Resin Infusion Research Articles

Effects of nanodiamonds on the mechanical properties, acoustic properties, vibration damping, and flame retardancy of ramie-fiber epoxy composite panels used for indoor applications

This research aims to systematically analyze the impact of nanodiamonds (NDs) in ramie fiber-reinforced epoxy resin acoustic panels used for indoor applications. The panels (four variants) are fabricated using six layers of ramie fiber with various weight percentages of NDs (0.0, 0.2, 0.4, and 0.6) in epoxy resin by the vacuum resin infusion process (VRIP). Mechanical characterization (tensile and flexural strength) was carried out using Instron 8801 universal testing machine. The impedance tube-based sound absorption coefficient (SAC) test was performed at low frequency and higher frequency, respectively. The void content in the panel is evaluated using a micro-x-ray computed tomography (CT) scanner. The dispersion of nanoparticles is studied using scanning electron microscopy (SEM) images. The vertical flame-retardant test and the horizontal flame-retardant test were conducted according to the UL-94 standard. The 0.4 wt.% NDs sample showed good tensile strength (59.178 MPa) and flexural strength (69.134 MPa) compared with other panels. The panels showed differences in SAC values for different weight percentages of NDs, both at lower and higher frequencies. The 0.6 wt.% NDs sample attained the maximum SAC of 0.906 at 6000 Hz in the high-frequency and 0.34 at 1112 Hz in the low-frequency. The SEM reveals an even distribution of NDs in both the 0.2 and 0.4 wt.% NDs panels, while agglomerates form in the 0.6 wt.% panels. The CT scan result shows void content both internally and externally in the panels. There are no voids in the panels where NDs are uniformly distributed. The synergistic effect of NDs in epoxy resin forms a char over the burnt surfaces of samples, enhancing the flame-retardant properties of the panels. According to this study, adding NDs to ramie fiber epoxy composites has improved the panels’ necessary qualities, making them suitable for use as indoor acoustic conditioning materials.

Shear strength comparison of single lap and joggle lap adhesive joints in carbon fiber composites manufactured via vacuum-assisted resin infusion

The extensive utilization of composite materials has spurred the advancement of diverse joining techniques suitable for components constructed from such materials. This study focuses on the examination of two specific types of joints: single lap and joggle lap joints. The specimens utilized were composed of unidirectional carbon fiber composite combined with vinyl ester resin, manufactured via the vacuum-assisted resin infusion method. Vinyl ester adhesives were employed in the bonding process, with the joint surfaces undergoing sanding treatment prior to testing. Mechanical testing was conducted on the specimens according to ASTM D5868 standard, employing a constant crosshead speed until failure occurred. The test results reveal that the shear strength of single lap joints surpasses that of joggle lap joints. Within the single lap joint configuration, a mixed failure mode comprising both adhesive and cohesive failure is observed. Conversely, in joggle lap joints, substrate delamination is prevalent, suggesting the predominance of peel stress during loading.

Investigations on the influence of thickness and preform structure on the mechanical performance of novel textile composites with woven Kevlar® fabric reinforcement and poly methylmethacrylate (Elium®) matrix

Abstract Elium (novel methyl methacrylate (MMA)) resin is a liquid thermoplastic resin curable at room temperature and a possible replacement for epoxies. The main objective of this work is to evaluate the mechanical characteristics of novel Kevlar fabric reinforced Elium composites with different thicknesses. The plain-woven structure Kevlar/Elium laminates were manufactured with 1.5 mm and 2.5 mm thicknesses through vacuum-assisted resin infusion moulding, where 8 and 12 layers of woven fabrics were used, respectively. The effect of laminate thickness was measured in terms of mechanical (tensile, flexural, shear, and dynamic mechanical analysis (DMA)) and physical (density and fibre volume fraction (FVF)) characteristics. The density of the laminates was found in the range of 1.18–1.31 g cm−3. FVF was 50.69 and 52.27% for 1.5 and 2.5 mm thick laminates, respectively. The composite with 1.5 mm thickness exhibited the highest tensile strength (667.9 MPa) and flexural strength of 330.7 MPa. Conversely, the highest interlaminar shear strength measured for 2.5 mm thick laminate is 16.5 MPa. The DMA analysis recorded the highest storage and loss modulus for 2.5 mm thickness laminates. The fractography analysis confirmed the quantified experimental observation of excessive interface debonding and delamination. Elium composites may be suitable for high-end structural applications, including marine and aircraft structures.

