Interlaminar Fracture Toughness Of Carbon Research Articles

Synergetic improvement of the thermal conductivity and interlaminar fracture toughness of carbon fiber/epoxy composites by interleaving BN@ZnO particles

AbstractSynergetic improvement of the thermal conductivity and interlaminar fracture toughness of carbon fiber/epoxy resin composites (CF/EP) is a challenging research job. In this work, hexagonal boron nitride coated ZnO (BN@ZnO) particles were firstly prepared by sol–gel method and BN@ZnO composite laminates were manufactured by mold pressing process. X‐ray diffraction, x‐ray electron spectroscopy and scanning electron microscopy were used to analyze the structure, chemical components and morphology of the BN@ZnO and composite laminates. The effects of BN@ZnO on the impact strength, model II interlaminar fracture toughness (GIIC) and thermal conductivity of composite laminates are investigated. The results show that the interlaminar fracture toughness and thermal conductivity of composite laminates are synergistically enhanced owing to the introduction of hybrid fillers with different dimensions and morphology. The thermal conductivity of the 10 wt% BN@ZnO coated composite laminates is increased by 78% and 90% at 25 and 100°C, respectively. The mechanical properties of composite laminates are enhanced. The model II interlaminar fracture toughness of 2 wt% BN@ZnO composite laminates is 15.4% higher than pure laminate. This work is of significance to realize the structural and functional integration of composite materials.

Improved interlaminar fracture toughness of carbon fiber/epoxy composites by a combination of extrinsic and intrinsic multiscale toughening mechanisms

Carbon fiber reinforced polymer (CFRP) composites with hierarchical structure interleave composed of nanoscale core-shell rubber (CSR) and microscale short carbon fiber (SCF) were fabricated. The hierarchical structure interleave exhibits superior interlaminar toughening efficiency than either CSR or SCF alone. Triggering intrinsic and extrinsic toughening mechanisms at different scales by CSR and SCF, respectively, the mode-I critical energy release rate (GIC) and mode-II critical energy release rate (GIIC) of multi-phase interleaved CFRP composite are 127% and 154% higher than those of unmodified sample. While the tensile properties and glass transition temperature (Tg) are not compromised. The fracture toughness of epoxy/CSR system was also investigated to better understand the effect of matrix toughness on interlayer toughness of CFRP. Numerical analysis and fracture surface observations revealed the synergistic toughening mechanisms in SCF/CSR interleaved CFRP composites. The synergy between nanoscale intrinsic toughening mechanism and microscale extrinsic toughening mechanism, evolving with crack propagation, contributes to a greater energy absorption. The usefulness of the present study for preparation of high-performance CFRP is discussed.

Effect of Fiber Mass Fraction on Microstructure and Properties of 2D CF-GO/EP Composite Prepared by VIHPS.

Graphene is often used to improve interlaminar fracture toughness of carbon fiber/epoxy resin (CF/EP) composites. It is still a challenge to improve the toughness while maintaining the in-layer properties. In this study, 2D graphene oxide carbon fiber reinforced epoxy resin matrix (2D CF-GO/EP) composites were prepared by a vacuum infiltration hot-press forming experimental system (VIHPS), and three-point flexural and end notch flexural (ENF) tests were carried out. With the increase of the fiber mass fraction in the composites, the mode II interlaminar fracture toughness (GIIC) layers decrease gradually, and the bond property between the fiber and matrix interface layer becomes worse, because the accumulation of dense fiber bundles reduces the matrix penetration ability of cracks. However, the flexural properties increased first and then decreased, and reached the best flexural properties at 64.9%. When the fiber mass fraction is too high, the interlamellar bonding properties will decrease, and the fiber bundles will compress and affect each other. The delamination phenomenon will occur between the layers of the composites, which affects the overall bearing strength and stress limit of the composites. The results of the study show that the composites prepared by VIHPS have excellent mechanical properties, and the content of carbon fiber plays an important role in the influencing factors of the interlaminar and in-layer properties of composites.

