Single Fiber Fragmentation Test 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.

Interfacial properties of carbon fiber‐reinforced biobased resin composites by single fiber fragmentation, fiber push‐out, and interlaminar shear strength

AbstractThe present study examines the interfacial properties of carbon fiber biobased resin composites by comparing the test methods such as the single fiber fragmentation test, fiber push‐out test, and interlaminar shear strength test. The composites were fabricated using a cold vacuum‐assisted resin infusion method for the preparation of fiber push‐out and interlaminar shear test specimens. The interfacial adhesion from the three different test methods is analyzed and compared to determine their relative effectiveness in evaluating interfacial adhesion. Plasma treatment is performed on the carbon fibers and the interfacial shear stress is evaluated by conducting the push‐out test. The surface characterization of the carbon fibers is done by scanning electron microscopy and x‐ray photoelectron spectroscopy to investigate the influence of the plasma treatment on the fiber surface. Plasma treatment resulted in significant improvement in the interfacial adhesion between the fiber and matrix.Highlights Analysis and comparison of interfacial adhesion by several test methods. Single fiber fragmentation and push‐out tests with IFSS of 40.5 and 42.2 MPa. Plasma surface treatment improved the IFSS by 88.1%. Surface characterization of treated and untreated fibers by SEM and XPS.

Interfacial shear strength of surface functionalized and functionalized CNT coated carbon fiber: A single fiber fragmentation study

The compatibility among nonpolar thermoplastics like polypropylene (PP) and carbon fibers (CF) having traditional sizing or coating is challenging. In this study, facile and effective surface functionalization of CF and its subsequent coating with functionalized carbon nanotubes (CNTs) were carried out to obtain improved interfacial shear strength (IFSS) which was validated by the single fiber fragmentation test (SFFT). Functional groups, -COOH, -OH, and -NH2, were separately grafted on the CF surface using different chemical routes. Additionally, ultrasonic assisted electrophoretic deposition (EPD) technique was used to coat -COOH, -OH, and -NH2 functionalized CNTs on the sized and surface functionalized CFs. Attenuated total reflection-infrared spectroscopy (ATR-IR), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FE-SEM) images confirmed the successful surface functionalization and coating on CF. Neat PP and a blend of PP and maleic anhydride-grafted-styrene ethylene butylene styrene (MA-g-SEBS) were used as two different base polymer matrixes in preparing a total of 26 different SFFT samples. Silane functionalized CF coated with amine functionalized CNTs using ultrasonic assisted EPD process showed IFSS of ∼29 MPa which was an impressive ∼758% higher than pristine CF and highest among all the surface modified CFs. Interestingly, this translated into useful increase of ∼13% in single fiber tensile strength of functionalized and treated CF over and above that of as received CF.

Experimental determination of bimodal strength distribution of S-glass fibers

Tensile strength distribution of S-Glass fibers at small gage lengths on the order of the ineffective length is required for both analytical and numerical models of composite unidirectional tensile strength. Historically unimodal Weibull strength distributions measured at large gage lengths are extrapolated to smaller length scales (5–200 μm). The accuracy of this approach is assessed by using 2 different experiments – the filament tensile test (gage lengths > 4 mm) and a continuously-monitored Single Fiber Fragmentation Test (SFFT, gage length = 544 μm). Extrapolation of the unimodal Weibull distribution to the 544 μm gage length leads to significant overprediction of fiber strengths (by ∼60%). The Weibull distribution obtained from SFFT also shows a significantly higher Weibull Modulus (12.9) as opposed to the tension dataset (4.5). This indicates that a different population of defects dominate at the shorter gage lengths. A bimodal Weibull equation has been fit to the combined data to account for the 2 different defect populations to provide accurate strength predictions over fiber lengths from ∼500 μm to 30 mm. An independent validation experiment was performed at 2 mm gage length to validate the Bimodal Equation.

