Preform Permeability Research Articles

Cyclic pressure on compression-moulded bioresorbable phosphate glass fibre reinforced composites

The use of thermoplastic composites based on poly(lactic) acid and phosphate glass fibres over metallic alloys for clinical restorative treatment is highly beneficial due to their biocompatibility and biodegradability. However, difficulties in achieving a thorough melt impregnation at high fibre contents while limiting polymer degradation is one of the main issues encountered during their manufacture. This paper reports for the first time on the effects of pressure cycling on the mechanical properties of compression moulded polylactic acid-phosphate glass fibre composites. The strength of the composites consolidated under pressure cycling were at least 30% higher than those in which conventional static pressure was used. The marked disparity was attributed to the influence of pressure cycling on the fibre preform permeability, the melt viscosity and the capillary pressure, leading to improved fibre wet-out with respect to static pressure. Implementation of a cyclic pressure appeared to promote the occurrence of transcrystallinity in the polymer matrix as suggested by DSC traces. The fibre content influenced PLA thermal degradation since the matrix molecular weight decreased as the fibre content increased on account of the moisture adsorbed by the glass surface. However, this extent of degradation did not impair the matrix mechanical performance in the composites.

Determination of the unsaturated through‐thickness permeability of fibrous preforms based on flow front detection by ultrasound

The permeability of fibrous preforms used as reinforcements for fiber‐reinforced polymeric composites is a decisive parameter for simulation‐based predictions of common defects that occur during the filling process. This study focuses on the transverse permeability which becomes important for high thickness parts. An instrument that detects the transverse flow front by ultrasound and determines the transverse permeability has been developed. In contrast to other approaches, the developed permeameter uses a nondeflecting (metallic) tool while the selected sensing method is nonintrusive to the material. Novel electromechanical features allow a wide range of measurable preforms. The remaining limitations of the system have been identified and the model that correlates raw ultrasound measurements with flow front has been verified by visual observations. The transverse permeabilities of 18 different preforms have been determined in an experimental scheme designed to isolate the influence of preform thickness. POLYM. COMPOS., 39:360–367, 2018. © 2016 Society of Plastics Engineers

Cyclical pressure on compression-moulded bioresorbable phosphate-glass fibre reinforced composites

Event Abstract Back to Event Cyclical pressure on compression-moulded bioresorbable phosphate-glass fibre reinforced composites Fernando Barrera Betanzos1, Miquel Gimeno Fabra1, David Grant1 and Ifty Ahmed1 1 University of Nottingham, Materials, Mechanics and Structures, United Kingdom Introduction: The use of composites based on poly(lactic) acid ‘PLA’ and phosphate glass fibres ‘PGF’ to replace metallic devices used for bone fracture repair has been deemed as highly beneficial due to their excellent biocompatibility and biodegradability. However, difficulties in achieving thorough melt impregnation whilst limiting polymer degradation during manufacture has been one of the main issues precluding their implementation. Therefore, alternative manufacturing techniques, other than those involving temperature or time increases that improve fibre wet-out will inevitably pave the way for product adoption. Materials and Methods: PGF with the composition 45P2O5-16CaO-13Na2O-24MgO-2Fe2O3 mol.% were melt drawn to fabricate unidirectional composites of 4 volume fractions vf (0.15, 0.25, 0.35, 0.45) by alternately stacking layers of PGF and PLA films inside a purpose-built compression moulding tool. The mould was placed into a heated press at 180°C for 10min, followed by consolidation for additional 10min following two loading schemes: i) static pressure ‘SP’ (pressure held constant at 40 bar) and, ii) cyclical pressure ‘CP’ (pressure cycled for 1.5min at the end of the consolidation stage). Finally the system was cooled under constant pressure. Composite mechanical properties were evaluated via 3-point bending test. Effects of pressure profile on the crystallisation kinetics were assessed through Differential Scanning Calorimetry. PLA thermal degradation was evaluated via Advanced Polymer Chromatography. Results and Discussion: In all cases the flexural strengths of CP composites were approximately 30% higher than those in which SP was implemented (cf. Figure 1). This was explained by the CP ability to affect fibre network permeability through relaxation and reapplication of pressure, leading to improved impregnation. CP could also alter the melt viscosity and the capillary pressure. The CP composites mechanical properties were found to be the highest reported up to now for this composite system (ca. 480 MPa and 23 GPa for flexural strength and modulus respectively for the 0.45 vf) and even greater to cases were the fibre was treated with coupling agents [1][2][3]. The observance of a crystalline shoulder in the DSC traces (Figure 2) suggested transcrystallinity formation exclusively in the CP composites, probably as a result of the local chain alignment induced by the pulsating motion, and possibly accounting for enhanced stress transfer. The PLA molecular weight showed a maximum reduction of 20% in the case of the 0.45 vf composite due to the moisture absorbed by the hydrophilic glass surface. The extent of degradation did not deleteriously affect the PLA mechanical properties in the composites. Figure 2.- Influence of the pressure profile on composites flexural strength with progressively higher fibre content (error bars indicate ± standard deviation). The blue dashed line represents the theoretical composite strengths calculated using the rule of mixtures. Figure 4.- DSC traces of representative samples of (upper) Cycled Pressure and (down) Static-Hold Pressure composite series. Insert shows an enlarged view of the cold crystallisation peaks for both composite series. Conclusion: Implementation of cyclical pressure during the consolidation stage of compression moulding led to enhanced fibre impregnation with limited PLA thermal degradation due to its influence on the fibre preform permeability, melt viscosity and capillary pressure. Additionally, cyclical pressure appeared to promote the development of transcrystallinity which may further enhance mechanical properties upon annealing. Consejo Nacional de Ciencia y Tecnología (CONACYT); MeDe Innovation

