Fiber-matrix Bond Research Articles

A neuro-fuzzy based prediction modeling and mechanical characterization of multiwalled-carbon nanotubes filled Luffa cylindrica hybrid core and isotropic skin-based sandwich plate

The study focuses on mechanical characterization and adaptive neuro-fuzzy inference system (ANFIS)-based prediction modeling of MWCNT-filled Luffa cylindrica hybrid core-based sandwich plates. Experiments determine natural frequencies using modal impact hammer tests with a Fast Fourier Transform (FFT) analyzer. Elastic properties from tensile tests utilized for numerical simulations of natural frequencies in ABAQUS, showing high consistency with experimental results. SEM analysis characterizes the fiber-matrix bond in the hybrid core. ANFIS modeling establishes input–output relationships for unseen data sets. Comparisons of numerical simulations with ANFIS predictions demonstrate an accuracy within a 5% margin of error, providing insights into dynamic behavior and potential applications.

Micromechanics stiffness upscaling of plant fiber-reinforced composites

Fiber-reinforced green composites made from natural plant fibers are an increasingly popular sustainable alternative to conventional high-performance composite materials. Given the variety of natural fibers themselves, and the even larger variety of possible composites with specific fiber dosage, fiber orientation distribution, fiber length distribution, and fiber–matrix bond characteristics, micromechanics-based modeling is essential for characterizing the macroscopic response of these composites. Herein, an analytical multiscale micromechanics model for elastic homogenization is developed, capable of capturing the variety. The model features (i) a nanoscopic representation of the natural fibers to predict the fiber stiffness from the universal stiffness of the fiber constituents, mainly cellulose, (ii) a spring-interface model to quantify the compliance of the fiber–matrix bond, and (iii) the ability to model any (and any combination of) orientation distribution and aspect ratio distribution. Validation is performed by comparing the predicted stiffness to experimental results for as many as 73 composites available in the literature. Extensive sensitivity analyses quantify the composite stiffening upon increasing fiber volume fraction, fiber alignment, fiber length, and fiber–matrix interface stiffness, respectively.

Characterisation of bond between cement paste and steel fibres with different surface roughness using SEM.

The performance of cementitious composites reinforced with fibres or/and bars depends on the bond strength between inclusion and cementitious matrix. The nature of formation of fibre-matrix bond is crucial for enhancing the reliability and utilisation of reinforced composites. The research provides a review on the recently published result about the changes in the microstructure of cement matrix surrounding steel fibres with different surface roughness, using a scanning electron microscope (SEM) coupled with k-means clustering algorithm for image segmentation. The debonding pattern of the fibre-matrix bond after the tensile loading cycles was discussed by observing the amount of adhered cement paste to the pulled out fibre surface with SEM. Therefore, analysis of SEM images enabled to explain the connection between the micro-scale properties of cement paste and fibre after application of cyclic loading.

Experimental and statistical study on the effect of process parameters on the quality of continuous fiber composites made via additive manufacturing

Ongoing research in additive manufacturing towards structural and industrial application has led to the use of commingled roving as a manufacturing feedstock for printing high fiber volume fraction composites. The prospects of using this technology for high performance applications necessitates the need for a comprehensive experimental investigation into the effects of processing parameters on the quality of an additively manufactured composite printed from commingled roving feedstock. In this work, transverse flexure and void fraction matrix pyrolysis testing are both performed to evaluate composite quality. The transverse flexure test is a testing approach that evaluates the quality of the interfacial fiber-matrix bond while the void fraction test estimates the void content in the printed composite. A full observational study consisting of 27 different test combinations is done to investigate the effects of three different process parameters namely, temperature, pressure, and print speed across three different levels. Composite samples were made from commingled roving of E-glass and amorphous PET using an in-house built continuous fiber composite digital manufacturing system. Least squares regression analysis is performed to study the main, interaction and quadratic effects of process parameters. A statistical regression model having an R2 adjusted value of 80.1% is generated from the transverse flexure study, which is used to explain main and interaction effects and also predict performance. Response surface plots are also generated and are used to optimize process parameters which can subsequently be of help in scaling up composite manufacturing. Results show that all three process parameters are highly statistically significant at the 0.01 level of significance. Pressure * Temperature and Pressure * Printspeed are significant interaction terms. Pressure plays a weightier role when print speed is increased or temperature is decreased as it closes more voids that would ordinarily have been introduced because of drop in polymer melt viscosity. Micrographic analysis is also performed.

