Fiber Pull-out Research Articles

Analytical modeling of cutting forces and investigation of the material removal mechanism in milling of HSF/PR composite

High silica fiber reinforced phenolic resin composites (HSF/PR composites) have wide applications in aerospace and electronics owing to their excellent ablative and corrosion resistance. However, there are few papers on the cutting mechanism of this material. In this paper, analytical modeling of cutting forces and investigation of the removal mechanism in the cutting of HSF/PR composite are studied. The machining process was studied in two aspects by using experiments: cutting force and surface quality. The cutting force is most affected by the axial depth of cut ap. The surface quality is most affected by the axial depth of cut ap. Removal mechanism presents different patterns depending on the fiber direction. In the meridional direction, the fibers undergo micro-buckling failure due to the compressive stress exceeding their compression limit. In the normal direction, the fibers are sheared off due to the shear stress exceeding the material's shear strength. In the zonal direction, the fibers are affected by different stresses and exhibit various fracture modes. The main defects on the processed surface are holes, cracks, delamination, matrix crack, and fiber pull-out. The research in this paper provides scientific and technical guidance for the processing and application of this material and similar materials.

Effect of silicon carbide on kerf convergence and irregularity of the surface during abrasive water jet machining of fiber-metal hybrid composites

The traditional way to machine hybrid composites is hard because they tend to break, have a high retraction, have a high service temperature, and have an uneven surface irregularity. For high-strength fiber/metal composite constructions, alternative machining methods have drawn interest as a solution to these problems. Current research focuses on enhancing the Abrasive Water Jet Machining process by optimizing its variables using a composite material of epoxy reinforced with silicon carbide, stainless steel wire mesh, and Kevlar. The variables assessed are the Nozzle-to-substrate gap (S), the Abrasive discharge molding and different percentages of silicon carbide (SiC) filler (0%, 3%, and 6% by weight), three different types of hybrid laminates (H1, H2, and H3) were produced. The response surface method (RSM) was utilized in this learning, specifically on a central composite design, to calculate and optimize machining variables based on the Kerf convergence ratio (Kt) and Surface irregularity (Ra) as responses. According to the results, the traverse feed velocity, Abrasive discharge proportion, and Nozzle-to-substrate gap are the critical factors in determining Surface irregularity and Kerf convergence width (H1 laminate) for a fiber/metal laminate with 0%, 3% and 6% weight fraction. In the case of a 3% weight fraction H2 laminate, the traverse feed velocity was identified as the primary factor affecting the Kerf convergence ratio. In contrast, traverse feed velocity and Nozzle-to-substrate gap had the most significant influence on Surface irregularity. The findings also indicated that S, followed by Abrasive discharge proportion and traverse feed velocity, are the variables that have the most significant influence when cutting 6 wt% SiC filler particle fiber/metal laminate (H3 laminate). For Surface irregularity, the combination of traverse feed velocity and Nozzle-to-substrate gap had the most significant impact. To validate the optimization results, confirmatory tests was conducted, and the findings were very similar to the experimental values, indicating the accuracy and effectiveness of the optimization process. To better understand the manufacturing processes, a scanning electron microscope was used to examine the morphological features of the machined surfaces, such as delamination, fibre breakage, and fibre pull-out.

Effect of interfacial coatings on mechanical properties of 2.5D Nextel™ 720 fiber toughened zirconia-mullite matrix composites