A New Fiber Preform with Nanocarbon Binder for Manufacturing Carbon Fiber Reinforced Composite by Liquid Molding Process.

Carbon fiber reinforced composite has been a good candidate of lightweight structural component in the automotive industry. As fast production speed is essential to apply the composite materials for the mass production area such as automotive components, the high speed liquid composite molding processes have been developed. Fast resin injection through the fiber preform by high pressure is required to improve the production speed, but it often results in undesirable deformations of the fiber preform which causes defectives in size and properties of the final composite products. In order to prevent the undesirable deformation and improve the stability of preform shape, polymer type binder materials are used. More stable fiber preform can be obtained by increasing the amount of binder material, but it disturbs the resin impregnation through the fiber preform. In this study, carbon nanomaterials such as graphene oxide were embedded on the surface of carbon fiber by electrophoretic deposition method in order to improve the shape stability of fiber preform and interfacial bonding between polymer and the reinforcing fiber. Effects of the modified reinforcing fiber were investigated in two respects. One is to increase the binding energy between fiber tows, and the other is to increase the interfacial bonding between polymer matrix and fiber surface. The effects were analyzed by measuring the binding force of fiber preform and interlaminar shear strength of the composite. This study also investigated the high speed liquid molding process of the composite materials composed of polymer matrix and the carbon fiber preforms embedded by carbon nanomaterials. Process parameter such as permeability of fiber preform was measured to investigate the effect of nanoscale surface modification on the macroscale processing condition for composite manufacturing.

Study on correlation between permeability and structural parameters of non-crimped fabrics

It is a challenge to predict the permeability due to the complex correlation between the permeability and structural parameters of fabric preform. In this paper, the correlation between the in-plane permeability and the structural parameters of the non-crimped fabrics is investigated by using the finite element method. The effect of the intra-ply structural parameters and ply orientations on the in-plane permeability of the fabric preform is investigated. In addition, the influence of four structural parameters on the in-plane permeability is analyzed by the Morris method. The results show that the in-plane permeability is most sensitive to the distance between fiber bundles, while the semi-major axis length of the ellipse section of the fiber bundle is relatively insensitive. The order of the in-plane permeability of non-crimped fabrics preform with different ply orientations is as follows: [0]2 > [0/90] > [−45/45]. The present research is helpful to predict permeability and to further simulate resin filling process.

Process-Oriented Determination of Preform Permeability and Matrix Viscosity during Mold Filling in Resin Transfer Molding

The resin transfer molding (RTM) offers great conditions for mass production of fiber reinforced plastics. In this process, preformed fiber textiles are infiltrated with matrix material (for example: epoxy resin). During the infiltration, the matrix material starts a curing process until the complete consolidation. After the de-molding and a short post-processing step, the final part is ready to use. To reduce the cycle time for the RTM manufacturing, it is necessary to model and predict the flow behavior of the matrix material in a realistic way. An important parameter is the preform permeability, which characterizes the flow resistance of fibers against the flowing matrix material.In this study a new measurement setup is presented, which is able to determine the permeability directly during the manufacturing process, with integrated pressure and temperature sensors. This approach has many advantages against conventional measurement setups, that try to recreate the RTM process with a simple replication. With these replicas, it is only possible to simulate low flow velocities and pressures. Dynamic effects that occur at higher velocities cannot be regarded. Furthermore, the new setup has the advantage that measurement artifacts, like capillarity, have a lower impact. In addition to that, the infiltration can be done with a constant viscosity test fluid as well as with reactive matrix material. Thus, it allows further determination of the time depending viscosity.