Fatigue delamination behaviour of carbon fibre/epoxy composites interleaved with thermoplastic veils

Interleaving thermoplastic veils has proved to enhance the interlaminar fracture toughness of carbon fibre/epoxy composites under static loading conditions. However, the fatigue delamination behaviour has yet to be investigated. Herein, meltable Polyamide-12 (PA) veils and non-meltable Polyphenylene-sulphide (PPS) veils were used for interlay toughening of unidirectional (UD) and non-crimp fabric (NCF) laminates that were manufactured using a prepreg process and resin transfer moulding process, respectively. The results of Mode-I fatigue delamination tests demonstrated a significant improvement in the fatigue life of the laminates due to interleaving. Additionally, the fatigue resistance energy has been maximumly increased by 143% and 190% for the UD and NCF laminates, respectively. The microscopy analysis revealed that the toughening mechanisms of thermoplastic veils were affected by the form of the thermoplastic veils in the laminates (melted or non-melted), the fracture mechanisms of the reference laminates and the adhesion/miscibility between the thermoplastic veils and the epoxy.

Improved interlaminar fracture toughness of carbon fiber/epoxy composites with a multiscale cellulose fiber interlayer

In this study, a multiscale cellulose fiber interlayer consisting of chopped flax fibers (FFs) and cellulose nanofiber (CNFs) was proposed for enhancing the interlaminar fracture toughness of carbon fiber/epoxy composites. The cellulose fiber interlayer was treated by waterborne epoxy to improve the interfacial compatibility with the epoxy matrix. The end-notched flexure results showed that the addition of the cellulose fiber interlayer in the carbon fiber/epoxy composites resulted in a remarkable increase in Mode II interlaminar fracture toughness, which was attributed to a synergistic effect of the FFs and the CNFs. The 3D network of the chopped FFs alleviated the agglomeration of the CNFs due to their good compatibility, leading to more fiber bridging and fiber pull-out during delamination. The presence of CNF further improved the interfacial properties of the FFs and epoxy matrix, which are beneficial for the fibrillation of flax fiber to hinder interlaminar crack growth.

Flexible Carboxylated CNT/PA66 Nanofibrous Mat Interleaved Carbon Fiber/Epoxy Laminates with Improved Interlaminar Fracture Toughness and Flexural Properties

Interleaf is often used to increase the interlaminar fracture toughness of carbon fiber/epoxy (CF/EP) composites, but it remains a challenge to develop high-performance interleaves that can greatly...

Structuring the thermoplastic interleaf with lotus-leaf-like structure and its interlaminar toughening for CFRPs

A new kind of self-supporting thermoplastic film with two-sided lotus-leaf-like structure was prepared and its effect on the interlaminar fracture toughness of carbon fiber/epoxy composite was studied. Phenolphthalein modified polyetherketone films with uniform, large scaled lotus-leaf-like structure were prepared by soft lithography. After interleaved with the structured films, the mode I interlaminar fracture toughness of the composite is slightly increased by 17%, whereas the mode II interlaminar fracture toughness is substantially increased as high as 325%. It is found that a special interlayer structure was formed, which contains thermoplastic nails and thermoplastic-rich layer. The mode I fracture path occurred mainly inside the carbon plies, whereas the mode II fracture path propagated through the highly tough thermoplastic nails and the thermoplastic-rich layer, and it frequently deflected near the thermoplastic nails, causing a high energy dissipation. This new method for preparing structured interleaves is expected to provide a new route for interlayer design.

Improving the interlaminar toughness of the carbon fiber/epoxy composites via interleaved with polyethersulfone porous films

In this study, a phase inversion approach was employed to fabricate four different thicknesses (20 μm to 100 μm) of polyethersulfone (PES) porous films with visible holes (1 hole/cm2) on the surface, applied as interleaves to improve the interlaminar fracture toughness of carbon fiber/epoxy composite laminates prepared by vacuum assistant resin infusion process (VARI). The film could dissolve into the epoxy resin which as clearly evident by the optical microscopy under a controlled condition. It was noted that the thickness of the resin-rich layer and the distribution of PES microspheres in the interlaminar layer depended on the thickness of the PES porous film. Also, mode I and mode II fracture toughness, interlaminar shear strength (ILSS), flexural properties as well as tensile properties of the CF/EP composites had all been characterized and analyzed in detail and in order. The results demonstrated that mode I and mode II fracture energies at the optimal interleaved laminates for the toughened system were increased by 61.5% and 55.1% compared to the composites without interleaves, respectively. Besides, PES porous film interleaved laminates displayed an increase of 32% for the interlaminar shear strength and no significant changes in the flexural and tensile properties. It was observed that the films induced toughening via two mechanisms: i) cohesive failure in a thicker resin region and ii) crack deflection and microcrack caused by PES microspheres, illustrated in the microstructure analysis of the failure surfaces and the observations of the crack propagation path.

