Liquid Resin Infusion Research Articles

Experimental analysis of low-velocity impact behaviour on flax-balsa biobased sandwich

This article deals with a detailed experimental study dedicated to the evaluation of the overall mechanical behaviour of a bio-based composite structure used in transportation industries. The sandwich structure is designed to increase the lightening, vibration damping, and composite recyclability. The considered materials consist of a Flax/Elium® laminate composite for skins associated with a balsa core. The sandwich structure was obtained using a one-shot liquid resin infusion process. Low-velocity impact tests were carried out on different sandwich configurations with the aim of characterizing the effects of the stacking sequence and the density and thickness of the core. Furthermore, an experimental comparative analysis was conducted involving two composite laminate types: Glass/Elium and Flax/Elium to enhance the specific behaviour of flax fibre composite to be used as skins in the sandwich structures. The impact tests were carried out at low velocities and at different levels of impact energy using a drop-weight test bench. Notable damage mechanisms have been identified, and a chronological sequence of their development has been suggested. Ultrasonic analyses using C-Scan imaging were applied to the opposite side of the impacted specimen. The research proves the efficient energy-absorbing capability of the biobased sandwich structure during impact. Finally, this study enables a deeper understanding of various parameters that influence the behaviour of sandwiches during low-velocity impacts, thereby facilitating more informed material selection for practical applications.

Wingbox Component Integration by Liquid resin Infusion

Wingbox Component Integration by Liquid resin Infusion

CFRP Conical Grid Space Structure with Embedded Fiber Optics: Design, Manufacturing and Test

This article discloses the activity developed in the framework of the research project “GRID” aiming at the feasibility demonstration of a fiber optic sensing system (FOS), based on fiber Bragg gratings (FGB), embedded in the ribs of a conical grid structure demonstrator in composite material (CFRP), manufactured by means of dry robotic winding, liquid resin infusion and oven curing. This structure represents an optimized and highly efficient conical adapter for satellite applications that was designed under the same requirements of a conventional CFRP benchmark solution in order to evaluate possible mass savings. Specific interfaces were conceived in order to facilitate the insertion of the fiber optics in the center of helical ribs—pausing the automated deposition phase of the dry preform—and secure them to the structure. Representative grid articles were produced and tested to select the materials and evaluate the preliminary feasibility of the integrated system in conjunction with the infusion process. The proper functioning and use of the sensing system were finally proven during the various phases of the mechanical testing campaign of the demonstrator. Such a campaign included stiffness and strength evaluations and culminated with the catastrophic failure of the structure. The significant amount of data collected from several sensors embedded in the ribs and from conventional sensors glued outside the ribs helped us to better understand the structural behavior and to validate the design and analysis models. The main steps of the design, manufacturing and tests of this project are here addressed.

A Constructal-Theory-Based Methodology to Determine the Configuration of Empty Channels Used in the Resin Impregnation of a Square Porous Plate

Liquid composite molding techniques are largely used to produce pieces such as truck cabins or wind turbine blades. The liquid resin infusion processes use a network of injection channels to improve the resin flow through a porous-reinforced medium. The present numerical study predicts the positioning of empty channels by applying constructal theory to an idealized problem. The channels’ position and size were not predefined but instead constructed (made to grow) from an elemental channel. Two strategies were tested for channel growth: each new elemental channel was placed next to the region with the lowest or highest resistance to resin flow. The geometric configuration of the channels was constructed using a control function instead of using pre-defined shapes. The conservation of mass and momentum and an additional transport equation for the resin volume fraction were solved using the finite volume method. The volume of the fluid model was used for the treatment of the multiphase flow (air + resin). The growth of an empty channel with the lowest resistance strategy led to a decrease in the injection time and waste of resin. The size (resolution) of the elemental channel also affected the performance indicators and geometric configuration of the injection channels.

