Resin Infusion Under Flexible Tooling Research Articles

Investigation of the resin infusion process and mechanical performance of carbon fiber reinforced plastic composites from recycled carbon fiber

The disposal of Fiber Reinforced Composites (FRCs) waste is becoming a very critical aspect, from both a technical and an economic point of view, due to the continuous increase of the production of such a class of materials. Thus, the possibility to produce new composites by employing recycled materials is a crucial aspect both to guarantee the circularity of the manufacturing processes and the reduction of costs. In this work, the manufacturing process, together with the performance of a carbon fiber-reinforced plastic (CFRP) laminate obtained by employing into sandwich structures a novel commercial recycled non-woven carbon fabric with an epoxy resin, have been investigated. The fabrication process based on the Resin Infusion under Flexible Tooling (RIFT) has been selected and performed in different conditions. The mechanical behavior of the resulting laminates has been investigated by quasi-static tensile, and flexural characterization, to evaluate both the optimal conditions for the process, and the possible anisotropy of the product. Moreover, thermogravimetric analysis (TGA) was applied to complete the post-processing characterization of the resulting laminate by determining the actual carbon fibers (CFs) content, thus, to validate the reproducibility of the manufacturing process. The laminates obtained by the RIFT method exhibited good mechanical properties and isotropy if cross-ply stratification is adopted. The use of recycled CFs allows high sustainability and reduced cost for the composites, making the RIFT method investigated a scalable process and the so-manufactured products a valid candidate for numerous applications.

Lightning strike damage resistance of carbon‐fiber composites with nanocarbon‐modified epoxy matrices

AbstractCarbon‐fiber reinforced polymer (CFRP) composites are replacing metal alloys in aerospace structures, but they can be vulnerable to lightning strike damage if not adequately protected due to the poor electrical conductivity of the polymeric matrix. In the present work, to improve the conductivity of the CFRP, two electrically conductive epoxy formulations were developed via the addition of 0.5 wt% of graphene nanoplatelets (GNPs) and a hybrid of 0.5 wt% of GNPs/carbon nanotubes (CNTs) at an 8:2 mass ratio. Unidirectional CFRP laminates were manufactured using resin‐infusion under flexible tooling (RIFT) and wet lay‐up (WL) processes, and subjected to simulated lightning strike tests. The electrical performance of the RIFT plates was far superior to that of the WL plates, independent of matrix modification, due to their greater carbon‐fiber volume fraction. The GNP‐modified panel made using RIFT demonstrated an electrical conductivity value of 8 S/cm. After the lightning strike test, the CFRP panel remains largely unaffected as no perforation occurs. Damage is limited to matrix degradation within the top ply at the point of impact and localized charring of the surface. The GNP‐modified panel showed a comparable level of resistance against lightning damage with the existing copper mesh technology, offering at the same time a 20% reduction in the structural weight. This indicates a feasible route to improve the lightning strike damage resistance of carbon‐fiber composites without the addition of extra weight, hence reducing fuel consumption but not safety.

Interaction mechanisms and damage formation in laser cutting of CFRP laminates obtained by recycled carbon fibre

The increase in the use of composite materials poses the problem of their disposal/recycling after the End of Life (EOL). Different strategies were developed to recycle composite material, resulting in the availability of new raw materials, characterised by overall good mechanical properties and significantly low cost. However, the applicability of these materials to industrial production also depends on the possibility of producing and processing them with likewise available technologies. Among the production and processing technologies that can be adopted for recycled composite materials, resin infusion under flexible tooling (RIFT) and laser machining, respectively, stand out above all due to the high production/machining speed compared to the cost. This paper investigates the possibility to apply both these technologies to carbon fibre–reinforced polymer laminates obtained by adopting recycled carbon fibres. Recycled CFRP plates of about 2.7 mm in thickness were produced by RIFT and characterised in tensile and flexural tests. After mechanical characterisation, cutting tests were performed by using a 450 W QCW fibre laser, varying the pulse power, the pulse length, and the pulse overlap. The kerf geometries and the HAZ extension were measured at the upper and bottom parts as well as in the section. Analysis of variance was adopted to define which and how the process parameters affect the kerf dimension and HAZ extension. Results showed that it is possible to cut the composite at a cutting speed up to 2000 mm/s, obtaining, in the best conditions, narrow kerf, limited HAZ, and taper angle of about 0°.Graphical abstract

CFRP Laminates with Recycled Carbon Fiber: Resin Infusion and Mechanical Characterisation

The possibility to produce new components using reclaimed non-woven carbon fabric has been investigated. Being composite waste production increased, different strategies and technologies for recycling are developing to face criticalities and economic aspects related to their disposal. In this scenario, CFRP laminates with recycled carbon fiber and epoxy vinyl ester resin have been fabricated by Resin Infusion under Flexible Tooling (RIFT) and mechanical characterization has been performed to investigate their behavior under tensile, flexural and macro-indentation loads.