In this study, 2.5D bent shallow cross-linked structure Nextel™ 720 (N720) fiber-reinforced yttria-stabilized zirconia-mullite composites with pyrolytic carbon (PyC) and fugitive pyrolytic carbon (FC) interfacial coatings were prepared by using a precursor infiltration and pyrolysis approach (called as N720f/PyC/YSZ-Mu and N720f/FC/YSZ-Mu, respectively). The effects of PyC and FC coatings on the failure mechanisms and mechanical properties of the composites were investigated. The N720f/PyC/YSZ-Mu composite shows ductile fracture behavior while the N720f/FC/YSZ-Mu composite shows brittle fracture behavior. The fracture toughness and flexural strength of the N720f/PyC/YSZ-Mu composite reach ∼7.00 MPa·m1/2 and ∼ 120.79 MPa, respectively. In contrast, the corresponding properties of the N720f/FC/YSZ-Mu composite are ∼3.66 MPa·m1/2 and ∼ 59.02 MPa, respectively. Microstructure analysis indicates that the weak PyC interfacial layer contributes to toughening by promoting fiber pull-out and debonding, thus enhancing the mechanical properties of the N720f/PyC/YSZ-Mu composite. The retrogression of the mechanical properties of the N720f/FC/YSZ-Mu composite originates from the damage to N720 fibers during the preparation procedure. This paper provides a new idea for the development of high-performance oxide CMCs with a 2.5D structure.

A 3D cohesive‐frictional coupled interface model for mesoscale simulation of steel fibre‐reinforced concrete

AbstractA 3D mesoscale finite element modelling approach is developed for simulating complicated damage and fracture behaviour in steel fibre‐reinforced concrete (SFRC) with explicit modelling of fibre–matrix interfaces. In this approach, a new 3D four‐noded cohesive‐frictional coupled interface element is developed to model the nonlinear interfacial bond‐slip behaviour, supplemented by a kinematic multiple‐point‐constraint (kMPC) algorithm to simulate the wrapping effect of the mortar around the fibres. They are implemented as a user‐defined element (UEL) and a user‐defined MPC subroutine in ABAQUS, respectively. Three cohesive‐frictional constitutive relationships are proposed to describe the nonlinear bond‐slip behaviour of different fibre–matrix compositions. The new approach is validated by single fibre pullout tests, direct tensile tests and three‐point bending tests of SFRC specimens with randomly distributed fibres. The results show that the new approach is capable of effectively capturing typical failure mechanisms in SFRC, such as fibre yielding, matrix failure, and fibre–matrix debonding and slipping.

Pull-out behaviour of steel fibres embedded in ultra-high-performance concrete after exposure to high temperatures

The paper examined the bond-slip behaviour of steel fibres embedded in ultra-high-performance concrete (UHPC) after exposure to elevated temperatures. Different types of steel fibres were cast into the halved UHPC dog-bone-shaped samples, including straight fibres, three types of hooked-end fibres and corrugated fibres. The bond response was investigated through single fibre pull-out tests on the samples unheated and heated to 200, 400 and 600 °C. In addition, the effects of polypropylene (PP) fibre addition and heating rate on steel fibre’s bond behaviour were also investigated. The results revealed an increase in bond strength when the straight and hooked-end fibre samples were heated to 200 °C, while the bond strength of the corrugated fibre decreased at the same temperature. Bond strength reductions were observed at higher temperatures. In addition, the straight fibres led to the lowest pull-out resistance as both the hooked-end and the corrugated fibres significantly enhanced the bond strength. With the hooked-end or corrugated fibres, the failure mode gradually shifted from pull-out failure to fibre rupture. Besides, adding PP fibres increased the bond strength of straight fibres at 400 °C but reduced the bond strengths of hooked-end fibres at ambient and high temperatures. High heating rate also led to a greater bond strength for the straight fibres at 200 °C and 400 °C.

Mechanical characterization of banana-nylon fibre reinforced Vinyl ester composites

ABSTRACT Hand lay-up was used to create banana and nylon Fibre-reinforced vinyl ester (VE) composites with random orientation of the short fibre ratio (banana:nylon = 1:1). To make it environmentally conscious, natural fibre (banana) was added in synthetic fibre (nylon). After fabrication, different mechanical testing was conducted. Tensile strength improves by 47% at 10 wt. % fibre loading and 13% at 20 wt.% fibre loading. Flexural strength improved by up to 213% at 15 wt. % fibre loading. At 20 wt. % fibre loading, the mean hardness number reaches its maximum. The mean impact energy is highest at 15 wt. % fibre loading. Furthermore, the highest water absorption is 2.3% with a fibre loading of 20 wt.%. After 15 wt.% fibre loading, which is suggested for optimal performance, the manufactured composites exhibit a declining trend in tensile, flexural, and impact capabilities. As a result, scanning electron micrographs were collected at 20 wt.% fibre loading to investigate the type of fibre-matrix bonding, voids, fibre agglomeration, and fibre pullouts phenomena. Fourier Transform Infrared spectroscopy was also explored to show a decline in hemicelluloses content. As-fabricated composites have several technological uses, including leisure and sports products, maritime sectors, and airplanes.