Pull-out behaviour of steel and carbon fibers in 3D-printable cement matrices of various compositions

The aim of this study was to investigate some of the factors which affect the fiber–matrix pull-out behaviour and bond strength. 3D-printable cement mixtures with various compositions were used as matrices. The effect of parameters such as type of fiber (steel or carbon), kind of aggregates (sand or limestone powder), and kind of modifier additives (metakaolin or complex nano-sized additive based on SiO2 (CNA)) on fiber–matrix pull-out behaviour were determined. The results demonstrated that the bond strength of a fiber-matrix mainly depends on the fiber type. The bond strength of a “steel wire matrix” was 2–4 times higher than the bond strength of a “carbon fiber matrix”. The fiber–matrix bond strength increased as the conditions for the wetting of a fiber’s surface improved, especially for carbon fiber. Microstructural investigation revealed that the congestion of hydration products in a fiber–matrix interface significantly improved the pull-out behaviour. The use of sand as an aggregate for a cement matrix enhanced the bond strength by 10–15% in “steel wire matrix” systems. The introduction of metakaolin and CNA into a cement matrix increased the bond strength by 15–20% for sand-based and powder-based cement matrices.

A conjugated bond-based peridynamic model for laminated composite materials

The bond-based peridynamic (BB-PD) theory is inadequate in describing the four independent engineering material constants of composite lamina, which results in fixed values its Poisson's ratios and shear moduli. This study presents a novel lamina conjugated BB-PD model encompasses not only the fiber bond and matrix bond, but also the transverse bond and conjugated bond pair. By defining these four basic PD bonds, the improved conjugated BB-PD model can overcome the restriction of material properties. The determination of the four basic PD micro-modulus parameters is achieved through the utilization of the equivalent relationship of strain energy density. In addition, the lamina conjugated BB-PD model is extended to deal with composite laminates with different stacking sequences. The present study validates the accuracy and applicability of the conjugated BB-PD model for composite materials by conducting simulations of the elastic deformation and progressive damage behavior of unidirectional laminae and laminates. Moreover, the proposed model provides an elucidation of the damage modes and failure mechanisms of laminated composite materials subjected to uniaxial loading.

Hybrid effect of polyethylene fibre and nano-calcium carbonate on the flowability and strength of a geopolymer composite

Using geopolymer composites to reduce the use of Portland cement can decrease carbon dioxide emissions. The focus of this study was on improving the strength of a geopolymer composite by assessing the positive hybrid effect of nano-calcium carbonate (NCC) and polyethylene fibres (PFs) of different lengths (6 mm and 12 mm). Fresh and hardened properties, including flowability and strength, were investigated to evaluate the hybrid effect. Generally, the hybrid effects from the PFs of different lengths and NCC were negative for flowability, but the hybrid effects were positive on strength. The combination of 12 mm PF + 6 mm PF + 1% NCC was found to have the highest hybrid effect on bending strength, resulting from the good fibre–matrix bond. The bending strength of the PF-reinforced geopolymer composite was assessed based on a new regression coefficient (A), which takes into account the hybrid effect, the fibre–matrix bond strength and fibre dispersion. The new model for the bending strength of PF-reinforced geopolymer composites introduced in this paper is simpler and more effective than previous models provided in the literature.