Multi-Functional Carbon Fiber Reinforced Composites for Fire Retardant Applications

Development of multifunctional flame retardant (FR) polymer composite was done. Flame retardant polymer composite was prepared by modifying diglycidylether of bisphenol-A (DGEBA) epoxy. Modification involved two types of FR. Reactive type FR used was phosphoric acid and additive type FR used was magnesium hydroxide. Composite was fabricated using resin infusion under flexible tooling (RIFT) process. Different FR epoxy samples were evaluated by compression test, UL 94. The carbon fiber reinforced polymer composite with attributes of flame retardancy were characterized using in-plane shear test, to estimate the structural properties, and UL-94 test, to estimate the fire performance. FR composite exhibited UL-94 rating of V-1 and a shear modulus of 9.7 GPa, which proved it to multifunctional.

Improvement on Fatigue Performance of 3-D Orthogonal Woven Composite with Nanoclay Modification

3-D orthogonal woven composite (3DOWC) has attracted great interest in the industrial and energy fields, due to their excellent mechanical properties. However, due to the poor bonding strength between fiber and epoxy, it’s mechanical properties, especially the fatigue behavior are critical for structural design in the practical applications. The nanoclay modification composite reinforced with 3-D orthogonal woven fabric (3DOWF)/epoxy resin was fabricated using resin infusion under flexible tooling (RIFT). The quasi-static tensile and fatigue behavior of 3-D orthogonal woven composite (3DOWC) in 0 ° and 90 ° inclined to warp direction were evaluated and compared to the pristine one or composite material not modified with nanoclay. The fatigue behavior such as the S-N curves, stress-strain curves, stiffness degradation curves and residual strength were also obtained. The results show that the tensile strength, modulus and the fatigue life were improved effectively due to nanoclay modification. However, the stiffness degradation of nanoclay addition in 90 ° direction was decreased.

Multifunctional structural supercapacitors based on polyaniline deposited carbon fiber reinforced epoxy composites

Structural energy storage devices are recently an area of special interest as they simultaneously exhibit load-bearing and electrical energy storage capabilities. These multifunctional composites, along with their better specific mechanical strength and electrochemical properties, can be used in civil and defense applications. In the current study, novel structural supercapacitors, fabricated from polyaniline deposited carbon fabric, filter paper, and epoxy-based polymer electrolyte, via resin infusion under flexible tooling (RIFT) method, are investigated. Both as-received, as well as chemically activated carbon fiber mats, are trialed to examine the effect of surface area and pseudo-capacitive mechanisms of the polyaniline coated CF electrodes in structural symmetrical supercapacitors. Structural supercapacitors, fabricated from the activated carbon fabric electrodes, at a polyaniline coating density of 0.05 mg.cm−2, show 22.2 mF.g − 1 specific capacitance with a resultant 49.4 mWh.kg−1 specific energy and a 58.4 W.kg−1 specific power along with a shear modulus of 1.1 GPa and a shear strength of 6.3 MPa. The results show that depositing polyaniline onto the activated carbon fibers increases both the electrical and mechanical properties of the fabricated supercapacitors.

Mechanical characterisation of CFRP laminates with recycled carbon fiber obtained by resin infusion under Flexible Tooling (RIFT) technology

The increasing use of composites in several industrial fields has increased composite waste production with the associated problems and costs related to their disposal. In this contest, different strategies and technologies for recycling composite material at the end of its life are available. The adoption of appropriate recycling policies allows using raw materials with excellent properties at a cost significantly low. In this scenario, the production of CFRP laminates by Resin Infusion under Flexible Tooling (RIFT) technology represents a possibility to produce new components, starting with reclaimed non-woven carbon fabric. This paper investigates the mechanical characteristics of CFRP laminates with recycled carbon fiber obtained: quasi-static and dynamic tests were carried out to investigate their behavior under tensile, flexural and low-velocity impact loading, respectively. In addition, the influence of the stratification was assessed on mechanical characteristics.

