Fiber Pull-out Research Articles

Surface Damage Mechanism and modes in single abrasive grinding Twill carbon fiber-reinforced-polymer laminates Basing on Stress Field Analysis

The scratch 2D twill carbon fiber-reinforced-polymer (CFRP) removal and surface evolution mechanism was studied with single abrasive scratch experiments, and the single abrasive scratch finite element model (FEM) was constructed considering progressive damage models. The surfaces evolution mechanism are revealed by FEM stress field analysis and by scanning electron microscope (SEM) images. There is weft -warp fiber woven coupling structure inside 2D twill CFRP, in this paper, woven structure coupling effect means the impedance force fields are formed by the other adjacent carbon fibers during single abrasive scratching weft or warp fibers inside CFRP. The FEM stress fields for the fiber bundles, interfaces and matrices can be analyzed, and provide an effective way to study scratch damage mechanism. Scratch damage mode for weft-containing CFRP starts with resin matrix cracks under low stress as the main feature, gradually transits to carbon fiber pull-out due to stress above interface strengthen and matrix cracks as the main features, and the damage modes finally characterize with weft carbon fibers breakage due to stress above carbon fiber shear fracture strength, fiber pull-out and matrix breakage as the main features. Scratches damage mode for warp-containing starts with the resin matrix breakage, woven structure coupling effect results in fibers stress above the tensile strength, and scratches damage mode transits to the warp fibers pull-out damage and warp carbon fibers breakage as the main features. By comparing the FEM to experimental results for scratch force and SEM, the FE model proves to be valid and accuracy.

Visualizing fiber end geometry effects on stress distribution in composites using mechanophores.

Localized stress concentrations at fiber ends in short fiber-reinforced polymer composites (SFRCs) significantly affect their mechanical properties. Our research targets these stress concentrations by embedding nitro-spiropyran (SPN) mechanophores into the polymer matrix. SPN mechanophores change color under mechanical stress, allowing us to visualize and quantify stress distributions at the fiber ends. We utilize glass fibers as the reinforcing material and employ confocal fluorescence microscopy to detect color changes in the SPN mechanophores, providing real-time insights into the stress distribution. By combining this mechanophore-based stress sensing with finite element analysis (FEA), we evaluate localized stresses that develop during a single fiber pull-out test near different fiber end geometries-flat, cone, round, and sharp. This method precisely quantifies stress distributions for each fiber end geometry. The mechanophore activation intensity varies with fiber end geometry and pull-out displacement. Our results indicate that round fiber ends exhibit more gradual stress transfer into the matrix, promoting effective stress distribution. Also, different fiber end geometries lead to distinct failure mechanisms. These findings demonstrate that fiber end geometry plays a crucial role in stress distribution management, critical for optimizing composite design and enhancing the reliability of SFRCs in practical applications. By integrating mechanophores for real-time stress visualization, we can accurately map quantified stress distributions that arise during loading and identify failure mechanisms in polymer composites, offering a comprehensive approach to enhancing their durability and performance.

In Situ Polymerization and Synthesis of UHMWPE/Carbon Fiber Composites.