Correction to: Snappy: A New Automated Testing Machine for Monitoring the Break Evolution Process during Single Fiber Fragmentation Test

Correction to: Snappy: A New Automated Testing Machine for Monitoring the Break Evolution Process during Single Fiber Fragmentation Test

Snappy: A New Automated Testing Machine for Monitoring the Break Evolution Process during Single Fiber Fragmentation Test

Snappy: A New Automated Testing Machine for Monitoring the Break Evolution Process during Single Fiber Fragmentation Test

L-DOPA coating improved phosphate glass fibre strength and fibre/matrix interface

The levodopa (L-DOPA) has been reported as a promising adhesive for various materials. In this study, we utilized L-DOPA as an interfacial agent for phosphate glass fibre/polycaprolactone (PGF/PCL) composites, with the aim to enhance the interfacial properties between the fibres and polymer matrix. The PGFs were dip-coated in varying concentrations of L-DOPA solution ranging between 5 and 40 g L-1. The fibre strength and interfacial shear strength (IFSS) of the composites were measured via a single fibre tensile test and single fibre fragmentation test, respectively. It was found that the L-DOPA agent (at conc. 10 g L-1) significantly improved the IFSS of the composites up to 27%. Also, the L-DOPA coating (at conc. 40 g L-1) significantly increased the glass fibre strength up to 18%. As a result, an optimum coating level could be tailored depending on application and whether fibre strength or IFSS was of greater importance. In addition, SEM and TGA analyses were used to detect and quantify the coating agents. FTIR and XPS further confirmed presence of the coating and indicated the zwitterionic crystals of L-DOPA and the formation of a melanin-like polymer layer. The spectroscopy data also evidenced that both catechol and amine groups contributed to the interaction between the L-DOPA and the PGF surface.

Interfacial modification between glass fiber and polypropylene using a novel waterborne amphiphilic sizing agent

High performance structural applications of utilizing glass fiber (GF) reinforced polypropylene (PP) composites are normally hindered by the notoriously weak interfacial bonding between GF and PP resulting from their chemical inertness and the great mismatch in surface energies of both raw materials. Tremendous efforts have been made on the development of fiber sizing agents for interfacial modifications of GF-PP composites, since a viable sizing agent can directly build robust and efficient coupling interface between GF and PP, enabling effective stress transfer between fiber and matrix. Herein, this paper reports an interfacial modification methodology of using a novel amphiphilic sizing agent that is a polyacrylate-based waterborne coating synthesized strategically following a one-step reversible addition-fragmentation chain-transfer (RAFT)-mediated polymerization-induced self-assemble (PISA) approach. Specifically, after the proposed sizing treatment the surface energy of the sized GF surface decreases from 74.51 mJ·m−2 (of the typical pristine GF surface) to 56.43 mJ·m−2, approaching to 30.2 mJ·m−2 (of the raw PP) and enabling strong possibility of facilitating GF-PP interfacial compatibility. Additionally, the GF-PP interfacial shear strength (IFSS) evaluated by single-fiber fragmentation tests increases from 8.34 MPa (for bare GF) and 11.14 MPa (for commercial GF) to 17.62 MPa for the sized GF. Notably, a series of the sized short GF/PP composite coupons were fabricated and demonstrates promoted tensile and flexural properties, validating the effectiveness and scalability of the proposed GF/PP interfacial treatment. We believe that this amphiphilic polyacrylate-based sizing agent can serve as an effective GF-PP interfacial modifier, offering great potential for practical applications of developing high performance GF-PP composites.

