Carbon Fiber Plies Research Articles

Composite Recycling with Biocatalytic Thermoset Reforming.

Carbon fiber reinforced polymers (CFRPs, or composites) are increasingly replacing traditional manufacturing materials used in the automobile, aerospace, and energy sectors. With this shift, it is vital to develop end-of-life processes for CFRPs that retain the value of both the carbon fibers and the polymer matrix. Here we demonstrate a strategy to upcycle pre- and postconsumer polystyrene-containing CFRPs, cross-linked with unsaturated polyesters or vinyl esters, to benzoic acid. The thermoset matrix is upgraded via biocatalysis utilizing an engineered strain of the filamentous fungus Aspergillus nidulans, which gives access to valuable secondary metabolites in high yields, exemplified here by (2Z,4Z,6E)-octa-2,4,6-trienoic acid. Reactions are engineered to preserve the carbon fibers with much of their sizing so that the isolated carbon fiber plies are manufactured into new composite coupons that exhibit mechanical properties comparable to those of virgin manufacturing substrates. In sum, this represents the first system to reclaim a high value from both the fiber fabric and polymer matrix of a CFRP.

Hybridization Effect on Interlaminar Bond Strength, Flexural Properties, and Hardness of Carbon-Flax Fiber Thermoplastic Bio-Composites.

Hybridizing carbon-fiber-reinforced polymers with natural fibers could be a solution to prevent delamination and improve the out-of-plane properties of laminated composites. Delamination is one of the initial damage modes in composite laminates, attributed to relatively poor interlaminar mechanical properties, e.g., low interlaminar strength and fracture toughness. This study examined the interlaminar bond strength, flexural properties, and hardness of carbon/flax/polyamide hybrid bio-composites using peel adhesion, three-point bending, and macro-hardness tests, respectively. In this regard, interlayer hybrid laminates were produced with a sandwich fiber hybrid mode, using woven carbon fiber plies (C) as the outer layers and woven flax fiber plies (F) as the inner ones (CFFC) in combination with a bio-based thermoplastic polyamide 11 matrix. In addition, non-hybrid carbon and flax fiber composites with the same matrix were produced as reference laminates to investigate the hybridization effects. The results revealed the advantages of hybridization in terms of flexural properties, including a 212% higher modulus and a 265% higher strength compared to pure flax composites and a 34% higher failure strain compared to pure carbon composites. Additionally, the hybrid composites exhibited a positive hybridization effect in terms of peeling strength, demonstrating a 27% improvement compared to the pure carbon composites. These results provide valuable insights into the mechanical performance of woven carbon-flax hybrid bio-composites, suggesting potential applications in the automotive and construction industries.

Performance of hybrid Innegra-carbon fiber composites

In this work material synergy with high stiffness carbon fiber with ductile high strength polypropylene fiber (Innegra S), (referred to as Innegra, herein) have been evaluated in a range of laminate designs. Both woven and discontinuous carbon fiber have been considered. The discontinuous fibers are based on three-dimensional deposition (3DEP) (referred to as 3DEP, herein) carbon fiber preform process. Eleven (11) variants of Innegra-carbon fiber hybrid laminates were investigated for tensile, flexure, compression, in-plane shear and low velocity impact response. The effect of position of Innegra within the laminate was studied and found to influence strength and stiffness properties. In terms of overall trends, Innegra provides upward of 18% improvement in strain (ductility) to the composite and eliminates brittle fracture of carbon fiber. The moduli trends follow the proportionality of Innegra fiber to carbon fiber plies. However, the strength is controlled by the interface between Innegra and carbon fiber. The primary failure mode in tension and compression is via onset of debonding between Innegra and carbon fiber. The 3DEP carbon fiber constituents provided highest values of in-plane shear indicating that three-dimensional (3D) network of carbon fiber provides higher shear resistance. The Innegra intensive variants exhibited superior energy absorption under low velocity impact, at energy levels 15–60 J. This work provides insight for designers to incorporate Innegra and carbon fiber hybrids in composite structures.

