Improvement In Interfacial Shear Strength Research Articles

Enhancing interfacial shear strength with tailored carbon nanotube orientations: A micromechanical hierarchical model of single fiber fragmentation tests

This study explores the effects of carbon nanotube (CNT) orientation on stress transfer in carbon fiber (CF) composites using the Single Fiber Fragmentation Test (SFFT). A micromechanical hierarchical model, utilizing the Finite Element Method (FEM), is developed to analyze a CF composite with a CNT-reinforced interfacial region, encapsulated within an epoxy resin matrix. The Mori-Tanaka method is utilized to calculate the effective properties of the CNT-reinforced interfacial region of the CF, taking into account different CNT orientations and volume fractions. Scenarios involving radial, longitudinal, and random CNT orientations are considered. Moreover, the study also incorporates the nonlinear plastic behavior of the epoxy matrix. A novel analytical framework that leverages FEM to compute variables such as critical length, interfacial shear strength (IFSS), and average normal stress is proposed to accomplish it. Numerical results are compared to existing experimental data for validation. For the validation of the proposed methodology, experimental data available in the literature were used. The model predictions show that specific orientations and volume fractions of CNTs have the potential to enhance IFSS. However, the enhancement in the elastic stiffness of the interfacial region, attributed to the inclusion of CNTs, does not entirely explain the improvements in IFSS observed in the experimental studies from the literature.

Designing Carbon Fiber Composite Interfaces: Reactive Sizing Derived from Terpenes

Terpenes, typically obtained from conifer plants, were chemically modified to include functional groups that could react with both the surface of carbon fiber and the surrounding epoxy resin. This strategy was coupled with the installation of reactive amines (NH2) and thiols (SH) on the fiber surface to specifically react with these sizings. Increases in interfacial shear strength (IFSS) up to 195% were observed for fibers coated in these reactive sizings in combination with the tailored surface chemistry. Improvements in IFSS were also observed for unmodified fibers, suggesting passive functionalization. The presence of persistent carbon-centered radicals was proposed as a way that the fiber surface could react with the sizing agents, stabilized by the inherent high degree of conjugation present within the fiber structure. Interrogating commercially available carbon fiber via electron paramagnetic resonance (EPR) spectroscopy confirmed the presence of radicals within or on the carbon fiber surface (g-value = 1.9984).

Interfacial Properties and Fragmentation Process in ZnO Nanowire Coated Hybrid Carbon Fiber Composite: A Multiscale Modeling Approach

AbstractA multiscale modeling framework is developed to investigate the effect of ZnO nanowires (NWs) on the fiber/matrix interface, and the fiber fragmentation mechanism of ZnO NW coated single fiber composites (SFC). Atomistic traction–separation analysis is conducted using molecular dynamics simulation technique to evaluate the interface properties between the functionalized carbon fiber surface and ZnO NW/polymer matrix. The results indicate that incorporating ZnO NW can significantly enhance interface stiffness, strength, and fracture energy. The results obtained in opening and sliding modes are implemented in the cohesive zone model to simulate the interface at the mesoscale. Microhomogenization analysis is performed on a representative volume element containing ZnO NW reinforced polymer matrix to determine the effective material properties of the enhancement layer. The interface and enhancement layer properties are imported into the macroscale hybrid SFC model. Single fiber fragmentation analysis is performed employing user material (UMAT) subroutine and ABAQUS finite element analysis package. Simulation results demonstrate that the load is transferred more efficiently from matrix to fiber in the hybrid than in the bare fiber model. The fiber fragmentation is increased in the hybrid composite structure, resulting in up to 100% improvement in interfacial shear strength of SFC incorporating ZnO NW.

Molecular Dynamics Modeling of Interfacial Interactions between Flattened Carbon Nanotubes and Amorphous Carbon: Implications for Ultra-Lightweight Composites.

Flattened carbon nanotubes (flCNTs) naturally form in many carbon nanotube-based materials and can exhibit mechanical properties similar to round carbon nanotubes but with tighter packing and alignment. To facilitate the design, fabrication, and testing of flCNT-based composites for aerospace structures, computational modeling can be used to efficiently and accurately predict their performance as a function of processing parameters, such as reinforcement/matrix cross-linking. In this study, molecular dynamics modeling is used to predict the load transfer characteristics of the interface region between the flat region of flCNTs (i.e., bi-layer graphene) and amorphous carbon (AC) with various levels and locations of covalent bond cross-linking and AC mass density. The results of this study show that increasing the mass density of AC at the interface improves the load transfer capability of the interface. However, a much larger improvement is observed when cross-linking is added both to the flCNT–AC interface and between the flCNT sheets. With both types of cross-linking, substantial improvements in interfacial shear strength, transverse tension strength, and transverse tension toughness are predicted. The results of this study are important for optimizing the processing of flCNT/AC composites for demanding engineering applications.

