Interfacial Shear Strength Values Research Articles

Enhancing the mechanical properties of CF-reinforced epoxy composites through chemically surface modification of carbon fibers via novel two-step approach by addition of epichlorohydrin

The chemical surface modification was carried out in this study to improve the interface connection between carbon fiber (CF) and epoxy matrix to study the mechanical and fracture behavior of CF-reinforced epoxy composites. Finite element analysis was carried out by using ABAQUS software to simulate the variation of the tensile strength (TS), interfacial shear strength (IFSS), and interlaminar shear strength (ILSS). The chemical surface modification was carried out by the chemical oxidation by nitric acid and subsequently, addition of monomer resin of epichlorohydrin in a solution at 80 °C. The Raman spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy were carried out to ensure the successful surface modification of CFs. Subsequently, surface-modified CF-reinforced epoxy composites were prepared through the hand lay-up method with the volume fraction of 20 wt.%, and curing was carried out at 80 °C for 4 h. The TS, IFSS, and ILSS values equaled 462.82 MPa, 156 MPa, and 4.1 MPa for modified CF/epoxy composites were achieved, respectively, which are improved remarkably compared to unmodified ones (380, 81, and 2.9 MPa). These improvements are attributed to the successful surface modification of CFs by epichlorohydrin. The surface modification causes the increase in wettability of CFs and the formation of mechanical interlocking and interaction between CFs and epoxy matrix was achieved through uniform and homogenous distribution of epichlorohydrin on the surface of CFs. Fractography was carried out, which indicated the sound and uniform adhesion between CF and epoxy matrix. Achieved results are consistent with simulated results.

Raman spectroscopic stress mapping of single high modulus carbon fibre composite fragmentation in compression

Fragmentation of high modulus carbon fibres is relevant to the failure mechanisms of advanced polymer matrix composites in compression. In situ spatially-resolved Raman spectroscopy during the fragmentation of model single fibre composites is used to map local stress distributions during failure events. The characteristic graphitic band (the G band) located around 1580 cm−1 is associated with the in-plane carbon-carbon bonds; this band shifts its position, and can be calibrated, with the local axial stress in the fibre. The analysis maps the evolution of local stresses with increasing overall composite compression strain, identifying a series of critical events, including fibre fracture, interfacial debonding, and the formation of inter-fragment ‘wedges’. Fitting shear lag models provides interfacial shear strength values. Multiple failure maps of two examples of high modulus PAN carbon fibres (M46J and M55J) demonstrate the possibility of local fragment bending due to fragment end contact. A timeline of potential fragmentation events is proposed for carbon fibres undergoing compression.

Constructing PANI@CF hybrids enhanced epoxy coatings with integrated functionalities of interfacial enhancement, erosion wear resistance and anti-corrosion

Factors such as sediment erosion and diffusion of corrosive ions in the splash zone result in a serious decrease in the protective performance of organic coatings. Carbon fiber (CF) reinforced polymer coatings have attracted much attention due to the impressive high mechanical strength and reliable chemical stability, but their protection period for steel structures is usually limited by the surface inertness and poor interfacial compatibility of the original CF. Herein, we created a composite coating with excellent erosion and wear resistance and corrosion resistance through simple self-polymerization of polyaniline on carbon fibers. The PANI layer not only helped to improve the interfacial compatibility between fibers/resin, but also exerted its corrosion inhibition effect. The interfacial shear strength (IFSS) value of the modified PANI4@CF monofilament and resin (60.63 MPa) was 46.73 % larger than that of the unmodified CF monofilament. In the simulated splash zone, PANI4@CF5/EP composite coating showed the best erosion resistance and corrosion resistance, and the mass loss and volume loss after erosion test were reduced by 53.39 % and 50.10 %, respectively, compared with pure epoxy coating. The local electrochemical impedance spectroscopy (LEIS) value of PANI4@CF5/EP coating with artificial defect was one order of magnitude higher than the epoxy coating after 48 h immersion. Finally, the environmental conditions of the splash zone were simulated to evaluate the anti-corrosion performance and erosion resistance of the CF reinforced composite coatings, and the protective mechanism was discussed in depth, which has great significance to the development of protective coatings for the splash zone under extreme marine environments.