Mechanical Properties Improvement of Nanoclay Addition Epoxy 3D Orthogonal Woven Composite Material

In this study, the influence of nanoclay on mechanical properties of epoxy/3D orthogonal glass fiber woven composite was studied. The DK2 polymer-grade organic nanoclay modification composite specimen reinforced with 3D orthogonal woven fabric/epoxy was manufactured by means of Resin Infusion under Flexible Tooling (RIFT) process. Firstly, the modification mechanism with nanoclay was characterized by means of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and transmission electron microscope (TEM). Secondly, as far as the tensile behavior between the fiber/matrix of the composite was concerned, the modification process was optimized by means of nonlinear least square fitting. The results show that the bonding strength between the fiber and matrix was improved and the delamination and debonding between fiber and matrix was retarded and shifted to cohesive failure of the matrix due to the nanoclay modification with respect to results from FT-IR, XRD and TEM. The tensile strength and modulus of composite were increased by 23.32 % and 16.42 % respectively due to 3 of nanoclay addition. The contact angle also shows that the dispersion effect and wettability at this state. The tensile stress-strain curve was fitted by applying nonlinear fitting. It can be concluded that there has a good modification effect with 3 wt% of nanoclay addition.

Translaminar fracture toughness and fatigue crack growth characterization of carbon‐epoxy plain weave laminates

An experimental investigation of mode‐I translaminar fracture toughness and fatigue crack growth behavior of a carbon fiber‐epoxy plain weave laminate manufactured by resin infusion under flexible tooling (RIFT) is presented in this article. Pre‐cracked compact tension (CT) specimens were used to perform both quasi‐static and fatigue tests. Different data reduction techniques for fracture toughness calculation were used and compared with each other. The ASTM E399 test method was modified to account for the material orthotropy and specimen geometry effects using a correction function based on a numerical evaluation of the strain energy release rate. The proposed modification shows good agreement against other experimental methods found in the literature and its application was validated for fatigue tests. Fatigue testing shows that failure in undesired modes is likely to occur prior to translaminar fracture, which was attributed to a higher tensile fatigue threshold than compression or shear fatigue threshold presented by the composite in analysis. Increasing the specimens’ initial notch length was a solution for avoiding these types of failure. The experimental results were compiled in the form of a Paris curve, and their particularities were discussed. A fractographic analysis was carried out to define damage patterns and its evolution process in both types of tests. POLYM. COMPOS., 40:3791–3804, 2019. © 2019 Society of Plastics Engineers

Multifunctional structural supercapacitors based on graphene nanoplatelets/carbon aerogel composite coated carbon fiber electrodes

Multifunctional structural energy storage composites have gained an increasing interest as they offer volume and weight savings in different military and civilian applications. Current engineering approach is to develop structural energy storage materials having ability to perform energy storage and load bearing functions simultaneously. Energy storage composites have ability to simultaneously store electrical energy and bear mechanical loads. We have successfully fabricated structural fiber reinforced polymer composites that can simultaneously store electrochemical energy and withstand structural loads. Structural supercapacitors are fabricated by using graphene nanoplatelets (GNPs)/aerogel composite modified carbon fibers as electrodes and reinforcement, filter paper as a separator and multifunctional epoxy resin as an electrolyte and matrix. The structural supercapacitors were prepared by using resin infusion under flexible tooling (RIFT) method. The increasing concentrations of graphene nanoplatelets in carbon aerogels boost the electrochemical and shear performance of structural supercapacitors. A structural supercapacitor with an energy density of 0.8 Wh. kg−1, power density of 108 W.kg−1 and a normalized shear modulus of 2.6 GPa has been displayed in the current study.

Carbon fiber reinforced modified bisphenol-a diglycidylether epoxy composites for flame retardant applications

We have developed novel multifunctional flame retardant polymer composites that exhibit better fire performance. Flame retardant polymer composites are prepared by infusing woven carbon fibers with phosphoric-acid-modified crosslinked diglycidylether of bisphenol-A epoxy matrix through the resin infusion under flexible tooling (RIFT) process. In this paper, we have explored various design factors of the fire retarding epoxy resin by modifying the resin physically as well as chemically. Different flame retardant epoxy samples are evaluated by compression test, UL 94, thermogravimetric analysis and dynamic mechanical thermal analysis. The fabricated flame retardant polymer composites have been characterized using in-plane shear test, to estimate the structural properties, and UL-94 test, to estimate the fire performance. In this study, a flame retardant composite, simultaneously exhibiting a UL-94 rating of V-0 and a shear modulus of 9.5 GPa, has been reported.