A novel mold design for one-continuous permeability measurement of fiber preforms

One-continuous permeability measurement experiments allow measuring permeability of a fiber preform within a range of fiber volume fractions by conducting a single unsaturated (a.k.a. transient) flow experiment on a dry specimen at an initial thickness, and a set of saturated flow experiments on the wetted specimen by varying the thickness of the mold cavity. This approach allows quicker database construction and reduces the effect of inherent variation of fabric structure caused by inconsistent labor on permeability. In this study, the drawbacks of previous mold designs are eliminated by using appropriate sealing, gap thickness adjustment mechanism and features that allow straightforward and reliable manual operation. Experiments for three different fabric types are conducted and the results are discussed. It is mainly observed that the unsaturated permeability is higher than the saturated permeability.

A numerical study of the influence from architecture on the permeability of 3D-woven fibre reinforcement

Various modelling aspects of the permeability of three-dimensional (3D) woven textile preforms are studied using computational fluid dynamics (CFD). The models are built using a recently developed technique able to generate close to authentic representations of 3D textile arrangements. One objective of the study is to investigate how parameters such as the tow architecture and the level of detail in the CFD models influence the results. A second objective is to investigate how the inter and intra-tow porosity affect the permeability. They are varied in a way that somewhat resembles how they would change during compaction, although compaction as such is not modelled. It is concluded that the intra-tow porosity has little effect on the overall permeability of a 3D-woven preform. Detailed modelling of local variation of the intra-tow porosity is thus redundant, which is also demonstrated. The inter-tow porosity, on the other hand, has a prominent influence on the overall permeability. The overall permeability is inherently anisotropic but when the inter-tow porosity is increased the permeability does not increase uniformly but becomes more isotropic. Good agreement is obtained between the numerical simulations and experiments performed in a parallel study.

Characterisation of woven flax fibres reinforcements: Effect of the shear on the in-plane permeability

This paper describes a method to characterise the influence of in-plane shear on the permeability of fibrous preforms used in liquid composite moulding processes. An optical method for measuring the local shear variation of the woven textile is presented and used in conjunction with an in-plane permeability measurement system. Two flax fibre fabrics were tested and compared with a woven glass fibre fabric of similar architecture. The system presented here can be used either as a validation tool for permeability prediction models or to compile semi-empirical permeability models for the use in liquid composite moulding process simulation tools.

Experimental characterization to determine the influence of different binder systems on the preform permeability during RTM manufacturing

Experimental characterization to determine the influence of different binder systems on the preform permeability during RTM manufacturing

Permeability measurements and flow simulation for polyaniline carbon nanofibers modified nanopaper on glass fiber preform

Carbon nanofibers (CNFs) nanopapers have shown great potential to improve the surface of fiber‐reinforced polymeric composites, including providing electromagnetic interference shielding and erosion resistance. During typical resin transfer molding (RTM) process, the CNF nanopaper is incorporated into the fiber preform as a surface layer. To learn how resin flows through the fiber preform and nanopaper layer, permeabilities of the fiber preform and nanopaper need to be measured. As is well known, measuring the permeability of fiber preforms is experimentally challenging. Results usually exhibit large experimental variability. Measuring permeability of nanopapers is even more complicated. To improve the accuracy of results, permeability of CNF‐based nanopapers was measured using different experimental setups. In‐plane permeability of nanopaper was measured by both unidirectional microslit flow and radial flow approaches. Trans‐plane permeability was measured as well, using a trans‐plane flow cell and a flow visualization mold. In this article, we discuss the methods used and provide experimental results. We also conducted computational fluid dynamics simulations to study the detailed flow patterns of the nanopaper/RTM process and compared the simulated effect of the nanopaper on retarding the flow (length of the lag) with respect to the glass preform with flow visualization results. POLYM. COMPOS., 37:435–445, 2016. © 2014 Society of Plastics Engineers

