Single Fiber Pull-out Test Research Articles

Uniform grafting of amino-functionalized multi-walled carbon nanotubes on the surface of oxidized bamboo fiber to enhance the interfacial strength with epoxy resin

The objective of this paper is to improve the interfacial bonding between the oxidized bamboo fiber and epoxy resin by grafting amino-functionalized multi-walled carbon nanotubes. Bamboo fiber was oxidized by a 2,2,6,6-Tetramethylpiperidine-1-oxyl oxidation system. The amino-functionalized multi-walled carbon nanotubes were then grafted on its surface by impregnation method. It was found by single fiber pull-out testing that the interfacial bonding between the bamboo fiber and epoxy resin was improved by 31.5% after the oxidation treatment of the fiber. After further grafting 0.5 wt% amino-functionalized multi-walled carbon nanotubes, the interfacial bonding was improved by 106.4%. The fracture morphologies and AFM scanning results of individual sample revealed the mechanism of the treatment from amino-functionalized multi-walled carbon nanotubes strengthens interfacial bonding between the fiber and epoxy. The effect of the amino-functionalized multi-walled carbon nanotubes content on the interfacial properties of the bamboo fiber/epoxy resin was investigated, a threshold for the content was identified.

Predicting the Tensile Behaviour of Ultra-High Performance Fibre-Reinforced Concrete from Single-Fibre Pull-Out Tests.

In this paper, a prediction model for the tensile behaviour of ultra-high performance fibre-reinforced concrete is proposed. It is based on integrating force contributions of all fibres crossing the crack plane. Piecewise linear models for the force contributions depending on fibre orientation and embedded length are fitted to force–slip curves obtained in single-fibre pull-out tests. Fibre characteristics in the crack are analysed in a micro-computed tomography image of a concrete sample. For more general predictions, a stochastic fibre model with a one-parametric orientation distribution is introduced. Simple estimators for the orientation parameter are presented, which only require fibre orientations in the crack plane. Our prediction method is calibrated to fit experimental tensile curves.

Effect of lyocell fiber cross-sectional shape on structure and properties of lyocell/PLA composites

Abstract Three kinds of lyocell fibers with different cross-sectional profiles including circular, Y-shape, and H-shape (abbreviated as O-, Y-, and H-lyocell) and similar mechanical properties were used to reinforce polylactic acid (PLA) by melt compounding and injection molding. The influence of lyocell cross-section shape on the interfacial shearing force, interface morphology, and mechanical properties of lyocell/PLA composites was investigated. Single fiber pull-out tests showed that the interfacial shearing force between lyocell fibers and PLA matrix was in the order of H-lyocell > Y-lyocell > O-lyocell, which was correlated with the fiber non-roundness factor. The higher the non-roundness factor of lyocell fibers, the better were the mechanical properties of lyocell/PLA composites. The tensile strength, impact strength, and initial dynamic storage modulus of different lyocell/PLA composites were in the order of H-lyocell/PLA > Y-lyocell/PLA > O-lyocell/PLA, which was attributed to higher interfacial contact area and stronger interfacial adhesion of profiled lyocell/PLA composites. Therefore, profiled lyocell fibers may be more promising for use in bio-composite reinforcement than conventional circular lyocell fibers.

Study on the Properties of Fiber/Matrix Interface and Strain-Hardening Behavior of ECC Containing Municipal Solid Waste Incineration (MSWI) Powder.

In this paper, the mechanical properties of micropowder cement mortar and engineered cementitious composites (ECC), using different processing municipal solid waste incineration (MSWI) as a mineral admixture, were investigated. Through the direct ball milling method, ball milling heat treatment method, water washing ball milling method and water washing heat treatment ball milling method, the mechanical properties of MSWI bottom slag-regenerated micropowder cement mortar were tested. Compared with other groups, the flexural strength and compressive strength of the specimen prepared by the MSWI after washing and heating (750 °C, 5 h) were the highest, which reached 82.0% and 81.0% of the reference group, respectively. Based on this treatment, a uniaxial tensile test, three-point bending test and single fiber pull-out test were then carried out to explore the relevant ECC properties containing MSWI. The strain-hardening index PSH of ECC was determined by analyzing the fracture toughness and elastic modulus, fiber/matrix interface chemical bond and friction bond strength of ECC containing MSWI. The results showed that the PSH index of ECC was higher when the treated powder content was 2.2, the w/c ratio was 0.25 and the fiber volume content was 2.0%. This led to higher tensile ductility, which made it easier to achieve stable multi-slit cracking and strain-hardening behavior.