A novel study of biological and structural analysis on Cissus quadrangularis fiber-reinforced CaO particulates epoxy composite for biomedical application

Natural fibers derived from renewable, environmentally sustainable sources are being considered for use as reinforcements in polymer composites. The current study focuses on the fabrication of composite materials using fiber extracted from the Cissus quadrangularis (CQ) natural plant as reinforcement, an epoxy polymer as a matrix, and calcium oxide (CaO) nanoparticles as filler material, with the weight ratio of Cissus quadrangularis fiber (CQF) and CaO filler materials are varied to quantify the biological and structural effects of CQF composite. X-ray diffraction (XRD) results demonstrate a 58% amorphous zone in this composite, while Fourier transforms infrared spectroscopy (FTIR) examination revealed the hydrophobic nature, chemical bonding, and cellulose content. Because of the increased amount of chopped CQF loading in this composite, the mechanical qualities result in an average of 23% better tensile strength. Scanning electron microscopic (SEM) analysis was used to analyze the failure analysis for fiber interaction with matrix, filler, and fiber pullouts under mechanical stress. The antibacterial research revealed that this CQF composite exhibits bacterial inhibitory activity suitable for biomedical applications.

Effect of red mud on mechanical and thermal properties of agave sisalana/glass fiber–reinforced hybrid composites

Abstract The mechanical, thermal, and morphological analysis of red mud filled sisal/glass fiber–reinforced polyester composites have been investigated. In this study, four composite specimens were prepared through hand layup technique by changing the weight percentage of sisal fiber and red mud. Weight percentage of glass fiber and polyester resin are kept constant. The fabricated composite specimens were subjected to mechanical properties such as hardness, impact and tensile behavior, thermal, and morphological analysis. From the results, it is observed that, maximum tensile strength of 45.6 MPa was obtained for C1 specimen. Maximum hardness and impact strength of 85.67 and 391.5 J m−1 was achieved for C2 specimen. In TGA study, C1 and C2 specimen exhibited 85 % of weight loss with the temperature ranges from 300 °C to 400 °C. From SEM analysis, good bonding between fiber and matrix, voids, fiber breakages, fiber pullout, delamination, rich matrix area, poor adhesion between fiber and matrix, poor arrangement of fibers, interlinked fibers, and crack propagation were observed. Based on the results, C2 specimen which contains 30 wt% of sisal fiber and 5 wt% of red mud is performed well than other composites and it is suitable for various applications such as marine, automobile, and aeronautical.

Cutting performance and wear behavior of diamond, coated cemented carbide and PCBN tools during milling of Cf/SiC composites

As an advanced material, Cf/SiC composites are wildly used in many aerospace industries due to their excellent properties. However, machining the material often encounters many problems, such as poor machining quality, severe tool wear, and low processing efficiency. Tool materials have a significant influence on the cutting performance of tools and the surface quality of the workpiece being machined. In this study, milling experiments have been performed on Cf/SiC composites with different tools. The tool wear pattern, progression, mechanisms, and milling temperature were investigated. The machined surface quality and removal mechanisms of Cf/SiC composites were studied. The results indicated that polycrystalline diamond (PCD) tools have better cutting performance in milling Cf/SiC composites than other tools. Surface defects, milling temperature, and machined surface roughness (Sa = 2.9 μm) obtained by machining Cf/SiC composites using the PCD tool would be lower. The material removal mode is brittle fracture, and the surface damage (including fiber debonding, fiber pullout, and pits, etc.) is related to the direction of the fibers. Fibers in the X and Y directions can lead to more machined surface defects. Since hard particles formed in the machining process and protruding fibers constantly scratched the flank face, diamond grains were spalled off from PCD tools, resulting in abrasive wear.