Effects of Irradiation Dose of Sheet-Like Electron Beam and its Cathode Voltage on Impact Strength of Carbon Fiber Reinforced Thermoplastic Polyamide just before Shipping

Achieving a strong bond between carbon fiber (CF) and recyclable thermoplastic polymer (TP) has always been highly sought after. So far, applying electron beam (EB) irradiation with optimal dose and cathode potential (Vc) has shown success in increasing mechanical properties of interlayered CFRTPs. However, with concern for durability and safety, higher strength is desired. Therefore, EB setting applying electron beam (EB) irradiation with cathode potential (Vc) to 170, 210, 225 or 250 kV was applied to CFRTPA (carbon fiber reinforced thermoplastic polyamide) articles just before shipping. Specimens were 9 CF plies alternating between 10 PA (polyamide) sheets, designated [TPA]10[CF]9. When optimal EB dose of 43.2 kGy is applied to both finished specimen surfaces after fabrication, experimental results show higher Vc setting of 250 kV can increase impact strength of the [TPA]10[CF]9 over that at 170 kV. In summary, the 250 kV-EB (250 kV) strengthens [TPA]10[CF]9 significantly, about 25 to 27% larger than that of 170 kV and zero (untreated). Based on Christenhusz and Reimer equation to calculate penetration depth, Dth of EBI into polymers, increasing Vc to 250 kV increased Dth to more than 2 times that at 170 kV.

Bioinspired Hard–Soft Interface Management for Superior Performance in Carbon Fibre Composites

Nature has evolved to create materials of unmatched performance governed by the interfacial interactions between hard and soft surfaces. Typically, in a carbon fibre composite, one polymer and one type of carbon fibre is used throughout a laminate. In this work, we use a carbon fibre surface modification approach to vary the fibre–matrix interface throughout the laminate to tailor the soft–hard interfaces. We demonstrate this effect using reclaimed carbon fibre materials in a thermoset polymer, then extend this concept to a thermoplastic polymer matrix–polypropylene. The thermoset specimens examined in this work consist of 5 carbon fibre plies, featuring 0, 1, 3 or 5 surface-modified layers located at the centre of the composite. The largest improvements in physical properties for these composites (yield strength, ultimate flexural strength, and tensile modulus) were found when only 1 modified layer of carbon fibre was placed directly within the centre of the composite. Subsequent investigations revealed that for a polypropylene matrix, where the surface chemistry is tailored specifically for polypropylene, improvements are also observed when mixed surface chemistries are used. This work shows that surface modification of reclaimed carbon fibres as non-woven mats can provide significant improvements in mechanical properties performance for structural composites when used in strategically advantageous locations throughout the composite.

Mechanical Behavior of Hybrid Laminated Nano Composite Containing Equal Numbers of Glass and Carbon Fiber Plies

Hybrid fiber reinforced polymer with nanofiller composite was introduced into a lot of industries due to its extreme mechanical properties in comparison with non-hybrid material. In this investigation, cross and quasi-fiber laminated epoxy composites with and without nano Al2O3 were fabricated using Vacuum Assisted Resine Infusion Method and Ultrasonic Dual Mixing Method. In general, the results of mechanical properties indicated that the addition of 2% nano Al2O3 enhances the tensile and flexural properties. Cross number 2 with nano Al2O3 laminate had the maximum tensile strength 628 MPa and maximum tensile strain of 1.74%, while cross number 1 with nano Al2O3 laminate had the maximum tensile modulus of 37.756 GPa in the cross group. In the quasi group, quasi number 2 with nano Al2O3 had the maximum tensile strength, maximum tensile strain, and maximum tensile modulus, equal to 294 MPa, 1.98%, and 16.409 GPa, respectively. Regarding the flexural properties, cross number 1 with nano Al2O3 laminate had a maximum flexural strength of 708.2 MPa and maximum flexural strain of 2.027%, while cross number 2 with nano Al2O3 laminate had a maximum flexural modulus of 38.73 GPa in the cross group. On the other hand, quasi number 1 with nano Al2O3 laminate had the maximum flexural strength, maximum flexural strain, and maximum flexural modulus equal to 596 MPa, 2.424%, and 29.2 GPa, respectively in the quasi group. The internal structures of the failure laminated composites through scanning electronic microscopy confirm that the adhesion between fibers and matrix is good.