Electrochemical oxidation of recycled carbon fibers for an improved interaction toward alkali-activated composites

In this study, recycled carbon fibers (rCF) obtained from pyrolysis are utilized as reinforcements in fly ash-GGBS alkali-activated composites. Since the bond between the fiber and matrix is relatively poor, anodic oxidation was conducted by applying various voltages to enhance the interfacial interactions. Cyclic voltammetry (CV) was performed to investigate the chemical reaction process during the electrochemical fiber modification. Scanning electron microscopy showed the removal of contaminations and impurities from the fiber surfaces by anodization. Thermogravimetric analysis (TGA) analysis was performed to compare the heat resistance properties of the CF reinforced composites and single-fiber tension tests were carried out to evaluate the influence of the electrochemical treatment on the fiber's properties. Single fiber pullout tests and energy dispersive X-ray mapping indicated a remarkable improvement of compatibility between the modified fibers and the matrix, since chemical bonds are formed between oxygen-related functional groups from the anodized fiber surfaces and the alkali-activated matrix. With the addition of 1 wt.% rCFs compressive and flexural strengths have been enhanced by up to 25% and 19%, respectively, compared to the plain composites. The results reveal that electrochemical surface treatment of rCFs is beneficial for enhancing the flexural behavior of rCF-reinforced composite owing to enhanced interfacial bonding. However, this method also provokes a slight increase of porosity compared with untreated fiber-reinforced samples, as proved by mercury intrusion porosimetry (MIP). This study provides a promising utilization of rCF in the production of waste-based fiber-reinforced alkali-activated composites, promoting the management of carbon fiber-reinforced plastic waste.

Demonstration of Hybrid Effect in Single Fiber Pull-Out Tests for Glass/Cellulose-Reinforced Polypropylene with Different Fiber-Matrix Adhesions.

In hybrid fiber reinforcement, the combination of glass and regenerated cellulose fibers is a promising combination because the different properties of the fibers can be combined. The properties of the regenerated cellulose fiber in combination with the absorption of energy by fiber pull-outs can thus significantly increase the toughness of the composite in the event of failure, while the glass fiber significantly increases the stiffness and strength due to its properties. In this study, the interaction of the two fiber types in a composite is demonstrated by fiber pull-outs. For this purpose, the fibers are embedded in a PP matrix and simultaneously pulled out. Different bondings of the fiber by, e.g., coupling agent and/or a pretreatment of the regenerated cellulose fiber, were also investigated. The results show that each type of fiber has a characteristic force–deformation curve, and the hybrid reinforcement is a combination of both curves. The use of a coupling agent leads to an increase in the interfacial shear stress from 4.5 to 7.5 MPa. A treatment of the regenerated cellulose fiber by UV light further increases the interfacial shear stress to 11 MPa.

Effect of low temperature and moisture on bond properties of PVA fibres and engineered cementitious composite matrix

The chemical debonding energy, initial interfacial frictional bond strength and slip-hardening coefficient between polyvinyl alcohol (PVA) fibres and an engineered cementitious composite (ECC) matrix were obtained by means of single PVA fibre pull-out tests. The effect of three moisture states (fully saturated, semi-saturated and fully dry) on the bonding properties between the PVA fibre and ECC matrix at three target temperatures (25°C, 0°C and −20°C) was investigated. It was found that, at 25°C, the bonding properties decreased with an increase in moisture content. At 0°C and −20°C, the bonding properties increased with an increase in moisture content. At −20°C in the fully saturated state, the bonding load was too large to cause fibre rupture. The bonding properties were found to increase with decreasing temperature in the fully saturated and semi-saturated states and decrease with decreasing temperature in the fully dry state. This study of the effect of low temperature and moisture state on the bonding properties between PVA fibres and ECCs provides theoretical support for how to ensure good ductility when ECCs are in service at low temperature.