Self-healable epoxy/graphene oxide vitrimers and their recyclable glass fiber reinforced composites

Glass fiber-reinforced polymers (GFRPs) made from thermoset polymers have been widely used across various industries. However, these composites have significant drawbacks, including poor interfacial adhesion between the fiber and matrix, as well as a substantial contribution to waste and environmental pollution due to the challenges in recycling, reprocessing, and reuse. Herein, firstly graphene oxide (GO) was incorporated in vitrimer matrix to fabricate recyclable vitrimer nanocomposites with improved interfacial interaction, high thermal stability, low dielectric constant, fast stress relaxation as well as rapid self-healing ability. The nanocomposite with 0.2 wt% GO is optimized to achieve excellent remoulding (89% of flexural strength) and self-healing (60 min for a 48 μm scratch) properties due to dynamic disulfide bond exchange mechanism. Furthermore, epoxy/GO matrix was used to develop glass fiber reinforced composites via vacuum assisted resin infusion molding process (VARIM). The developed composites demonstrate tremendous mechanical strength (250 MPa), shape-memory, weldability, and degradable properties. Due to the rapid chemical degradation of epoxy vitrimer under mild conditions in the thiol (2-mercaptoethanol and 1-otanethiol), facilitated by thiol disulfide exchange reaction, glass fibers (GFs) can be effectively recycled. The performance of recycled glass fibers closely matches that of original fibers, exhibiting nearly identical woven structure and mechanical properties. The single yarn of recycled glass fibers can achieve tensile strength of 85% (1-octanethiol) and 72% (2-mercaptoethanol) of the original glass fibers, thus, the recycling of glass fibers would be highly advantageous in terms of achieving the sustainability goals.

Vacuum Chamber Infusion for Fiber-Reinforced Composites

A new approach to an automatable fiber impregnation and consolidation process for the manufacturing of fiber-reinforced composite parts is presented in this article. Therefore, a vacuum chamber sealing machine classically used in food packaging is modified for this approach—Vacuum Chamber Infusion (VCI). Dry fiber placement (DFP) preforms, made from 30 k carbon fiber tape, with different layer amounts and fiber orientations, are infused with the VCI and with the state-of-the-art process—Vacuum Assisted Process (VAP)—as the reference. VCI uses a closed system that is evacuated once, while VAP uses a permanently evacuated open system. Since process management greatly influences material properties, the mechanical properties, void content, and fiber volume fraction (FVF) are analyzed. In addition, the study aims to identify how the complexity of a resin infusion process can be reduced, the automation potential can be increased, and the number of consumables can be reduced. Comparable material characteristics and a reduction in consumables, setup complexity, and manufacturing time by a factor of four could be approved for VCI. A void content of less than 2% is measured for both processes and an FVF of 39% for VCI and 45% for VAP is achieved.

Interlaminar fracture properties of UV and plasma‐treated glass fiber epoxy composites