Mode I and mode II fracture behavior in nano‐engineered long fiber reinforced composites

AbstractDelamination still remains one of the common concerns in continuous fibers reinforced polymer composites. In the literature, the incorporation of nanoconstituents into constitutive composites plies has been suggested with the aim of improving interface toughness. In this study, vertically aligned carbon nanotubes forests (VACNTs) are transferred at composites interfaces, and mode I (DCB tests) and mode II (ENF tests) fracture tests carried out on composite samples. Microscopic analysis of reference and nano‐engineered composites help to understand fracture behavior and toughness. While the crack path in ENF samples is observed at interlaminar VACNTs‐resin interfaces, the crack path in DCB samples is intralaminar, located within the unidirectional carbon fiber plies. These microscopic observations give explanation for unstable crack propagation in nano‐engineered ENF samples and the unchanged toughness from the nano‐engineered to the reference zone in DCB samples.

Strengthening Process by Electron Beam to Carbon Fiber for Impact Strength Enhancement of Interlayered Thermoplastic-Polypropylene Carbon Fiber Composite.

Strong adhesion between recyclable thermoplastic (TP) polymer and carbon fiber (CF) has always been highly sought after. Therefore, for an interlayered CF reinforced TP polypropylene (CFRTPP) composite composed of 3 sized CF plies, alternating between 4 PP sheets, designated [PP]4[CF]3, a process of activating CF plies directly on both sides with homogeneous low energy electron beam irradiation (EBI) under N2 gas, prior to lamination assembly and hot press of 4.0 MPa at 493 K for 3 min was carried out. Experimental results showed EBI dose of 43.2, 129, or 216 kGy significantly raised Charpy impact values, auc at all fracture probabilities, Pf. The 129 kGy dose appeared to be at or near optimum increasing auc 103%, 83%, and 65% at low-, median-, and high-Pf = 0.07, 0.50, and 0.93; while raising statistically lowest impact value, as at Pf = 0 calculated by 3-dimensional Weibull equation about 110%, indicating increased safety and reliability. It is assumed dangling bonds generated by the EBI rapidly form covalent bonds CF:C:O:C:PP and CF:C:C:PP at the interface, along with cross-linking in the PP near the CF. This is by charge transfer from CF to PP.

Thermal Mending of Electroactive Carbon/Epoxy Laminates Using a Porous Poly(ε-caprolactone) Electrospun Mesh.

For the first time, a porous mesh of poly(ε-caprolactone) (PCL) was electrospun directly onto carbon fiber (CF) plies and used to develop novel structural epoxy (EP) composites with electro-activated self-healing properties. Three samples, i.e., the neat EP/CF composite and two laminates containing a limited amount of PCL (i.e., 5 wt.% and 10 wt.%), were prepared and characterized from a microstructural and thermo-mechanical point of view. The introduction of the PCL mesh led to a reduction in the flexural stress at break (by 17%), of the interlaminar shear strength (by 15%), and of the interlaminar shear strength (by 39%). The interlaminar fracture toughness of the prepared laminates was evaluated under mode I, and broken samples were thermally mended at 80 °C (i.e., above the melting temperature of PCL) by resistive heating generated by a current flow within the samples through Joule’s effect. It was demonstrated that, thanks to the presence of the electrospun PCL mesh, the laminate with a PCL of 10 wt.% showed healing efficiency values up to 31%.