Mechanical performance of 3D-printed continuous fibre Onyx composites for drone applications: An experimental and numerical analysis

As drone technology grows in popularity, its application to automate aspects of society is increasing at a similar rate, where drones are now being trialled for delivering payloads over short distances. In order to progress the technology, 3D composite printing is being used to develop complicated parts for improved aerodynamic design that can be produced efficiently, where the resultant composite part has high specific strength and rigidity. This article reports 3D printing of high specific strength, high-temperature Polyamide 6 (Onyx), continuous glass-fibre reinforced Onyx, and carbon-fibre reinforced Onyx composites and characterising their mechanical and fracture behaviour. The Onyx + CF composites displayed up to 1243 % and 1344 % improvement in Young's modulus and tensile strength over neat Onyx samples. The flexural strength of Onyx + CF samples was up to 316.6 % higher than the flexural strength of the neat Onyx sample. SEM micrographs showed a strong bond between the hydration products and the carbon fibres, increasing their tensile and flexural strengths by preventing micro-crack propagation through fibre pull-out and breaking. The statistical analysis was conducted to ensure the validity of the results for the population and establish stress-strain relations, along with estimating errors. In addition, the carbon-fibre-reinforced Onyx composite was compared with commercially used alternatives for producing drone components. Finally, a finite element model was developed using a numerical homogenisation approach and validated to predict the tensile and flexural behaviour of Onyx and carbon-fibre reinforced Onyx samples. This study provides a direction for the next generation of drone manufacturers.

Comparison of Mechanical Properties of Ductile/Brittle Epoxy Resin BFRP-AL Joints under Different Immersion Solutions.

The bonding properties of BFRP composites have been demonstrated in previous studies, satisfying the strength and durability criteria. In this paper, a further in-depth study is carried out to bond Basalt Fibre Reinforced Polymer (BFRP) to Aluminum Alloy 5052 using two bonding agents, Aralite® 2012 and Aralite® 2015, respectively. The salt sprays under 80 °C, 3.5% NaCl environment; 80 °C, 5% NaCl environment; and pure water environment are also considered for comparison. Experimental results show that joints created with Araldite® 2012 adhesives show higher average breaking strength (10.66 MPa at 720 h) and better ductility in a 5% NaCl environment. While the Araldite® 2015 adhesive joint exhibits a combination of tear failure and interface failure, along with thin-layer cohesion failure. In the SEM images of the two adhesive joints' failure, fiber pullout due to tension and damage at the interface between fiber and resin is apparent. To validate the experimental outcomes, water absorption testing, DSC, TGA-DTG, and FTIR experiments were conducted on dog-bone-shaped adhesive specimens to elucidate the results.

Effect of nano‐silica on fatigue behavior of glass fiber‐reinforced epoxy composite laminates: A Weibull distribution approach

AbstractThe aim of this study is to assess the impact of nano‐silica in glass fiber‐reinforced epoxy composite (GFEC) subjected to static and fatigue loading. Laminates were prepared in compression molding machine followed by the tensile test and tension‐tension fatigue testing at five different stress levels (from 50% to 90% of ultimate tensile strength). The addition of 3 wt% of nano‐silica with epoxy improved the tensile and fatigue strength as compared to neat GFEC. Scanning electron microscope (SEM) images of the fractured specimen showed the damage pattern which indicates that neat GFEC laminate exhibited damage patterns characterized by fiber breakage and matrix cracking. On the other hand, the modified GFEC with nano‐silica showed damage patterns including fiber pullout accompanied by fiber breakage and matrix cracking. During cyclic loading, the stress–strain hysteresis loop shows a reduced slope, indicating a decrease in the dynamic modulus of the specimen. This reduction in slope signifies a loss of stiffness during cyclic loading, particularly at high‐stress levels. The highest dynamic modulus at high‐stress levels indicates a rapid progression of severe damage and a shorter fatigue life. On the other hand, at low‐stress levels, the lower magnitude of dynamic modulus suggests a moderate damage progression and a longer fatigue life.Highlights Effect of nano‐silica in GFEC under static and fatigue loading conditions. GFEC with 3 wt% of nano‐silica shows improved tensile and fatigue strength. Examination of damage patterns through SEM analysis of the fractured surface. Depiction of the failure modes using damage pattern under fatigue loading. Comparison of fatigue life and dynamic modulus for neat and modified GFEC.