Role of pH value on electrophoretic deposition of nano-silica onto carbon fibers for a tailored bond behavior with cementitious matrices

Electrophoretic deposition (EPD) of nano-silica (NS) onto carbon fiber (CF) surfaces may considerably improve the bond properties toward cementitious matrices. In the article at hand, varied pH conditions (neutral, acidic, and alkaline environments) are studied during EPD for a tailorable interfacial bond. Zeta potential measurements and cyclic voltammetry (CV) confirmed the importance of pH with regard to the EPD process. Scanning electron microscopy (SEM) and X- ray photoelectron spectroscopy (XPS) revealed that an acidic environment enables the most pronounced and homogeneous NS coating on the CF surfaces. X-ray diffraction (XRD) analysis delivered deeper insights into the microstructures of modified CFs, indicating a decreased graphite interlayer spacing d002 and an increased crystallite size Lc after treatment. This results in a changed temperature-stability as well as mechanical properties, as revealed by thermogravimetric analysis (TGA), single-fiber tensile tests, and Weibull analysis.To assess the interaction of the modified CFs with cementitious matrices, single-fiber pullout tests were performed, showing the highest bond strength and total pullout work of CFs treated in an acidic environment. This is mainly explained by a reaction of the high number of NS particles with calcium hydroxide to form calcium silicate hydrate (C-S-H) gel and, thus, intensifying the interfacial transition zone, subsequently increasing the bond properties of CF to a matrix. As well, abundant oxygen-related functional groups were introduced on the CF surfaces from anodic oxidation, leading to an enhanced bond by promoting precipitation of cement hydration products onto the CF surfaces.

Interfacial adhesion and thermal stability of high-density polyethylene glass fiber composites

The fiber-matrix adhesion and the thermal stability of glass fiber reinforced high-density polyethylene composites with increasing content of maleic anhydride coupling agent and zinc-based thermal stabilizer have been analyzed by the single fiber pullout test and oxidation induction time. High-density polyethylene compounds containing 8% by weight maleic anhydride grafted polyethylene increases the apparent interfacial shear strength to glass fibers by 3.5x; however, the strength was reduced by 45% with the addition of the thermal stabilizer. The thermal stabilizer was found to greatly improve the oxidative resistance. The oxidation induction time of the non-stabilized compounds is less than 1 min compared to over 25 min for the stabilized high-density polyethylene blends.

Predicting tensile properties of strain-hardening concretes containing hybrid fibers from single fiber pullout resistance

Tensile properties of strain-hardening fiber-reinforced concrete are the key engineering parameters in determining bending resistance of the material. In this paper, an analytical model to predict tensile properties of ultra-high-performance fiber-reinforced concrete (UHPFRC), a type of strain-hardening fiber-reinforced concretes, was performed based on single fiber pullout test. The studied UHPFRCs contained hybrid fiber system, including macro steel fiber combined with micro steel fiber. Three types of macro steel fibers were used, including long smooth fiber (LS), hooked A fiber (HA), and hooked B fiber (HB); they had different lengths and geometries but same volume content (1.0 %). The only short smooth fiber (SS), one type of micro steel fiber,was employed with various volume content (0.5 %, 1.0 %, 1.5 %). The experimental data from the fiber pullout tests in the available references were used to predict the first crack/post crack strength and cracking parameters of UHPFRCs with hybrid fibers. The predictive equations for strengths and crack resistance of UHPFRC containing hybrid fibers were proposed with modified coefficients.