Multifunctional structural lithium ion batteries for electrical energy storage applications

Multifunctional structural batteries based on carbon fiber-reinforced polymer composites are fabricated that can bear mechanical loads and act as electrochemical energy storage devices simultaneously. Structural batteries, containing woven carbon fabric anode; lithium cobalt oxide/graphene nanoplatelets coated aluminum cathode; filter paper separator and cross-linked polymer electrolyte, were fabricated through resin infusion under flexible tooling (RIFT) technique. Compression tests, dynamic mechanical thermal analysis, thermogravimetric analysis and impedance spectroscopy were done on the cross-linked polymer electrolytes while cyclic voltammetry, impedance spectroscopy, dynamic mechanical thermal analysis and in-plane shear tests were conducted on the fabricated structural batteries. A range of solid polymer electrolytes with increasing concentrations of lithium perchlorate salt in crosslinked polymer epoxies were formulated. Increased concentrations of electrolyte salt in cross-linked epoxy increased the ionic conductivity, although the compressive properties were compromised. A structural battery, exhibiting simultaneously a capacity of 0.16 mAh L−1, an energy density of 0.32 Wh L−1 and a shear modulus of 0.75 GPa have been reported.

Tough, natural-fibre composites based upon epoxy matrices

Flax fibres and cellulose fibres were used to manufacture composites with particle-modified epoxy matrices in order to develop ‘green’ composites which possess relatively high values of interlaminar fracture energy, G c. The flax used had a unidirectional architecture of continuous yarns spun from short, interlocked fibres. The regenerated cellulose consisted of continuous and non-twisted pure cellulose fibres in a plain-woven architecture. The natural-fibre-reinforced-polymer (NFRP) composites employed an anhydride-cured diglycidyl ether of bisphenol-A epoxy as the matrix. The epoxy polymeric matrix was modified with (a) silica nanoparticles, (b) rubber microparticles, and (c) a combination of both of these types of particles to give a hybrid-toughened epoxy matrix. The composites were manufactured via a resin infusion under flexible-tooling (RIFT) process. Preliminary studies on the NFRP composites manufactured using the initial-RIFT process clearly showed the deleterious effect that moisture present in the natural fibres had upon the properties of the NFRP composites, since the trapped water cannot escape from the composite panel. Hence, an optimised-RIFT process was developed whereby the natural fibres were dried in a fan oven prior to being employed in the RIFT process. This reduced the water content of the fibres from around 9 to 10 wt% to about 1 wt%. Significant improvements in the physical and mechanical properties were recorded for the NFRP composites manufactured using this optimised-RIFT process. Indeed, in particular, very dramatic improvements in the G c of the NFRP composites were measured, especially when the epoxy polymeric matrix was modified using the silica nanoparticles and/or rubber microparticles. For example, a steady-state propagation value of G c of about 1935 J/m2 was measured for the flax–fibre composite with the hybrid epoxy matrix, compared to values of 1110 and 535 J/m2 for the flax–fibre and glass–fibre composites based on the unmodified (i.e., the ‘control’) epoxy matrix, respectively.

Resin infusion under flexible tooling process and structural design optimization of the complex composite part

Employing optimum structural design strategies and accompanying optimal production processing while employing efficient and cost effective methods is a key for the expansion of composite structures in various industrial applications. Within this context, Resin Infusion under Flexible Tooling (RIFT) process has become a rapidly growing manufacturing approach for large scale and complex parts. In this study, replacement of automotive body parts with glass woven fabric/epoxy composite manufactured by RIFT Type I (RIFT I) process is investigated both experimentally and numerically to improve the mechanical characteristics with weight saving. The optimization of the laminate stacking sequence is the first step taken. Then the simulation of resin infusion for the optimum location of gates and vents in order to shorten the filling time, decrease dry spots and voids, and avoid costly and time consuming trial-and-error procedures. Numerical results of the filling time and fluid front position over time are assessed by comparison with the experimental data and good accuracy was obtained. Based on the results of the optimization, an automotive part with a complex geometry is fabricated with 50% weight saving relative to steel.