High-quality multi-walled carbon nanotubes toughened glass-ceramic by a two-dimension carbon nanotube film interlayer

The brittleness of bioglass/ceramics limits their applications in bone repair. The toughness of the glass matrix can be enhanced by adding nanoscale reinforcements at random; however, the effect is quite limited. This study proposes a novel strategy to prepare controllable fabricating lamellar precursors with multiwalled carbon nanotubes (MWCNTs) film/glass/MWCNTs film sandwich structure by a high-temperature foaming method. Subsequently, the precursor was sintered by spark plasma to obtain a composite material with strong cross-linking between MWCNTs and the glass matrix. The mechanical properties of the composites were characterized, and mechanisms were analyzed by the finite element method. The results revealed that the glass composite with 1.0 wt% MWCNTs had a significantly enhanced fracture toughness (2.65 MPa m1/2) and flexural strength (145 MPa), which were 2.1 times and 1.8 times higher than those of pure glass, respectively. This increase in toughness is attributed to the strong resistance of the well-combined bent and entangled MWCNTs to the fiber pull-out process. The glass/MWCNTs composite showed a low electrical resistivity of 5.8 Ω cm, which would aid skeletal restoration. Thus, this strategy paves a facile way to prepare the highly toughed bio-glass with multifunctional properties.

Studies on interfacial shear strength of pineapple leaf fibre from agro-waste reinforced polypropylene composites: Influence of fibre length and carding parameters

This work investigates the potential utilisation of the agro-waste pineapple leaf fibre (PALF) as a green reinforcement in polypropylene (PP) composites. Generally, chemical treatment is used to clean the scratched PALF, and the effluents of those chemicals are discharged into nature. A new mechanical approach (carding) was used in this work to remove the remaining extraneous substances from the scratched and sun-dried PALF instead of using any chemical treatment. The percentage of sticky fibres and dust content decreased, and fibre breakage increased with the increasing number of carding passages. The individualized fibre properties were also influenced by the number of carding passages. The carding process reduced the diameter of PALF due to removal of extraneous materials. The tensile properties of raw PALF improved significantly until the fourth carding passage and further increase in the number of passages did not show any significant influence on the tenacity and modulus. Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) confirmed the elimination of hemicellulose along with other gummy and waxy substances from the individualized PALF due to the carding action. The crystallinity % also increased after the carding process due to the removal of amorphous substances. As the reinforcement-matrix interfacial shear strength (IFSS) strongly influences the physico-mechanical properties of composites, IFSS of carded PALF reinforced finer and coarser PP fibre micro-bonded composites was also studied using the single fibre pull-out test (SFPT). Among different composites, the fourth carding passed PALF-reinforced finer PP fibre micro-bonded composite showed the highest IFSS. Additionally, the load- extension curves and SEM images of the tensile pulled-out surface were investigated to study the interfacial adhesion between PALF and PP micro-droplets. The increased surface roughness of PALF due to the carding action resulted in an improvement in the IFSS of PALF-reinforced PP micro-bonded composites.

Single-grain scratching of SiCf/SiC composite under minimum quantity lubrication: Force and material removal mechanism study

As one of the most novel fiber-reinforced ceramic matrix composites, SiCf/SiC composites are difficult to be processed machine materials. On top of that, the underlying material removal mechanism not yet completely understood. Along these lines, in this work, single-grain scratching orthogonal tests with different MQL methods were carried out to systematically analyze the influence of the different processing directions and lubrication methods on the material removal lubrication mechanism and the scratching force in the scratched surfaces. From the acquired results, it was demonstrated that the scratch force was the smallest when the processing direction is was 0° to the fiber direction. In addition, the utilization of MQL from vegetable oil can effectively reduce the cutting force. Diamond indenter caused significant damage to the surface of SiCf/SiC composites when the machining direction was 90° to the fiber direction, while narrow but deep grooves on the surface were observed when the angle was 0°. The dominant mode of material removal of SiCf/SiC composites was a brittle fracture, and the damage features mainly included direct fiber breakage, matrix fragmentation, fiber pullout, and fiber outcropping. The increase of the processing ratio of 0° and implementation of vegetable oil for MQL was proven as one of the best methods.