Effect of multi-scale reinforcement on fracture property of ultra-high performance concrete

This paper aims to achieve multi-scale crack control of concrete by using graphene oxide (GO) and macroscopic steel fiber in combination, and to reveal the multi-scale collaborative reinforcement mechanism of GO and steel fiber. A three-point bending fracture mechanics test was employed to analyze the macroscopic fracture properties of ultra-high performance concrete (UHPC) reinforced by GO, and a single fiber pull-out test was utilized to assess the impact of GO on the fiber–matrix interface properties. The results showed that 0.04% GO reinforced UHPC had the best fracture property, and steel fiber and GO showed good synergistic crack control effect. GO directly acted on controlling the cracking of concrete matrix at the nanoscale, thus improving the fracture energy of UHPC matrix by 14% from 73.08 N/mm to 83.39 N/mm. This micro-scale matrix reinforcement provided by GO further improved the pull-out property of steel fibers, and the pull-out energy dissipation of straight steel fibers and hook-end fibers was increased by 43.7% and 31.5%. A micromechanical prediction model for fracture energy of straight steel fiber UHPC was established, which could construct the quantitative relationship between UHPC fracture energy and micromechanical parameters. The model showed that the initial fiber–matrix bond strength (τ0) and slip hardening coefficient (k0) had a powerful influence on the UHPC fracture energy.

Impact Behaviour of Steel-Fibre-Reinforced Alkali-Activated Slag Concrete Exposed to Elevated Temperatures.

Concrete protective structures are mainly meant to withstand impact loads. However, fire events weaken concrete and reduce its impact resistance. This study investigated the impact behaviour of steel-fibre-reinforced alkali-activated slag (AAS) concrete before and after exposure to elevated temperatures (i.e., 200 °C, 400 °C, and 600 °C). Hydration products' stability under elevated temperatures, their effects on the fibre-matrix bond, and, consequently, AAS's static and dynamic responses were investigated. The results reveal that adopting the performance-based design concept to achieve a balance between AAS mixtures' performance under ambient and elevated temperatures is a crucial designing aspect. Advancing hydration products' formation will increase the fibre-matrix bond at ambient temperature while negatively affecting it at elevated temperatures. High amounts of formed and, eventually, decomposed hydration products at elevated temperatures reduced the residual strength due to lowering the fibre-matrix bond and developing internal micro-cracks. Steel fibre's role in reinforcing the hydrostatic core formed during impact loads and delaying crack initiation was emphasized. These findings highlight the need to integrate material and structure design to achieve optimum performance and that low-grade materials can be desired based on the targeted performance. A set of empirical equations for the correlation between steel fibre content in the AAS mixture and corresponding impact performance before and after fire exposure was provided and verified.

Steel Fiber–Matrix Interfacial Bond in Ultra-High Performance Concrete: A Review

Ultra-high performance concrete (UHPC) is a relatively new cementitious concrete composite with significant application potential in infrastructure construction because of its excellent mechanical strength and durability. The steel fiber–matrix interfacial bond is the main factor that governs other mechanical properties of UHPC, including tensile, flexural, and compressive strengths and failure mode (fracture behavior). This paper presents a comprehensive review on the research progress of fiber–matrix bond behaviors of UHPC by discussing and comparing a range of fiber pullout testing methods and analytical models. The parameters of the fiber–matrix bond, including the geometry and orientation of fibers, surface treatment, and composition and strength of the matrix, are identified and discussed in detail. Lastly, recommendations for future research related to UHPC strengthening methods and testing details are provided based on recent progress.

Behaviour of structural engineered cementitious composites under dynamic tensile loading and elevated temperatures

This paper presents a systematic study on dynamic splitting tensile properties of polyvinyl alcohol (PVA) fibre reinforced engineered cementitious composites (ECC) after exposure to elevated temperatures up to 800 °C under strain rates of 4.34 to 10.95 s−1. A series of tests were conducted to characterise the weight loss, elastic modulus, uniaxial tensile properties, static and dynamic splitting tensile behaviour, and pore pressure, as well as the chemical and microstructural evolution of ECC. Results indicate that the dynamic splitting tensile properties of ECC went up with the increasing strain rate regardless of heated temperatures due to strain rate effect. The dynamic splitting strength, dynamic increase factor and energy dissipation of ECC reached the maximum values at 105 °C, which can be ascribed to the enhanced fibre-matrix bond and further hydration of fly ash. However, the dynamic tensile properties of ECC reduced at over 250 °C due to the melting of PVA fibres, thermally induced microcracks and dehydration of hydration products. At 800 °C, the dynamic splitting tensile strength and dissipated energy of ECC dropped by 81.0–83.2% and 88.4–89.1% over the measured strain rate range, relative to that at 20 °C. In addition, the main role for resisting dynamic loading was gradually transferred from fibre debonding-elongating action to crack propagation at over 400 °C. Accordingly, the failure patterns of ECC changed from tensile failure with the main central crack to coupled tensile-shear failure with multiple cracks.