Effect of graphene oxide on the interlaminar fracture toughness of carbon fiber/epoxy composites

Graphene oxide (GO) nanoparticles were introduced in the interlaminar region of carbon fiber–epoxy composites by dispersing it in a thermoplastic polymer carrier such as polyvinylpyrrolidone (PVP). Mode‐I fracture toughness (GIC) was investigated using double cantilever beam testing to evaluate the effect of the GO on the delamination behavior of the composite. The GO content was varied from 0% to 7% by weight as a function of the PVP content. Improvement of ∼100% in the Mode I fracture toughness (GIC) was observed compared to composites with no GO. The optimum amount of nanoparticles for improving the interlaminar fracture toughness was found to be ∼0.007% by weight of the composite. The increase in the value of flexural strength value was also observed. Scanning electron microscopy of fracture surfaces, X‐ray diffraction, and transmission electron microscopy, and reflectance Fourier transform infrared spectra, as well as Raman spectroscopy results, are presented to support the conclusions. POLYM. ENG. SCI., 59:1199–1208 2019. © 2019 Society of Plastics Engineers

Improvement of the mode I interlaminar fracture toughness of carbon fiber composite reinforced with electrospun nylon nanofiber

The effect of nylon 6/6 electrospun nanofibers interleaved in carbon fiber/epoxy laminates is highlighted in this article. A layer of nylon nanofibers is spun directly on the surface of the carbon fabric which is subsequently used to produce the laminates. The nylon fibers were characterized using SEM, TGA and DSC analysis. The results showed homogeneous fiber size distribution and excellent thermal stability. The effect of the nylon nanofiber layer on interlaminar fracture toughness of carbon fiber/epoxy composites was studied using DCB test. The results showed major improvement in interlaminar fracture toughness. Furthermore, the thickness of the interleaved nanofiber layer is studied and found to have major role on interlaminar fracture toughness. The toughening mechanism is studied and discussed using SEM analysis.

Influence of sprayed multi-walled carbon nanotubes on mode I and mode II interlaminar fracture toughness of carbon fiber/epoxy composites

Unidirectional carbon fiber/epoxy prepregs were sprayed over their surfaces with different multi-walled carbon nanotubes (MWCNTs) concentrations in order to evaluate their effect on interlaminar fracture toughness of composite laminates under modes I and II loading and the influence in fracture mechanisms. To this aim, determination of the mode I and mode II interlaminar fracture toughness of composite laminates reinforced with sprayed MWCNTs were experimentally investigated using double cantilever beam and end notched flexure tests. Composite laminates without MWCNTs were also fabricated as a reference material. MWCNT characterization using Fourier Transform Infrared and Raman spectroscopy was also carried out in order to evaluate their functional groups and structural defects. The results show that the mode I and mode II interlaminar fracture toughness of the composite laminates can be moderately increased as MWCNT concentrations varying from 0.05 to 0.2 wt.%. Scanning electron microscope images of fracture surfaces provide evidence that the MWCNTs bridged and pulled out at the interface of composite laminates. It was also demonstrated that the optimum weight percentage of MWCNTs needed to improve the mode I and mode II interlaminar fracture toughness was 0.05%, due to the fact that higher concentrations promote the agglomeration of MWCNTs weakening the laminate interfaces.

Effect of cooling rate on the interlaminar fracture toughness of unidirectional Carbon/PPS laminates

The effect of cooling rate on the interlaminar fracture toughness of Carbon reinforced PPS laminates was investigated experimentally. A typical stamp forming process was utilised in a novel manner to achieve high average cooling rates, of up to 3500 °C/min, while ensuring a good consolidation quality. Differential scanning calorimetry measurements were used to characterise the degree of crystallinity of the samples, while the interlaminar fracture toughness of the laminates was characterised under mode I using the Double Cantilever Beam test. Finally, micrographic analysis of the fracture surfaces was carried out to correlate the degree of crystallinity to the failure modes. A strong correlation between fracture toughness and degree of crystallinity was found. The samples with a low degree of crystallinity showed a high interlaminar fracture toughness and large plastic deformation of the matrix during fracture.