The tensile fatigue behaviour of a silica nanoparticle-modified glass fibre reinforced epoxy composite

An anhydride-cured thermosetting epoxy polymer was modified by incorporating 10 wt.% of well-dispersed silica nanoparticles. The stress-controlled tensile fatigue behaviour at a stress ratio of R = 0.1 was investigated for bulk specimens of the neat and the nanoparticle-modified epoxy. The addition of the silica nanoparticles increased the fatigue life by about three to four times. The neat and the nanoparticle-modified epoxy resins were used to fabricate glass fibre reinforced plastic (GFRP) composite laminates by resin infusion under flexible tooling (RIFT) technique. Tensile fatigue tests were performed on these composites, during which the matrix cracking and stiffness degradation was monitored. The fatigue life of the GFRP composite was increased by about three to four times due to the silica nanoparticles. Suppressed matrix cracking and reduced crack propagation rate in the nanoparticle-modified matrix were observed to contribute towards the enhanced fatigue life of the GFRP composite employing silica nanoparticle-modified epoxy matrix.

A 3-D micromechanical model for predicting the elastic behaviour of woven laminates

This paper presents an analytical model for the prediction of the elastic behaviour of plain-weave fabric composites. The fabric is a hybrid plain-weave with different materials and undulations in the warp and weft directions. The derivation of the effective material properties is based on classical laminate theory (CLT). The theoretical predictions have been compared with experimental results and predictions using alternative models available in the literature. Composite laminates were manufactured using the resin infusion under flexible tooling (RIFT) process and tested under tension and in-plane shear loading to validate the model. A good correlation between theoretical and experimental results for the prediction of in-plane properties was obtained. The limitations of the existing theoretical models based on classical laminate theory (CLT) for predicting the out-of-plane mechanical properties are presented and discussed.

Intralaminar toughness characterisation of unbalanced hybrid plain weave laminates

A numerical and experimental investigation on the mode-I intralaminar toughness of a hybrid plain weave composite laminate manufactured using resin infusion under flexible tooling (RIFT) process is presented in this paper. The pre-cracked geometries consisted of overheight compact tension (OCT), double edge notch (DEN) and centrally cracked four-point-bending (4PBT) test specimens. The position as well as the strain field ahead of the crack tip during the loading stage was determined using a digital speckle photogrammetry system. The limitation on the applicability of the standard data reduction schemes for the determination of intralaminar toughness of composite materials is presented and discussed. A methodology based on the numerical evaluation of the strain energy release rate using the J-integral method is proposed to derive new geometric correction functions for the determination of the stress intensity factor for composites. The method accounts for material anisotropy and finite specimen dimension effects regardless of the geometry. The approach has been validated for alternative non-standard specimen geometries. A comparison between different methods currently available for computing the intralaminar fracture toughness in composite laminates is presented and a good agreement between numerical and experimental results using the proposed methodology was obtained.

Low-pressure (vacuum infusion) techniques for moulding large composite structures

Resin transfer moulding (RTM) involves the long-range flow of resin into a dry fibre pack that is preloaded into a defined mould cavity. Resin infusion under flexible tooling (RIFT) can be considered as a variant on RTM in which one tool face is replaced by a flexible film or a light splash tool. The flow of resin results only from the vacuum drawn under the film and any gravity effects. In RTM the dimensions of the component are defined by the separation of the mould faces, whilst in RIFT processes the thickness of the part is a function of the pressure history during the process. This paper reviews current developments in resin infusion processes.

Development of the Double RIFT Diaphragm Forming Process

In the 1930’s composites, promised a revolution in materials design and utilisation. This did not happen. At the turn of the twentieth century, with Resin Transfer Moulding (RTM) growing in acceptance, injection rates, quality and preforming of the non-structural fibres to the required 3D shape, are still major problems. The preforming of structural fibres (unidirectional) is very rare. DRDF is a combination of Resin Infusion under Flexible Tooling (RIFT) and Diaphragm Forming. The Advanced Technology Centre at Warwick, has been experimenting with this novel solution to combine these two “independent” processes, RIFT and diaphragm forming, into a simple cost-effective injection method to produce the basic microstructure (fibre/resin interface) and a forming process that gives the part geometric complexity. In a single continuous operation, either “low specification high quality” (non-directional fibres) or “high specification high quality” (directional fibres), 3D composites, can be produced.