The Improvement of the Tribological Behaviour of Chemically Treated Abaca Fibre-Reinforced Polymer Composites.

Abaca fibres that have excellent mechanical properties are widely applied in the production and preparation of eco-friendly polymer composites as reinforcement materials. However, the weak interfacial bonding property of the abaca fibre and composite matrix limits the further extended application of abaca fibre-reinforced polymer composites. In this research, the findings demonstrate that, compared to raw abaca fibres, the interfacial shear strength (IFSS) value between the treated fibre and matrix is improved by 32% to 86%. Moreover, chemically treated abaca fibres could not only improve the wear resistance of the polymer composites, but also could promote the formation of primary and secondary plateaus. The best wear resistance behaviour was demonstrated by the sample with abaca fibres treated with 3% NaOH and 5% silane solutions, which had a maximum reduction in the sum wear rate of 28.44%. This research will provide detail on theoretical guidance and technical support for the development of eco-friendly natural fibre-reinforced polymer composites.

Mechanical properties of boron nitride nanotube reinforced PEEK composite: a molecular dynamics study

Poly (ether-ether-ketone) (PEEK) is one of the most promising engineering plastics in aerospace engineering because of their reliable mechanical properties under various conditions. However, next-generation engineering plastics also call for more comprehensive outputs, such as higher thermal conductivity and antiwear performances. Boron Nitride Nanotubes (BNNT) have been proven to have outstanding physical properties as additives to the resin of the composites. In this article, the influence of BNNT additives on the PEEK resin is studied to provide a more insightful understanding of the development of BNNT-reinforced engineering plastics in the future. It has been found that the interfacial shear strength (IFSS) between BNNT and PEEK is 151% higher than carbon nanotube reinforcements., and amino groups (–NH2) modified BNNT can further improve the IFSS value by 14%. This mechanical improvement is further evaluated, and the molecular mechanisms are explained with an atomistic resolution.

Experimental study on interfacial shear strength between date palm fibers and thermoset resins

Date palm fibers (DPFs) can be potentially used in novel applications including composites. In this study, the Microbond technique was used to measure the interfacial shear strength (IFSS) between DPFs extracted from the mesh (ME), the midrib (MI), and the Spadix stem (SS) and three types of thermoset resins, i.e., unsaturated polyester (P), epoxy (E), and phenolic Resol (R). The fibers’ tensile strength was measured and the aspect ratio of the fibers (critical length/diameter) for different fiber-resin systems was determined. It was shown that there is a clear relationship between resin droplet contact angle and IFSS. SS fibers provided the highest and ME fibers the lowest IFSS values among the fibers. Among the resins, E provided the highest and R the lowest adhesion to all fibers. The IFSS values of the E with MI, SS, and ME fibers were 7.62, 8.89, and 5.88 MPa, for the R matrix were 2.94, 3.02, and 2.33 MPa, and for the P matrix were 5.59, 5.97 and 5.17 MPa, respectively. It was shown that there is a clear relationship between IFSS values and contact angles of different fiber/matrix systems.

Insights into nanomechanical behavior of B. mori silk fibroin-hydroxyapatite bio-nanocomposite using MD simulations: Role of varying hydroxyapatite content