Improvement of interfacial shear strength between syndiotactic polystyrene and carbon fiber by Self-localization of acid modified poly(2,6-dimethyl-1,4-phenylene ether) on the surface of carbon fiber

To improve the interfacial shear strength between syndiotactic polystyrene (sPS) and carbon fiber (CF), sPS was blended with poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and acid-modified PPE (mPPE), which are compatible with sPS and whose interfacial shear strength with CF is sufficiently greater than that of sPS. The interfacial shear strength between sPS and CF dramatically increased with the addition of mPPE, whereas the addition effect of PPE was not always observed. Notably, the addition of 10% mPPE improved the interfacial shear strength of sPS/CF by 270%. A micro-Raman spectroscopy study revealed the localization of mPPE in the vicinity of the CF surface. We demonstrate a novel concept of the self-localization of a minor, but high adhesiveness component in a polymer blend matrix to the CF surface to improve the interfacial shear strength between the major polymer matrix and CF.

Using redox active molecules to build multilayered architecture on carbon fibers and the effect on adhesion in epoxy composites

Carbon fibres with redox-active surface functionalities have shown potential applications in environmental remediation, and as burgeoning materials for structural batteries and super capacitors. In this work we describe the tethering of anthraquinone, capable of a reversible 2 electron transfer in aqueous medium, to the carbon fibre surface, and the corresponding effect on interfacial adhesion. The anthraquinone alone results in a >150% improvement in interfacial shear strength and the redox activity is preserved. Further to this, we then use this conductive film as a means to grow an acrylic acid polymer on top of the anthraquinone base layer, characterized by water contact angle, infrared spectroscopy, and depth-profiling X-ray photoelectron spectroscopy. This outermost layer imparts additional benefit to fibre-to-matrix adhesion and preserves the redox activity of the modified carbon fibers. This work demonstrates the ability to grow dual component and covalently-attached sizings to the carbon fiber surface, without compromising the inherent benefits of the underlying carbon fibers.

Effect of polyetherimide sizing on surface properties of carbon fiber and interfacial strength of carbon fiber/polyetheretherketone composites

AbstractThe sizing process is almost invariably performed after the manufacture of carbon fiber (CF) and the sizing agent takes the effect of protecting CF surface. However, the traditional sizing agent is not suitable for processing continuous CF reinforced thermoplastic composites (CFRTPs) with high processing temperature. In this work, polyetherimide (PEI) is chosen as the sizing agent for CF reinforced polyetheretherketone (CF/PEEK) composites, and the sizing content as well as the type of sizing agent (including solvent‐based and emulsion type) were systematically researched. After a series of characterization of CF surface properties and interfacial strength of CF/PEEK, the improvement of interfacial shear strength (IFSS) and mechanical performances of sized CF/PEEK proves the enhancement of interfacial adhesion after sizing. CF/PEEK composites which contain CF handled by emulsion type sizing agent have good mechanical properties, indicating that it has the potential to replace solvent‐based sizing agent. Besides, the miscible feature of PEEK with PEI, the raise of CF surface roughness and surface energy might cause the reinforcement of interfacial mechanical properties. This research may create a potential way for CF production field, aiming at improving the interfacial performance of CFRTPs.

Interconnected Ni(OH)2 and polyether amine on carbon fiber surface for simultaneously improving interfacial adhesion of epoxy composites and electrochemical properties