Carbon-fiber-reinforced composites of ultra-high-molecular-weight polyethylene (UHMWPE) are not easily prepared because of their high viscosity, although they can be advantageous in advanced engineering applications due to their superior mechanical properties in combination with their low specific weight and versatility. Short polyacrylonitrile-based carbon-fiber-reinforced UHMWPE composites with fiber contents of 5, 10, and 15 wt.% could easily be prepared using in situ ethylene polymerization. Therefore, MgCl2 was generated at the Brønsted acidic groups of the fiber surface by employing a reaction between the co-catalysts Mg(C4H9)2 and AlEt2Cl. Titanation with TiCl4 resulted in a catalyst directly on the fiber surface. The catalyst polymerized ethylene (2 bar pressure at 50 °C), forming a UHMWPE matrix near the surface; its fragmentation led to polymer particles associated with the fiber. The catalyst activity on the fiber surface of untreated (CF-Pr, 3.48 ± 0.24 wt.%) and oxidized fibers (CF-Ox, 7.41 ± 0.03 wt.%) was 20% lower. CF-Pr compression-molded samples showed tensile strengths of up to 50.4 ± 1.3 MPa, while CF-Ox samples reached 39.1 ± 0.6 MPa, surpassing the performance of composites prepared by melt compounding. The stiffness of 1.58 ± 0.17 GPa for a melt-compounded material was lower than the 3.24 ± 0.10 GPa for CF-Pr and 2.19 ± 0.07 GPa for CF-Ox composites. A fracture examination showed fiber pull-outs, matrix residues on the fibers, and the formation of some extensional polymer fibrils. The latter explains the higher stress at yield and the breakage of the CF-Pr based composites in particular. The potential of in situ polymerized UHMWPE composites for the utilization in high-performance structural applications is thus demonstrated.

Mechanical and ballistic performance of individual and synergistic filler reinforced glass fiber epoxy composites

AbstractThis study examines the influence of individual (Graphene) and synergistic fillers (Graphene + Boron Carbide (B4C)) on the mechanical and ballistic performance of glass fiber epoxy‐reinforced composites (GFERCs). The different filler‐reinforced GFERCs were processed using the compression molding technique and cut as per testing standards. The results showed that the sample GF3 which had both the graphene and B4C filler together had significantly enhanced the tensile, flexural, hardness, and impact properties. The properties showed an improvement of 23.3%, 34%, 7%, and 13%, respectively when compared with the unfilled GF1 sample. The ballistic test results also revealed this synergistically filled GF3 sample had the least back‐face signature (BFS) value of 23.5 mm after impact. Fractographic studies showed that the synergistic effect of graphene and B4C also improved the bonding between the epoxy resin and glass fiber. The high toughness required for energy absorption is provided by matrix hardening, strong interfacial bonding, and fiber pullouts. Mainly the hard strike face created by the B4C particles and the energy transfer provided by the graphene particles proved pivotal in ensuring energy dissipation in the composite. Finally, it was observed that the synergistic fillers played the most important role in improving the performance of GFERCs by enhancing the energy dissipation mechanisms.Highlights Multiple fillers (Graphene+B4C) enhanced the mechanical and ballistic properties. Synergistic toughening provided by the B4C and graphene particles. Hybrid fillers exhibited strong interfacial bonding.

Hybrid Composite Materials from Crotalaria and Borassus Fibers: Mechanical and Water Absorption Properties

Agricultural waste is one of the major concerns in present society. The present work investigates the possibility of agricultural waste materials, Crotalaria and Borassus short fibers, as hybrid reinforcement in composite materials. The study examines a novel approach by investigating the combined effect of hybridization and random fiber orientation on the mechanical and water absorption properties of untreated Crotalaria Juncea (CJ) and Borassus Flabellifier (BF) fibre reinforced hybrid polyester resin composites. The outcomes provide awareness into the possibility of utilizing agricultural waste for sustainable and eco-friendly hybrid composite materials. Hybrid composites were developed through the hand lay-up method, incorporating two distinct short fibres. These composites were then evaluated for their mechanical properties and water absorption characteristics, following the guidelines set by ASTM standards. A hybrid composite (HC20CJ30BF) composed of 20g of CJ and 30g of BF exhibits the highest tensile strength of 22.59 MPa, which is a notable improvement of 96.26% compared to single reinforced composites. An enhanced flexural strength of 47.46% was achieved, surpassing the performance of the single reinforced composite materials. The water absorption resistance of the hybrid composite, HC20CJ30BF, is demonstrated by its least absorption rate of 1.65% after 24 h of immersion. The fractographic analysis exposed fiber pull-out as well as rough surfaces in tensile tests, and fiber bending with matrix cracks during flexural loads, emphasizing the significant role of fiber orientation in enhancing composite performance. Such work provides valuable insight into the fabrication of highly efficient and durable hybrid composite materials employing natural fibers.