A Modified Fiber Bridging Model for High Ductility Cementitious Composites Based on Debonding-Slipping Rupture Analysis

Modified micromechanical bridging model is established with consideration of the fiber rupture effect at debonding and slipping stages. The bridging model includes the debonding and slipping rupture of fibers and establishes the fiber/matrix interfacial parameters (friction τ 0 , chemical bonding force G d , slip-hardening coefficient β ). A different interfacial bonding can cause fiber rupture. The influence of the interfacial conditions on the fiber rupture risk was investigated. In the modified bridging model, the effective bridging stress, the debonding rupture stress, and the slipping rupture stress were clearly identified. Finally, single-fiber pullout tests with different embedded lengths were carried out to validate the bridging model. The relationship between the fiber bridging stress and the crack opening predicted by the bridging model was consistent with the experimental results. This modified micromechanical bridging model can be used to quantitatively calculate the actual fiber bridging capacity and to predict the ductility of the high ductility cementitious composites reinforced by different types of fibers.

Development of PA6/GF Long-Fiber-Reinforced Thermoplastic Composites Using Pultrusion and Direct Extrusion Manufacturing Processes

The mechanical properties of polyamide 6 glass fiber (PA6/GF) long-fiber-reinforced thermoplastic (LFT) composites were characterized by studying the process conditions in terms of manufacturing methods (direct extrusion and pultrusion) and material characteristics (void content and fiber volume fraction). The LFT composites prepared through the pultrusion process have higher mechanical properties than those prepared via the direct extrusion process. The PA6/GF composite prepared via pultrusion had the tensile and flexural strengths of 233 MPa and 338 MPa, respectively. The impact strength measured using the Izod method was 296 J/m, which is 64% higher than that of the composite fabricated via the direct process. The optical microscope images showed that the glass fiber length of the pultruded composites is longer than the fiber length of the direct composites, leading to higher mechanical properties of the LFT composites prepared through the pultrusion process. Moreover, the interfacial shear strength between the resin and the fiber, measured via single fiber pullout tests, can account for the higher fiber reinforcing efficiency. If the void content of a composite is sufficiently small to not be detrimental to the composites, the mechanical properties are observed to be proportional to the fiber volume fraction of the composites.

Tannic acid/ethanolamine modification of PE fiber surfaces for improved interactions with cementitious matrices

The paper at hand deals with the surface functionalization of polyethylene (PE) fibers by using tannic acid/ethanolamine (TA/EA) as an affordable and highly effective approach in enhancing the bonding characteristics in cement-based matrices. Surface morphology, charge formation, wetting behavior, and thermal properties of the fibers were investigated using environmental scanning electron microscopy (ESEM), electrokinetic measurements, water contact angle tests, and thermogravimetric analysis (TGA). Both one-sided and two-sided, single-fiber pullout tests were carried out to shed light on the effect of TA/EA deposition on the interactions between the cementitious matrix and the modified fibers as regards various EA concentrations and treatment durations. For the samples with the modified PE fibers notable enhancements were observed in interfacial shear strength, pullout energy, crack-bridging force, and crack-bridging energy when compared to the samples containing raw PE fiber. This is explained by the effective surface activation of PE fibers by TA/EA through introducing amino and hydroxyl groups onto the fiber surfaces, thus providing more reactive groups with the cement hydrates and yielding improved bonding in the fiber-matrix interfaces. Moreover, the TA/EA coatings not only showed no negative impact on the mechanical behavior of the fibers but even slightly enhanced their tensile strengths and moduli of elasticity.

Flexural behavior evaluation and energy dissipation mechanisms of modified iron tailings powder incorporating cement and fibers subjected to freeze-thaw cycles