Multi-stage, in-situ polymerisation for low-exotherm, liquid resin infusion of thick thermoplastic laminates at room temperature

This study exploits the unique attributes of a reactive thermoplastic acrylic resin system (room-temperature liquid-resin infusibility, in-situ polymerisability, and room-temperature weldability) to achieve additive-free mitigation of exothermic heat generation during thick laminate production. Additives are typically required when thicknesses exceed 12 mm, but their use often compromises the degree of polymerisation and mechanical performance. An innovative multi-stage manufacturing scheme has been used to achieve a 55 °C reduction in exothermic peak temperature during the production of a 16-mm-thick laminate compared to the use of a standard resin infusion (89 °C) for the same thickness. Laminates produced using the multi-stage scheme were also found to exhibit 24 % higher short-beam shear strengths than those obtained via standard resin infusion, suggesting improved part quality as an additional benefit. Further demonstrating the applicability of the proposed method, a 40-mm-thick laminate was successfully produced with a peak temperature of only 60 °C. This work highlights the potential of room-temperature welding for practical and low-cost production of ultra-thick laminates at room temperature.

Ad-hoc solutions for ultrasonic inspection of highly complex aircraft composite structures

Nowadays, the ultrasonic inspection (UT) is the most common non destructive technique (NDT) for composite components in the aerospace industry, due to its high accuracy, reliability and the degree of industrialization. Although UT is widely developed, new manufacturing processes and part concepts are continuously pushing the technology for new improvements and applications. This is the case of the geometries resulting from novel out of autoclave composites manufacturing technologies, Liquid Resin Infusion (LRI) or Resin Transfer Moulding (RTM), allow the fabrication of parts in one shoot, with focus in bringing answers to the challenge of manufacturing fully assembled parts and avoiding secondary assembly phases but also limiting the accessibility for NDT inspections. In this sense, one of the critical issues in the aeronautic sector is the improvement of the inspection of geometries with difficult access and small dimensions. The requirement of the aeronautic industry of guaranteeing the quality of the primary composite structures implies the inspection of the whole component through certified technologies. This constraint, together with the lack of technological solutions for the inspection of regions with limited accessibility is blocking the industrial implementation of optimized manufacturing processes. The present work describes the design and development of adaptive hardware solutions for the single and phased array UT inspection of internal structures on a highly integrated composite aeronautic component. The final solution has been obtained as result of an iterative design process and manufactured through additive manufacturing technology (Powder Bed Laser Fusion, formerly Selective Laser Sintering) using polyamide. This device was validated in a for inspection of flat surfaces of stiffener internal structure, belonging to the composite flap demonstrators of lengths: 3 meters in a first approach, and 8 m for final validation. This novel inspection solution has been performed in the framework of the FLAP project to develop and innovate the manufacturing process for complex mobile surfaces in a collaboration between Aernnova, through its Composites Division, and CATEC teams.

Influence of fibre orientation, moisture absorption and repairing performance on the low-velocity impact response of woven flax/Elium® thermoplastic bio-composites

The importance of natural reinforced bio-composite materials with desirable properties such as high modulus-to-weight ratio, good impact resistance, and the ability to be easily repaired is crucial in the industry. A woven flax/Elium® thermoplastic bio-composite is manufactured to challenge these needs. Elium® is the only resin that permits the manufacture of large parts with thermoset-like processes, as Liquid Resin Infusion presented in that work. The paper highlights the influence of stacking fibre orientation, moisture absorption, and repair aptitude on its impact resistance. An instrumented drop tower was needed to conduct low-velocity impact tests at several energies and high-speed image coupled with microscopic observations was used to assess the damage evolution. The impact resistance was improved for the dry (0/90)6 orientation, but moisture absorption decreased its impact peak force by 20%. A three-point bending test was preferred to compression after impact for studying the residual properties after impact. The bio-composites with (±45)6 orientation showed higher impact residual performance than the (0/90)6 orientation, and corresponded to the reduction of maximum bending force by 20% than that of the reference. In addition, a thermo-compression process was applied to repair the impacted plates and conduct multiple impact/repair cycles which showed a significant recovery of stiffness and maximum impact force at 4J on (0/90)6 plates, highlighting their potential for repair in the automotive and marine industries.

Effects of reactive and non-reactive tackifying agents on mechanical neat resin and composite performance for preforming processes and Liquid Resin Infusion (LRI) techniques

Preforming processes can be used for automated manufacturing of fiber reinforced polymers. Different technologies are used for processing of dry textile fabrics into 2D or 3D preforms. Due to missing tack of dry fabrics, auxiliary binder systems are used for fixation of the fabrics onto a substrate material and in order to achieve sufficient adhesion between layers. In this study, seven reactive and non-reactive tackifying agents have been dissolved in neat resin samples of three epoxy resin systems, showing different degrees of solubility and a variation on neat resin tensile properties (ΔσAVG = 20%) as well as a reduction on thermal properties (up to ΔTg = −18 °C). Subsequently, fiber reinforced polymers were manufactured using Liquid Resin Infusion techniques in order to characterize the influence of binder systems on water absorption (cs,max = 1.38 wt%) and Interlaminar Shear Strength (ILSS). It was shown that ILSS properties are negatively affected by non-reactive tackifying agents (up to −27%).