Finite element modelling of the single fibre composite fragmentation test with comparison to experiments

This paper develops a finite element (FE) model of the single fibre fragmentation test designed for direct comparison with experimental results on an E-glass/epoxy system by McCarthy et al. (2015). Interface behaviour is modelled via a cohesive surface, and stochastic Weibull fibre strengths (determined by independent experiments) assigned at random to the elements along the fibre. Predictions from the model agree with experiment for a range of outputs: The evolution of the number of fibre breaks with strain is similar and breaks occur at random locations as required. The model also captures a transition to a Uniform (rather than Weibull) statistical distribution of break locations at later stages of the test consistent with recent experiments. The evolution of the cumulative distribution of fragment lengths is also similar to that of the experiment. In addition, fibre axial stress and interfacial shear stress distributions conform with experimental observation. Correct model predictions of break locations confirm the approach taken on assigning stochastic (Weibull) strengths along the fibre. The effectiveness of the FE model in capturing a number of key aspects of the fragmentation phenomenon suggest its usefulness as a tool in analysing and interpreting fibre fragmentation tests, including back-calculation of interfacial shear strength.

Effects of carbon nanotube-polydopamine hybridization on the mechanical properties of short carbon fiber/polyetherimide composites

Recently, it is shown that hybrid sizing agents of nanomaterials and polymers are more effective than their single components in enhancing the mechanical properties of fiber reinforced polymer composites. However, the effects of the hybrid sizing agents are scarcely examined from both experimental and theoretical aspects. In this study, short carbon fiber (SCF) surfaces were modified by applying the hybrid sizing agents of polydopamine (PDA) and carbon nanotubes (CNTs). Then the polyetherimide (PEI) composites reinforced with modified SCFs were manufactured by extrusion compounding and injection molding techniques. A single fiber fragmentation test was experimentally carried out and the results were numerically analyzed to elucidate the effects of CNT-PDA sizing layer on the interfacial properties. The effects of hybrid sizing agent on the mechanical behaviors of PEI composites were investigated from both experiment work and theoretical predictions. The PEI composites with PDA-CNT treated SCFs exhibit the improved tensile strength at 25 °C and −60 °C due to the enhanced interfacial properties between SCFs and PEI after PDA-CNT treatment. The Fu-Lauke model predictions were conducted to interpret the reinforcing mechanisms of coated SCFs by hybrid sizing agent. Moreover, the temperature-dependent tensile behaviors of the composites were studied to examine the suitability of hybrid PDA-CNT sizing in modifying SCFs at various temperatures. Finally, the short term creep behavior of PEI composites was investigated by using Burger's model and the results indicate that the creep resistance of the PEI composites was obviously enhanced by the CNT-PDA sizing treatment at 25 °C.

Evaluation and Analysis of Fracture Modes in Single Composite Basalt/Epoxy Fibres by Photoelastic Method and Single Fibre Fragmentation Test

Evaluation and Analysis of Fracture Modes in Single Composite Basalt/Epoxy Fibres by Photoelastic Method and Single Fibre Fragmentation Test

Synthesis, Characterization, and Modeling of Aligned ZnO Nanowire-Enhanced Carbon-Fiber-Reinforced Composites.

This paper presents the synthesis, characterization, and multiscale modeling of hybrid composites with enhanced interfacial properties consisting of aligned zinc oxide (ZnO) nanowires and continuous carbon fibers. The atomic layer deposition method was employed to uniformly synthesize nanoscale ZnO seeds on carbon fibers. Vertically aligned ZnO nanowires were grown from the deposited nanoscale seeds using the low-temperature hydrothermal method. Morphology and chemical compositions of ZnO nanowires were characterized to evaluate the quality of synthesized ZnO nanowires in hybrid fiber-reinforced composites. Single fiber fragmentation tests reveal that the interfacial shear strength (IFSS) in epoxy composites improved by 286%. Additionally, a multiscale modeling framework was developed to investigate the IFSS of hybrid composites with radially aligned ZnO nanowires. The cohesive zone model (CZM) was implemented to model the interface between fiber and matrix. The damage behavior of fiber was simulated using the ABAQUS user subroutine to define a material’s mechanical behavior (UMAT). Both experimental and analytical results indicate that the hierarchical carbon fibers enhanced by aligned ZnO nanowires are effective in improving the key mechanical properties of hybrid fiber-reinforced composites.