Nanocomposite material composed of Bombyx mori Silk Fibroin and hydroxyapatite (B. mori SF-HA) is a potential biomaterial for bone tissue engineering. Here, Bombyx mori Silk Fibroin (B. mori SF) is a flexible and tough organic, polymer phase, and hydroxyapatite (HA) is hard and stiff mineral phase. Knowledge about mechanical deformation behavior together with governing mechanisms, and the role of the two phases (SF and HA phase) and interfacial interactions between them, in B. mori SF-HA biomaterial, at fundamental level is an important factor to consider while developing the tissue grafts. Such nanometer scale behavior is often preferably investigated using molecular dynamics method. Present study aims at understanding the mechanical deformation behavior and associated physical mechanisms in B. mori SF-HA bio-nanocomposite, at nanoscale. For this purpose, computational atomistic models of B. mori SF-HA bio-nanocomposite are developed with varying HA content. Mechanical behavior analysis of these composite models under tensile loading were performed using Molecular Dynamics (MD) simulations. Elastic modulus and tensile strength values in the range of 7–20 GPa and 200–700 MPa, respectively, are obtained for B. mori SF-HA composite, in case of different HA contents, wherein, increased mechanical properties are observed with increase in HA content. Analyses of the deformation trajectories show that the deformation flow behavior in B. mori SF-HA bio-nanocomposites is mainly defined by the soft SF phase. However, energetics analyses show that, the HA phase and SF-HA interfacial interactions also play a considerable role in mechanical performance of B. mori SF-HA bio-nanocomposite. Additionally, interfacial shear strength values in B. mori SF-HA bio-nanocomposite, for different HA contents, have also been obtained. The observations made and insights gained in present work has contribution and impact in gaining an insight into the mechanistic interactions occurring at nanoscale between SF and HA phases in B. mori SF-HA bio-composite.

The Influence of Fiber Treatment and Matrix Type on the Impregnation Quality of Carbon Fiber Reinforced Thermoplastics

One of the main issues with Carbon Fiber Reinforced Thermoplastics (CFRTP) is the poor impregnation quality of the matrix on carbon fiber due to the high viscosity of the thermoplastic. Impregnation quality can significantly affect the mechanical properties of the composite. This study aims to compare the impregnation abilities of various types of thermoplastic matrices on carbon fiber. The matrices used in this study are HDPE, PC, and PET. Three variations of carbon fiber treatment were employed: the first variation involved immersion in liquid nitrogen at -196°C, the second variation included heating in an electric furnace at 600°C followed by rapid cooling in liquid nitrogen, and the third variation utilized treatment with a silane coupling agent. The research findings demonstrate that composites comprising a Polycarbonate matrix and carbon fiber reinforcement, treated with a silane coupling agent, exhibit superior impregnation quality, as evidenced by an Interfacial Shear Strength (IFSS) value of 9.34 MPa.. The lowest impregnation quality was observed in HDPE reinforced with carbon fiber that had been heated and rapidly cooled, with an IFSS of 5.52 MPa.

Interfacial Shear Strength of Single-Walled Carbon Nanotubes-Cement Composites from Molecular Dynamics and Finite Element Studies

Carbon nanotubes (CNTs) are nanometer-sized structures that can be used to reinforce cement matrices. The extent to which the mechanical properties are improved depends on the interfacial characteristics of the resulting materials, that is, on the interactions established between the CNTs and the cement. The experimental characterization of these interfaces is still impeded by technical limitations. The use of simulation methods has a great potential to give information about systems lacking experimental information. In this work, molecular dynamics (MD) and molecular mechanics (MM) were used in conjunction with finite element simulations to study the interfacial shear strength (ISS) of a structure formed by a pristine single-walled CNT (SWCNT) inserted in a tobermorite crystal. The results show that, for a constant SWCNT length, ISS values increase when the SWCNT radius increases, while for a constant SWCNT radius, shorter lengths enhance ISS values.

Hybrid green composites using rice straw and jute fabric as reinforcement for soy protein-based resin