AbstractDespite the low density and high specific strength properties, the fiber‐reinforced composites are characterized by a relatively low interlaminar fracture toughness and their ultimate properties are strongly affected by the fiber matrix adhesion. This study aims to investigate the influence of fiber surface treatments, such as UV and atmospheric plasma, and of the interfacial shear strength, on the flexural properties and Mode I interlaminar fracture toughness of glass fiber epoxy composites. The vacuum‐assisted resin infusion technique is used for the composite fabrication. Scanning Electron Microscopy analysis is used to observe and to explain the changes in the morphology of the fibers after surface treatment. Remarkably, the results showed an overall reduction in the mechanical properties. The interfacial shear strength values of the UV and plasma‐treated samples were reduced by 34.9% and 49.5% respectively. The flexural strength was reduced by 7.9% and 5.9% respectively. The Mode I fracture toughness values for the UV and plasma‐treated samples were also reduced by 49.8% and 62.2% respectively.Highlights UV and plasma treatments were performed on glass fibers to improve performance. Push‐out tests were carried out to evaluate fiber/matrix adhesion. An aerospace grade epoxy resin curing in thermal press‐clave was used. Mechanical tests related Interfacial Shear Strength to composites performance.

Flexural and interlaminar shear response of novel methylmethacrylate composites reinforced with high-performance fibres

This experimental work presents a comparative study on the mechanical behaviour of novel infusible methylmethacrylate matrix (Elium®) composites reinforced with different types of high-performance fibres. A vacuum-assisted resin infusion process was employed to fabricate the laminates using carbon, basalt, Kevlar®, and high molecular weight polyethene (UHMWPE) fibres. Flexural and interlaminar shear properties of the composites were evaluated. Test results revealed that carbon fibre composites had superior flexural strength, stiffness and interlaminar shear stress as compared to the other composites tested. Further, composites containing Kevlar and UHMWPE fibres demonstrated significantly higher flexural strains to failure. Post-testing, specimens were examined using scanning electron microscopy (SEM). Microscopy revealed possible interfacial interaction differences based on the reinforcement fibre type, which was further confirmed by an analytical approach for analysing the flexural behaviour of various types of composites. The sequence of damage progression in specimens was also analysed.

Effects of crosslinker concentration on curing process and performances of needled fiber preform reinforced phenolic aerogel composite using process simulation and comprehensive experiments

A kind of needled quartz/carbon fiber preform reinforced phenolic aerogel composite (NQCF/PR) was fabricated through impregnating needled fiber preform with phenolic resin precursor solution, followed by sol–gel polymerization and solvent drying. The needled fiber preform serves as lightweight quasi-three-dimensional reinforcement, while phenolic aerogel matrix provides high porosity and low thermal conductivity. During fabrication of aerogel composite part using vacuum-assisted resin infusion process, distribution of crosslinker hexamethylenetetramine (HMTA) in precursor solution can be problematic, as precipitated crosslinker particles may be filtered by fibrous preform. In this study, the impact of HMTA filtration induced heterogeneous structure on subsequent curing process was investigated using process simulation. Temperature effects of sol–gel polymerization and solvent evaporation were considered through establishment of corresponding kinetic models. Impacts of heterogenous structure on distribution of temperature, resin curing degree and solvent conversion degree in large hemispherical aerogel composite structure were investigated. This leads to variations in gel network and pore structure of aerogel, thereby affecting final material performance. Based on experimental results, as HMTA concentration increases, compressive performance of NQCF/PR obviously increases. Among these, NQCF/PR with 4.7 wt% HMTA provides a balance of lightweight nature (0.25 g/cm3), excellent thermal insulation property (0.052 W·m−1·K−1) and compressive performance (strength of 0.35 MPa).

Development of High-Performance Large-Scale Structural Supercapacitors via the Resin Infusion Process and Encapsulation Process

Development of High-Performance Large-Scale Structural Supercapacitors via the Resin Infusion Process and Encapsulation Process

Research of influence of diluent on the mechanical behavior of triaxial warp-knitted composites