Enhancing mechanical strength of carbon fiber-epoxy interface through electrowetting of fiber surface

The interfacial shear strength between carbon fiber and polymer matrices plays a critical role in bulk mechanical performances of carbon fiber-reinforced polymer composites. However, finding simple and effective methods for modulating the interfacial adhesion remains challenging even after over a decade of research and development. Herein, a novel method based on electrically-assisted wetting technique was developed to strengthen the interfacial adhesion between carbon fiber and polymer matrix. The results indicated the polymer completely infiltrated the small grooves on the fiber surface under applied external electric field during the curing process, leading to the formation of conformal contact interface. The interfacial properties were characterized by utilizing the microdroplet debonding and single fiber fragmentation tests. It is found that the as-prepared composites exhibit a maximum increased interfacial shear strength (IFSS) reaching up to 119.69 MPa, a value 81.02% higher than that of the original fiber-based composites. The reinforcement mechanism was ascribed to the improved wettability and mechanical interlock effect induced by the applied electrical stimulus which was supported by dynamic simulation of two-phase flow. In sum, the suggested simple, facile, and environmentally friendly strategy can effectively regulate the interfacial load transfer capacity, thereby suitable for the optimal design of fiber-reinforced composites. • A green, and economical electrically-assisted wetting method is proposed to improve the interfacial properties. • Electrically-assisted wetting promotes preferable resin wetting and formation of mechanical interlocking. • The two-phase flow dynamic simulation reveals the rheological behaviors of the resin and the reinforcement mechanism. • The proposed method will not cause damage to the fiber and is compatible with other modification methods.

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.

Fragmentation of Beaded Fibres in a Composite.

The fibre–matrix interface plays an important role in the overall mechanical behaviour of a fibre-reinforced composite, but the classical approach to improving the interface through chemical sizing is bounded by the materials’ properties. By contrast, structural and/or geometrical modification of the interface may provide mechanical interlocking and have wider possibilities and benefits. Here we investigate the introduction of polymer beads along the interface of a fibre and validate their contribution by a single fibre fragmentation test. Using glass fibres and the same epoxy system for both matrix and beads, an increase of 17.5% is observed in the interfacial shear strength of the beaded fibres compared to fibres with no polymer beads. This increase should lead to a similar improvement in the strength and toughness of a beaded fibre composite when short fibres are used. The beads were also seen to stabilise the fragmentation process of a fibre by reducing the scatter in fragment density at a given strain. A case could also be made for a critical beads number—4 beads in our experimental system—to describe interfacial shear strength, analogous to a critical length used in fibre composites.

Micromechanical Tests on Natural Fibre Composites with Enzymatically Enhanced Fibre–Matrix Adhesion

Natural fibre–reinforced composites are more sustainable than other composites with respect to the raw materials. Their properties are attractive due to high specific properties, and especially so wherever high damping is valued. As the interphase between fibre and matrix is the region of highest stresses, a strong bond between fibre and matrix is essential for any composites’ properties. The present study compares two methods of determining the interfacial shear stress in natural fibre–reinforced composites: the single fibre fragmentation test and the single fibre pullout test. The studied composites are flax fibre reinforced epoxy. For a variety of fibre–matrix interaction, the fibres are treated with a laccase enzyme and dopamine, which is known to improve the fibre–matrix shear strength. In the observed samples, single fibre fragmentation test data, i.e. of fracture mode and fragment length, scatter when compared to pullout data. In single fibre pullout tests, the local interfacial shear strength showed a 30% increase in the laccase-treated samples, compared to the control samples. The method also permitted an evaluation of the frictional stress occurring after surface failure.