Interconnected Ni(OH)2 nanoflakes and polyether amine (PEA) were deposited on carbon fiber tows via a facial and effective process of chemical bath deposition and dip coating. Based on this, a win–win benefit of simultaneously improvements in interfacial shear strength (IFSS) of carbon fiber/epoxy composites and the electrochemical activity has been achieved. Compared with CF and CF-Ni(OH)2 composites, the IFSS of CF-Ni(OH)2-PEA/epoxy composite respectively increased 7.9% and 45.4%, which was put down to the covalent bonding of Ni(OH)2-PEA coating with fiber and epoxy matrix, as well as the effective stress transfer by the uniform honeycomb structure of Ni(OH)2. In aqueous KOH electrolyte, the CF-Ni(OH)2-PEA electrode presented the maximum specific capacitance of 689.98F·g−1 at 5 mV·s−1, 572.28F·g−1 at a current density of 0.5 A·g−1 due to the strong adhesion of carbon fiber with Ni(OH)2 by PEA, the reservation of the three-dimensional hollow honeycomb structure of Ni(OH)2 for easy ion-transport and –NH2 functional groups from PEA for providing more active sites. The excellent performance of CF-Ni(OH)2-PEA reinforcement demonstrates its promising potential for application in high performance composites with integrated structure and function, which shows great advantages in various fields of aerospace, energy, electronics, automobile, civil engineering, sports, etc.

Examining interfacial interactions in a range of polymers using poly(ethylene oxide) functionalized carbon fibers

It is commonly assumed that a higher oxygenated content on the surface of carbon fibers will lead to high interfacial adhesion. Thus, carbon fibers are exposed to oxidizing treatments to increase surface polarity. Here, we examine the interfacial interactions of a range of thermoset and thermoplastic polymers with carbon fibers that have a grafted polyethylene oxide (PEO) chains to their surface. This provides an extremely hydrophilic surface, without potential degradation of the fiber via chemical oxidation. We find that high surface polarity does not always correlate to high interfacial adhesion; in some instances, unsized hydrophobic carbon fibers possess equal or better fiber-to-matrix adhesion than treated hydrophilic carbon fibers. The most notable example is in vinyl ester resin, in which the presence of an alkyne group, able to participate in the radical polymerization process, provides significant improvements in interfacial shear strength (IFSS) compared to a larger, and polar, PEO chain.

Improving interfacial shear strength between graphene sheets by strain-induced wrinkles

Graphene has been widely used as new generation reinforcing nanofiller to achieve significantly improved mechanical properties in composites. However, its reinforcing effect has been considerably affected by the poor interfacial strength between graphene and the matrix. By using molecular dynamics simulations, the present work explores an effective route to improve the interfacial shear strength (ISS) of graphene sheets through the introduction of mechanically induced wrinkles that are formed by applying shear/compressive strains to graphene. The slide-out tests of a wrinkled graphene sliding over the graphene substrate show that the strain-induced wrinkles in graphene slider gives rise to larger surface roughness which leads to stronger interfacial interactions between graphene layers and consequently, significant improvement in ISS. Compared with compression induced wrinkles, shear induced wrinkles are found to be much more effective in enhancing ISS. Our results indicate that applying mechanical pre-strain, in particular, shear strain to graphene is a very useful strategy to improve its reinforcing effect in composites.

Using molecular entanglement as a strategy to enhance carbon fiber-epoxy composite interfaces

The tethering of an amphiphilic molecule to the surface of carbon fiber resulted in significant (+283%) improvements in interfacial shear strength. Molecular dynamics simulations revealed that lateral association of hydrophobic sections lead to a ‘hooked’ conformation through which polymer chains become entangled. Further simulations indicated that a small molecule, forced into this conformation via two covalent attachment points to the fiber surface (similar to a ‘horseshoe’), would provide similar adhesion improvements and confirm this conformational effect on interfacial phenomena. This prediction was confirmed by the synthesis and grafting of such a molecule to a carbon fiber surface, giving an almost identical improvement in interfacial adhesion (+276%). This work validates the use of molecular dynamics to inform molecular architectural design and demonstrates the translation of molecular conformation and shape at a composite interface from nano-to macroscale.

Comparative study on effects of epoxy sizing involving ZrO2 and GO on interfacial shear strength of carbon fiber/epoxy composites through one and two steps dipping routes

GO and ZrO2 were added into the epoxy sizing agents of carbon fibers via one-step (CF/ZrO2-GO) and two-step (CF/ZrO2/GO) dipping approaches to create different particle arrangements on fiber surface. Synergistic strengthening effects of GO and ZrO2, as well as the effects of their arrangement, on interfacial shear strength (IFSS) of composites were discussed and compared. IFSS of CF/ZrO2/GO is 98.9 MPa, respectively 41.6%, 28.3% and 18.1% exceeding those of untreated fibers, oxidized fibers and CF/ZrO2-GO. IFSS enhancement of CF/ZrO2/GO is mainly ascribed to its surface inside ZrO2/outside GO structure, which is more effective to deflect cracks and dissipate energy. Moreover, interphase with ladder-shapped modulus transition, interfacial synergetic interactions of covalent bonding, hydrogen bonding and π-π stacking, and higher surface energy also contribute its improvement in IFSS. Therefore, the design of fiber surface with appropriate structure via regulation of particle arrangement opens a promising door for obtaining high-performance composites.