Study Of The Effect Of Variations In Fiber Orientation On The Tensile Strength Properties Of Polyester Composites Reinforced Abaca Fiber

A composite is a material formed from a combination of two or more constituent materials using a heterogeneous mixing process, whose mechanical properties vary. The aim of this research is to compare the tensile strength values ​​of abaca banana stem fiber polyester composites with variations in fiber orientation. The fiber orientation used is parallel, random and woven. The method used is a hand lay-up press with a fiber volume fraction of 30% and the resin itself uses BQTN 157 EX polyester resin with a hand lay-up method using a glass mold. The test was carried out by tensile testing using the ASTM D3039 measurement standard and macro photos. The results of research on tensile testing show that composites with variations in parallel fiber orientations reinforced with abaca banana stem fibers have an average tensile strength of 39.63 MPa, variations in random fiber orientation have an average tensile strength of 32.87 MPa and variations in fiber orientation woven has an average tensile strength of 25.90 MPa. From the results of macro photo fracture observations, it was found that the type of fracture is a brittle fracture on an uneven fracture surface which causes fiber pull-out where the fibers appear to be coming out of the specimen because the matrix and fibers are not strongly bonded and the fracture is also caused by voids near the fibers.

Graphene nanoplatelets inclusion effects on mechanical properties of the hybrid kevlar/basalt fiber reinforced epoxy composites

Abstract This study experimentally examined the effects of hybridizing Basalt and Kevlar fibers on the tensile, and flexural performance of composite materials with the inclusion of Graphene nanoplatelets (GnPs). Various hybrid composites were fabricated, incorporating Basalt and Kevlar fiber composites with 1, 3, and 5 wt% of GnPs as well as without GnPs, as well as hybrid composites featuring different weight content of GnPs reinforcing with with Basalt and Kevlar fibers. The findings of this study indicated that the mechanical properties of epoxy resin were significantly enhanced through the synergistic effects of hybridization with basalt and Kevlar fibers, as well as the incorporation of graphene nanoplatelets (GnPs). The significant increasing in mechanical properties was attributed to the strong interfacial interactions between the epoxy matrix and GnPs nanoparticles, which facilitate improved stress transfer from the fibers and nanoparticles to the matrix. This enhanced stress transfer capability accounts for the superior resistance to fiber pullout observed in composites reinforced with GnPs compared to those without nanoparticles.

Experimental and numerical study of damage mechanisms in cementitious materials reinforced with twisted steel fibers

This study proposes to investigate damage mechanisms in the fiber/matrix interface, considering the use of twisted steel fibers incorporated into conventional and high-strength cementitious matrices. The methods employed include fiber pull-out tests and X-ray tomography for the detection and analysis of microcracks in the interface region. Additionally, elastoplastic finite element models will be developed, integrated with contact formulations, using the commercial software ABAQUS. Validation of the numerical models will be performed by comparing the characteristics of damage propagation obtained through microCT images with the simulated results.

The Effect of Differences in Fiber Sizes on the Cutting Force During the Drilling Process of Natural Fiber-Reinforced Polymer Composites

This experiment aimed to analyze the impact of different fiber sizes on cutting forces during the drilling of Natural Fiber-Reinforced Polymer Composites (NFRPC) while also evaluating surface quality attributes, including delamination, fiber pullout, and overhanging fibers, influenced by variations in coconut fiber dimensions within the NFRPC material. The manufacturing process for composite panels utilized various methods, including hand layup for 200 mm long coconut fibers and composite casting for shorter fibers (2, 4, and 6 mm) mixed with polymer-epoxy. The results indicate that panels made from NFRPC with continuous fiber lengths of 200 mm exhibit higher cutting force values (253,650 N) compared to epoxy panels without fibers (235,288 N), suggesting that a significant force is required to sever the continuous fibers within the NFRPC. Conversely, the incorporation of short coconut fibers measuring 2, 4, and 6 mm reduces the cutting forces on the composite panels. However, excessive surface roughness in the final hole quality can be detrimental, primarily due to issues of delamination and fiber pull-out.