The composites are prepared by different processes of reinforcement and matrix, which are affected by the properties of reinforcement and matrix. In this study, composite specimens were fabricated using vacuum-assisted resin infusion (VARI) with varying mass fractions (0%, 5%, 10%, and 15%) of a diluent mixed with the resin and curing agent, serving as the matrix. Triaxial warp-knitted glass fabric was employed as the reinforcement material. The impact of the diluent mass fraction on the bending, impact, and creep properties of the composites was investigated. The least squares fitting method was applied to analyze the experimental data, leading to the establishment of a mathematical model correlating the diluent mass fraction with the bending strength. The optimal diluent mass fraction for achieving the best bending properties was determined. Furthermore, the failure mechanisms of the composites were examined through an analysis of their thermodynamic properties, reaction principles, and fracture morphologies. The results show that the epoxy group in the diluent will be connected to the cross-linking network structure of epoxy resin by ring-opening reaction, and excessive addition will lead to the increase of flexible chain segments, which makes the mechanical properties of the specimens increase first and then decrease. The mathematical model was verified by experiments, and the mass fraction of diluent was 9.65% when the bending property was optimal.

Reprocessable carbon fiber vitrimer composites: Reclamation and reformatting of carbon fibers for second generation composite materials

AbstractCarbon fibers (CFs) are experiencing a growing demand owing to their low specific weight, exceptional mechanical properties, superior temperature, and corrosion resistance, however, their sustainability and energy consumption during manufacturing is still a challenge. Therefore, reclamation of waste CFs and their reformatting has gained significant attention. Herein, we synthesized a chemically degradable vitrimer matrix by curing bisphenol‐A diglycidyl ether (BADGE) with 2‐aminophenyl disulfide (2‐AFD) and further utilized the matrix for the development of CF reinforced composites (CFRCs) through vacuum‐assisted resin infusion molding (VARIM) process. The obtained vitrimeric system and its composites show excellent mechanical, self‐adhering, shape‐memory, and reprocessing properties. Meanwhile, the developed CFRP vitrimer composites can be rapidly dissolved in thiol solvent (1‐octanethiol), resulting in the efficient recycling of CFs. X‐ray diffraction, scanning electron microscopy, and Raman spectroscopy validate that the chemical structure of the recycled fibers closely resembles the structure of the original CFs. The recycled CFs were further used to prepare second generation composite materials with excellent thermal, dynamic, and mechanical properties for nonstructural applications (e.g., sports, automotive, etc.). Thus, with an effective CF recycling method, this study can assist in preparing reliable, long‐term functional, recyclable, and high‐performance composites.

Failure mode maps for glass fibre-reinforced polymer/polyvinyl chloride foam-cored sandwich structures

Purpose This study aims to understand how the facesheet size, orientation and core size influence the analytical failure mechanism mode of glass fibre reinforced polymer (GFRP)/polyvinyl chloride (PVC) sandwich structures subjected to three-point bending. The purpose of this study was to develop failure-mode map of GFRP/PVC sandwich structures. Sandwich structures with different facesheet and core thicknesses were used to develop the failure map. Design/methodology/approach The sandwich structure and facesheet were fabricated using a vacuum-assisted resin infusion method with core sizes of 10, 15 and 20 mm and facesheet thicknesses of 1.5 and 3 mm and were arranged in three different orientations: angle-ply, cross-ply and quasi-isotropic. The key failure modes that occur in sandwich structures were used to predict possible failures in the developed material. Analytical equations were used in MATLAB for each observed failure mode. The probable failure modes, namely, face yielding, core shear and indentation equations, were used to construct the failure maps and were compared with the experimental data. Findings The boundary of the two failure modes shifts with changes in the facesheet and core thicknesses. The theoretical stiffness of sandwich panels was higher than the experimental stiffness. Based on strength-to-weight ratio, specimens E10-4, A15-8 and E20-8 exhibited the best optimum values owing to their shorter distance to the boundary lines. Originality/value In this study, a failure map was used to predict the possible failure modes for different GFRP facesheet orientations and thicknesses and PVC core thickness sandwich structures. Little is known about the prediction of the failure modes of unidirectional GFRP arranged in different orientations and thicknesses and PVC core thicknesses for sandwich structures. Few studies have used failure mode maps with unidirectional GFRP oriented in angle-ply, cross-ply and quasi-isotropic directions as a facesheet for sandwich structures compared to bidirectional mats. This study can serve as a guide for the correct selection of materials during the design process of sandwich structures.