Mixed Mode I/II interlaminar fracture toughness of carbon Fiber/RTM‐6 laminates manufactured by VARTM

This work investigates and compares the interlaminar fracture behavior of composites manufactured by vacuum‐assisted resin transfer molding subjected to three different temperatures (–54, 25, and 80°C) and mode ratios (25, 50, and 75%). The results indicate ductility enhancement with increasing temperature, which were confirmed by fractographic analyses. In tested specimens with 25% mode ratio, the GI and GII values were not greatly affected by the temperature. As the temperature and the mode ratio increases, the specimens exhibited higher GI and GII values compared with those measured at −54°C. In the tested specimens with 75% mode ratio, an unstable crack propagation was observed at −54°C due to brittle behavior of matrix, which is promoted by the decrease of the adhesion represented by cusps and broken fibers in SEM images. The cusps formation is less pronounced for specimens tested at 80°C and the fracture surface is flatter compared with those tested at −54 and 25°C. POLYM. COMPOS., 40:E1029–E1040, 2019. © 2018 Society of Plastics Engineers

Mixed-mode I/II interlaminar fracture toughness of carbon fiber/epoxy composites with the addition of multiwalled carbon nanotubes by spraying technique

This work reports the effect of multiwalled carbon nanotubes on mixed-mode I/II interlaminar fracture toughness ([Formula: see text]) of unidirectional carbon fiber/epoxy composite laminates made by prepregs. The carbon fiber/epoxy laminates were fabricated in an autoclave with a previous deposition of different multiwalled carbon nanotube contents at their middle plane interface by spraying technique. Mixed-mode bending tests were conducted on carbon fiber/epoxy laminate specimens under different mixed-mode ratios. The results of mixed-mode bending tests showed that the addition of multiwalled carbon nanotubes can effectively improve the [Formula: see text] of carbon fiber/epoxy laminates. With a 0.2 wt.% multiwalled carbon nanotubes content in carbon fiber/epoxy laminates, the [Formula: see text] under mixed-mode ratios of 0.2, 0.5 and 0.8 increased by 25%, 12% and 19%, respectively. These results were explained in terms of the damage mechanisms observed at the fracture surfaces of tested specimens by scanning electron microscopy.

Simultaneous enhancement of electrical conductivity and interlaminar fracture toughness of carbon fiber/epoxy composites using plasma-treated conductive thermoplastic film interleaves.

Multiwalled carbon nanotube (MWCNT)-doped polyamide 12 (PA12) films with various nanofiller loadings were prepared via a solution casting method to simultaneously improve the electrical conductivity and fracture toughness of carbon fiber/epoxy (CF/EP) composites. The films were interleaved between CF/EP prepreg layers and melted to bond with the matrix during the curing process. To improve the interfacial compatibility and adhesion between the conductive thermoplastic films (CTFs) and the epoxy matrix, the CTFs were perforated and then subjected to a low temperature oxygen plasma treatment before interleaving. Fourier transform infrared (FTIR) spectra results confirm that oxygen-containing functional groups were introduced on the surface of the CTFs, and experimental results demonstrate that the electrical conductivity of the laminates was significantly improved. There was a 2-fold increase in the transverse direction electrical conductivity of the laminate with 0.7 wt% MWCNT loading and a 21-fold increase in the through-thickness direction. Double cantilever beam (DCB) tests demonstrated that the Mode-I fracture toughness (GIC) and resistance (GIR) of the same laminates significantly increased by 59% and 113%, respectively. Enhancements of both interlaminar fracture toughness and electrical conductivity are mainly attributed to the strong interfacial adhesion achieved after plasma treatment and to the bridging effect of the carbon nanotubes.

Interlaminar fracture toughness of carbon fibre/RTM6-2 composites toughened with thermoplastic-coated fabric reinforcement

Abstract Thermoplastic toughening of epoxy (RTM6-2)/carbon fibre (CF) laminate composites without modification of the resin is reported, in which a CF fabric coated with 20 wt % of a poly (aryl ether ketone) (PAEK) was used to toughen composites. Dissolution of the PAEK during resin infusion, with subsequent reaction-induced phase separation and phase inversion during curing, formed PAEK-rich continuous layers with dispersed RTM6-rich particles within the interlaminar regions. These layers provided significant toughening during interlaminar fracture testing, in which the Mode I and Mode II fracture energies for the toughened system increased from 216 ± 7.2 to 751 ± 105 and 857 ± 99 Jm-2 to 3316 ± 372 Jm-2, respectively. Thus, coating of the CF fabric with PAEK avoided the significant increases in viscosity observed with resin systems containing dissolved thermoplastics; whilst generating multiphase toughening layers at the CF fabric – matrix interfaces which provide efficient interlaminar toughening.