Statistical Analysis of Uncertainties in Deterministic Computational Modeling – Application to Composite Process Resin Infusion Flow Model

Deterministic physics-based flow modeling provides an effective way to simulate and understand the resin flow infusion process in liquid composite molding processes and its variants. These are effective to provide optimal injection time and locations prior to gelation for given process parameters of resin viscosity and preform permeability. However, there could be significant variations in these two parameters during actual manufacturing. This paper presents simulation-based statistical analysis of uncertainties of these process parameters involved in the resin flow infusion. Two key process parameters, viscosity and permeability, and their statistical variations are examined individually and subsequently in combination for their impact on the associated injection time. Values from statistical probability distribution of the process parameters were employed to find the solution space for this engineering application through deterministic physics-based process flow modeling simulations. A bivariate confidence envelope was developed using the appropriate Cumulative Density Function for a 95% probability of successfully completing resin infusion prior to physical resin gelation time. A logistic regression model for the influence of resin viscosity and permeability on the binary response of successful resin infusion is presented and conforms well to the sensitivity analysis inferences.

Experimental Studies and Computer Simulation of Permeability Determination of Porous SiC Preforms

Permeability of SiC preform is a key parameter during the pressure infiltration studies of molten metal (Copper and Aluminium alloy) into porous SiC preforms during preparation of SiC particle reinforced metal matrix composites (MMC) with high content of SiC reinforcement. Its characterization could be quite helpful to reveal the defect formation mechanism of the composite productions and further optimize the preparation processes of such composites. The objectives of this study were to assess the pore distribution and determine the permeability of porous SiC preforms. We compared the values of permeability obtained from experimental data, calculation by Carman-Kozeny equation and simulation of micro-models. The results of experiment illustrated that permeability were 0.64 × 10-12 m2 (ε=30%), 1.76 × 10-12 m2 (ε=37%) and 10.20 × 10-12 m2 (ε=44%) respectively, which are quite similar to the value both of calculation and computer simulation. Additionally, results indicate that the permeability substantially affected by porosity and both size and shape of filling particles into SiC preform.

Resin flow monitoring inside composite laminate during resin film infusion process

In this article, a novel method of measuring resin flow front under vacuum condition is presented. The in situ monitoring system with metal hollow probe based on gas flow balance can be used in resin film infusion (RFI) process, where resin film is used and transverse flow is dominated along thickness direction of fiber preform. The diameter of the probe was chosen to increase the measuring accuracy, and the reliability of the method was evaluated by comparison of visualization experiment. Experimental results demonstrate that the method is suitable for monitoring resin flow in RFI process with and without autoclave, and can obtain the information about resin filling time, nonuniform flow front, and the permeability of fiber preform. Furthermore, by means of the established monitoring system, the influences of pressure and lay‐up sequence of carbon fiber fabric on epoxy resin flow during RFI process were investigated. In addition, resin flow pattern with changing viscosity of epoxy resin was studied. POLYM. COMPOS., 35:681–690, 2014. © 2013 Society of Plastics Engineers

Dry fiber automated placement of carbon fibrous preforms

The superior material properties of carbon fiber-reinforced composites make them especially attractive for applications in aeronautics and aerospace industries. Cost reduction and time saving are continuously driving industry, leading to new industrial challenges which include manufacturing composite structures with optimal mechanical performances using the potential of advanced processes using robotics.To produce complex part shapes, technologies implying fabric draping in a mold imply large waste amount, fabric structure variability and uncertainties concerning local fiber volume fraction amount and thus final mechanical properties. To overcome such issues and comply with cost and time efficiency, automated dry fiber placement for preform manufacturing is proposed. This approach allows to integrate many functions in a complex part thank to the ability of the robot to steer fiber tows at specific locations. The final composite part is obtained by injecting the produced preform with resin using RTM (Resin Transfer Molding) or infusion process.The presented project aims to define the influence of the process driving parameters during fiber placement on the final preform properties range. Preforms were produced using a lab-scale automated placement demonstrator. Three preforms configurations were tested to highlight the influence of the preform structure on permeability and mechanical parameters through characterization of the compression behavior and permeability of the produced preforms. Choice of configuration will affect mechanical properties on the manufactured preforms, whereas creation of open channels to enhance the flow propagation during manufacturing does not necessarily increase the preform permeability.