Damage mechanism characterisation of plain weave ceramic matrix composites under in-plane shear using in-situ X-ray micro-CT and deep-learning-based image segmentation

This paper investigates the microstructure and damage evolution of plain weave ceramic matrix composites under in-plane shear using the in-situ X-ray computed tomography approach. The actual microstructure and damage evolution of material under several successive loading levels have been revealed precisely. A deep-learning-based image segmentation method has been employed to accurately identify material damages, including matrix cracks, delamination, fibre pull-outs and interface debonding. Besides, three-dimensional visual characterisation and quantitative analysis of damage have been carried out to gain a better understanding on the failure mechanisms. For longitudinal tows under shear, the cracks propagate along the loading direction and cause the splitting and sliding failure of tow; For transverse tows under shear, they undergo coupling effects of shear and tension, which results in kink band damage with fibre bridging mechanism. Finally, the connection of longitudinal tow splitting and transverse tow kinking leads to the catastrophic fracture of CMCs under in-plane shear.

Effects of the tool geometry, cutting and ultrasonic vibration parameters on the cutting forces, tool wear, machined surface integrity and subsurface damages in routing of glass-fibre-reinforced honeycomb cores

Honeycomb structured materials have been increasingly used for high-load applications; however, machining of the highly elastic honeycomb cores is still facing challenges from tool wear issues and degraded machined surface integrity. In this work, experimental evaluations were carried out in routing glass-fibre-reinforced honeycomb cores under the parametric control of tool geometries (straight and helical flutes), vibration amplitude (0–12 μm) and cutting speeds (30–120 m/min) in a full factorial design. The recorded cutting forces, cutting temperatures, tool wear and the machined surface integrity indicators were statistically tested and discussed, with their main effects and interactions. Executive findings indicated that the helical-flute routers in the oblique cutting produced lower cutting forces; in contrast, the straight-flute routers in the orthogonal cutting produced lower cutting temperatures. Moreover, the flank wear of the straight-flute routers decreased with the amplitude; whereas the flank wear of the helical-flute routers increased with the amplitude. The use of ultrasonic vibration-assisted energy would reduce propagations of cracks and pull-out fibres, compared to using conventional machining. Additionally, the internal damages such as out-of-plane cracks and fractures were characterised by their width and area via computed tomography scans. When routing at a high cutting speed (~90 m/min), the superimposed assisting energy coupled with the straight-flute routers could adversely convert the minor delamination into severe out-of-plane cracks. Causes and the underlying mechanisms are all discussed and detailed.

Cohesive Zone Modeling of Pull-Out Test for Dental Fiber-Silicone Polymer.

Several analytical methods for the fiber pull-out test have been developed to evaluate the bond strength of fiber-matrix systems. We aimed to investigate the debonding mechanism of a fiber-silicone pull-out specimen and validate the experimental data using 3D-FEM and a cohesive element approach. A 3D model of a fiber-silicone pull-out testing specimen was established by pre-processing CT images of the typical specimen. The materials on the scans were posted in three different cross-sectional views using ScanIP and imported to ScanFE in which 3D generation was implemented for all of the image slices. This file was exported in FEA format and was imported in the FEA software (PATRAN/ABAQUS, version r2) for generating solid mesh, boundary conditions, and material properties attribution, as well as load case creation and data processing. The FEM cohesive zone pull-out force versus displacement curve showed an initial linear response. The Von Mises stress concentration was distributed along the fiber-silicone interface. The damage in the principal stresses' directions S11, S22, and S33, which represented the maximum possible magnitude of tensile and compressive stress at the fiber-silicone interface, showed that the stress is higher in the direction S33 (stress acting in the Z-direction) in which the lower damage criterion was higher as well when compared to S11 (stress acting in the XY plane) and S23 (stress acting in the YZ plane). The comparison between the experimental values and the results from the finite element simulations show that the proposed cohesive zone model accurately reproduces the experimental results. These results are considered almost identical to the experimental observations about the interface. The cohesive element approach is a potential function that takes into account the shear effects with many advantages related to its ability to predict the initiation and progress of the fiber-silicone debonding during pull-out tests. A disadvantage of this approach is the computational effort required for the simulation and analysis process. A good understanding of the parameters related to the cohesive laws is responsible for a successful simulation.

