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Visualization of resin flow progression through fibrous preforms is often sought to elucidate flow patterns and validate models for filling prediction for liquid composite molding processes. Here, conventional X-ray radiography is compared to X-ray phase contrast technique to image in-situ constant flow rate impregnation of a non-translucent unidirectional carbon fabric. X-ray attenuation of the fluid phase was increased by using a ZnI2-based contrasting agent, leading to enough contrast between the liquid and the low density fibers. We proved the suitability of conventional X-ray transmission to visualize fluid paths by elucidating different flow patterns, spanning from capillary to viscous regimes and a macro-void entrapment phenomenon, Aerospace Manufacturing Technologies

In this study, a 2-D Darcy’s law based numerical model is developed in order to investigate the effect of saturation on the propagation of the resin in the die chamber of a pultrusion line. The numerical model is established using the finite volume method and alternating direction implicit scheme. The implemented saturation and relative permeability curves are adopted from relationships presented in the literature. The results of the numerical model highlights the importance of accurately determining thesaturation curve when included in a numerical solver that is used to predict the resin flow in injection pultrusion. Further research is planned within this field in order to identify realistic saturation curves for fiber reinforcements used in resin injection pultrusion.

The manufacture of polymer composite materials has benefited greatly from the development of computer-based simulation tools and sensor-based instrumentation. The present research offers a unique and powerful interface for collecting, integrating, analyzing, and rendering critical data related to a dynamic composite manufacturing process. These operations are executed in real time over the internet, permitting unprecedented flexibility and speed in deploying and using the manufacturing "tools." These tools include, but are not limited to, resin flow sensors, a model-based resin-flow reconstruction procedure, and a user friendly display for remotely manipulating and monitoring composite process events. The interface developed herein is critical not only in improving the fundamental visualization of a process but also as a means of practically communicating process information between geographically distinct locations. Thus, manufacturing concerns with only modest computer infrastructure can remotely leverage these tools to improve the quality, performance, and cost of their products without the need for significant investment in high performance computing infrastructure.

The effects of cure pressure on resin flow, compaction, void content, and mechanical properties of fiber reinforced composites were investigated. Tests were performed on laminates made of Fiberite T300/976 and T300/934 unidirectional prepreg tape. Data are presented on compaction, resin flow, and void content which tend support to the validity of the Springer-Loos model. Data are also given showing the effects of cure pressure on void content and on the compressive strength and short-beam shear strength and modulus.

This work addresses the characterisation of the micro-structure of fibre bundles in reinforcement textiles for composites and its influence on resin flow in liquid composite moulding (LCM) processes. Random variations in local filament spacing result in a non-uniform flow velocity field. Merging flow fronts due to differences in local flow velocities can lead to gas entrapment in the matrix phase. This results in formation of micro-scale defects, which can significantly reduce the matrix-dominated mechanical properties of the finished composite. An automated image analysis method was developed to precisely determine local filament distributions within complete fibre bundles. Based on two-dimensional micrographs, filament arrangements were characterised statistically by means of nearest neighbour distance and angle distributions. It was observed that the micro-structure becomes more uniform with increasing level of compaction. A micro-structure generator to reconstruct filament arrangements was adapted incorporating these measurement data. Transverse permeabilities derived from numerical simulations of steady-state flow on automatically discretised model domains were found to be log-normally distributed. With increasing model size, average values and widths of the distributions decrease, converging to the permeability of a complete fibre bundle. Similarly, average values and scatter decrease with increasing fibre volume fraction. The transverse permeability of random filament arrangements was found to be significantly smaller than for uniform filament arrangements. The void content in composite specimens produced by resin injection along and perpendicular to the fibre bundles was characterised with a developed image analysis process. Due to the more uniform micro-structure at increased bundle compaction, a decrease in void content was observed in the case of transverse resin injection. A first step towards void content prediction in a fibre bundle by numerical simula

This work addresses the characterisation of the micro-structure of fibre bundles in reinforcement textiles for composites and its influence on resin flow in liquid composite moulding (LCM) processes. Random variations in local filament spacing result in a non-uniform flow velocity field. Merging flow fronts due to differences in local flow velocities can lead to gas entrapment in the matrix phase. This results in formation of micro-scale defects, which can significantly reduce the matrix-dominated mechanical properties of the finished composite. An automated image analysis method was developed to precisely determine local filament distributions within complete fibre bundles. Based on two-dimensional micrographs, filament arrangements were characterised statistically by means of nearest neighbour distance and angle distributions. It was observed that the micro-structure becomes more uniform with increasing level of compaction. A micro-structure generator to reconstruct filament arrangements was adapted incorporating these measurement data. Transverse permeabilities derived from numerical simulations of steady-state flow on automatically discretised model domains were found to be log-normally distributed. With increasing model size, average values and widths of the distributions decrease, converging to the permeability of a complete fibre bundle. Similarly, average values and scatter decrease with increasing fibre volume fraction. The transverse permeability of random filament arrangements was found to be significantly smaller than for uniform filament arrangements. The void content in composite specimens produced by resin injection along and perpendicular to the fibre bundles was characterised with a developed image analysis process. Due to the more uniform micro-structure at increased bundle compaction, a decrease in void content was observed in the case of transverse resin injection. A first step towards void content prediction in a fibre bundle by numerical simula

This work addresses the characterisation of the micro-structure of fibre bundles in reinforcement textiles for composites and its influence on resin flow in liquid composite moulding (LCM) processes. Random variations in local filament spacing result in a non-uniform flow velocity field. Merging flow fronts due to differences in local flow velocities can lead to gas entrapment in the matrix phase. This results in formation of micro-scale defects, which can significantly reduce the matrix-dominated mechanical properties of the finished composite. An automated image analysis method was developed to precisely determine local filament distributions within complete fibre bundles. Based on two-dimensional micrographs, filament arrangements were characterised statistically by means of nearest neighbour distance and angle distributions. It was observed that the micro-structure becomes more uniform with increasing level of compaction. A micro-structure generator to reconstruct filament arrangements was adapted incorporating these measurement data. Transverse permeabilities derived from numerical simulations of steady-state flow on automatically discretised model domains were found to be log-normally distributed. With increasing model size, average values and widths of the distributions decrease, converging to the permeability of a complete fibre bundle. Similarly, average values and scatter decrease with increasing fibre volume fraction. The transverse permeability of random filament arrangements was found to be significantly smaller than for uniform filament arrangements. The void content in composite specimens produced by resin injection along and perpendicular to the fibre bundles was characterised with a developed image analysis process. Due to the more uniform micro-structure at increased bundle compaction, a decrease in void content was observed in the case of transverse resin injection. A first step towards void content prediction in a fibre bundle by numerical simula