Waste iron tailings with cement-based inorganic binder is an economical and sustainable highway engineering base material, which is an effective way to reduce iron tailings inventory and affinity for engineering promotion. The flexural behavior considering the freeze-thaw action plays a crucial role for highway engineering base material. In this study, two types of fibers including polypropylene (PP) fiber and glass fiber were used to modify cement iron tailings powder (CITP), i.e., PPCITP or GCITP. Based on flexural tests, the influences of fiber length and freeze-thaw cycles on flexural behavior of modified CITPs were discussed. The results showed that the failure flexural strength of PPCITP reached the highest value at PP fiber length of 12 mm, while the flexural strength of GCITP presented a wavy downward trend with the increase of glass fiber length. The freeze-thaw cycle test results showed that the flexural strength of both PPCITP and GCITP decreased with the increase of freeze-thaw cycles, and the frost resistance of GCITP was better than that of PPCITP under the condition of the same volume of fibers. Then the single fiber pull-out test results implied that the interface action between glass fiber and CITP (G-CITP) was higher than that between PP fiber and CITP (PP-CITP) considering various curing ages and freeze-thaw cycles. Moreover, it is corroborated that PP fiber and glass fiber with length of 12 mm have the better reinforcement role in CITP specimens from the perspective of dissipative energy of fiber failure. Meanwhile, the dissipative energy results of both modified CITPs with fibers showed a downward trend with freeze-thaw cycles as a whole, and the dissipative energy of GCITP was higher than PPCITP at the specimen broken, which is consistent with the conclusion drawn in the single fiber pull-out test. The quantitative relationship models among dissipative energy, effective fiber length and freeze-thaw cycles of PPCITP and GCITP were further established, which could provide a reference for the large-scale production of waste iron tailings in highway engineering base materials.

3D meso-scale investigation of ultra high performance fibre reinforced concrete (UHPFRC) using cohesive crack model and Weibull random field

Ultra high performance fibre reinforced concrete (UHPFRC) is composed of fibres, mortar, fibre-mortar interfaces, and pores randomly distributed in space, and thus has heterogeneous mechanical properties and complicated failure mechanisms at micro/meso-scales. This study aims to develop a highly effective 3D finite element modelling approach to simulate both the mortar heterogeneity and the complicated failure mechanisms in UHPFRC materials and structural members. In this approach, Weibull random fields are used to characterize random properties (such as moduli, strength and fracture energy) of the mortar caused by defects such as pores and microcracks; pre-inserted cohesive interface elements with softening constitutive laws are applied to model multi-cracking behaviour; specific probability density distributions are adopted to describe the random orientation of fibres in the mortar, and orientation-dependent bond-slip relations are developed to model fibre-mortar interactions. The fibres are rigidly embedded in the mortar so that non-conforming finite element meshes can be used conveniently. The modelling approach has been validated by extensive simulations of single fibre pull-out tests and direct tensile tests of UHPFRC specimens with thousands of fibres in agreement with experimental data. It is found that the modelling approach is highly efficient in capturing the fibre crack-bridging effect, simulating the damage and fracture initiation and evolution, and quantifying the load-carrying capacities with statistical analyses considering fibre orientation and mortar heterogeneity.

Carbon nanotube enhanced carbon Fibre-Poly(ether ether ketone) interfaces in model hierarchical composites

Poly (ether ether ketone) (PEEK) has a high continuous service temperature, excellent mechanical properties, and good solvent and abrasion resistance, which can be further improved through the addition of carbon nanotubes (CNTs). CNT-PEEK nanocomposites are promising matrices for continuous carbon fibre composites; powder processing can mitigate the high melt viscosities in these systems. In this study, model single fibre (hierarchical) composites were produced by embedding sized and desized carbon fibres in nanocomposite CNT-PEEK powders followed by single fibre pull-out tests to assess interfacial characteristics. Carbon fibre-PEEK interfacial shear strength is typically 40–45 MPa. Increasing CNT loadings increased fibre-matrix interfacial shear strength linearly up to ∼70 MPa at 5.0 wt%, which was attributed to the CNT-based mechanical modification of the PEEK matrix. Apparent interfacial shear strength was inversely correlated with the embedded fibre length irrespective of carbon fibre sizing or CNT loading, indicating brittle fracture of the fibre-matrix interface. Pulled out carbon fibres were still coated with the matrix, which indicated strong adhesion at the interface in all samples, likely related to a transcrystalline region. Adhesion was, however, negatively affected by the presence of epoxy sizings. Frictional shear strength was independent of embedded fibre length and CNT content for all samples.