An experimental investigation on damage mechanisms of thick hybrid composite structures under flexural loading using multi-instrument measurements

In this study, damage characterization of thick carbon/glass fiber reinforced hybrid composites is performed under flexural loading conditions via two non-destructive evaluation (NDE) techniques, i.e., digital image correlation (DIC) and acoustic emission (AE). Experimental results demonstrate that the flexural modulus of the hybrid composites is strongly correlated with the location of carbon fiber plies; the closer these plies are to the laminate faces, the higher is the modulus. On the other hand, the flexural strength depends on the type and extent of damage initiation in the laminates. Interply hybridization of carbon fiber reinforced composites (CFRPs) with glass fiber not only improves their flexural strength and failure strain but also facilitates failure predictability in CFRPs. The transverse and shear strains associated with various failure modes in thick hybrid laminates are efficiently captured by the DIC technique. In addition, AE results reveal that the strain levels associated with the onset of acoustic activity are linked to failure in the carbon fiber plies of the hybrid laminates. Furthermore, these observations made by DIC and AE on thick hybrid laminates are confirmed with optical fractography. Finally, it is revealed that ply lay-up sequence and laminate thickness notably alter both the mechanical performance and damage mechanisms of hybrid composites.

Cover Image, Volume 138, Issue 25

This cover designed by Muhammad Irfan and colleagues shows how High Performance Polyethylene (HPPE) fibers are relatively tougher than carbon fibers and can be used to improve impact tolerance of carbon epoxy composite laminates. Composite laminates containing carbon fibers suffer from delamination upon impact. An interleave of a tough material like HPPE fibers inserted between these carbon fiber plies can reduce the damage due to impact. HPPE fibers do not undergo brittle fracture, rather ductile fracture is observed along with fibrillation. Nonwoven interleaves comprising HPPE fibers can be used to improve impact properties of carbon-epoxy composite laminates for various applications. DOI:10.1002/app.50683

Micro-mechanics modeling of compressive strength and elastic modulus enhancements in unidirectional CFRP with aramid pulp micro/nano-fiber interlays

Compressive strength and elastic modulus of unidirectional carbon fiber reinforced polymer (UD-CFRP) have been enhanced experimentally by using soft micro-length Aramid pulp (AP) micro/nano-fiber interlays. This study presents a micro-mechanics model to prove theoretically such enhancements in the compressive strength and elastic modulus of UD-CFRP are possible. The micro-mechanics model recognizes the importance of in-situ formed graded interfacial region between carbon fiber plies generated from the random distribution and out-of-plane movements of micro-length AP micro/nano-fibers. The micro-mechanics model shows that even an areal density of only ~4 g/m2 of AP micro/nano-fibers (with the interlay thickness < 30 μm) is sufficient to generate the enhancements in both compressive strength and elastic modulus along the carbon fiber direction of UD-CFRP. The new micro-buckling or shear failure mechanism has been identified to be responsible for the compressive strength enhancement, instead of local delamination in plain UD-CFRP. The theoretical and experimental findings show interfacial microstructural designs at the carbon fiber ply interface can be critical to the bulk properties of CFRP.

Experimental study on the mechanical properties of laminates made of thin carbon fiber plies

Thin carbon-fiber prepregs can improve the designability of the number and the angle of layup at a constant laminate thickness, and meet the requirements of the load bearing capacity of the thin-walled structure. In this work, experiments based on the MIL17 method were performed to investigate the performance of carbon-fiber laminates manufactured from thin prepregs, and compare to those of conventional prepregs. Besides the performance advantages of thin prepregs and conventional prepregs hybrid laminates were explored. It is shown that longitudinal compression properties, tensile properties and mechanical joint properties of the thin unidirectional plates have been improved to some extent. The initial damage strength of the longitudinal tensile of thin laminates is increased by 30%, which indicates that the thin prepregs can delay the generation of initial damage in laminates. It is worth noting that the basic mechanical properties of the hybrid laminates are obviously improved and the longitudinal tensile/compressive strength is approximately increased 50%. In addition, these performance improvements are accompanied by changes in failure modes. The failure modes of thin specimens, especially hybrid specimens, tend to be brittle failure. The results of present study have certain guiding significance for the engineering application of thin prepregs in thin-walled structures.