Fracture toughness of fibre failure modes in laminated composites under dynamic loading

Abstract The fracture toughness regarding fibre tensile failure and fibre compression kinking was measured using compact tension and compact compression specimens on a uniaxial bi-directional electromagnetic Hopkinson bar system. During the dynamic tests, the strain/displacement fields were monitored using the digital image correlation technique with a high-speed camera. Digital and scanning electron microscopy were used to investigate the fracture faces of the tested specimens. The initial fracture toughness for fibre tensile failure under quasi-static and dynamic loading was 166 kJ/m2 and 113 kJ/m2, respectively. For fibre compression kinking, the initial fracture toughness was approximately 120 kJ/m2 for both loading conditions. Less fibre pull-out may be responsible for the decrease in fracture toughness for fibre tensile failure under dynamic loading. Whereas for fibre compression kinking failure, there was no significant difference in the fracture faces of the damaged specimens at different loading rates.

Dynamic behaviour and failure mechanism of bamboo scrimber panels under single and repeated impacts: Experimental tests

Bamboo scrimber, as a renewable and sustainable material engineered from bamboo, is inevitably subjected to impact loadings in engineering applications. To study the dynamic behaviour and failure mechanism of bamboo scrimber panels under low-velocity impact, a series of drop hammer impact tests were conducted on 36 panels. The peak force, deformation and energy absorption of bamboo scrimber panels were obtained and analysed. The influence of impact energy, impactor shape and impact angle on the dynamic behaviour of panels was quantitatively characterised. Besides, based on test observations and microscopic views, the failure mechanism of bamboo scrimber panels under different impact types was revealed, including the energy absorption mechanism through fibre fracture, fibre debonding, fibre pull-out and matrix failure. Test results showed that with increasing impact energy, the peak force of panels impacted by the spherical and flat impactors increased, while that of panels impacted by the wedge impactor did not vary significantly. The deformation and energy absorption of panels also increased with increasing impact energy. Notably, the impactor shape obviously influenced the dynamic behaviour of panels, causing a higher peak force of panels impacted by the flat impactor and a larger deformation of panels impacted by the wedge impactor. The failure mechanism of panels depended highly on the impact energy and the impactor shape. Finally, a comparative study of single versus repeated impacts revealed that the deformation of bamboo scrimber panels under repeated impacts was less than that of panels under a single impact when the same amount of energy was imposed to the panel. This study provided a basis for the use of bamboo scrimber to resist impact loadings.

Assessment of surface quality and damages induced during dry helical milling of hybrid composite fiber metal laminates

Abstract The present work investigates the effectiveness of helical milling for making holes with excellent surface quality in carbon fiber aluminum laminates (CARALL) under dry cutting conditions. The impact of cutting speed and axial pitch on hole surface quality was analyzed. The findings show that axial pitch and cutting speed have a major impact on surface roughness. Utilization of lower cutting speed (30 m min−1) and axial pitch (0.1 mm rev−1) results in material adhesion and feed marks, thus lowering the surface roughness. Nevertheless, the surface finish was enhanced by using higher levels of process variables. Surface defects like chip adhesions, deformation marks, and material smearing were observed. The orientation of the cutting edge with the fibers greatly influenced the surface morphology. Exposed fibers with varying lengths were noted when machining fiber layers oriented at 135°, thus creating an irregular surface. Scanning Electron Microscopic observation of the carbon fiber layers displayed a cleanly cut surface without fiber pullout and crack or interlayer burrs. Moreover, the holes in the CARALL were devoid of delamination/debonding for all the combinations of process variables. In general, results demonstrate the suitability of helical milling for processing holes with superior surface quality and satisfying the stringent requirements of the aircraft industries.