The influence of geometric characteristic on the pullout behavior of basalt FRP minibar embedded in concrete

AbstractWith the increasing demand on structural toughness and energy absorption capacity, the addition of fiber to concrete has become an issue of significance. This paper studies the bond behavior of Basalt FRP (BFRP) minibar with straight, twisted and crimped geometric characteristics. The failure modes, pullout curves and bond strength were compared, and their interface degradation, damage evolution and failure mechanism between single fiber and concrete matrix were analyzed. Additionally, commercial steel fibers and polypropylene fibers were compared with the BFRP minibars to clarify the effect of fiber type on failure morphology, bond strength and interface properties. The results showed that the pulling out process for straight BFRP minibars, twisted BFRP minibars and crimped BFRP minibars was constituted by the elastic bonding stage, the partial de‐bonding stage, the complete de‐bonding stage and the pullout of fiber. The bond strength was composed of chemical adhesion and mechanical bond, where the mechanical bond play important role after the initial failure of chemical adhesion. The bond strength of crimped BFRP minibar, the hooked steel fiber, the indented polypropylene fibers and the twisted BFRP minibar were enhanced by 358%, 324%, 115%, and 54.5% compared to straight BFRP minibars. The interface bonding strengths improve with the increase of matrix strength. Dense microstructures of matrix improve the bond strength. The bond‐slip constitutive model was proposed for crimped, twisted and straight BFRP minibars with regression coefficient of 0.978, 0.891, and 0.992, respectively.Highlights Influence of fiber geometry and concrete strength on the pullout behavior Interface degradation, damage evolution and failure mechanism between minibar and concrete Bond‐slip constitutive model of straight, twisted and crimped BFRP minibars

Experimental and numerical simulation of pull-out response in textile-reinforced concrete

Textile-reinforced concrete (TRC) is a construction material that uses continuous fibres such as carbon to create a lightweight and durable structural system. Even though TRC possesses vast possibilities in terms of its usage, identification of bond-slip behaviour at the material interface is one of the limitations that need to be addressed. Based on the literature, there are difficulties in determining the bond-slip relationship both experimentally and numerically, creating inconsistency in the results. This study aims to determine the bond-slip relation of TRC through pullout tests and validated through finite element analysis to replicate the actual bond-slip behaviour at the interface. The bond characteristics of TRC were assessed using a double-sided pullout test setup with different bond lengths of textile, namely 20 mm, 30 mm, 40 mm, 50 mm, and 60 mm. It was noticed that in short bond specimens (20 mm, 30 mm, and 40 mm), the phenomena of pullout failure were due to weakened bond at the interface until pre-peak, followed by complete loss of adhesive bond due to debonding of fibre. However, for the specimens with longer bond lengths (50 mm and 60 mm), rupture of the textile leading to a sudden loss of bond capacity was observed. Additionally, the general fibre pullout phenomenon curve was used to explain the debonding process. Using a calibrated tri-linear bond-slip interface relation, the numerical model was developed to simulate the pull-out response of fibre. The numerical model was able to reproduce experimental results, including maximum load, post-peak behaviour, and interfacial slip. The difference of maximum shear stress between pull-out tests and numerical modelling was within 2 % while the slip difference was between 4 and 31 % for different bond lengths. However, for longer bond lengths, the fibre failure mode was due to pullout instead of rupture, unlike the experimental results.