This work addresses the characterisation of the micro-structure of fibre bundles in reinforcement textiles for composites and its influence on resin flow in liquid composite moulding (LCM) processes. Random variations in local filament spacing result in a non-uniform flow velocity field. Merging flow fronts due to differences in local flow velocities can lead to gas entrapment in the matrix phase. This results in formation of micro-scale defects, which can significantly reduce the matrix-dominated mechanical properties of the finished composite. An automated image analysis method was developed to precisely determine local filament distributions within complete fibre bundles. Based on two-dimensional micrographs, filament arrangements were characterised statistically by means of nearest neighbour distance and angle distributions. It was observed that the micro-structure becomes more uniform with increasing level of compaction. A micro-structure generator to reconstruct filament arrangements was adapted incorporating these measurement data. Transverse permeabilities derived from numerical simulations of steady-state flow on automatically discretised model domains were found to be log-normally distributed. With increasing model size, average values and widths of the distributions decrease, converging to the permeability of a complete fibre bundle. Similarly, average values and scatter decrease with increasing fibre volume fraction. The transverse permeability of random filament arrangements was found to be significantly smaller than for uniform filament arrangements. The void content in composite specimens produced by resin injection along and perpendicular to the fibre bundles was characterised with a developed image analysis process. Due to the more uniform micro-structure at increased bundle compaction, a decrease in void content was observed in the case of transverse resin injection. A first step towards void content prediction in a fibre bundle by numerical simula

This work addresses the characterisation of the micro-structure of fibre bundles in reinforcement textiles for composites and its influence on resin flow in liquid composite moulding (LCM) processes. Random variations in local filament spacing result in a non-uniform flow velocity field. Merging flow fronts due to differences in local flow velocities can lead to gas entrapment in the matrix phase. This results in formation of micro-scale defects, which can significantly reduce the matrix-dominated mechanical properties of the finished composite. An automated image analysis method was developed to precisely determine local filament distributions within complete fibre bundles. Based on two-dimensional micrographs, filament arrangements were characterised statistically by means of nearest neighbour distance and angle distributions. It was observed that the micro-structure becomes more uniform with increasing level of compaction. A micro-structure generator to reconstruct filament arrangements was adapted incorporating these measurement data. Transverse permeabilities derived from numerical simulations of steady-state flow on automatically discretised model domains were found to be log-normally distributed. With increasing model size, average values and widths of the distributions decrease, converging to the permeability of a complete fibre bundle. Similarly, average values and scatter decrease with increasing fibre volume fraction. The transverse permeability of random filament arrangements was found to be significantly smaller than for uniform filament arrangements. The void content in composite specimens produced by resin injection along and perpendicular to the fibre bundles was characterised with a developed image analysis process. Due to the more uniform micro-structure at increased bundle compaction, a decrease in void content was observed in the case of transverse resin injection. A first step towards void content prediction in a fibre bundle by numerical simula

Axial flow through gaps between aligned straight yarns with realistic cross-sectional shapes, described by power-ellipses, was analysed numerically. At a given fibre volume fraction, equivalent gap permeabilities have a maximum at minimum size of elongated tapering parts of the gap cross-section and a ratio of gap width to height near 1. When the yarn spacing is given in addition to the fibre volume fraction, calculated maximum and minimum values for the equivalent permeability of inter-yarn gaps, which occur at near-rectangular and lenticular cross-sections, differ by factors of up to 3.3. Novel approximations for the shape factor and the hydraulic diameter in Poiseuille flow were derived as a function of the fibre volume fraction, the yarn cross-sectional aspect ratio and the exponent describing the shape of the power-elliptical yarn cross-section. This allows the equivalent gap permeability to be predicted with good accuracy for any fibre volume fraction and yarn cross-section.

Axial flow through gaps between aligned straight yarns with realistic cross-sectional shapes, described by power-ellipses, was analysed numerically. At a given fibre volume fraction, equivalent gap permeabilities have a maximum at minimum size of elongated tapering parts of the gap cross-section and a ratio of gap width to height near 1. When the yarn spacing is given in addition to the fibre volume fraction, calculated maximum and minimum values for the equivalent permeability of inter-yarn gaps, which occur at near-rectangular and lenticular cross-sections, differ by factors of up to 3.3. Novel approximations for the shape factor and the hydraulic diameter in Poiseuille flow were derived as a function of the fibre volume fraction, the yarn cross-sectional aspect ratio and the exponent describing the shape of the power-elliptical yarn cross-section. This allows the equivalent gap permeability to be predicted with good accuracy for any fibre volume fraction and yarn cross-section.

Axial flow through gaps between aligned straight yarns with realistic cross-sectional shapes, described by power-ellipses, was analysed numerically. At a given fibre volume fraction, equivalent gap permeabilities have a maximum at minimum size of elongated tapering parts of the gap cross-section and a ratio of gap width to height near 1. When the yarn spacing is given in addition to the fibre volume fraction, calculated maximum and minimum values for the equivalent permeability of inter-yarn gaps, which occur at near-rectangular and lenticular cross-sections, differ by factors of up to 3.3. Novel approximations for the shape factor and the hydraulic diameter in Poiseuille flow were derived as a function of the fibre volume fraction, the yarn cross-sectional aspect ratio and the exponent describing the shape of the power-elliptical yarn cross-section. This allows the equivalent gap permeability to be predicted with good accuracy for any fibre volume fraction and yarn cross-section.

Axial flow through gaps between aligned straight yarns with realistic cross-sectional shapes, described by power-ellipses, was analysed numerically. At a given fibre volume fraction, equivalent gap permeabilities have a maximum at minimum size of elongated tapering parts of the gap cross-section and a ratio of gap width to height near 1. When the yarn spacing is given in addition to the fibre volume fraction, calculated maximum and minimum values for the equivalent permeability of inter-yarn gaps, which occur at near-rectangular and lenticular cross-sections, differ by factors of up to 3.3. Novel approximations for the shape factor and the hydraulic diameter in Poiseuille flow were derived as a function of the fibre volume fraction, the yarn cross-sectional aspect ratio and the exponent describing the shape of the power-elliptical yarn cross-section. This allows the equivalent gap permeability to be predicted with good accuracy for any fibre volume fraction and yarn cross-section.

Axial flow through gaps between aligned straight yarns with realistic cross-sectional shapes, described by power-ellipses, was analysed numerically. At a given fibre volume fraction, equivalent gap permeabilities have a maximum at minimum size of elongated tapering parts of the gap cross-section and a ratio of gap width to height near 1. When the yarn spacing is given in addition to the fibre volume fraction, calculated maximum and minimum values for the equivalent permeability of inter-yarn gaps, which occur at near-rectangular and lenticular cross-sections, differ by factors of up to 3.3. Novel approximations for the shape factor and the hydraulic diameter in Poiseuille flow were derived as a function of the fibre volume fraction, the yarn cross-sectional aspect ratio and the exponent describing the shape of the power-elliptical yarn cross-section. This allows the equivalent gap permeability to be predicted with good accuracy for any fibre volume fraction and yarn cross-section.