Impact Behaviors of Sandwich Composites Produced by Liquid Resin Infusion: Influences of the Process Parameters

Impact Behaviors of Sandwich Composites Produced by Liquid Resin Infusion: Influences of the Process Parameters

Manufacturing and Characterization of Interply Hybrid Polymeric Biocomposite Material Reinforced with Glass and Carbon Fibers

AbstractThe objective of this study is to investigate the mechanical properties of the polymeric composite hybrid type interply reinforced with glass fibers GF and carbon fibers CF with the structure of the material consisting of: a) three layers CF:GF with the sequence [CF/GF/CF]; b) five layers CF:GF with the sequence: 1) [CF/GF/CF/GF/CF] and 2) [CF/CF/GF/CF/CF]. The GF:CF hybrid biocomposite interply type is made using the working methodology based on the Liquid resin Infusion (LRI) and Vacuum infusion techniques. The general mechanical properties are evaluated experimentally using standard tensile and bending tests using five specimens made according to ASTM standards. Based on the experimental results and the diagrams obtained at the tensile and bending tests of the hybrid polymeric biocomposite type interply comparisons are made regarding the mechanical properties of the composite for each type of structure. The general results confirm, from a mechanical point of view, the usefulness of this type of composite for engineering and biomedical applications.

ELADINE: sensor monitoring and numerical model approach for composite material wing box shape distortions prediction

Out-of-Autoclave technologies are emerging as cost-effective alternatives to autoclave cure prepreg. However, their implementation in aerospace industry is still presenting many challenges. A common problem is the shape distortions that results in geometry mismatches with the tool. A way to avoid this and ensure a good final quality part is identifying the mechanisms that induce these deformations and optimize the manufacturing process of each component with the aim of reducing the production of faulty parts. The main objective of ELADINE project is to provide a method for shape distortions prediction on composite integral structures using an experimental-numerical approach. Different manufacturing parameters were monitored using Fiber Bragg Grating (FBG) sensors and DC-dielectric (DC) sensors and the resulting part geometry was examined by means of 3D coordinate analysis. The study performed for LRI (Liquid Resin Infusion) manufactured parts and the scenarios considered for the calibration of a Finite Element Method (FEM) based simulation tool are presented in the article. The resulting model will be implemented in a sub-scale demonstrator and, eventually, in a full 7-meter composite wing-box.

Improvement of European thin haul mobility: the role of small Green commuter aircraft

In the last years, transportation demand has grown up as consequence of the increase in leisure, and business for both heavily travelled routes (between major cities) and thin routes (between remote areas, and remote areas with major cities).In parallel, aviation sustainability issues have become more and more important, being aviation pollution an important source of global environmental pollution. Moreover, several States, as well as private Companies travelling for business, have introduced bans and/or special taxes on short flights covering distances that could be travelled by train in less than 3 hours. These regulations have a major impact on short haul thin routes, which could be covered by small air transport (up to 19 seats). Thus, dedicated research and technology innovation effort has been put in place over the last years to develop eco-friendly, and economically viable, aircraft able to answer sustainability needs, market demand, and cost-effectiveness.In particular, Clean Sky 2 Joint Undertaking, a public-private partnership between the European Commission and the European aeronautics industry, has co-financed the SAT (Small Air Transport) TA (Transverse Activity) initiative. SAT TA main goal is to address technology innovations to reduce environmental impact as well as operational cost of small commuters, ensuring improved levels of operational safety. SAT TA is a Project with an overall EU (European Union) funding of about 68 mln€, including small aircraft OEMs (Original Equipment Manufacturers), major aircraft suppliers, SMEs (Small and Medium Enterprises), research centres and academia (more than 80 Partners involved).The research activity has focused on the following main technology streams:•New generation turboprop engine with reduced fuel consumption, emissions, noise and maintenance costs for 19 seats aircraft.• More electric digital systems including:• Affordable fly-by-wire architecture for small aircraft (CS23 certification rules).• More electric systems replacing pneumatic and hydraulic aircraft systems (hybrid de-ice system, landing gear and brakes, high voltage EPGDS –Electrical Power Generation and Distribution System –).• Advanced avionics for small aircraft, to reduce pilot workload, paving single pilot operations for 19 seats.• Affordable airframe structures including:• Low cost composite wing box and nacelle using OoA (Out of Autoclave) technology, LRI (Liquid Resin Infusion) and automated deposition process.• Affordable small aircraft manufacturing of metallic fuselage by means of FSW (Friction Stir Welding) and LMD (Laser Metal Deposition).• Advanced cabin comfort with new materials and more comfortable seats.To address the abovementioned technologies, two different platforms have been designed: a Reference and a Green aircraft. Reference aircraft is a virtual aircraft designed considering 2014 technologies with an existing engine assuring requested take-off power. Green aircraft is designed integrating the technologies developed within Clean Sky 2.The present work describes designed aircraft, and preliminary mission analyses, showing the achievement of Project goals (20% CO2, 20% NOx reduction for the design mission).