In this research, high amounts of the world's most wasted agricultural residue (rice straws) were utilized to produce hybrid green composites. Rice straws (RS) were needle-punched into jute fabric to form hybrid reinforcement mats which were impregnated with a soy protein isolate resin (SPR). Thermoset hybrid composites were produced at three different fiber contents of 40, 50, and 60% by wt. They were characterized for their tensile, flexural, interfacial, fractural, and hygroscopic properties. The hybrid composites with 40% fiber content enhanced Young's modulus (Ey) and ultimate tensile strength (TS) of the pure resin by 200% and 47%, respectively, compared to pure resin. With increasing fiber content, mechanical properties such as Ey, TS, flexural modulus, and flexural strength decreased, indicating insufficient resin volume. Interfacial shear strength values of RS/SPR and Jute/SPR were measured at 2.68 and 4.25 MPa, respectively. The high volumes of low-density RS and higher viscosity of the resin used in the hybrid composites seemed to overwhelm the resin's capacity to effectively wet the fibers. Insufficient wetting and low interfacial shear strength (IFSS) resulted in fiber pull-outs at fracture surfaces. Furthermore, as fiber content increased from 40 to 50 to 60%, moisture absorption increased from 10.4 to 12.9 to 22.6%, respectively. This is in spite of the fact that SPR was the most hydrophilic component of the three constituents. These results suggest that the high volumes of low-density fibers induce structural defects and exhaust the resin's wettability. Overall, the hybrid biodegradable composites had good tensile properties for use in packaging, transportation, housing, and furniture.

Preparation and Interfacial Properties of Hydroxyl-Containing Polyimide Fibers

Developing polyimide (PI) fibers with excellent interfacial adhesion and high mechanical properties for the PI fiber-reinforced polymer matrix composites (PFRPs) industry has been challenging. In this work, 4,4'-diamino-(1,1'-biphenyl)-3,3'-diol (HAB) diamine was introduced into the rigid molecular chains, and the high-performance PI fibers, presenting an interfacial shear strength (IFSS) value of 46.33 MPa, tensile strength of 2.62 GPa, and modulus of 100.15 GPa, were successfully manufactured when the content of HAB in mixed diamines was 30 mol %. Fourier transform infrared (FTIR) spectroscopy identified the presence of intermolecular H-bonding interactions, and 2D small-angle X-ray scattering indicated that the introduction of HAB moiety contributed to reducing the radii of microvoids in the fibers, which were considered to be the key factors leading to a significant enhancement in the mechanical properties of the fibers. X-ray photoelectron spectroscopy (XPS) and the static contact angle intuitively illustrated that the synthetic fiber surface contained active hydroxyl groups. The IFSS value of PI fiber/epoxy resin composites (PI/EPs) was 56.47 MPa when the content of HAB reached 70 mol %. Failure morphologies confirmed that the interfacial adhesion of PI/EPs was enhanced owing to the surface activity of PI fibers. Consequently, this study provides an effective strategy to the long-standing problems of high mechanical performances and poor surface activity for traditional PI fibers used in the PFRPs industry.

The dependence of interfacial shear strength on temperature and matrix chemistry in glass fibre epoxy composites

The present work focuses on a fundamental investigation into the influences of the chemistry of epoxy and the testing temperature on the stress-transfer capability of the fibre-matrix interface in a glass fibre reinforced epoxy composite. We discuss how the interfacial shear strength (IFSS) is influenced by the hardener-to-resin ratio, testing temperature and fibre silane coating respectively. It was observed that the IFSS showed a significant inverse dependence on testing temperature for both silanes, with IFSS values dropping as the temperature was increased, for all ratios studied. Notably, it was shown that once the testing temperature was raised above the glass transition temperature that ratios possessing excess amine hardener had larger IFSS values. From the results presented it is hypothesized that residual radial compressive stresses at the interface are influenced by the chemistry of the matrix system and then relax away at the higher testing temperatures.

Pull-Out of Pristine and Functionalized Carbon Nanotubes from Cement: A Molecular Modelling Study

Carbon nanotubes (CNTs) are widely used as reinforcements in cement-based composites. The improvement in the mechanical properties of the resulting materials depends on the characteristics of the interface formed between CNTs and the cement matrix. The experimental characterization of the interfacial properties of these composites is still limited and hard to achieve with currently available technologies. In this work, molecular dynamics and molecular mechanics pull-out simulations of pristine and functionalized CNTs, taken from a tobermorite crystal, were carried out to study interfacial shear strength (ISS) from an atomic perspective. ISS was calculated from the potential energy of the systems. The effects of the CNT diameter and the degree of functionalization on the pull-out process were analyzed according to the ISS and non-bonded energy results. The influence of H-bonding and electrostatic interactions between the CNT and the matrix were also studied. The results show that ISS decreases with increasing CNT radius for pristine CNTs and depends upon the number of H-bonds for functionalized CNTs. ISS values are positively correlated to Enon-bonded energy, which is related to the number of carboxyl groups on the CNT surface. A high degree of functionalization increases both the number of H-bonds and the number of Ca2+-O interactions between the CNT and the tobermorite surface. This results in a stronger interfacial interaction and, therefore, an elevated ISS value.