Whole process analysis on splitting tensile behavior and damage mechanism of 3D/4D/5D steel fiber reinforced concrete using DIC and AE techniques

In recent years, the application of a new type of end hook steel fiber (ESF) in concrete has gradually become a hot spot due to its excellent properties. In order to investigate the influences of ESF content, end hook number and aspect ratio on the splitting tensile properties and damage characteristics of end hook steel fiber reinforced concrete (ESFRC), a set of splitting tensile test device was improved in this study to measure the complete splitting tensile load-deformation curves of ESFRC. The influence of 3D/4D/5D steel fiber on the crack development and damage evolution of ESFRC specimens under splitting tensile load was analyzed by digital image correlation (DIC) and acoustic emission (AE) techniques. The results showed that the splitting tensile strength and crack resistance of ESFRC were gradually improved by increasing the content and end hook number of ESF. The splitting tensile load-deformation curves of the specimens with single-ended hook (3D) steel fibers could be divided into five stages, and the curves appeared two or even more fiber strengthening stages with the increase of end hook number, which mainly depends on the end hook form of steel fiber. Concrete cracking, ESF debonding and end hook straightening were the main reasons for the development of AE events and ringing counting. As the ESF content or the number of end hooks increased, the proportion of shear cracks gradually increased from 59.82% to 71.34%, and the AE energy of cracking damage also increased accordingly. The strain band at the failure interface first appeared in the middle of the specimen and gradually extended to the loading end, and the failure mode gradually changed from a single crack to a main crack, accompanied by multiple scattered cracks. Finally, a prediction model for the splitting tensile strength of ESFRC was proposed and verified based on the fiber pull-out bonding theory.

Study on dynamic mechanical properties and damage characteristics of wollastonite fiber reinforced oil well cement paste

In cement engineering, the cement sheath is not only influenced by elevated temperatures, increased pressure, and the static load confining pressure within the formation but also encounters external impact loads. These loads can rupture the cement paste, compromising the cement sheath’s interlayer sealing capability. Consequently, this can give rise to an annular flow of oil, gas, and water. Hence, this study introduces wollastonite fiber (WF) into the cement slurry to modify the cement paste. The investigation explores the mechanical properties, energy evolution, and damage characteristics of the cement paste with WF under dynamic impact loads. This is achieved by simulating the dynamic impact loads experienced downhole using the separated Hopkinson pressure bar (SHPB) technique. A straightforward SHPB model is constructed using ABAQUS finite element simulation software, and its accuracy is confirmed through experimental validation. The impact test outcomes revealed a notable enhancement in the dynamic load peak strength of the cement paste cured for 14 days. Specifically, there was an increase of 136.75%, 202.10%, and 320.55% compared to the control group at impact speeds of 6 m/s, 8 m/s, and 10 m/s, respectively. The absorption energy increased remarkably, showing 356.03%, 388.61%, and 142.14%, respectively. The simulation findings confirm that the devised simple SHPB model effectively replicates electrical signals aligned with the observed experimental results. The dispersed fibers create a three-dimensional network within the cement paste. This network enhances the impact resistance of the cement paste by leveraging the mechanisms of crack deflection, fiber fracture, and energy dissipation through fiber pull-out.

Prediction of bond strength between fibers and the matrix in UHPC utilizing machine learning and experimental data

The bond strength between fibers and the matrix plays a crucial role in the tensile strength and post-cracking performance of ultra-high-performance concrete (UHPC). However, existing studies have not attempted to utilize machine learning models for the prediction of bond strength. In this study, machine learning techniques were employed to predict the bond strength of fibers in UHPC. A dataset comprising 658 experimental records was compiled and advanced unsupervised Isolation Forest techniques were utilized to identify and remove outliers, thereby ensuring the accuracy and reliability of the data. Six machine learning models, including ANN, GBDT and XGBoost are utilized in this study, with a focus on evaluating their performance in predicting the maximum pull-out force of fibers. The results indicate that the XGBoost model exhibits exceptional predictive performance, achieving R² value of 0.98, which demonstrates the model's capability to accurately predict the fiber pull-out process. Furthermore, feature importance analysis, visualized through advanced techniques, reveals the significant influence of fiber tensile strength on the pull-out force. A new equation is proposed to predict the maximum pull-out force of fibers and correction factors for different fiber shapes are introduced, significantly enhancing the precision of the calculations. The newly proposed predictive equation has R² value of 0.72, which increases to 0.74, 0.77, and 0.86 after the introduction of shape correction factors, significantly enhancing the accuracy of the computed results. This study not only provides an efficient and reliable method for predicting fiber bond strength in UHPC but also offers an innovative tool for calculating fiber pull-out force.

