gap permeability by tracking the wetting resin flow front; however, there is no closed form solution that gives an expression for effective wetting permeability due to the uncertainty in determining tow permeability explicitly. If one were to have prior knowledge of tow permeability, effective wetting permeability can be formulated that can reduce the effort of experimental characterization. The current study proposes closed form permeability model for dual scale unidirectional (UD) fabric that combines both the tow and inter-tow gap permeability while taking into account the effect of partially saturated zone during dual scale flow. Thus, it accounts for the effects of inter-tow gap permeability, tow permeability and length of partially saturated zone. Comparisons of the analytic model results with numerical simulations are presented that are encouraging.

An 18-in hybrid wheel consisting of an aluminum alloy disk and a composite rim under 13° impact test is considered in this study. The rim is made of carbon fabric/polyurethane composites fabricated by resin transfer molding. Explicit finite element analysis with progressive failure function is used to investigate the failure situation of the hybrid wheel and the suitable braid angle of the braided composite. The effective elastic constants and strengths of the braided composites predicted by basic finite element analyses are adopted, whereas the true stress–strain curve of aluminum is used for the disk. Simulation results indicate that the aluminum alloy disk is safe after the impact test, whereas the rim is damaged. The volume of failed elements after impact simulation is selected as an indicator to obtain a quantity that can be used to represent the damage situation of the rim. Compared with the test results of a real hybrid wheel with [±30°] fiber angle in the rim, the hybrid wheel with fiber angle in the rim that is greater than [±30°] could pass the impact test.

A novel sandwich-structured composite comprising a three-dimensionally (3D) printed core and a woven carbon fiber/polyamide-6 facesheet was fabricated and characterized. By using selective laser sintering, which is a 3D printing technology, a structurally reinforced honeycomb-truss hybrid core was produced, which had superior compressive stiffness in various directions compared with conventional honeycomb cores. The interface between the core and the facesheet was enhanced by laser power control during the sintering as well as plasma surface treatment. The sandwich composite was produced by the reactive thermoplastic resin transfer molding (T-RTM) technique using anionic polymerization of e-caprolactam, which has an ultra-low viscosity in the molten state. This in-situ polymerization not only enabled manufacturing process simplification by combining fabrication and bonding processes of the facesheet, but also provided excellent resin impregnation into the fiber fabrics and core surface. Therefore, the 3D printing technology, interfacial strengthening techniques, and T-RTM process induced synergistic effects on mechanical properties of the sandwich composite by forming structural reinforcement and strong mechanical and chemical interactions. The edgewise compressive properties of the hybrid core were significantly better than those of a normal honeycomb core. In addition, the interlaminar fracture toughness, impact energy absorption, and penetration limit of the sandwich composite consisting of the structurally and interfacially strengthened hybrid core increased by 76, 77, and 125%, respectively, compared to those of a nonreinforced sandwich composite.