Effect of nano-SiO2 on fiber–matrix bond in ultra-high-performance concrete as partial substitution of silica flour

This study investigated the effect of nano-SiO2, which partially substituted silica flour, on the rate-dependent bond behavior of straight steel fibers in ultra-high-performance concrete (UHPC). As much as 0%–50% by weight of the silica flour was replaced with the nano-SiO2. The packing density of the granular particles increased with the nano-SiO2 content up to 15%. However, upon increasing the nano-SiO2 content further, the packing density gradually decreased. A higher packing density was obtained at a replacement ratio of 15% than those of conventional UHPC. The static bond performance of steel fiber in UHPC was improved by adding up to 40% of nano-SiO2. Moreover, the best pullout resistance was observed in UHPC containing 10%–15% nano-SiO2 because of its filling effect and secondary pozzolanic reaction. The equivalent bond strength obtained on adding proper amounts of nano-SiO2 was thus nearly twice that of the plain UHPC. The impact pullout resistance for the UHPC matrix incorporating up to 30% of nano-SiO2 was higher than that for the plain UHPC; however, the best impact pullout resistance was observed at 10%–20% nano-SiO2 contents. A remarkable rate sensitivity of the bond strengths of straight steel fibers in the UHPC matrices was observed. The rate sensitivity of the average bond strength in the plain UHPC decreased on adding nano-SiO2. However, the rate sensitivity of the equivalent bond strength was insignificantly affected by the nano-SiO2 content. Overall, a 10%–15% nano-SiO2 content was considered to be the optimal in terms of the improved static and dynamic bond performances.

Effect of the fiber-matrix bond on the toughness of soft, short-fiber composites

In this work, we investigate toughening mechanisms in soft polymers reinforced with stiff fibers, particularly focusing on the effect of the strength of the fiber-matrix bond on the toughness. We print polydimethylsiloxane with short milled glass fibers using direct ink writing, an extrusion-based 3D printing method. This process produces composites with aligned fibers. Fibers can be treated with acid prior to printing, which improves the strength of the fiber-matrix bond. This results in higher yield stress and toughness. The higher toughness of the composites can be attributed to intrinsic mechanisms such as matrix deformation and fiber pullout, as well as to extrinsic mechanisms like mechanical dissipation. The intrinsic toughness of the composites is analytically estimated using a micro-mechanical model and experimentally measured by stretching the composites in the direction of fiber alignment. Finally, we demonstrate partial healing of the fiber-matrix bond after initial pre-stretch. Thermal treatment of the damaged composites results in partial recovery of stiffness and toughness.

Permeation and Fiber Matrix Bond Behaviour of Ultra High Performance Concrete – A Review

Abstract A brief review of the evolution and origins of Ultra-High Performance Concrete (UHPC) is covered in this article. UHPC is a unique concrete with unique features such as workability, mechanical properties, and durability that differs from regular concrete and high-performance concrete in terms of mix composition, needs, and manufacturing methods. In terms of the material ingredients of UHPC, Silica Fume (SF) plays a critical role in the production of UHPC due to its unique physical and chemical properties. Ground Granulated Blast Furnace Slag (GGBS), a highly reactive pozzolan similar to SF, is another viable contender among mineral admixtures. As a result, this article examines the effects of SF and GGBS in the UHPC combination. This paper also reviews the durability of UHPC in terms of water and chloride-ion permeability. A brief review of the importance of steel and polypropylene fibre (PPF) in UHPC blends, as well as their pull-out behaviour, is also reviewed.