An improved analytical model for inversely determining multiple interfacial parameters from single fiber micro-Raman and fragmentation tests

Inverse identification of fiber/matrix interfacial properties from single fiber micro-Raman or fragmentation test requires an accurate model prediction of stress transfer near a fiber break. The existing models adopt very simplified interfacial constitutive law, and hence the three key interfacial parameters, i.e. interfacial shear strength, fracture energy and frictional stress, cannot be determined simultaneously from the single fiber composite test. In this work we develop an analytical model for stress transfer analysis near a fiber break, in which the three important interfacial parameters are all introduced. The present model is well validated by finite element simulations through comprehensive comparisons of stress profiles in fiber and fiber/matrix interface. As demonstrated by several examples, our model shows a good ability to inversely identify interfacial shear strength, fracture energy and frictional stress simultaneously for both single fiber micro-Raman and fragmentation tests. This unified model is also expected to minimize the error between the interfacial parameters identified by different test methods.

Milkweed floss-reinforced thermoplastics: interfacial adhesion and related mechanical properties

ABSTRACT This research aimed to evaluate the improvement of the mechanical properties of composites and their reduction of weight induced by milkweed floss (MW). As MW is severely affected by surface treatments, a good inherent affinity with the matrix is required for efficient reinforcement. Thus, composites made of MW and polyamide (PA11) (or polypropylene (PP) for reference) were studied, as PA11 should have a good physical interaction with natural fibers. The interfacial adhesion between MW and both matrices was determined by single fiber fragmentation tests (SFFTs) and composites with different MW amounts were produced. The length of MW, the density of the composites and their mechanical properties were measured. SFFT results revealed a better affinity between MW and PA11, with a critical length of 85 µm compared to 335 µm in PP. This had a direct impact on the fiber length efficiency factor, which was found to be lower in PP than in PA11. The addition of 2.5 wt.% of MW fibers in PA11 led to an increase of 29% of Young’s modulus but only 4% in PP. However, the density decrease was limited for all the composites as the lumen of the fibers was partially filled (80–100% filling rates).

Effect of carbon nanotube addition in two sizing agents on interfacial properties of carbon fiber / polycarbonate composites

In order to improve the interfacial bonding between carbon fiber (CF) and polycarbonate (PC), sizing agents of water-borne polycarbonate (WPC) and water-borne polyurethane (WPU) containing carbon nanotubes (CNTs) were used to treat CFs. CNTs were dispersed in the two sizing agents after treated with concentrated nitric acid. The effects of the type of sizing agents and the CNT content on the interfacial properties of composites were investigated by two methods, single fiber fragmentation test (SFFT) for monofilament reinforced composite and transvers tensile for directional bundle composite. Results show that WPU is more conducive to improving the interfacial bonding properties of CF/PC composites because of its better film-forming property than WPC, and the addition of CNTs has a beneficial effect on the interfacial properties of composites when the content of CNTs is 0.1 wt%. Over dose of CNTs causes agglomeration, which is unfavorable for the improvement in interfacial properties. CNTs can effectively prevent interfacial slip, thus significantly improve the interfacial properties in SFFT, while the improvement is not obvious in transvers tensile because the adhesion of the sizing agents plays a leading role.

Scalable coating methods for enhancing glass fiber–epoxy interactions with cellulose nanocrystals

Two scalable coating techniques, slot die and spray coating (SC), are used to apply cellulose nanocrystals (CNCs) to the surface of glass fibers with the goal of enhancing interfacial interactions between glass fibers and epoxy and, consequently, the strength of fiber-reinforced composites. The quality of the cellulose coatings and the interfacial shear strength, assessed via the single fiber fragmentation test, are determined as a function of the method and conditions used to coat the fibers. In addition, a comparison with glass fibers coated with identical CNC formulations using a laboratory-scale dip coating (DC) technique is provided. Results from both scalable methods were found to be comparable or superior to the DC technique, with SC outperforming DC by up to 18% on average depending on the coating applied. Further analysis was conducted on coating morphology, fracture behavior, elemental composition, and surface loading. The observed differences can be used to determine which technique is most appropriate for a given application. This work demonstrates the viability in adapting existing, scalable processes for CNC glass fiber coatings and establishes key avenues for future process optimization.