Effect of halloysite addition on the dynamic mechanical and tribological properties of carbon and glass fiber reinforced hybrid composites

Composite materials have become prominent in the aerospace, automotive, wind energy, biomedical, and machine tool industries. This has demanded the evaluation of the dynamic mechanical and tribological behaviour of composites to understand their performance and ensure their reliability and safety in varied operating conditions. In this study, the effect of halloysite nano-clay addition on the dynamic mechanical and tribological properties of the carbon/glass hybrid composites was investigated. The composites were produced with the vacuum assisted resin infusion process. by varying the content of halloysite nano-clay (1, 3, and 5 wt%). The dynamic mechanical properties of the manufactured composites were examined at temperatures ranging from 30 °C to 180 °C. The tribological properties of the specimens were assessed by varying the applied load (10, 20, and 30 N), sliding speed (1.5, 3, and 4.5 m/s) and sliding distance (500, 1000, and 1500 m). Box-Behnken design was utilized to optimize the number of experiments. The results showed that the halloysite-added samples had better dynamic mechanical and tribological properties than the carbon/glass hybrid composites. Especially, hybrid composites containing 3 wt% halloysite outperformed the other composites investigated. A scanning electron microscope (SEM) was used to examine the worn surface and wreckage in the investigated composite specimens.

Interlaminar fracture behaviour of emerging laminated-pultruded CFRP plates for wind turbine blades

Laminated pultruded composite plates are gaining interest for use in wind turbine blades due to their excellent structural performance with affordable cost. However, there is limited understanding of their fracture properties. The present work explores the interlaminar fracture behaviour of pultruded composite plates, bonded through resin infusion, to form thick CFRP structures. Mode-I, −II, and mixed-mode (I/II) tests were performed to obtain fracture properties at different mixed-mode ratios. Mode I crack propagation exhibits stick–slip behaviour, resulting in brittle failure in a few steps, while mode II provides more stable crack propagation along with cohesive failure. The mixed-mode fracture patterns follow the trend of the mode-mix ratios, in which higher mode-mix ratios (more mode II) induce more stable crack propagation. Benzeggagh-Kenane and power law criteria were compared regarding their prediction of crack initiation toughness given a mode mix ratio, and a linear relation between the mixed-mode I/II fracture toughness components could exist at interfaces of laminated pultruded plates. Meanwhile, applicability of testing standards and the effect of manufacturing-induced defects on fracture properties are thoroughly discussed. The results show that existing standards provide sufficient support for characterising fracture properties of bonded pultruded plates; and that manufacturing-induced defects can be detrimental to crack propagation and cause more brittle behaviour in mode I dominant cases, while beneficial effect of defects by toughening the interface was exhibited in mode II dominant cases.

Comparison of carbon‐reinforced composites manufactured by vacuum assisted resin infusion with traditional and fully recyclable epoxy resins

AbstractThis study presents a comparative analysis of carbon fiber reinforced polymer (CFRP) composites manufactured through vacuum assisted resin infusion (VARI) using a traditional epoxy resin (E), a fully‐recyclable epoxy resin system with (BBR10) and without (BBR) the addition of a reactive diluent (R*Diluent). Various mechanical and thermal tests were conducted to assess their performance. The BBR10 laminate, incorporating 10 wt% R*Diluent, exhibited competitive mechanical performance, comparable to traditional (E) and fully‐recyclable laminates (BBR). Despite a slightly lower ultimate tensile strength (UTS) compared with BBR, BBR10 demonstrated improved flexural strength and modulus. Low‐velocity impact testing confirmed comparable strength between VARI‐produced composites with the recyclable matrix (BBR and BBR10) and the traditional one (E). X‐ray mCT investigations revealed distinct void arrangements in the CFRP laminates. Additionally, a chemical approach was employed for recovering high fractions of fibers from CFRP laminates with a recyclable matrix (BBR and BBR10). Chemical recycling achieved an almost 100% yield for long carbon fibers.Highlights Comparative analysis of CFRP composites manufactured through VARI. Diluent addition allowed to tailor the recyclable epoxy viscosity. Mechanical characterization of traditional and fully recyclable epoxy resins. Investigation by X‐ray mCT of potential flaws and manufacturing defects. Chemical recycling of CFRP laminates with a recyclable matrix.