Mechanical properties, flexural behavior, and chloride permeability of high-performance steel fiber-reinforced concrete (SFRC) modified with rice husk ash and micro-silica

To improve the fiber-matrix bond and enhance the macro-mechanical performance of SFRC, this study is focused on the modification of the cement matrix by using two eco-friendly supplementary cementitious materials (SCMs), rice husk ash (RHA) and micro-silica (MS). The modification effects of SCMs on the steel fibers were observed and characterized by conducting several macro-mechanical tests i.e., compressive strength, splitting tensile strength, and load-deflection behavior. Besides that, ultrasonic pulse velocity, water absorption, and chloride migration tests were performed to characterize the durability of modified SFRC mixes. The results showed that the incorporation of RHA and MS at low levels notably enhanced the efficiency of steel fibers under splitting tensile and flexural strength testing. SFRC made with 7.5% MS and 7.5% RHA showed 79% and 96% more flexural strength than plain concrete (PC), respectively. Whereas SFRC experienced 14% and 26% further improvement in flexural toughness with the addition of 7.5% RHA and 7.5% MS, respectively. The addition of 7.5% and 12.5% RHA showed a beneficial effect on the resistance of SFRC against the penetration of chloride ions and water. The results of this study confirmed the synergistic interaction of steel fiber and SCMs.

Predicting the strain-hardening behaviour of polyethylene fibre reinforced engineered cementitious composites accounting for fibre-matrix interaction

Mechanical properties of engineered cementitious composites (ECC) are highly dependent on the pore structural characteristics and fibre-matrix interaction. The relationship between them has not been extensively explored. This paper proposes a practical micromechanical analytical model accounting for pore structure characteristics and crack-bridging properties to predict the strain-hardening and multiple microcracking behaviour of ECC. Using polyethylene fibre reinforced ECC (PE-ECC) as an example, Monte Carlo simulations were undertaken to investigate the tensile behaviour in terms of crack strength, fibre bridging strength and uniaxial tensile properties against heterogeneity of material property, which were validated with experimental data. A parametric study was then conducted to estimate the effects of fibre-matrix bond and fibre properties on stress-strain relationship and microcracking features of PE-ECC. Results indicate that the tensile properties of PE-ECC can be reasonably predicted. Under constant fibre dosages, the tensile ductility of PE-ECC is dominated by interfacial bond, followed by fibre location, orientation and diameter. Such insights are helpful to the design of ECC composites for practical applications.

Characterization of the Neuropeltis acuminatas liana fiber treated as composite reinforcement

Treatment of plant fibers with sodium hydroxide (NaOH) is an effective solution to dissolve their non-cellulosic substances and reduce their sensitivity to moisture or water, and to improve fiber-matrix adhesion in composites. The presence of these non-cellulosic substances in Neuropeltis acuminatas (NA) fibers still limits their use in biocomposite development. In this study, tropical fibers extracted by wet retting from the bark of NA lianas native to Cameroon, were treated for the first time with NaOH solution at weight concentrations of 3%, 5% and 8%. Thermal, FTIR, and SEM analyses reveal that NaOH treatment is effective in removing non-cellulosic substances, resulting in thermal stability up to 230.3 °C, allowable friction capacity (1.25<Sq/Sa=1.27<1.31) for the fiber-matrix bond, and a reduction in water absorption rate up to 74.7%. Tensile tests were performed on both raw and treated fibers, and the results showed that the fiber treated with 5% NaOH had higher tensile strength (321 MPa) and tensile stiffness (8.4 GPa). A large variability of mechanical properties with fiber diameter was observed. The two-parameter Weibull model was used to quantify the degree of dispersion of the mechanical properties of the fibers. A low dispersion for the fibers treated at 5% was observed, compared to those treated at 3% and 8%. These results compared to plant fibers from the literature show that it is relevant to recommend for NA fibers a surface treatment with 5% NaOH for the reinforcement of composites.