To provide an alternative for manufacturing auto parts using composite materials, the Vacuum Assisted Resin Transfer Molding (VARTM) process was utilized to prototype the bumper for the Chevrolet Aveo vehicle. This technique emerges as an alternative for composite material manufacturing, allowing for rapid and high-quality production of advanced composites. In this study, a hybrid composite material reinforced with fiberglass, cabuya fiber, IN2 epoxy resin, an infusion mesh, peel ply, and a vacuum bag was employed. To optimize the VARTM process in bumper prototyping, several simulations of resin flow were conducted with different locations of resin injection and vacuum entry points. Autodesk Moldflow Insight software facilitated the modification and addition of resin injection points to observe the flow evolution, thus determining the filling time for each proposed design. Six different designs were applied for the bumper mold filling. The proposed linear flow design reduced the total filling time of the bumper mold by 81.56% compared to the other five designs analyzed. The result of the numerical simulation was validated through the experimental process, where a high degree of concordance in the mold filling time was achieved between both methods., Con el fin de brindar una alternativa para la manufactura de autopartes utilizando materiales compuestos, se aplicó el proceso VARTM en el prototipado del guardachoque del vehículo Chevrolet Aveo. Esta técnica surge como una alternativa para la fabricación de materiales compuestos, ya que permite realizar una producción rápida y de alta calidad de compuestos avanzados. En el presente estudio, se utilizó un material compuesto híbrido reforzado con fibra de vidrio, cabuya, resina epóxica IN2, una malla de infusión, peel ply y una bolsa de vacío. Para la optimización del proceso VARTM en el prototipado del guardachoque, se llevaron a cabo varias simulaciones de flujo de resina con distintas ubicaciones de los puntos de entrada de resina y de vacío. El software Autodesk Moldflow Insight permitió modificar y agregar puntos de entrada de resina con el fin de observar la evolución del flujo y de esta forma llegar a determinar el tiempo de llenado para cada diseño planteado. Se aplicaron seis diseños diferentes para el llenado del molde del guardachoque. El diseño propuesto de flujo lineal reduce un 81,56 % el tiempo total de llenado del molde del guardachoque en comparación con los otros 5 diseños analizados. El resultado de la simulación numérica fue validado mediante la experimentación del proceso, donde se obtuvo una gran concordancia del tiempo de llenado del molde entre ambos métodos.

Pine resin is a valuable non-wood forest product with an increasing interest in multiple industrial sectors. Resin-tapping activities also provide valuable ecosystem services in timber-oriented and highly productive pine forest of Atlantic regions, where little previous experience in resin-tapping is available. The objectives of this study were to determine the efficiency of different stimulant pastes and its variation with pine species, site conditions, seasonality and frequency of tapping interventions. We conducted parallel experiments using both conventional and micro-tapping techniques in mature pine stands in NW Spain. We tested four stimulants (control and Zeta, Cunningham and Salicylic pastes) and two groove frequencies (every 2 or 3 weeks). All stimulant pastes significantly increased resin yield compared to the control, being resin stimulation highly consistent across years, sites and species. In conventional resin tapping, resin yield was maximized with the Cunningham and Salicylic pastes while in micro-tapping Salicylic was the most outstanding stimulant treatment. According to the rapid decay of resin flow after wounding, total resin yield decreased with more spaced grooves. However, the reduction was low, and the global efficiency of the tapping operations are likely maximized with grooves applied every three weeks, which would allow increasing the number of tapped trees. Micro-tapping techniques were valuable for screening stimulant pastes and anticipating variation among sites in resin production. Altogether, the Salicylic paste is recommended, especially at the beginning of the resin campaign, when the effect of the pastes was maximized, and if tapping is conducted using closed atmospheres and containers.

This PhD thesis concerns resin-injection pultrusion (RIP), a low-cost and continuous process to mass-produce fibre-reinforced polymer composite profiles. The thesis follows a clear trend in modern manufacturing engineering (Industry 4.0) that is to exploit simulation models to analyse processesing steps. This work represents the state of the art of simulating material flow in RIP processes. The thesis first presents pultrusion in a societal and economic context, followed by a short overview of related literature. Then, the conservation equations that govern the material flow (mass, momentum, or energy) are derived and applied to RIP processes. The theoretical background is given with a focus on steady-state modelling of the coupled physics (multiphysics) that take place inside the pultrusion die. The impregnation flow is considered to be single-phased and characterised by Darcy’s law. To analyse flow-induced fibre compaction, resin flow in a compliant porous medium is introduced as well. In this relation, the thesis also presents material characterisation methodologies to measure permeability and compaction behaviour. To model the resin flow front, both Eulerian (that utilise a level-set) and arbitrary Lagrangian-Eulerian (ALE) methods are introduced. Nonisothermal flow in a compliant porous medium is presented, and finally, a steady-state and Eulerian approach is introduced to model process induced stress and deformation. Numerical and experimental results are presented in seven appended publications that reflect different aspects of the material flow in RIP processes. First, a new level-set method to model the resin flow front is presented. It is demonstrated how the framework tracks the flow front itself and can advance it with CFL-sized time. Using this level-set method, it is shown how RIP processes can utilise permeable areas to improve impregnation flow. Then, experimental material characterisation of pultrusion-specific glass fibre roving

This thesis explores the use of numerical methods to simulate composite manufacturing processes. These simulation methods are more effective at conducting manufacturing trials for evaluating the material and processing parameters for a given process. This helps to reduce the risk of manufacturing processes, whilst also reducing the cost and time of manufacturing. This work will focus on dry fabric vacuum forming and resin infusion processes, with the use of two separate case studies. The first case study is of a vacuum preforming process of a dry non-crimp fabric and the second is the resin infusion of a large-scale dry preform. Both case studies set up manufacturing process simulations using commercial off the shelf software (PAM-RTM and PAM-Form by ESI) and compare the results of the simulations against the results of manufacturing trials. The vacuum preforming process compares the shear angles found within the part, the predicted part edge and the size, location and type of defects induced through the manufacturing process. The large-scale resin infusion process compares the resin flow front after a set time, as well as information from resin arrival, flow rate and flow pressure sensors. This work helps to build confidence from industry in the simulation tools available by quantifying the error associated with these tools. The simulations set up within this thesis are then used to perform a sensitivity study, which aims to determine which material parameters are driving the outputs of the manufacturing process. For the vacuum preforming process, the shear angles and defects are used as the main outputs of the process, and for the resin infusion process, the filling time is investigated as the main process output. The results of this work will help to make decisions and prioritise material and processing parameters in future work.

Utilisation of the Vacuum Assisted Resin Infusion (VARI) process has increased in recent years for the manufacture of large scale components for the transport industry. Quality control and repeatability are two key areas where the VARI process requires greater understanding due to the scale of the infusions. The marine industry has a history of being at the cutting edge of large scale composite manufacturing. This research focusses on utilising the processes and knowledge at Princess Yachts International (PYI) to monitor and analyse the process variability and uncertainty for large scale VARIs. A detailed process review was conducted at PYI to evaluate the level of process monitoring and variability as well as the defect controls that are used in industry. Core samples were extracted from infusions where surface visible defects had been recorded. The core samples were analysed using Micro Computed Tomography (µ-CT) to generate a three-dimensional reconstruction of the defects. The location and structure of the defects indicated matrix failure towards the mould surface of the component, an area which is not monitored during the VARI process. Having identified a requirement to monitor the manufacturing process, a review of available sensors was conducted identifying Fibre Bragg Grating (FBG) fibre optics as the most suitable monitoring method. The sensors measured the residual stress development during resin curing as well as the high loads exerted on the component during demoulding which were five times larger than during the infusion and resin curing process. The measured strains were lower than the failure strain of the resin suggesting the presence of defects that result in premature matrix failure. A novel approach to monitoring resin flow was then developed to analyse the through thickness resin flow progress using µ-CT. Both monolithic and sandwich laminates were analysed both in-situ and exsitu to evaluate the effect of variable laminate layup.