Development of New Lignin-Based Coatings with Ultraviolet Resistance for Biobased Composite Materials.

Nowadays, there is a challenge in searching for more sustainable alternatives to decrease the environmental impact of composite materials. In this work, we fabricate new composites based on a biobased-content epoxy system, lignin, and flax fiber; considering these materials could be promising due to their high renewable content of around 40%. In addition, another key requirement for composites, besides being sustainable, is that they present improved properties such as UV resistance. Therefore, throughout this work, priority was given to improving UV resistance in addition to taking into account sustainability. In order to carry out a complete characterization of the materials developed, the mechanical properties, brightness, and thermal, rheological, and fire behavior of these kinds of materials were analyzed by using vacuum-assisted resin infusion processes. By way of conclusion, it should be noted that the manufactured composite with the optimized formulation showed improved UV resistance using lignin and that it could be applied on internal and external walls according to the railway fire regulations.

Effect of MWCNTs on static, dynamic, and wear performance of Vacuum Assisted Resin Infusion Molding (VARIM) processed glass fabric/epoxy polymer composites

In the present work, MWCNTs were used in wt.% of 0.075, 0.15, and 0.3 in epoxy resin, and then glass fabric/epoxy polymer (GF/EP) composites were fabricated using VARIM setup. The mechanical and wear properties of GF/EP composites were compared with and without the addition of MWCNTs. Maximum improvement in tensile and flexural performance were seen in GF/EP composites at 0.15 weight percent MWCNT addition when compared to a neat GF/EP one, based on static testing such as tensile and flexural tests. High-cycle fatigue test results show a relatively higher cycle count with 0.15 wt.% MWCNTs addition in the GF/EP composite compared to the GF/EP without the addition of MWCNTs. The wear performance also improved with a lower friction coefficient as well as a lower track depth and width for MWCNTs with added GF/EP than plain GF/EP composite. Therefore, in addition to decreasing surface softening and improving the wear performance of glass fabric epoxy composites, MWCNTs (0.15 weight percent) increased the interfacial adhesion at the fiber/matrix interface. This study establishes an optimum ratio of 0.15 wt.% of MWCNTs addition in glass fabric/epoxy polymer composites for enhancement in their mechanical and wear performance.

Mechanical properties of glass/epoxy composites under artificial seawater environment: Numerical simulation and experimental validation

In ocean engineering applications, glass fiber reinforced composite materials undergo degradation over time due to various aging processes. Accurately assessing the mechanical properties of these materials as they experience aging conditions in marine environment becomes a crucial factor. Although various approaches, such as experimental, theoretical, or finite element methods (FEM), have been employed to investigate the impact of aging processes on composite materials, limited attention has been given to examining the damage of composite plates under the exposure of artificial seawater environments using the MAT162 material model. The objective of this study is to outline a methodology for identifying a group of MAT162 parameters in LS-DYNA through a unit single element analysis. S2 glass/epoxy composites were produced by vacuum assisted resin infusion method. Aging was carried out in artificial seawater environment for 4, 8 and 12 months. Tensile, through thickness tensile, compression, through thickness compression tests were performed and then the finite element modeling was conducted. Maximum strength (X1T, X1C, X3T and SFC), element eroding axial strain (E_LIMT), modulus of elasticity (E1 = E2, E3), scale factor for residual compressive strength (SFFC), coefficient for strain softening property (AM) parameters were analyzed. It was determined that the proposed model for aging was in good agreement with the experimental study.