Enhancement of mechanical properties of carbon fabric/epoxy composites using micro/nano-sized bamboo fibrils

Micro/nano-sized bamboo fibrils (MBFs) were fabricated from raw bamboo using the alkaline treatment technique and the mechanical extraction method (micro-grinding). The fracture toughness of epoxy resin significantly increased by 84.6% from 0.639MPam1/2 to 1.18MPam1/2 due to 0.8wt.% MBF inclusion into the resin in comparison with the epoxy resin without MBF. Both mode-I interlaminar fracture toughness of carbon fabric/epoxy (CF/EP) composites at crack initiation and propagation also improved by 35.3% and 47.3%, respectively when 0.8wt.% MBF was dispersed in the epoxy matrix. The fatigue life of modified composites at all of MBF content up to 0.8wt.% dramatically increased 12–25 times longer than those of unmodified composites at high cycle fatigue while the tensile strength slightly increased. Scanning electron microscopy (SEM) observations revealed that MBF delayed the onset of matrix crack, and reduced the crack growth in the CF/EP composites.

Characterization of transverse tensile, interlaminar shear and interlaminate fracture in CF/EP laminates with 10 wt% and 20 wt% silica nanoparticles in matrix resins

The transverse tensile properties, interlaminar shear strength (ILSS) and mode I and mode II interlaminar fracture toughness of carbon fibre/epoxy (CF/EP) laminates with 10 wt% and 20 wt% silica nanoparticles in matrix were investigated, and the influences of silica nanoparticle on those properties of CF/EP laminates were characterized. The transverse tensile properties and mode I interlaminar fracture toughness ( G IC) increased with an increase in nanosilica concentration in the matrix resins. However, ILSS and the mode II interlaminar fracture toughness ( G IIC) decreased with increasing nanosilica concentration, especially for the higher nanosilica concentration (20 wt%). The reduced G IIC value is attributed to two main competing mechanisms; one is the formation of zipper-like pattern associated with matrix microcracks aligned 45° ahead of the crack tip, while the other is the shear failure of matrix. The ratio of G IIC/ G IC decreased with the concentration of silica nanoparticles, comparable with similar CF/EP laminates with dispersed CNTs in matrix. Fractographic studies showed that interfacial failure between carbon fibre and epoxy resin occurred in the neat epoxy laminate, whereas a combination of interfacial failure and matrix failure occurred in the nanosilica-modified epoxy laminates, especially those with a higher nanosilica concentration (20 wt%).

Interlaminar Fracture Toughness of Carbon Fibre‐Reinforced Polymer Laminates With Nano‐ and Micro‐Fillers

Abstract: Vapour growth carbon nanofibres (CNF) and lead zirconate titanate (PZT) piezoelectric particles were added in the matrix of carbon fibre‐reinforced polymer laminates. The fracture toughness of the modified composites was measured under mode I and mode II loading and compared with plain epoxy carbon fibre‐reinforced composites. The mode I fracture toughness of the composites improved with the incorporation of the carbon nanofibres and deteriorated with the incorporation of PZT piezoelectric particles. When both fillers were added in the composite matrix, the mode I fracture toughness improved but to a lesser extend. The mode II fracture toughness of the modified composites was improved in all three cases. The aforementioned behaviour was attributed to competing fracture mechanisms instigated by the different fillers, and backed by fractographic evidence from the failed composite coupons; during the tests, the acoustic emission activity of the coupons was monitored and classified in three major energy absorbing mechanisms which were attributed to the failure of distinct composite phases.

Improving interlaminar fracture toughness of carbon fibre/epoxy laminates by incorporation of nano-particles

Double-cantilever-beam tests were applied to investigate the mode I interlaminar fracture toughness of carbon fibre/epoxy laminates, in which the epoxy matrices were incorporated with rubber and silica nano-particles, either singly or jointly. It is shown that the toughness is improved owing to the presence of these nano-particles although nano-rubber is more effective than nano-silica. Further, by keeping the total particle weight percentage constant in epoxies (e.g., at 8 and 12 wt.%) filled with equal amount of nano-silica and nano-rubber, the interlaminar toughness values of the hybrid laminates are always higher than those with nano-silica filled epoxies but lower than those with nano-rubber filled matrices. Scanning electron microscopy examination of the delaminated surfaces of composite laminates filled with nano-particles revealed that cavitation of nano-rubber particles/void growth and debonding of nano-silica from epoxy matrix are responsible for the improved interlaminar toughness observed. It is also shown that the bulk toughness of nano-particle filled epoxies cannot be fully transferred to the interlaminar toughness of composite laminates, being limited by the constraint effect imposed by the carbon fibres. Finally, the role of fibre-bridging on the delaminated crack and hence delamination toughness is discussed.