In this investigation, a comprehensive Vacuum Assisted Resin Transfer Molding (VARTM) process simulation model was developed and verified. The model incorporates resin flow through the preform, compaction and relaxation of the preform, and viscosity and cure kinetics of the resin. The computer model can be used to analyze the resin flow details, track the thickness change of the preform, predict the total infiltration time and final fiber volume fraction of the parts, and determine whether the resin could completely infiltrate and uniformly wet out the preform. Flow of resin through the preform is modeled as flow through porous media. Darcy's law combined with the continuity equation for an incompressible Newtonian fluid forms the basis of the flow model. During the infiltration process, it is well accepted that the total pressure is shared by the resin pressure and the pressure supported by the fiber network. With the progression of the resin, the net pressure applied to the preform decreases as a result of increasing local resin pressure. This leads to the springback of the preform, and is called the springback mechanism. On the other side, the lubrication effect of the resin causes the rearrangement of the fiber network and an increase in the preform compaction. This is called the wetting compaction mechanism. The thickness change of the preform is determined by the relative magnitude of the springback and wetting deformation mechanisms. In the compaction model, the transverse equilibrium equation is used to calculate the net compaction pressure applied to the preform, and the compaction test results are fitted to give the compressive constitutive law of the preform. The Finite Element/Control Volume (FE/CV) method is adopted to find the flow front location and the fluid pressure. The code features the ability of simultaneous integration of 1-D, 2-D and 3-D element types in a single simulation, and thus enables efficient modeling of the flow in complex mold geome

Permeability of fibrous microstructures is a key material property for predicting the mold fill times and resin flow path during composite manufacturing. In this work, we report an efficient approach to predict the permeability of 3D microstructures from deep learning based permeability predictions of 2D cross-sections combined via a circuit analogy. After validating the network's predictions in 2D and extending it to 3D, we investigate its capabilities for handling images of various sizes obtained from virtual and real microstructures. More than 90% of 2D predictions is within ± 30% of their counterparts obtained via flow simulations, similarly for 3D transverse permeability predictions, while in 3D case computational time is reduced from several thousands of seconds to less than 10 s. This work provides a robust and efficient framework for characterizing the permeability of fibrous microstructures and paves the way for extending this capability to estimate the permeability of fabric mesostructures., Aerospace Manufacturing Technologies

Any composite manufacturing method requires an application of a carefully designed consolidation process to ensure the suppression of voids in the laminate, establish bonding in laminate layers and prevent dimensional or fibre-path defects. The optimisation of consolidation processes relies on the characterisation of the composite precursors’ deformability. There are multiple mechanisms occurring in consolidation and various experimental programmes have been suggested in the literature to describe these mechanisms and deduce relevant material properties. The selection of a testing methodology often relies on an initial hypothesis or prior knowledge regarding the deformation modes. This may be a source of significant errors. This research poses questions on the testing rationales, on subjectivity in material testing and on how data-rich programmes should be designed. The proposed solution to the consolidation characterisation problem is a real-time adaptive testing strategy that enables a “conversation with the material” – flexible autonomous steering of a testing programme reacting on the obtained output. Such system is implemented within this research and is called adaptive consolidation sensor framework. The system’s algorithm is set to analyse composite precursor’s feedback to compression in real time and to track characteristic signatures relevant to existing consolidation models. Based on that feedback the framework formulates a load programme for the test in a reactive manner. The developed testing system focuses on the identification of the underlying physical mechanisms rather than material properties identification in a rightly or wrongly assumed resin flow mode. To validate the proposed testing approach, a series of characterisation experiments for different material systems was performed. The obtained results highlight a way forward in terms of rethinking experiments for materials used in manufacturing and beyond.

Conventional fibre polymer composite materials consist of a single matrix system for a whole part and are selected on the dominant requirements of the part. A multi-matrix composite would provide an expanded design space for a composite part. However, there are few processes available to realise such a composite and these rely on modified forms of resin transfer moulding. These processes require active venting using an expensive vacuum system and the quality is reliant on bag quality. This research is devoted to developing a foundational principle for a processing strategy that uses the localised introduction of resin combined with an out-of-bag consolidation process containing a preheating stage that can form a multi-matrix composite. The resin flow in local deposition and consolidation processes is determined by a complex interplay between the resin and preform. Hence the chosen resin and fabric were characterised extensively. A range of viscosity-tailored consolidation schemes was implemented using a setup to estimate the in-line viscosity using the rheo-kinetics of the fast-curing resin system. By initiating the consolidation pressure at a higher resin viscosity, the voids were found to be suppressed. A simplified model to capture the dominant mechanisms during consolidation was developed. The dominant flow transitioned from a 2D yarn-scale to macro-scale flow on increasing the activation viscosity. The increased resin pressure associated with high resin viscosity during consolidation was found to be a dominating factor in reducing the voids. The model was then used to develop a simple analytical design tool for tailoring the consolidation parameters to minimise the void content. A feasibility study was conducted on combining different matrices to improve the mechanical performance of composites in an open hole tension test. The use of high stiffness carbon nanotube modified resin to locally manipulate the region around the hole increased the strength of the

Any composite manufacturing method requires an application of a carefully designed consolidation process to ensure the suppression of voids in the laminate, establish bonding in laminate layers and prevent dimensional or fibre-path defects. The optimisation of consolidation processes relies on the characterisation of the composite precursors’ deformability. There are multiple mechanisms occurring in consolidation and various experimental programmes have been suggested in the literature to describe these mechanisms and deduce relevant material properties. The selection of a testing methodology often relies on an initial hypothesis or prior knowledge regarding the deformation modes. This may be a source of significant errors. This research poses questions on the testing rationales, on subjectivity in material testing and on how data-rich programmes should be designed. The proposed solution to the consolidation characterisation problem is a real-time adaptive testing strategy that enables a “conversation with the material” – flexible autonomous steering of a testing programme reacting on the obtained output. Such system is implemented within this research and is called adaptive consolidation sensor framework. The system’s algorithm is set to analyse composite precursor’s feedback to compression in real time and to track characteristic signatures relevant to existing consolidation models. Based on that feedback the framework formulates a load programme for the test in a reactive manner. The developed testing system focuses on the identification of the underlying physical mechanisms rather than material properties identification in a rightly or wrongly assumed resin flow mode. To validate the proposed testing approach, a series of characterisation experiments for different material systems was performed. The obtained results highlight a way forward in terms of rethinking experiments for materials used in manufacturing and beyond.

Knowledge of permeability of fibrous microstructures is crucial for predicting the mold fill times and resin flow path in composite manufacturing. Herein we report a method to rapidly predict the permeability of 3D fibrous microstructures. Our method relies on predicting the permeability of 2D cross-sections via deep neural networks and extending this capability to 3D microstructures via circuit analogy as a means of reduced order modeling. Approximately 50% of the permeability predictions of 2D cross-sections have 10% or less deviation from the permeability results obtained via flow simulations in Geodict. Computational time required for predicting the permeability of 3D microstructures is reduced from hours to less than 10 seconds. This framework enables fast and accurate prediction of micro-permeability and serves as the first building block towards prediction of fabric mesostructures’ permeability via deep learning based methods., Aerospace Manufacturing Technologies