Liquid Resin Infusion Process Validation through Fiber Optic Sensor Technology.

In the proposed work, a fiber-optic-based sensor network was employed for the monitoring of the liquid resin infusion process. The item under test was a panel composed by a skin and four stringers, sensorized in such a way that both the temperature and the resin arrival could be monitored. The network was arranged with 18 Fiber Bragg Gratings (FBGs) working as temperature sensors and 22 fiber optic probes with a modified front-end in order to detect the resin presence. After an in-depth study to find a better solution to install the sensors without affecting the measurements, the system was investigated using a commercial Micron Optics at 0.5 Hz, with a passive split-box connected in order to be able to sense all the sensors simultaneously. The obtained results in terms of resin arrival detection at different locations and the relative temperature trend allowed us to validate an infusion process numerical model, giving us better understanding of what the actual resin flow was and the time needed to dry preform filling during the infusion process.

Optimization of liquid resin infusion process (LRI) using finite element simulation software

Infusion processes as LRI (Liquid Resin Infusion) can lead to a significant cost reduction but are not yet so widespread in aeronautical applications. Some of its advantages are: no need of autoclave, lower costs of materials, and the possibility of fabricating integrated structures that reduce the number of joints. However this process still presents some drawbacks such as the need to apply the "Test-Error" method or availability of extensive experience in the design of structures. The risk and cost associated with the infusion process is high, so the industry tends to use more conservative designs or adopt other less competitive alternative technologies and materials. For this reason, a simulation tool is essential to optimize the LRI process. In this work, the optimization and validation of a demonstrator of a wing box of an aircraft has been carried out using the PAM-COMPOSITES simulation software. Firstly, a geometric study and discretization of model has been carried out, secondly, the parameters that govern the process have been defined, and finally an analysis and validation of results have been carried out by means of a experimental infusion of the demonstrator. The obtained results have allowed us to control manufacturing times, improve injection and vacuum ports, and predict dry zones and front flow velocity. Simulations have allowed us to optimise the LRI process of the demonstrator, thus giving continuity to other studies on the viability of the infusion processes in primary structures in the aeronautical sector.

Simulation strategy to compensate spring-in deformations in aeronautical panel made by liquid resin infusion

Spring-in in composite manufacturing is a relevant non desired effect that complicates the industrialization process of new composite parts. Geometrical deviations of the part with regard to the nominal dimensions  hinders posterior assembly operations or even can cause unconformities (part rejection). Although some correction operations may be introduced in the assembly method to absorb these deviations, a preferred approach is to compensate the tool geometry to produce the part within tolerances. This contribution presents a methodology that, in an iterative process, links a MEF simulation workflow for the prediction of process induced distortions, a routine to compute deviations and updating tool cavity surface, till the deviations are within a target tolerance. The spring-in calculation engine is implemented in Abaqus Standard with specific subroutines to model resin curing kinetics, heat generation, cure dependent mechanical constitutive model with consideration of thermal expansion and cure shrinkage, and specific strategies to simulate the tool/part interactions. The spring-in engine is incorporated in an external Python manager in charge of post-processing results, updating the mesh and launching the executions. This methodology aims at proposing a modified tool surface geometry that could be used to build a compensated tool at first, reducing industrialization time and cost.