Pullout behaviour of shape memory alloy fibres in self-compacting concrete and its relation to fibre surface microtopography in comparison to steel fibres

Superelastic nickel-titanium shape memory alloy (SMA) can recover large strains. Hence, SMA fibres (SMAFs) have been incorporated into concrete to provide re-centring and crack-closing ability to the concrete. Since the structural performance of fibre-reinforced cementitious composites is significantly influenced by the fibre pullout mechanism, this research was focused on the pullout behaviour of SMAFs and their associated parameters. Single fibre pullout tests were performed on straight and hooked-end SMA and steel fibres (SFs) embedded in self-compacting concrete. The experimental investigation considers three variables: the type of hooked-end, embedded length, and loading rate. The full range of pullout load-slip behaviour was obtained under two different loading rates. The results were analysed in the slip corresponding to maximum pullout load, maximum tensile stress induced in fibre, material use factor, pullout energy, average and equivalent bond strength. Straight SMA fibres showed a weaker interfacial bond with concrete than steel counterparts. SMA fibre with 45° hooked-end showed the highest bond strength among SMA fibres considered in this study. The increase in the embedded length of most of SMAFs and SFs caused a significant increase in the pullout load without changing the configuration of the pullout load-slip curve. The pullout behaviour of SMAFs was almost rate-insensitive, whereas SFs exhibited evident rate sensitivity in the pullout. The observed differences between SMA and steel fibres were clarified based on fibre surface micro-topography and roughness and matrix damage. This difference was explained based on the surface micro-topography of fibres and matrix damage.

Prediction of (Steel-Glass) Fiber/Concrete Interfacial Friction Properties in FRC Composites Using Calibration Method and Evaluation of Fiber Diameter Role

AbstractThis paper presents a series of single fiber pull-out tests on steel and glass fiber embedded in a cementitious matrix. First, the phase of fiber sliding in the concrete matrix was defined ...

Aramid Nanofiber Interphase for Enhanced Interfacial Shear Strength in Ultra‐High Molecular Weight Polyethylene/Epoxy Composites

AbstractUltra‐high molecular weight polyethylene (UHMWPE) fibers are used in ballistic composites due to their high tenacity; unfortunately, their use in structural composites remains limited due to their poor adhesion with polymer matrix materials. Interphase design to the fiber surface is a promising approach to improve the interfacial properties of composite materials. This work describes the use of an aramid nanofiber (ANF) dip‐coating treatment of plasma‐treated UHMWPE fibers that increases surface roughness and enhances mechanical interlocking with the matrix. The ANFs also populate the fibers with polar functional groups, specifically hydroxyl, amide, ketone, and carboxyl, allowing for chemical bonding opportunities between the fiber and the epoxy matrix. The UHMWPE fiber surface chemical structure and composition is characterized using Fourier‐transform infrared spectroscopy and X‐ray photoelectron spectroscopy. The ANF dip‐coating treatment yielded up to a 267% increase in fiber surface roughness, measured using atomic force microscopy. Using single fiber pullout testing, a maximum increase of 173% in interfacial shear strength is measured due to the ANF interphase, while completely maintaining the tensile strength of the fibers measured through single fiber tensile testing. These results demonstrate a simple and cost‐efficient technique to improve the interfacial properties of UHMWPE composites through an ANF surface reinforcement.

Effect of microbially induced calcite precipitation treatment on the bonding properties of steel fiber in ultra-high performance concrete

Bonding performance between steel fiber and cement matrix is critical for the stress transformation and crack control, which significantly affects the mechanical properties of ultra-high performance concrete (UHPC). To enhance the fiber/matrix bond, this study proposed a microbiological technique to pretreat the steel fiber surface via microbially induced calcite precipitation (MICP) treatment. MICP generates calcium carbonate (CaCO3) crystals bonded on the surface of steel fiber, leading to an increase in roughness and hydrophilicity. The results obtained from single steel fiber pullout tests indicate that the bond strength and pullout energy of steel fiber are both increased by MICP treatment. The good bonding consequently resulted in more residual hydration products attached to the fiber surface after the pullout test. The tests on the UHPC samples with untreated and treated fiber confirmed the benefits of MICP treatment in improving the mechanical properties of UHPC. It is demonstrated that MICP treatment on steel fiber can increase the compressive and flexural strength of UHPC by ∼16% and ∼50%, respectively.