Additively Manufactured Carbon Fibre PETG Composites: Effect of Print Parameters on Mechanical Properties.

This study investigates the quasi-static and viscoelastic properties of additively manufactured (AM) PETG reinforced with short carbon fibres. Samples were manufactured using different parameters in terms of the infill pattern, porosity, and annealing condition. Tensile and compressive tests were conducted to determine quasi-static properties such as Young's modulus and toughness, and dynamic mechanical analysis was used under a frequency sweep of 1-100 Hz to describe the viscoelastic behaviour of the composites. The major impacts and responses between the print parameters were quantified using Analyses of Variance (ANOVAs), which revealed the major contributor to each mechanical property. Fractography on the tensile samples using scanning electron microscopy demonstrated fibre pull-out, indicating poor fibre-matrix bonding, but also revealed interfacial bonding between raster lines in the annealed samples. This had a prominent effect on the properties of latitudinal samples where the force applied was perpendicular to the raster lines. Generally, porosity appeared to have the greatest contribution to the variance in the mechanical properties, with the exception of the tensile modulus, where the infill pattern had a more substantial effect. Annealing caused a consistent increase in the tensile modulus of the tested samples, which can be used to support the design and optimisation of AM parts when they are used under specific loading conditions.

An organic-inorganic interface structure for CFRP and the enhancement of mechanical properties at room/high temperature

The performance of carbon fiber reinforced polymers (CFRP) depends on various factors, with particular emphasis on the intricate microscopic interface. Through the combined interface modification by nanomaterials (ZrO2) and polyimide (PI), an organic-inorganic interface enhanced structure of CFRP with phenolic resin (PR) have been successfully devised and fabricated. The analysis encompassed the surface morphology, contact angle and surface energy of carbon fibers (CF), aimed at characterizing the interaction of grafted ZrO2/PI on interfacial properties. Single fiber pull-out testing was employed to ascertain both the failure mode of the interface and the interfacial shear strength (IFSS). The results revealed that the surface modification augmented the IFSS by 70 %. The fortified organic-inorganic interface layer resulted in enhancements of 14 % and 15 % in tensile strength and flexural strength, respectively, in comparison to untreated CFRP. Moreover, even under high-temperature condition (300 °C), the tensile properties of modified CFRP exhibited only 22 %–26 % reduction, which demonstrated the advantages of composites in harsh environments. This can be primarily attributed to the strengthened layers of ZrO2/PI, which securely anchored the matrix and reinforcement, thereby mitigating stress concentration in CFRP under extreme conditions.