Laser-assisted tape placement (LATP) and thermoplastic composites (TPCs) pre-impregnated (prepreg) tapes are a promising combination of technologies; given the in-situ capabilities of the TPCs and the high degree of automation achievable with LATP. However, laminate quality, measured as final void content, tends to decrease when increasing placement speed. Heating and consolidation windows in LATP of TPCs are very short, especially when increasing the placement speed. For TPCs, resin flow is heavily influenced by melt viscosity above melting temperature (Tm). Therefore, the degree of intimate contact (Dic) resulting from the compaction phase can be significantly influenced by the tape’s degree of melt at the end of the heating phase. Due to melting being a kinetically controlled process[1,2], both temperatures and times above Tm need to be considered. The relationship between the degree of melt, both through thickness and in time, prior to compaction and the final Dic has not been explored yet. In this study, the final Dic and degree of melt of a CF/PEEK tape as a function of heating power, heating length and placement speed will be evaluated and correlated. The experimental investigation will consist of calorimetric data on melting kinetics of the polymer, and LATP experiment runs with different process parameters. Simulations of the thermal history (see Figure 1) and melting in the heating phase will be performed and validated with experiments. The research aims to understand the melting behaviour of the tapes during the heating stage in LATP, its dependence on the process parameters, and how it affects the final Dic and laminate quality., Wind Energy, Aerospace Manufacturing Technologies

Conventional fibre polymer composite materials consist of a single matrix system for a whole part and are selected on the dominant requirements of the part. A multi-matrix composite would provide an expanded design space for a composite part. However, there are few processes available to realise such a composite and these rely on modified forms of resin transfer moulding. These processes require active venting using an expensive vacuum system and the quality is reliant on bag quality. This research is devoted to developing a foundational principle for a processing strategy that uses the localised introduction of resin combined with an out-of-bag consolidation process containing a preheating stage that can form a multi-matrix composite. The resin flow in local deposition and consolidation processes is determined by a complex interplay between the resin and preform. Hence the chosen resin and fabric were characterised extensively. A range of viscosity-tailored consolidation schemes was implemented using a setup to estimate the in-line viscosity using the rheo-kinetics of the fast-curing resin system. By initiating the consolidation pressure at a higher resin viscosity, the voids were found to be suppressed. A simplified model to capture the dominant mechanisms during consolidation was developed. The dominant flow transitioned from a 2D yarn-scale to macro-scale flow on increasing the activation viscosity. The increased resin pressure associated with high resin viscosity during consolidation was found to be a dominating factor in reducing the voids. The model was then used to develop a simple analytical design tool for tailoring the consolidation parameters to minimise the void content. A feasibility study was conducted on combining different matrices to improve the mechanical performance of composites in an open hole tension test. The use of high stiffness carbon nanotube modified resin to locally manipulate the region around the hole increased the strength of the

Permeability of fibrous microstructures is a key material property for predicting the mold fill times and resin flow path during composite manufacturing. In this work, we report an efficient approach to predict the permeability of 3D microstructures from deep learning based permeability predictions of 2D cross-sections combined via a circuit analogy. After validating the network's predictions in 2D and extending it to 3D, we investigate its capabilities for handling images of various sizes obtained from virtual and real microstructures. More than 90% of 2D predictions is within ± 30% of their counterparts obtained via flow simulations, similarly for 3D transverse permeability predictions, while in 3D case computational time is reduced from several thousands of seconds to less than 10 s. This work provides a robust and efficient framework for characterizing the permeability of fibrous microstructures and paves the way for extending this capability to estimate the permeability of fabric mesostructures., Aerospace Manufacturing Technologies

Induced defences in conifers are an effective strategy that allows individuals to increase resistance against pests and pathogens by optimizing associated costs. Studies exploring inducibility of defences in conifers have usually been conducted in young individuals (i.e., seedlings and saplings) whereby effects were addressed within weeks or months after induction, limiting knowledge and generalization of long-term patterns in mature individuals growing under natural conditions. In addition, few studies have explored how plasticity and genetic differentiation among populations may affect the inducibility of defences in mature trees. We took advantage of two long-term Pinus pinaster common gardens to explore the interactive and independent contribution of genetic differentiation (i.e., variation among populations) and the environment (i.e., plasticity between sites) as drivers of variation in short-term, long-term and systemic inducibility of chemical defences (resin flow, non-volatile resin, phenolics) in response to simulated herbivore damage associated with jasmonate signalling. We provide evidence that the external application of methyl jasmonate increased the production of resin based defences in mature P. pinaster trees for at least two years after its application. We found that inducibility of defences did not differ among populations, but was rather contingent on local environmental conditions. Systemic effects of methyl jasmonate were also observed and suggest that induced responses likely involve complex within-individual reallocation of chemical defences. Our results contribute to better understanding of the ecological and evolutionary relevance of induced defence strategies in conifers and have important implications for integrating forest management practices aiming to improve forest health and resistance to pests and pathogens.

Increasing dimensions and production volumes of composite parts led to the development of Out-of-Autoclave manufacturing (OoA), a complex process which combines heat transfer, air, resin flow and viscosity development in a consolidating fibrous medium during curing. A multi-physics simulation framework is developed, enabling virtual testing of production cycles and material down-selection. A commercial OoA semipreg is characterized as input for the simulation, while a monolithic demonstrator manufactured from the same material is used for validation purposes., Wachsende Produktionsvolumen und steigende Bauteilgrößen von Faserverbundstrukturen führten zur Entwicklung der Out-of-Autoclave Verfahren (OoA), bei welchem Evakuierung von Luft, Harzfluss und Wärmeübertragung simultan im konsolidierenden Fasermaterial während des Aushärtezyklus ablaufen. Hierzu wurden Modelle zur virtuellen Optimierung des Produktionsprozesses und der Auswahl des Materialsystems entwickelt. Ein kommerzielles OoA Semipreg wurde zum Abgleich der Simulation charakterisiert; zur Validierung diente ein monolithischer Demonstrator auf Basis desselben Materials.

Increasing dimensions and production volumes of composite parts led to the development of Out-of-Autoclave manufacturing (OoA), a complex process which combines heat transfer, air, resin flow and viscosity development in a consolidating fibrous medium during curing. A multi-physics simulation framework is developed, enabling virtual testing of production cycles and material down-selection. A commercial OoA semipreg is characterized as input for the simulation, while a monolithic demonstrator manufactured from the same material is used for validation purposes., Wachsende Produktionsvolumen und steigende Bauteilgrößen von Faserverbundstrukturen führten zur Entwicklung der Out-of-Autoclave Verfahren (OoA), bei welchem Evakuierung von Luft, Harzfluss und Wärmeübertragung simultan im konsolidierenden Fasermaterial während des Aushärtezyklus ablaufen. Hierzu wurden Modelle zur virtuellen Optimierung des Produktionsprozesses und der Auswahl des Materialsystems entwickelt. Ein kommerzielles OoA Semipreg wurde zum Abgleich der Simulation charakterisiert; zur Validierung diente ein monolithischer Demonstrator auf Basis desselben Materials.

Tomographic imaging using both microfocus radiation and synchrotron radiation was performed to assess the void defects in resin transfer moulded woven carbon fibre composites. The focus of this study is on characterising the void homology (e.g. local void size and spatial distribution) in relation to weave orientation, infusion direction and potential effects on damage formation in tensile loading. As the orientation angle between the fibre direction of unidirectional layer in the laminate and the direction of the global resin flow increases, from parallel to perpendicular, larger voids and a greater volume fraction of voids were observed, which led to increased damage formation upon loading. Significant accumulation of voids around both the layer interfaces and yarn fibres were also observed. With regard to yarn design, it is recommended to balance the benefits (e.g. fabric handling, structural integrity of preform) and drawbacks (e.g. lower fibre content, more voids) of the supporting yarn. Also, sensible placement of resin inlets and outlets could reduce the amount of deleterious voids, i.e. by promoting resin flow along the fibre direction in the most defect-sensitive off-axis layers.