Effect of graphene nanoplatelets addition in benzoxazine carbon fiber laminates properties

In this work, the effect of graphene nanoplatelets (GNPs) addition in the mechanical, thermal and electrical properties of carbon fiber composites was studied. GNPs were incorporated into benzoxazine matrix and nanocomposites with a 0.5 and 2 wt.% of graphene nanoplatelets were manufactured. The effect of this nanoreinforcement in benzoxazine mechanical properties as well as in its thermal and electrical conductivity was evaluated. Carbon fiber composites has been manufactured by means of liquid resin infusion (LRI) technique using the nanocomposites prepared. The manufacturing process with the nanocomposite containing a 2 wt.% of GNPs presented some filtration problems which hindered its characterization. The laminate with a 0.5wt.% of nanoreinforcement showed an increase in both thermal and electrical conductiviy regading to the panel with unmodified benzoxazine.

Evaluation of the flexural properties and failure evolution of a hybrid composite manufactured by automated dry fibre placement followed by liquid resin infusion

The market for composites is developing rapidly due to the widespread general requirement for lightweight design in various industries. However, the proliferation of fibre-reinforced composites is limited partly due to the lack of ductility associated with these materials. Hybridisation of fibres has emerged as an important strategy to increase the ductility of polymer composite materials. In the present work, water based dispersion was used to develop a dry fibre carbon tape and a hybrid glass/carbon tape which are both compatible with automated deposition techniques. Dry fibre preforms were manufactured using laser-assisted dry fibre placement (DFP) and laminates were subsequently manufactured using vacuum assisted liquid resin infusion. The hybrid composite exhibited both higher flexural strength (8%) and higher strain-to-failure (58%) relative to the carbon based laminate. To understand the failure modes, X-ray micro-computed tomography was used in conjunction with interrupted flexural tests to monitor the evolution of damage. The progressive failure analysis revealed that for hybrid composites, damage propagation was delayed due to the staggered arrangement of glass and carbon fibres. The majority of damage in the hybrid composite was located in the carbon fibres tows.

LRI-fabricated composite demonstrators for an aircraft fuselage on the basis of a Building Block design approach

A Liquid Resin Infusion (LRI) fabrication process is presented for manufacturing of composite aircraft demonstrators. A Building Block (BB) assessment approach is adopted, structured in coupon, element and subcomponent level. The quality of fabrication is quantified in terms of porosity and fiber volume fraction and the properties of the composite ply are determined by means of micromechanical models and coupon mechanical tests. At element and subcomponent level, an aft-fuselage bulkhead joint and a floor beam are modeled and tested in full scale. Results provide a measure of process capabilities and parts quality, indicating low void content and stiffness comparable to a similar prepreg.

Influence of environmental conditioning on mechanical properties of carbon dry fibre preformed thermoplastic matrix composites manufactured via automated placement-resin infusion process

In the present work, dry fibre placement (DFP) of co-polyamide based carbon fibre spreadtow bindered tape for fabrication of thermoplastic acrylic resin composites was explored. The DFP followed by vacuum assisted liquid resin infusion (LRI) is expected to be an alternative process to traditional preforming approaches. This research work looks at the influence of water immersion on the performance of the composites was studied. The thermo-mechanical behaviour of the aged and unaged samples were carried out as a function of temperature. The flexural strength of aged samples dropped by 4 and 17% after one and three months respectively. However, no significant changes were observed in flexural modulus compared to unaged. The interlaminar shear strength decreased by 19% and 35% after one month immersion and three months immersion. The results were complimented by fractographic and morphological studies.

Development of Detailed FE Numerical Models for Assessing the Replacement of Metal with Composite Materials Applied to an Executive Aircraft Wing

This work provides a feasibility and effectiveness analysis, through numerical investigation, of metal replacement of primary components with composite material for an executive aircraft wing. In particular, benefits and disadvantages of replacing metal, usually adopted to manufacture this structural component, with composite material are explored. To accomplish this task, a detailed FEM numerical model of the composite aircraft wing was deployed by taking into account process constraints related to Liquid Resin Infusion, which was selected as the preferred manufacturing technique to fabricate the wing. We obtained a geometric and material layup definition for the CFRP components of the wing, which demonstrated that the replacement of the metal elements with composite materials did not affect the structural performance and can guarantee a substantial advantage for the structure in terms of weight reduction when compared to the equivalent metallic configuration, even for existing executive wing configurations.