Interlaminar toughening of carbon fiber/epoxy composites via interleaving co‐polyamide (Co‐PA) veils

AbstractThermoplastic veil interlayers offer a promising approach to improve interlaminar reinforcement in composite materials. This study investigates co‐polyamide (Co‐PA) interleaved veils, fabricated through the hot melt adhesive (HMA) technique. These veils are then applied with varying areal weight densities as interleaves to simultaneously toughen and strengthen carbon fiber/epoxy (CF/EP) composites, utilizing the vacuum‐assisted resin infusion (VARI) method. Integrating Co‐PA veils with a low melting point in the interlaminar of CF/EP composites improves compatibility and promotes strong adhesion between thermoplastics and epoxy resins. As result, The Co‐PA laminates exhibited significant improvements compared with the untoughened composites, with a maximum enhancement of 148.1% and 67.8% for Mode‐I (GIC) and Mode‐II (GIIC), respectively. Moreover, ILSS, tensile strength, and flexural strength improvements were also 20.9%, 34.9%, and 14.5%, respectively. The fracture surface analysis via scanning electron microscopy directly revealed the crack propagation on the fracture surfaces of Mode‐I and Mode‐II specimens. This analysis revealed that Co‐PA demonstrated excellent compatibility with epoxy resin, melts during the stage of epoxy curing, and undergoes phase separation in the later stage, resulting in the formation of “bead‐like” structures within the fibrous network. Remarkably, this structure significantly enhanced the toughness of the CF/EP composites. The Co‐PA veils can improve the interlaminar toughness of CF/EP composites due to their compatibility with the epoxy matrix and high inherent toughness and strength. This method is straightforward to manage and can be utilized for manufacturing large‐scale composite materials incorporating CF fabrics, demonstrating promise for industrial applications.Highlights With its low melting point, co‐polyamide helps prevent structural failure or excessive damage and is proposed to be utilized in composites to enhance the interlaminar fracture toughness properties. The effects of Co‐PA veils of different areal densities on the mechanical characteristics of interlaminar composites were examined. Co‐polyamide particles with fiber‐carbon laminates offer superior fatigue properties and an optimum carbon fiber‐bridging mechanism. Co‐polyamide veils with CF/EP laminates are feasible for structural use in high‐tech automotive applications.

Nanomechanical characterization of carbon nanotube-based composite interfaces tailored by electrophoretic deposition

Carbon nanotube (CNT) addition to composite materials can offer both nanoscale reinforcement and a multifunctional element due to their extraordinary mechanical, thermal and electrical properties. Electrophoretic deposition (EPD) offers a scalable processing technique to incorporate CNTs into conventional fiber-reinforced polymer composites (FRPCs), facilitating the production of unique nanoscale structures in the critical interphase region. In this study, CNTs functionalized with polyethyleneimine (CNT-PEI) were deposited onto a planar substrate via EPD followed by the infusion of epoxy matrix in order to replicate the nanocomposite interphase region present in nanomodified FRPCs. The nanocomposite films have thicknesses ranging from several hundred nanometers to a few microns to represent different fiber-matrix interphase regions found in FRPCs. The morphology and mechanical performance of CNT-PEI/epoxy nanocomposites are examined using atomic force microscopy (AFM) in both tapping and nanoindentation modes. The EPD creates a homogeneously distributed porous CNT network bridged by PEI, forming the pathway of epoxy resin infusion through interconnected pores with diameters less than 100 nm. CNT-PEI/epoxy nanocomposites exhibited significant improvements in stiffness, hardness, and creep resistance compared to constituent porous CNT-PEI films and neat epoxy. The improvement was directly related to the ability of the load bearing CNTs chemically bonded with the epoxy matrix through the grafted PEI, providing an efficient load transfer mechanism. The chemical bond between the porous CNT-PEI and epoxy also produced far greater fracture surface in nanoscale scratch tests compared to unmodified epoxy, indicating the CNT-PEI/epoxy nanocomposite is capable of distributing load and absorbing more energy prior to fracture.