Liquid Composite Molding (LCM), which includes Resin Transfer Molding(RTM), Vacuum As-sisted Resin Transfer Molding(VARTM), Reactive Injection Molding(RIM) and others subsets is considered as one of the most viable and eco-friendly process for manufacturing high quality parts. All the LCM applications involve resin flow into a fibrous network i.e the reinforcement, which can induce defects such as voids and dry spots. Resin flow induced defects are known as the largest source on quality and reproducibility problems. These defects are often caused by unbalanced resin flows, which are directly related to the fiber permeability. Currently many computers simulations tools for predicting LCM processes behavior are available. Using these tools, process engineers can replace the traditional time-consuming trial-and-error pro-cess design procedures by optimized ones. One of the most critical input parameters with respect to the LCM modeling tools is the permeability of the reinforcement.Without a reliable character-ization of the fiber preform neither mathematical models nor computer simulations would be able to provide useful information . To fully characterize a fiber reinforcement it is necessary to measure its principal permeabilities. However, since LCM molded parts are, most of the time, thin shells, the through the thickness permeability is usually neglected and only planar permeabilities need to be evaluated. Permeability measurements have always been a source of disagreement among researchers of LCM process, results obtained from various installations show significant contra-dictions. As permeability is an intrinsic property of a fibrous material, it ought to be evaluated experimentally following a reliable and standardized procedure. The main objective of this thesis is the design of a set-up to measure in-plane (parallel to woven plane) permeabilities of LCM reinforcements by performing unidirectional injections. This method uses a rectangular mold of constant wi

Liquid Composite Molding (LCM), which includes Resin Transfer Molding(RTM), Vacuum As-sisted Resin Transfer Molding(VARTM), Reactive Injection Molding(RIM) and others subsets is considered as one of the most viable and eco-friendly process for manufacturing high quality parts. All the LCM applications involve resin flow into a fibrous network i.e the reinforcement, which can induce defects such as voids and dry spots. Resin flow induced defects are known as the largest source on quality and reproducibility problems. These defects are often caused by unbalanced resin flows, which are directly related to the fiber permeability. Currently many computers simulations tools for predicting LCM processes behavior are available. Using these tools, process engineers can replace the traditional time-consuming trial-and-error pro-cess design procedures by optimized ones. One of the most critical input parameters with respect to the LCM modeling tools is the permeability of the reinforcement.Without a reliable character-ization of the fiber preform neither mathematical models nor computer simulations would be able to provide useful information . To fully characterize a fiber reinforcement it is necessary to measure its principal permeabilities. However, since LCM molded parts are, most of the time, thin shells, the through the thickness permeability is usually neglected and only planar permeabilities need to be evaluated. Permeability measurements have always been a source of disagreement among researchers of LCM process, results obtained from various installations show significant contra-dictions. As permeability is an intrinsic property of a fibrous material, it ought to be evaluated experimentally following a reliable and standardized procedure. The main objective of this thesis is the design of a set-up to measure in-plane (parallel to woven plane) permeabilities of LCM reinforcements by performing unidirectional injections. This method uses a rectangular mold of constant wi

The constitution of prepreg tack in automated fiber placement (AFP) is affected by a sensitive balance between adhesive interfacial bond strength and cohesive strength of the prepreg resin. In an effort to explore the role of interfacial liquid-solid interaction on the tack of commercial aerospace-grade epoxy prepreg, a surface wetting analysis was performed on AFP-related substrates. The standard test liquid combination water/diiodmethane and extracted neat epoxy resin were used for contact angle measurement employing the sessile drop method and the Owens-Wendt-Rabel-Kaelble (OWRK) model. Additional rheological and topographical analyses were carried out to account for viscous resin flow on surfaces of different roughness. The results from the material characterization are discussed against the background of tack measurement by probe tack testing utilizing a rheometer. Significant differences between the investigated surfaces in terms of both the maximum tack level and the onset temperatures of adhesion were found as a function of test parameters relevant for contact formation. General agreement with the experimental tack results was observed employing a topographically extended version of the Dahlquist criterion. For each substrate, a temperature-dependent critical storage modulus could be determined that conforms to the onset temperature of tackiness. Contact angle measurements revealed a correlation between the thermodynamic work of adhesion and maximum tack and, moreover, the tack onset in the adhesive regime when additionally incorporating surface topography. Matching ratios of polar and dispersive surface free energy and surface tension components were found to favor the molecular interaction at the interface between prepreg resin and substrate.

The constitution of prepreg tack in automated fiber placement (AFP) is affected by a sensitive balance between adhesive interfacial bond strength and cohesive strength of the prepreg resin. In an effort to explore the role of interfacial liquid-solid interaction on the tack of commercial aerospace-grade epoxy prepreg, a surface wetting analysis was performed on AFP-related substrates. The standard test liquid combination water/diiodmethane and extracted neat epoxy resin were used for contact angle measurement employing the sessile drop method and the Owens-Wendt-Rabel-Kaelble (OWRK) model. Additional rheological and topographical analyses were carried out to account for viscous resin flow on surfaces of different roughness. The results from the material characterization are discussed against the background of tack measurement by probe tack testing utilizing a rheometer. Significant differences between the investigated surfaces in terms of both the maximum tack level and the onset temperatures of adhesion were found as a function of test parameters relevant for contact formation. General agreement with the experimental tack results was observed employing a topographically extended version of the Dahlquist criterion. For each substrate, a temperature-dependent critical storage modulus could be determined that conforms to the onset temperature of tackiness. Contact angle measurements revealed a correlation between the thermodynamic work of adhesion and maximum tack and, moreover, the tack onset in the adhesive regime when additionally incorporating surface topography. Matching ratios of polar and dispersive surface free energy and surface tension components were found to favor the molecular interaction at the interface between prepreg resin and substrate.

In liquid composite molding processes, e.g., resin transfer molding, fiber preforms deform when mold is closed. This deformation of fiber preform due to mold closure causes inconsistencies to the permeability, and thus has a negative impact on resin flow. The variations in resin flow cause defects, e.g., dry spots and voids, resin-rich surfaces/zones, fiber distortions, which result in large variations in the product dimensions and mechanical performance. Thus, good understanding of the effects of process parameters on the deformation of fiber preform is necessary for developing high-quality affordable composites. An experimental study on the deformation of fiber preform for making angle-shaped composite parts is presented in this paper. The effects of enclosed angle, radius, fiber volume fraction, and stacking sequence were studied efficiently using design of experiments (DOE). Two open-channel molds were designed and fabricated for varying the design parameters. In each experiment run, the fiber preform was loaded into the mold and the mold was closed. The gaps formed between the fiber preform and inner mold surface were visually inspected by a microscope, and quantitatively characterized. The data were then analyzed. It is shown from the experiments that gaps occur at two locations: at corner radii and beside corner radii. The following conclusions are drawn from this experimental study: (1) fiber volume fraction is the most significant factor affecting the gaps at corner radii, and the gap thickness decreases with increasing fiber volume fraction; (2) the gap thickness decreases with increasing radius; and (3) the gap thickness of unidirectional preforms is larger than that of the cross-ply preforms.