Transverse and longitudinal flexural properties of unidirectional carbon fiber composites interleaved with hierarchical Aramid pulp micro/nano-fibers

Unidirectional carbon fiber reinforced polymer (UD-CFRP) composites designed for ultimate tensile strength and stiffness along the fiber direction are vulnerable in the transverse direction. In this study, UD-CFRPs were reinforced in the transverse direction using sparsely distributed hierarchical Aramid pulp (AP) micro/nano-fibers between 2 and 8 g per square meter (gsm) per ply interface. Those AP micro/nano-fibers, a few hundred microns in length, effectively formed an ultra-thin interleaving layer around 20 μm in thickness between carbon fiber plies. Flexural properties along and perpendicular to continuous carbon fiber direction were measured under three-point-bending (3-P-B) to determine the toughening effects of AP. Flexural loads in both longitudinal and transverse directions have been enhanced by 30% and over 100% respectively from those randomly distributed AP micro/nano-fibers with diameters varied from a few hundred nanometers to 10 μm. Even slight increase in the elastic modulus of AP-toughened CFRP along the fiber direction was observed. Total fracture energy absorption, initial cracking and final fracture loads were measured and compared, indicating AP micro/nano-fibers have contributed to the high strength, high toughness and high modulus characteristics of AP-interleaved UD-CFRPs. Details on toughening mechanisms were revealed from SEM and cross-section optical microscopy examinations. Comparisons of unreinforced UD-CFRP and AP-toughened UD-CFRP showed the hierarchical AP micro/nano-fibers indeed played an important role in composite microstructure design and property optimization. The ultra-thin interleaved AP veil around 20 μm in thickness can be conveniently incorporated into pre-preg fabrication so that the extra interleaving step can be eliminated, i.e. the toughened pre-pregs can be used as normal pre-pregs in the final composite forming.

High performance functional composites by in-situ orientation of carbon nanofillers

A simple route for the in-situ orientation of carbon nanofillers applied during the curing process of a carbon fiber reinforced polymer (CRFP) in a hot press, is demonstrated. Neat MWCNT, amine-functionalized MWCNT (MWCNT-NH2) and CNF were dispersed in an epoxy resin using a three-roll-mill (TRM) to ensure good dispersion. The process leads to a hierarchically structured functional composite where MWCNT/CNF are aligned in the z-direction (out-of-plane) of the carbon fiber plies, giving rise to improved mechanical and electrical performance. Our results demonstrate that aligned carbon nanofillers yield significantly more pronounced improvements than non-oriented fillers. An applicable processing route towards advanced functional composite materials with major practical importance is presented in this study.

Dual-energy computed tomography investigation of additive manufacturing aluminium–carbon-fibre composite joints

In this work, aluminium–carbon-fibre reinforced plastic joints have been studied. Three types of samples were designed as double lap joints where the aluminium inserts were fabricated using both classical methods (milling) and additive manufacturing. Two versions of the joint were fabricated using additive manufacturing, one flat, and the other with small teeth designed to hook into the carbon-fibre plies. The joints were characterised using a non-linear, dual-energy computed tomography method to evaluate the bond between the composite and the metal inserts. The mechanical strength of the bonds was evaluated, both through tensile tests and four-point bending. A simple finite element model was used to discuss the joints behaviour. It was found that the joints fabricated using additive manufactured inserts were more resistant to peel stress than the milled inserts. In four-point bending tests the moment that the joint could withstand was increased by roughly 300% with the use of additive manufacturing and 400% with the use of additive manufacturing and small teeth. However, in tensile tests it was found that the teeth design reduced the maximum load capacity of the joints by roughly 30% due to porosity. Further, it was found that the additive manufactured samples did not add to the capability of withstanding shear stress. The information gained with the dual-energy computed tomography method was highly valuable as the behaviour of the joints would have been difficult to explain without the porosity information.