Preparation of waterborne polyurethane with high surface activity for regulating the interfacial properties of carbon fiber/polyamide 6 composite

The poor wetting and spreading performances of waterborne polyurethane dispersion (WPUD) on carbon fiber (CF) surface limited its application in regulating the interfacial properties of CF reinforced polyamide 6 (PA6) composites. Unlike previous studies, this work diversified into improving the film-forming property of WPUD on CF surface. Two novel WPUD sizing agents named WPUD-Y1 and WPUD-F1 were synthesized by introducing block polyether and organic fluorine into the molecular chain. Results showed that surface energies of the elaborately designed WPUD-Y1 (35.5 mN/m) and WPUD-F1 (32.7 mN/m) were significantly lower than that of ordinary WPUD (40~55 mN/m). Especially, both sizings formed a complete and uniform film on CF surface. Interfacial shear strength (IFSS) analysis from micro-droplet test showed that sizing relieved the thermal residual stress at composite interphase by over 40%, at the cost of reducing its interfacial strength by 20%. More importantly, although sizing had not enhanced interfacial adhesion, the IFSS values between the sized CF and PA6 were still 20% higher than the maximum interlaminar shear strength (ILSS) values reported in literatures.

Characterization of the effects of testing temperature on the interfacial shear strength of fiber/resin single-filament-composite

In the micromechanical test of fiber-reinforced composites, single fiber pull-out test is the most widely used test method. However, for high performance fibers/matrix, different test equipment and sensor accuracy can affect the single fiber pull-out test results very much. In this study, an innovative single fiber pull-out test method is proposed for testing the interfacial shear strength (IFSS) of high performance fibers/resins at different temperatures. Single fiber pull-out test was carried out on PBO fiber/epoxy resin (EP) composites at room temperature and elevated temperature. The IFSS was found to have an inverse relationship with the test temperature. The IFSS value of PBO/EP decreased from 25.25 MPa at room temperature to 6.25 MPa as the temperature approached the glass transition temperature. COMSOL simulations showed that fiber pull-out with angular tilt exhibited better interfacial strength, demonstrating the validity of the method. The results of this paper provide ideas to study the effect of temperature on the mechanics of fiber-reinforced resin matrix composites and expand the way to design stiffer, stronger and more robust composites.

Interfacial stress transfer factor and tensile strength of polymer halloysite nanotubes systems

AbstractEven though numerous papers have studied the mechanical properties of polymer halloysite nanotubes (HNT) nanocomposites by experimental characterizations, only a few researchers have simulated the characteristics of these materials. Moreover, the previous papers have disregarded the interphase features for the mechanical performance of HNT‐reinforced systems. In this article, two simple models are progressed for tensile strength of HNT‐based nanocomposites supposing HNT size and interphase section. The models' calculations are linked to the measured data and the characters of all factors in the strength are explained. In addition, the advanced models are used to define the “s” as interfacial stress transfer factor for HNT‐filled nanocomposites. The influences of various factors on the “s” are validated to approve the novel equation. All forecasts appropriately follow the measured data at various HNT loadings. “s,” interfacial shear strength, interphase thickness, and HNT length directly control the nanocomposite's strength, but HNT radius and polymer's strength have inverse effects. Additionally, the highest value of interfacial shear strength produces the maximum level of “s,” but HNT size negligibly manipulates the “s.”