Effect of fibers addition on mechanical properties of eco-friendly phosphogypsum-based composite at high temperatures

In this study, the mechanical properties of an eco-friendly hemihydrate phosphogypsum-based composite (HPGC) added with basalt, glass, and PVA fibers upon exposure to high temperatures (250°C, 450°C, 650°C, and 850°C) were investigated. The fibers content (0%-1.35 vol%) did not have a significant effect on compressive strength at ambient temperature, while the flexural strength of HPGC was enhanced optimally at 1.0% fiber volume. For the investigation at high temperatures, the fiber inclusion could effectively reduce the cracks but increased the mass loss of HPGC. Compared to other fiber types, HPGC with PVA fiber, which did not melt at 250°C, exhibited the highest compressive strength and flexural strength (32.59 MPa and 10.56 MPa, respectively) at the temperature of 250°C but had a greater strength reduction between temperatures of 450°C and 850°C. At 850°C, HPGC with basalt fiber exhibited higher flexural strength than HPGC added with other fibers, and with 133.3% higher flexural strength than HPGC without fiber. The microstructural investigation confirmed that the changes of calcium sulfate forms (dihydrate to hemihydrate and anhydrite) and ettringite in the matrix contributed to the strength loss of all HPGC mixtures at high temperatures, while the existence of basalt fiber-matrix bond allows the HPGC added with basalt fibers to have the best residual properties at 850°C compared to the other mixes.

Substitutive effect of nano-SiO2 for silica fume in ultra-high-performance concrete on fiber pull-out behavior

This study investigated the effect of substituting nano-SiO2 for silica fume on the fiber-matrix interfacial bond performance of ultra-high-performance concrete (UHPC). In this study, silica fume was substituted by nano-SiO2 in the weight range of 0–50%. The degree of pozzolanic reaction of binder materials was evaluated using the thermogravimetric analysis (TGA) and compressive strength measurement. The single fiber pull-out test was conducted along with a measurement of autogenous shrinkage to evaluate the interfacial bond. The degree of pozzolanic reaction of nano-SiO2 was found to be higher than that of other binder materials. Although the packing density was predicted to increase continuously up to a substitution ratio of 50%, the highest compressive strength was obtained when 10% of silica fume was replaced by nano-SiO2, which improved the compressive strength by 5.9% compared to that of the plain sample. The autogenous shrinkage increased with an increasing content of nano-SiO2 up to 30%; however, it remained similar beyond the nano-SiO2 content of 30%. The best pull-out performance was obtained when 20% of silica fume was replaced by nano-SiO2, in which the average bond strength and pull-out energy were improved by approximately 21 and 68%, respectively. Therefore, substitution of 10–20% of silica fume by nano-SiO2 was recommended as an optimal amount considering the improvements of the compressive strength and fiber-matrix bond performance of UHPC.

Impact of micromechanics on dynamic compressive behavior of ultra-high performance concrete containing limestone powder

To improve sustainability and reduce costs, interest in using limestone powder (LP) in ultra-high performance concrete (UHPC) has been increasing in recent years. Incorporating LP changes packing, characteristics of C–S–H and pore structure of interfacial transition zone (ITZ) and matrix by physical and chemical effects. However, the influences of LP replacement on the mechanical properties of UHPC, from micromechanics to macroscopic impact behaviors, have not been well understood. Herein, mercury intrusion porosimetry (MIP), thermal gravimetric (TG), nanoindentation test and Split Hopkinson pressure bar (SHPB) test are performed to reveal the relationships between the micromechanical properties and the dynamic performances of UHPC. Results show that appropriate amount of LP incorporation optimizes the packing, leading to a narrower space and more densely compacted C–S–H that improves the percentages of high-density C–S–H and ultra-high density C–S–H in ITZ. The higher density of C–S–H results in a higher steel fiber-matrix bond strength, which benefits a higher dynamic compressive strength and energy absorption while a lower dynamic increase factor. More low-density C–S–H are generated due to the dilution effect of excessive LP, leading to a weak steel fiber-matrix bond strength that deteriorates the impact resistance. Additionally, the mechanism of LP enhancing the quality of C–S–H in ITZ is proposed, which favors understanding the relation between macro dynamic performance and interfacial behavior at the micro and nanoscale.