An effective method to improve the interfacial shear strength in GF/CF reinforced epoxy composites characterized by fiber pull-out test

Abstract We proposed an effective method for filling multiwall carbon nanotubes (MWCNTs) into the interfacial region of glass (GF), carbon fiber (CF)/epoxy. The MWCNTs were dispersed with dissolving sodium dodecyl sulfate in deionized water using ultrasonic dispersion, and then they were coated onto fiber surface. The functionalized GF/CF coated with MWCNTs was adopted to prepare the microbond specimens, and fiber content effect on interfacial shear strength (IFSS) was discussed. Results show that our method dose not impair the inherent fiber strength. The microbond test results show that the failure load of GF/epoxy has increased by 10%, 9.45% and 8.3% when fiber contents are 3–5, respectively. In terms of CF/epoxy, it increases by 61.5%, 8.88% and 20%. The IFSS improvement is due to the enhanced mechanical interlocking between MWCNTs, polymer chains and fiber surface. Our method presents high potential to give rise to high performance composites.

Interphase engineering in carbon fiber/epoxy composites: Rate sensitivity of interfacial shear strength and interfacial fracture toughness

AbstractDesigning the interface in polymer composites is fundamentally a challenging task. Here, we demonstrate a strategy to engineer the interphase microstructure in carbon fiber/epoxy composites (CFRPs) using carbon nanotubes (CNTs). The incorporation of CNT modifies the interfacial mechanics and interfacial chemistry in conventional CFRPs by creating concentrated, dispersed and mixed type interphase. Therefore, a detailed study is warranted to establish the interfacial microstructure‐property relationship in CNT modified CFRPs. Experimental results show that the relative improvement in interfacial shear strength (IFSS) and interfacial fracture toughness (Gic) depends on the microstructure of interphase. It is shown that simultaneous improvement in IFSS and Gic is possible with certain types of microstructural designs. Moreover, it is observed that IFSS and Gic are not constant material parameters but both of them show a power‐law type dependence on the applied loading rate. The range of rate sensitivity parameters as a function of interphase type suggests that while concentrated and mixed interphase is more suited to maintain the interfacial integrity, dispersed interphase is beneficial for energy dissipating applications of CFRPs. In addition, IFSS and Gic exhibit negative rate sensitivity for certain cases. Finally, it is shown that interphase designing using CNT is an excellent tool to accurately tailor the average interfacial properties of CFRP in a broad range of 16‐79 MPa and 100‐453 J m−2 for IFSS and Gic, respectively.

Ultrastable and Durable Silicone Coating on Polycarbonate Surface Realized by Nanoscale Interfacial Engineering.

Delamination of coating layer from polymer substrate limits the lifetime and functionality of the protective films. Silicone coating is especially vulnerable to photo irradiation, hydrothermal degradation, and mechanical deformation due to the low interfacial adhesion and mechanical robustness. Herein, an ingenious approach is developed to fabricate ultrastable and durable silicone coating on polycarbonate (PC) substrate through well-controlled nanoscale interfacial engineering. A nanopillar array is fabricated on the PC surface by vacuum-assisted hot embossing using anodic aluminum oxide (AAO) templates. Significant improvement in interfacial shear strength (ISS) is achieved for the silicone coating on the nanostructured PC surface. The delamination mechanism can be controlled by tuning the nanopillar size, and the maximum ISS of 9.9 MPa was reached on a surface with a nanopillar diameter of 320 nm. Attributed to the increased interfacial area and mechanical interlocking structure, the nanostructured interface can effectively dissipate interfacial stress and prevent cracking; therefore, maintaining excellent transparency and performance in the harsh environment. The coating exhibits extraordinary stability and durability when subjected to UV irradiation for 168 h, hydrothermal aging for 120 h, mechanical bending for 1000 cycles, and even surface damage. Thus, the tough silicone coating on polymer substraterealized by nanoscale interfacial engineering is a promising technique for highly stable and durable transparent surface protection.