Theoretical Analysis on Needle-Punched Carbon/Carbon Composites

Needle-punched carbon/carbon composites (NP-C/Cs) are advanced materials widely used in aerospace applications. The needle-punching technique improves the integrality of carbon-fibre plies, however, it also introduces many defects, affecting the mechanical behavior of NP-C/Cs. A theoretical model of irregular beams is suggested to investigate the mechanical behavior of unidirectional needle-punched carbon/carbon composites. Stress distributions in punched and squeezed fibres and an effect of the needle-punching technology are assessed.

An advanced anti-icing/de-icing system utilizing highly aligned carbon nanotube webs

A carbon nanotube (CNT) web is a horizontally oriented continuous film, obtained by drawing CNT forests produced by chemical vapour deposition (CVD). As the CNTs are highly conductive and predominantly aligned along the draw direction, by controlling the aspect ratio of these CNTs and the number of stacked web layers, a tailored resistance can be achieved. Layers of CNT web are compared to plies of carbon fiber (CF), as the heating elements within a glass fiber laminate assembly. Compared with the CF-heater as well as existing state-of-the-art heating systems, the highly aligned CNT-web-heater possesses negligible weight (e.g. compared with eight CF plies (3633.8 g m−2), an equivalent 20-CNT-web heater (0.38 g m−2) is ∼104 times lighter), rapid and uniform heating, efficient energy consumption and its electro-thermal behaviour can be tuned to suit any surface and power requirement to achieve rapid anti-icing/de-icing. Both anti-icing and de-icing performance have been verified and in particular, for de-icing, with a constant 4.9 kW m−2 power supply, the GF laminate with 40 layers of CNT web could remove accreted ice within 15 s.

Energy storage in structural composites by introducing CNT fiber/polymer electrolyte interleaves

This work presents a method to produce structural composites capable of energy storage. They are produced by integrating thin sandwich structures of CNT fiber veils and an ionic liquid-based polymer electrolyte between carbon fiber plies, followed by infusion and curing of an epoxy resin. The resulting structure behaves simultaneously as an electric double-layer capacitor and a structural composite, with flexural modulus of 60 GPa and flexural strength of 153 MPa, combined with 88 mF/g of specific capacitance and the highest power (30 W/kg) and energy (37.5 mWh/kg) densities reported so far for structural supercapacitors. In-situ electrochemical measurements during 4-point bending show that electrochemical performance is retained up to fracture, with minor changes in equivalent series resistance for interleaves under compressive stress. En route to improving interlaminar properties we produce grid-shaped interleaves that enable mechanical interconnection of plies by the stiff epoxy. Synchrotron 3D X-ray tomography analysis of the resulting hierarchical structure confirms the formation of interlaminar epoxy joints. The manuscript discusses encapsulation role of epoxy, demonstrated by charge-discharge measurements of composites immersed in water, a deleterious agent for ionic liquids. Finally, we show different architectures free of current collector and electrical insulators, in which both CNT fiber and CF act as active electrodes.

Flexural response of carbon fiber reinforced aluminum foam sandwich

Sandwich panels with carbon fiber fabric/epoxy resin face-sheet and aluminum foam core have a potential application value in the engineering field. To study the bending mechanical properties of the reinforced sandwich structure, three-point bending test was conducted by using WDW-T100 electronic universal tensile testing machine. The relation between load and displacement of the aluminum foam sandwich was obtained. Deformations and failure modes of the specimens were recorded. Scanning electron microscopy was used to observe the failure mechanism. Results showed that when aluminum foam was reinforced by carbon fiber fabric as face-sheet, its flexural load-carrying capacity and energy absorption ability improved significantly. Foam core density and number of carbon fiber plies had serious impacts on the peak load value and energy absorption value of the composite structure. It was suggested that aluminum foam core sandwich structure with low foam core density of 0.49 g/cm3 and 5 plies of carbon fiber fabric had the highest energy absorption ability and medium load-carrying ability. Failure modes analysis showed that shear failure leaded to the final failure of sandwich panels with medium peak load and interface de-bonding leaded to the final failure of sandwich panels with high peak load.