Pultrusion is a continuousmanufacturing process used to produce high strength composite profiles with constant cross section.The mutual interactions between heat transfer, resin flow and cure reaction, variation in the material properties, and stress/distortion evolutions strongly affect the process dynamics together with the mechanical properties and the geometrical precision of the final product. In the present work, pultrusion process simulations are performed for a unidirectional (UD) graphite/epoxy composite rod including several processing physics, such as fluid flow, heat transfer, chemical reaction, and solid mechanics. The pressure increase and the resin flow at the tapered inlet of the die are calculated by means of a computational fluid dynamics (CFD) finite volume model. Several models, based on different homogenization levels and solution schemes, are proposed and compared for the evaluation of the temperature and the degree of cure distributions inside the heating die and at the postdie region.The transient stresses, distortions, and pull force are predicted using a sequentially coupled three-dimensional (3D) thermochemical analysis together with a 2D plane strain mechanical analysis using the finite element method and compared with results obtained from a semianalytical approach.

The MetRIX RIP (metal recovery through ion exchange) system uses a series of stirred tanks as resin-slurry contactors. The resin and pulp are transferred through the contactors in a countercurrent manner, allowing the slurry and resin flow rates to be adjusted independently to achieve the optimum metallurgical conditions even when subjected to varying feed flow rates and concentrations. The resin is transferred hydraulically and standard, commercially available equipment is employed throughout the plant. The technology can be applied cost effectively over a wide range of slurry densities making it suitable for use with leach processes including heap, in situ and tank leaching, without the need for a clarification circuit. The process functions efficiently at chloride concentrations of up to 70 g/l, employs a commercially available ion exchange resin and conventional eluant solutions of 1 M H2SO4, does not require a separate Fe removal step and produces an eluate suitable for direct precipitation of U. Test work carried out in the development of the process is described, including resin selection, optimisation of adsorption conditions in relation to impurities such as Cu and elution and stripping., The MetRIX RIP (metal recovery through ion exchange) system uses a series of stirred tanks as resin-slurry contactors. The resin and pulp are transferred through the contactors in a countercurrent manner, allowing the slurry and resin flow rates to be adjusted independently to achieve the optimum metallurgical conditions even when subjected to varying feed flow rates and concentrations. The resin is transferred hydraulically and standard, commercially available equipment is employed throughout the plant. The technology can be applied cost effectively over a wide range of slurry densities making it suitable for use with leach processes including heap, in situ and tank leaching, without the need for a clarification circuit. The process functions efficiently at chloride concentrations of up to 70 g/l, employs a commercially available ion exchange resin and conventional eluant solutions of 1 M H2SO4, does not require a separate Fe removal step and produces an eluate suitable for direct precipitation of U. Test work carried out in the development of the process is described, including resin selection, optimisation of adsorption conditions in relation to impurities such as Cu and elution and stripping.

Ion exchange using resin in pulp provides considerable capital and operating cost savings compared with conventional U flowsheets. A description is given of the MetRIX technology in which the resin and U-bearing pulp are continuously transferred through the contactors in a countercurrent manner, allowing the slurry and resin flow rates to be independently adjusted to achieve optimum metallurgical conditions at varying flow rates and concentrations. The resin is transferred using eductors which have been widely used in the water treatment industry and shown to have little effect on resin durability. A 1:150 scale demonstration plant was constructed in connection with the implementation of the technology at the Harmony Au operation in Witwatersrand, South Africa, where it is planned to extract U from ores from the Tshepong, Phakisa and Masimong mines prior to Au extraction. The flowsheet involves U extraction from an acid leached pulp using RIP, purification by solvent extraction and precipitation of ammonium diuranate. The plant was used to investigate resin bead size distribution, adsorption equilibrium isotherms at design pH, effect of chlorides in solution on U loading, loading kinetics, stripping equilibrium isotherms, resin durability and silica poisoning. The Purolite A500 ion exchange resin was selected based on the results of comparative tests. The demonstration plant programme successfully achieved the design objectives., Ion exchange using resin in pulp provides considerable capital and operating cost savings compared with conventional U flowsheets. A description is given of the MetRIX technology in which the resin and U-bearing pulp are continuously transferred through the contactors in a countercurrent manner, allowing the slurry and resin flow rates to be independently adjusted to achieve optimum metallurgical conditions at varying flow rates and concentrations. The resin is transferred using eductors which have been widely used in the water treatment industry and shown to have little effect on resin durability. A 1:150 scale demonstration plant was constructed in connection with the implementation of the technology at the Harmony Au operation in Witwatersrand, South Africa, where it is planned to extract U from ores from the Tshepong, Phakisa and Masimong mines prior to Au extraction. The flowsheet involves U extraction from an acid leached pulp using RIP, purification by solvent extraction and precipitation of ammonium diuranate. The plant was used to investigate resin bead size distribution, adsorption equilibrium isotherms at design pH, effect of chlorides in solution on U loading, loading kinetics, stripping equilibrium isotherms, resin durability and silica poisoning. The Purolite A500 ion exchange resin was selected based on the results of comparative tests. The demonstration plant programme successfully achieved the design objectives.

A new method to manufacture damage tolerant textile composites, which combines Resin Film Infusion with a fast and cost·efficient curing technology QuickstepTM, was investigated. The effect of process parameters on resin flow through carbon fibre preforms was analysed and model-based parameter optimisation resulted in considerable improvement of resin flow properties.

Models were developed which describe the curing process of composites constructed from continuous fiber-reinforced, thermosetting resin matrix prepreg materials. On the basis of the models, a computer code was developed, which for flat-plate composites cured by a specified cure cycle, provides the temperature distribution, the degree of cure of the resin, the resin viscosity inside the composite, the void sizes, the temperatures and pressures inside voids, and the residual stress distribution after the cure. In addition, the computer code can be used to determine the amount of resin flow out of the composite and the resin content of the composite and the bleeder. Tests were performed measuring the temperature distribution in and the resin flow out of composites constructed from Hercules AS/3501-6 graphite epoxy prepreg tape. The data were compared with results calculated with the computer code for the conditions employed in the tests and good agreement was found between the data and the results of the computer code. A parametric study was also performed to illustrate how the model and the associated computer code can be used to determine the appropriate cure cycle for a given application, which results in a composite that is cured uniformly, has a low void content, and is cured in the shortest amount of time.

Characterizing the interface bond of thin-ply composites is important for assessing the overall structural integrity. Due to the flexibility of thin composite laminates, it is not feasible to carry out mode I double cantilever beam (DCB) and mode II end notch flexure (ENF) tests, due to the large geometric changes undergone during testing. To reduce the compliance during testing, thick aluminum substrates are bonded to the two free-surfaces of the test laminates. DCB and ENF tests are specifically carried out in this configuration. A specific glass fiber plain weave interface of a 7-ply composite structure is tested. µCT imaging shows the presence of periodic voids of size scales of 200 µm, and local delaminated regions of 0 . 7 − 5 . 6 mm. The former is attributed to capillary effects from the glass tows, while the latter is due to insufficient resin flow during the two-cure manufacturing process.

The US Navy is aggressively pursuing larger components constructed using fiber-reinforced plastic or composite materials. However, the overall processes involved in manufacturing high-strength low weight composite components are still relatively new to US Navy shipbuilders. Vacuum Assisted Resin Transfer Molding (VARTM) a common composite fabrication methodology for composite structures is extremely sensitive to the material systems used and the production set-up or design. Any infusion-related defects easily lead to significant rework costs and schedule interruptions. Focusing on the DDG 1000 composite deckhouse and hangar the objective of this project was to develop a resin infusion process for each of two carbon fiber/vinyl ester resin composite joints that is predictable repeatable and reduces the defect rate experienced with current processes. Two common types of DDG 1000 composite deckhouse joints were examined in this project. Computer software was used to model and analyze the proposed VARTM infusion process designs yielding optimized composite panel joint infusion processes. Resin flow sensors were installed in each joint and were used to monitor resin flow fronts for the VARTM infusions. Non-Destructive evaluation of test specimens was performed to identify any potential defects in the test articles produced and also validate the computer models.