Interface improvement of carbon fiber/PMMA resin composites by fiber surface coating

The surface of the carbon fiber (CF) has been pretreated by liquid phase deposition of microcrystalline cellulose (MCC).X-ray photoelectron spectroscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM) have beenused to analyze and characterize the surface morphology and structure of carbon fiber, and the shear strength test and SEMobservation of single fiber interface have been performed. The interfacial adhesion properties of carbon fiber compositeshave been investigated. The results have shown that the pretreated carbon fiber deposition increases the shear strength of thesingle fiber interface by 259.3%. The analysis results have shown that the improvement of interfacial shear strength has beenrelated to the mechanical riveting between the fibers/resin and the force of the interface. Pretreatment has increased thecarboxyl groups on the surface of carbon fibers and forms hydrogen bonds between carboxyl groups, thereby improving theinterfacial properties of carbon fiber composites.

The improvement in interfacial shear strength of wood fiber/epoxy composite by sizing with epoxy sizing agent containing MWCNTs

This paper discloses a feasible and high efficient strategy for wood fiber treatment to introducing multi‐wall carbon nanotubes (MWCNTs) to the surface of wood fibers for the aim of improving the interfacial shear strength of wood fiber/epoxy composite. Briefly, a layer of MWCNT was deposited on wood fibers through sizing wood fibers with epoxy sizing agent containing amine‐treated MWCNTs (MWCNT‐PEI). The surface functional groups, morphology, wettability, and interphase properties of MWCNTs on the surface of wood fiber were studied. The remarkable enhancements were achieved in interfacial shear strength of reinforced composites by dipping wood fiber in MWCNTCOOH suspension and wood fiber sizing containing MWCNT‐PEI.

Effect of carbon nanotube grafting on the wettability and average mechanical properties of carbon fiber/polymer multiscale composites

An experimental investigation is performed to relate the wetting behavior of unsized and carbon nanotube (CNT) grafted carbon fibers to the average mechanical properties of unsized and CNT grafted carbon fiber/polymer multiscale composites. Contact angle measurements and single fiber pull out tests show that the choice of polymer matrix plays a crucial role in determining whether the incorporation of CNTs on the fiber surface enhances or degrades the wettability and hence average mechanical properties of carbon fiber/polymer composites. CNT grafting leads to a significant improvement in interfacial shear strength as well as flexural and tensile response of carbon fiber/polymer composites with the epoxy resin. However, incorporation of CNTs on fiber surface has no significant effect on the average mechanical properties of carbon fiber/polyester composites. Moreover, it is recorded that the relative enhancement in properties after CNT grafting depends on the fiber orientation in CNT grafted carbon fiber/epoxy composites. POLYM. COMPOS., 39:E1184–E1195, 2018. © 2018 Society of Plastics Engineers

Fabrication of a three-dimensional reinforcement via grafting epoxy functionalized graphene oxide onto carbon fibers

We explored a novel three-dimensional reinforcement consist of petal-like epoxy functionalized graphene oxide (EG) and amine-capped polyphosphazene modified carbon fibers (CF-ACP). The grafted EG sheets with numerous epoxy groups obviously changes the surface topography of carbon fibers. A significant improvement of interfacial shear strength was achieved from 47.3MPa for virgin CF composites to 97.7MPa for functionalized CF composites. Therefore, such multiscale reinforced composites show great potential to be used as high-performance structural applications.

Influence of aramid fiber treatment and carbon nanotubes on the interfacial strength of polypropylene hierarchical composites

Abstract The microbond test was used to evaluate the interfacial shear strength (IFSS) of multiscale composites based on a polypropylene (PP) matrix reinforced with aramid fibers (AFs) chemically treated by two methods and coated with multiwall carbon nanotubes (MWCNTs). AFs were treated by two types of acid solutions and coated with oxidized MWCNTs. Scanning electron and atomic force microscopies were conducted to observe the failure modes and correlate the fiber roughness to the IFSS. While both acid treatments caused a small change in fiber roughness, MWCNT deposition largely increased the fiber roughness. The microbond test results indicate that the acid treated fibers exhibited slightly higher IFSS than the untreated fibers and such IFSS is even higher for AFs containing MWCNTs. For chemically treated fibers covered with MWCNTs, a rougher surface with matrix cohesive failure at the edge of the sheared droplet suggests that the IFSS improvement is mainly due to the physicochemical interactions among AF, MWCNT and PP, in addition to mechanical interlocking.