Research progress on laser processing of carbon fiber composite materials

AbstractCarbon fiber reinforced polymer (CFRP) is a high‐performance composite material composed of carbon fibers embedded in a polymer matrix. CFRP is extensively used in various sectors such as aerospace, automotive, sports equipment, and construction due to its advantageous properties. Laser processing offers numerous advantages when working with carbon fiber‐reinforced composites, including its non‐contact nature, precision, efficiency, and controllability. However, disparities between carbon fibers and the polymer matrix can lead to challenges during laser processing, such as delamination, heat‐affected zones, and fiber pullout. Consequently, there is a substantial body of literature focusing on improving the quality and efficiency of laser processing for CFRP materials. This paper provides a comprehensive review of various studies investigating the impact of laser parameters (laser mode, pulse frequency, pulse width, and laser wavelength) on carbon fiber‐reinforced plastics. It discusses how different laser parameters affect the processing quality and performance of these materials. Additionally, drawing from recent research findings, the paper explores potential future trends in laser processing for carbon fiber‐reinforced plastics.Highlights The application of laser technology in CFRP, including laser cutting, drilling, welding, and surface treatment, has been extensively researched. A detailed discussion is held regarding the impact of laser mode, wavelength, frequency, and pulse width on the quality of machining. More auxiliary processing has evolved in CFRP manufacturing due to the ongoing advancements in laser technology. The goals of laser processing CFRP technology are increasingly focused on reducing carbon emissions, enhancing energy efficiency, and minimizing waste.

Synergistic effect of alkali treatment and graphene filler on the mechanical characteristics of nettle fiber reinforced polymer composite

This study examines the synergistic effects of alkali treatment and the addition of graphene fillers to nettle fiber-reinforced polymer (NFRP) composites. NFRP composites were fabricated using NaOH-treated nettle fibers at concentrations of 3%, 5%, and 7%. Gr-NFRP composites were produced by varying the graphene content (1wt%, 2wt%, and 3wt%) in the epoxy resin that impregnated 5% NaOH-treated nettle fibers. The composites were prepared using a hand layup combined with a compression molding technique. A comprehensive analysis of the physical, mechanical, and wear properties of the treated NFRP composites was performed. FTIR analysis confirmed the effect of alkali surface treatment on the nettle fibers, whereas SEM was employed to examine the morphology of the fractured specimens. The experimental results revealed that a 5% NaOH solution was the optimal concentration for improving the characteristics of nettle fibers within the polymer composite. Moreover, the inclusion of 2wt% graphene noticeably enhanced the mechanical properties of the NFRP composites, resulting in increases of 21%, 17%, 65%, and 10% in the tensile strength, flexural strength, impact strength, and Shore D hardness, respectively. The wear resistance improved by 38%, and the water absorption decreased by 32%. SEM images revealed that a balanced contribution between fiber breakage and pullout was the primary failure mechanism in the Gr-NFRP composites. The NFRP composite containing 2wt% graphene demonstrated significant improvements in both mechanical and wear properties, along with reduced water absorption, making it a highly promising material for structural applications.

Optimizing superelastic shape-memory alloy fibers for enhancing the pullout performance in engineered cementitious composites

Abstract This study explores the effect of integrated superelastic shape-memory alloy fibers (SMAFs) on the mechanical performance of engineered cementitious composites (ECCs). Various SMAF configurations – linear-shaped SMAFs (LS-SMAFs), hook-shaped SMAFs (HS-SMAFs), and indented-shaped SMAFs (IS-SMAFs) – with diameters of 0.8 and 1.0 mm were incorporated into ECC matrices, and surface texturization was achieved through abrasive paper treatment. Their mechanical properties were assessed through single fiber pullout tests on ECC mixtures containing 1.5 and 2.0% polyvinyl alcohol (PVA), subjected to both monotonic and cyclic loading conditions. Qualitative analysis, employing scanning electron microscopy, demonstrated that the IS-SMAF configuration provided superior mechanical interlocking and fiber–matrix adhesion, with a distinct flag shape observed during tensile testing. Quantitative data indicated that IS-SMAFs significantly improved the tensile strength and pullout resistance, with slip distances of ≥5 mm and average pullout loads ranging from 263 to 403 N. LS-SMAFs demonstrated better performance compared to HS-SMAFs and LS-SMAFs in terms of tensile and pullout characteristics. Additionally, ECCs with increased PVA content exhibited enhanced withdrawal performance. Thermogravimetry analysis and X-ray diffraction provided insights into the high-temperature stability and crystalline structure of the composites. These results underscore the effectiveness of IS-SMAFs in enhancing ECC properties, offering significant implications for the development and optimization of high-performance composite materials in civil engineering applications.