A process model that includes the coupled phenomenon of resin flow and preform compaction was developed and used to simulate resin infiltration of a fibrous preform using the vacuum-assisted resin transfer molding (VARTM) process. Flow of resin through the distribution medium and preform were modeled as flow through porous media. The finite element/control volume method was used to calculate the infiltrating fluid pressure distribution and track the progression of the flow front. The simulation results were compared with data obtained during infiltration of a carbon fiber preform with an epoxy resin. The parameters measured include the flow front location, resin pressure, and preform thickness change. With accurate inputs, the flow front locations and resin pressure distribution can be accurately predicted. The predicted transverse displacements do not agree well with the experimental measurements. The reasons for the differences are discussed, and further investigations are recommended to develop a more accurate compaction model., Presented at the International Conference on Flow Processes in Composite Materials (7th) held in Newark, DE on 7-9 July 2004. Pub. in Proceedings of the International Conference on Flow Processes in Composite Materials (FPCM7), p333-337, Jul 2004. Prepared in cooperation with the Dept. of Mechanical Engineering, Michigan State University, East Lansing, MI; NASA Langley Research Center, Hampton, VA; and the Dept. of Mechanical Engineering, McGill University, Montreal, Quebec, Canada. This article is from ADA433173 International Conference on Flow Processes in Composite Materials Held in Newark

The continued growth of vacuum-based processes has warranted the development of both models and experimental studies designed to capture the unique aspects associated with this manufacturing technique. To that end, this report summarizes an initial set of experiments that characterize both the process and the resulting mechanical properties of components fabricated under a variety of process conditions. Specifically resin flow studies are presented in part to demonstrate the relative influence of key parameters on the flow front developed during impregnation. The effect of the distribution medium, which is used in a commercial version of VARTM known as Seeman's Composite Resin Infusion Molding Process (SCRIMP), is explicitly characterized. In addition, the variation of part thickness is also examined, and potential mechanisms responsible for these variations are presented. A battery of mechanical tests designed to correlate the effect of various processing conditions are also presented. A major finding is that thickness variation can be significant and, to some degree, random; also, precompaction of the preform significantly influences the amount of consolidation pressure needed during impregnation. Dimensional variations due to gradients in the pressure distribution of the vacuum affect permeability (and hence resin flow), as well as dimensional tolerances in manufactured parts., Original contains color plates: All DTIC reproductions will be in black and white.

This document presents the results of the process control for a resin transfer molding (RTM) study. RTM is a composite materials processing method that involves placing a preform of dry reinforcement in a mold, injecting a thermoset resin into the mold, curing the resin, and demolding the finished part. This report describes the equipment and methodology for in-mold resin flow mapping and control. Mold port arrays are used to achieve directional control of in mold resin flow. A novel flow mapping system based on SMART Weave was implemented and tested. Combining the flow mapping and resin control schemes will lead to closed loop automation of the injection process.

The rapidly developing and widely distributed resin flow syndrom in Norway spruce (Picea abies) in southern Sweden has an unknown cause. One suggestion for its cause is the occurence of six "abnormally" mild winters from 1987/88 to 1992/93. This situation, together with hard spring frost is supposed to pose an unfavourable climatic combination for spruce. Daily temperature data (mean, maximum and minimum) for the period 1961-1994, from 20 synoptic stations from south Sweden have been used to investigate this hypothesis. In order to better analyse the effect of spring frost, a spring frost index (VFI) has been developed. This index is biologically based and defined as: "The largest temperature sum that can be calculated from the last day in a sequence of four days with air mean temperatures exceeding +5 °C, to the next following day with a minimum temperature that falls below -2 °C within the period April 1 to May 15. " The maritime influence on the air temperature in southern Sweden has increased since 1930. In a span of 65 years, the winter temperature in the 1990s has, in spite of this, not been exceptionally high, since mild winter periods appear frequently. It is also apparent that mild winters are commonly followed by a high VFI in the spring. The maritime influence is the main factor for where and when high VFI occur. A high VFI and spring frost during May is much more frequent in inland areas than in coastal settings. Hence, if spring frost is an important factor in developing the resin flow syndrom, inland areas ought to show more frequent damage. However, a survey in southern Sweden in 1994 does not indicate any higher frequency of the syndrom in the inland as compared to coastal areas. The observed resin flow syndrom can not be connected to a mild winter temperature climate nor to a high frequency or severety of spring frost.

This paper describes the role of surface energy effects, externally applied pressure, resin flow and fiber bed elasticity on the consolidation of thermoplastic-matrix composites manufactured by the powder impregnation route. Surface energy effects in the spreading of polymer droplets on fiber surfaces are discussed; then a model for the consolidation process is developed, relating the variables mentioned above. Consolidation experiments on powder-impregnated composites of the FIT type (Fibres Impregnees de Thermoplastique) were carried out using a mold attached to a servo-hydraulic testing machine. The model accurately predicts variations in void content during consolidation of carbon fiber/PEEK (CF/PEEK) and carbon fiber/PEI (CF/PEI) laminates. It was found that, at the pressures needed to achieve rapid consolidation, surface energy has a negligible influence on impregnation rate, but its effects on the void topology can be considerable. It was also shown that, when laminates of low void content are required, a minimum pressure is needed to overcome the effect of fiber bed elasticity., Correspondence Address: Connor, M.; Ecole Polytechnique Federale de, Lausanne, Lausanne, SwitzerlandNR 20140805

During the fabrication of a filament-wound composite case, which includes the winding and cure stages, the tension in the fiber can change significantly. If the level of fiber tension decreases excessively during fabrication, fiber slippage and clumping can occur. The resulting resin rich areas can significantly decrease the strength of the composite case. The objectives of the present investigation were 1) to measure the change in fiber tension during the winding and cure of a composite case wound with prepreg material, and 2) to calculate the change in tension during cure using a simulation computer program. Of particular interest was the loss of fiber tension due to resin flow (RFTL). A total of twenty-four tension loss experiments were performed using Amoco’s Thornel T40 fiber and T40/1908 prepreg materials. The parameters which were varied in the experiments were spool tension, oven heating rate, and the number of composite layers. Some of the experiments were designed to isolate and measure RFTL by comparing the changes in tension of winds of dry fiber and prepreg material. This method was not successful due to a similarity in prepreg and dry fiber tension loss characteristics. Low spool tensions were found to result in more tension loss due to resin flow (RFTL). RFTL was also greater for an increased number of layers, but was not affected by oven heating rate. During winding, significant tension loss occurred, probably due to deformation of the prepreg tow at room temperature. The change in fiber tension during cure was calculated using an existing cure simulation code (FWCURE) which was modified in this work to include the contribution to fiber tension made by the thermal expansion of the mandrel during cure. The revised code is called FWEXPAND. By adjusting the permeability model in FWEXPAND, the fiber tension during the cure of a single layer wind was accurately calculated. The predicted total RFTL of two multi-layer winds agreed reasonably well with the m