A new structure-related model to predict the permeability of non-crimp fabric preform

The permeability of the fabric preform is a critical input parameter for analyzing the liquid composite molding impregnation process. However, the permeability prediction is challenging due to its complex dependence on the fabric structure. In this paper, a novel analytical model is developed to predict the permeability of non-crimp fabric preform based on the relation between the pressure drop and geometric parameters of the microchannel cross section. The model takes into account four structural parameters including the width, the height, the semi-major axis length of the ellipse section of fiber bundle and the distance between fiber bundles. The permeability of the unit cell is calculated by the presented analytical model and the finite element simulation, respectively. The results show that the channels between fiber bundles play an important role in determining the fabric permeability. The structural parameters of the unit cell have important effects on the permeability. The new structure-related permeability model can accurately predict the permeability of the non-crimp fabric preform in a certain range.

Characterization of 3D fiber preform permeability tensor in radial flow using an inverse algorithm based on sensors and simulation

In Liquid Composite Molding (LCM), the fiber preform is placed in a mold and resin is injected through a gate to fill the empty spaces within the mold. LCM processes are modeled as resin flow through fibrous porous media in which if one knows the permeability values, one can determine the arrival times of the resin at any location. A mold with radial injection with 192 flow arrival detection sensors along 16 radial lines are mounted flush with the top and the bottom mold surface with an additional sensor on the top surface opposite to the injection hole of the bottom surface. The inverse problem addressed here is from the recorded resin arrival times at sensor locations, how accurately can one determine the permeability of the preform? The proposed method uses correlation between the experimentally recorded resin arrival times and 3D flow simulation of the experiment. The optimization routine varies the permeability components in the simulation to achieve the best possible match with the experimental arrival times at all the sensor locations. Currently, all in-plane permeability components and through-the thickness permeability are characterized from a single experiment with the potential to evaluate the cross-thickness off-diagonal terms as well. In addition, the technique also demonstrates how one can reduce the variation in through thickness permeability by the use of a distribution media at the injection hole to avoid blockage of the inlet by the fiber tows. The optimization routine sequentially optimizes the values of the individual components of the permeability tensor using golden search method, and then repeats the entire sequence until the best match is found. The validation and sensitivity of this method is explored and it has been shown that this technique is promising for characterization of all permeability components from a single radial flow experiment.

Experimental Study on Planar Unidirectional Permeability of Glass Fiber Preforms at Constant Flow Rate

During the resin flow of Resin Transfer Molding, the permeability of fiber performs is an important parameter, which reflects the interaction between the resin and fiber. In this paper the Darcy’s law was used as the fundamentals to determine the permeability of fiber performs, an experiment installation was designed, and do some experimental study on the one-dimensional permeability of resin in the multilayer fibrous plaids at a constant flow rate. The installation was designed base on condition of different flow rates and different fiber volumes (or porosity), and compared the results of the permeability of different flow rates. Then analyzed the results, and some content conclusions were obtained.

Permeability Predictions for Woven Fabric Preforms

A model is proposed to predict woven fabric permeability. The dual-scale fabric preform is represented by a unit cell of heterogeneous porous medium consisting of equivalent intertow and intratow porous media. The Stokes equation is used to model the flow in the intertow region of the unit cell, and the permeability of the equivalent intertow porous medium is calculated by back substituting the resultant pressure and velocity fields into Darcy’s law. With knowledge of the permeabilities of the two equivalent porous phases, the permeability of the unit cell for the fabric preform can be easily determined by solving the Darcy flow in the equivalent heterogeneous porous medium. The effects of geometrical parameters on the permeability of plain-weave fabric preforms are investigated. It is shown that, as well as the fiber volume fraction; other geometrical parameters such as the gap between adjacent tows also play an important role in determining permeability. Permeability predictions for three plain-weave fabrics show satisfactory agreement with experimental data available in the literature.

Optimal Injection Design for Resin Transfer Molding with In Situ Permeability Measurement and Process Simulation

Resin transfer molding (RTM) process has been gaining extensive attention because of its ability to produce complex structural composite parts. Researchers have made significant progress toward obtaining quality products. The preform permeability change during actual molding process brings up difficulty in achieving consistency in part quality. This article presents an adaptive RTM injection design approach in which process simulation and Hardware-In-the-Loop-Simulation (HILS) technique are used: the whole-field preform permeability profile is provided by an in situ gas-assisted permeability measurement system and then inputted to the process simulation right before each control step during molding; an open loop control method steering the resin flow is also proposed. It is found that the HILS can be used to realize optimal injection design and flow control with accurate online permeability estimation.