Towards robust synchronous belts: influence of surface characteristics on interfacial adhesion

ABSTRACT The use of carbon fibres is being explored in synchronous belts due to their excellent mechanical properties, chemical and dimensional stability. However, poor adhesion between fibres and the common rubber-fibre adhesive resorcinol-formaldehyde-latex (RFL) compromises load transfer between these constituents. We examined the influence of surface characteristics of commercial glass and carbon fibres, such as fibre surface chemistry, energy and area on carbon fibre-RFL matrix adhesion in model single fibre composites. Fibres with higher surface oxygen content and thus more polar functional groups resulting in a higher surface energy exhibited better adhesion to RFL. Fibre adhesion behaviour to RFL can be ranked using the aspect ratio of the fibre diameter to the critical fragment length as assessed by single fibre fragmentation tests, however, accurate interfacial shear strength values cannot be obtained using the Kelly-Tyson model due to statistical limitations in the treatment of single fibre tensile properties. Our results provide insight into factors affecting fibre-RFL adhesion and identified commercial T700GC-31E carbon fibres as candidates for improved fibre-matrix adhesion for the production of more robust synchronous belts.

Interfacial Bonding Enhancement Between Cryogenic Conditioned Carbon Fiber and Epoxy Resin Characterized by the Single-Fiber Fragmentation Method

Carbon fiber (CF) is an important structural material due to its favorable mechanical and physical properties. However, poor interfacial bonding with polymer resin severely affects the mechanical performance of carbon fiber reinforced polymer composites (CFRP). In this study, the single-fiber CFRPs were treated using multi-stage cryogenic approaches to optimize the interfacial shear strength (IFSS) between carbon fiber and epoxy resin. The carbon fiber was pretreated by cryogenic treatment with sharp and slow cooling rates, followed by the same treatment of the single-fiber CFRP composed of the pretreated carbon fiber to reach the optimal interfacial modification. The IFSS value was increased by 27.4% when the carbon fiber was pretreated at a slow cooling rate, and its single-fiber CFRP was treated at a sharp cooling rate.

Characterisation of interfacial adhesion in hemp composites after H2O2 and non-thermal plasma treatments

Interface optimisation for continuous hemp reinforcements in epoxy resin is a current challenge for the development of biocomposites. A chemical treatment based on hydrogen peroxide and a physical one using a non-thermal plasma have been tested to optimise interface adhesion, by varying several parameters. FTIR analysis and FE-SEM observations have shown the effects of the treatments on chemical and morphological aspects of the treated yarns. Tensile tests on hemp yarns have allowed the selection of the treatment parameters leading to the best strength. Fragmentation tests results showed that the two treatments lead to a decrease in the fragment lengths and thus, an enhancement of the Interfacial Shear Strength (IFSS) values in comparison with the untreated yarn. This is confirmed by the micro-CT observations of the debonding lengths in the vicinity of each yarn fragment extremity. Finally, the plasma treated samples exhibit a better interface adhesion quality (IFSS = 44.7 ± 4 MPa) than the chemically treated ones (IFSS = 24.2 ± 4 MPa), which are better than the non-treated ones (IFSS = 13.5 ± 4 MPa).

Waterborne epoxy sizing agent with hyperbranched structure to improve the interface performance of carbon fiber

AbstractThe epoxy resin was modified by hyperbranched structure of hydroxyl terminated to obtain waterborne epoxy resin for using as the carbon fiber (CF) sizing agent. By mixing method of waterborne epoxy resin and water, the waterborne epoxy sizing agent can be fabricated directly. In the sizing process, free of volatile organic solvents ensure the safety of operators and environment. Moreover, the introduction of tertiary amine group in hyperbranched structure will promote the reaction between epoxy and hydroxyl groups, and thus enhance the bonding strength between CF and epoxy resin. Results showed that the introduction of sizing agent does not sacrifice the CF single fiber tensile strength. The structure of epoxy resin retained in sizing agent is beneficial to the good wettability between CF and epoxy resin according to surface energy results. Interfacial shear strength value increases from 51.75 to 72.34 MPa, and interlaminar shear strength value increases from 80.32 to 90.34 MPa. These mechanical properties show that hyperbranched epoxy resin sizing agent with a large amount of hydroxyl groups can effectively improving the interface adhesion between CF and epoxy resin, showing a broad application prospect in composite materials field.