Fiber Pull-out Energy Research Articles

Interfacial properties of high-strength, limestone-calcined clay cement (LC3) matrix and PE fibers, surface-modified using dopamine and tannic acid

Polyethylene (PE) fibers exhibit superb mechanical and geometrical properties with respect to their use as dispersed reinforcement in cement-based materials. However, the fiber–matrix interaction in such composites is known to be poor due to the lack of active functional groups on the fibers’ polymeric backbones, leading to the limited affinity of PE fibers toward water-based, cementitious matrices. Therefore, to exploit the reinforcing effect of PE fibers in cementitious composites fully, fiber–matrix interactions need to be enhanced by functionalizing the fibers with hydrophilic polar groups. In the article at hand, the effects of dopamine (DA) and tannic acid (TA) surface functionalization and their combinations on interfacial properties with a high-strength, limestone-calcined clay cement (LC3) matrix have been explored. To assess the morphological changes as well as the physical–chemical properties of the fibers under investigation, they were characterized by environmental scanning electron microscopy (ESEM), Energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and zeta-potential (ZP). The presence of a DA and TA (DA/TA) coating layer was confirmed by ESEM and AFM images for modified samples, which showed rougher surfaces along with uniform coating distributions, proven via mapping images as well. TGA results yielded coating amounts of 7.8, 1.5, 1.5, 2.3 and 1.0 wt% for samples with DA/TA portions of 100/0, 70/30, 50/50 and 30/70 and 0/100, respectively. Compared with the pristine PE fiber, the DA/TA surface modification of PE fibers improved the tensile strength and modulus of elasticity values by 29% and 36%, respectively. According to micromechanical investigations, maximum pullout force and interfacial shear strength in specimens with modified fibers were three times higher than for the reference fibers, while fiber pullout energy was as much as six times higher

Long-term Pull-out behavior of coir fiber from cementitious material with statistical and microstructural analysis

In this study, the long-term pullout behavior and microstructure of the embedded coir fibers (a bundle of multi-monofilament fibers) from cementitious matrix were investigated. The experimental results were analyzed through statistical tests (i.e., Shapiro-Wilk test, Kolmogorov-Smirnov test, and Analysis of variance with Tukey’s honestly significant difference test) to address the reliability of the analyses and conclusions. The duration of fiber embedment in the matrix (i.e., 1, 2, 4, 8, 12, and 24 weeks), and the addition of fly ash (i.e., weight replacement ratio to cement for 0%, 10%, and 20%) were considered as the test parameters. The results show that the fibers with larger diameters tended to have tensile failure rather than pullout failure during the test. When the fibers had larger embedment length in the cementitious material, the pullout load–displacement curve changed from slip-hardening to slip-softening pattern. The highest fiber pullout strength was recorded when tested at 24-week. However, the highest fiber pullout energy was not recorded at 24-week but at 2-week. It can be concluded that with a longer embedment duration, the interfacial bond between fiber and matrix will increase but the coir fiber itself will be embrittled. This is due to the penetration of mortar into fiber surface along with a longer embedded duration, which was observed under scanning electron microscope. The pozzolanic reaction of fly ash did not improve the fiber–matrix interfacial bond strength. To the contrary, the pullout energy of the samples with 20% fly ash at week 1 was significantly lower than that with 10% fly ash or without fly ash. This was due to the unreacted spherical fly ash particles on the fibers surface that acted as lubricant during pullout.

Influence and Mechanism of Curing Methods on Mechanical Properties of Manufactured Sand UHPC.

The mechanical properties of ultra-high performance concrete (UHPC) made of manufactured sand (MS) under four curing methods (steam, standard, sprinkler and saturated Ca(OH)2) were investigated via compressive, flexural and uniaxial tensile tests, and the bond strength of steel fiber and manufactured sand UHPC (MSUHPC) matrix. Based on the analysis of the microstructure, the influence mechanism of curing methods on the mechanical properties of materials was explored. The results showed that the early compressive strength of MSUHPC under steam curing (SM) is much higher than that of the other three curing methods, but the difference gradually decreases with the increase of age. The compressive strength of MSUHPC under SM is higher than that of river sand UHPC (RSUHPC). The bending strength and compressive strength of MSUHPC under different curing methods are similar, and the bending strength of 28 days steam cured samples is the highest. The uniaxial tensile properties of MSUHPC did not show significant difference under standard curing (SD), sprinkler curing (SP) and saturated Ca(OH)2 curing (CH), and the uniaxial tensile properties of MSUHPC under SM are slightly better than RSUHPC. The ultimate bond strength and fiber pullout energy of steel fiber and MSUHPC increase with the development of age. The bond strength and fiber pullout work of SM is higher than those of the other three curing methods, but there are lower increases in the later stage than that of the other three curing methods.

Effect of Atmospheric Pressure Oxygen Plasma treatment on Bonding Characteristics of Basalt Fibre Reinforced Concrete

In this research work, the bonding characteristics of plasma treated basalt fibres were analysed by employing the fibre pull-out test. 80 samples were prepared with two different spans of basalt fibres (such as 25 mm and 50 mm) and four levels of embedded length (10, 15, 20 and 25) inside standard M20 grade concrete. Debonding and bonding characteristics of the plasma treated fibres were compared with raw basalt fibres through the fibre pull-out test. The plasma treated and raw basalt fibres were characterised through Field emission scanning electron microscope (FESEM) and Fourier transform infrared (FTIR) analysis. It was observed that confirmation of the presence of hydroxyl groups on the basalt fibre surface was realised through the FTIR test and that there was higher adsorption of concrete particles by the plasma treated basalt fibres through FESEM. The de bonding and fibre pull-out energy of the plasma treated basalt fibres were improved by about 9% and 10% compared with 25 mm and 50 mm raw basalt fibres. From the observation above, it can be stated that the surface modification of basalt fibre may lead to a change in the debonding and pull-out energy level.

Reactive Powder Concrete: Durability and Applications

Reactive powder concrete (RPC) is an ultra-high-performance concrete (UHPC) developed years ago by Bouygues, with the aim to build strong, durable, and sustainable structures. Some differences can be underlined between the RPC and high-performance concrete (HPC); that is to say, RPC exhibits higher compressive and flexural strength, higher toughness, lower porosity, and lower permeability compared to HPC. Microstructural observations confirm that silica fume enhances the fiber–matrix interfacial characteristics, particularly in fiber pullout energy. This paper reviews the reported literature on RPC, and it offers a comparison between RPC and HPC. Therefore, some RPC potential applications may be inferred. For instance, some examples of footbridges and structural repair applications are given. Experimental measurements on air permeability, porosity, water absorption, carbonation rate, corrosion rate, and resistivity are evidence of the better performance of RPC over HPC. When these ultra-high-performance concretes are reinforced with discontinuous, short fibers, they exhibit better tensile strain-hardening performance.

Enhancing the interfacial bonding between PE fibers and cementitious matrices through polydopamine surface modification

High-performance polyethylene (PE) fibers possess unique features to develop advanced cementitious composites with superior mechanical properties. Nonetheless, due to their hydrophobic nature, such fibers can develop only a poor interfacial affinity between themselves and the water-based cementitious matrices, which restricts a full exploitation of their intrinsic properties. The work described here is an expeditious and environmentally friendly strategy to enhance the bond strength in PE fiber-reinforced cementitious composites through utilization of polydopamine (PDA) surface modification. Environmental scanning electron microscopy (ESEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), water contact angle, and electrokinetic measurements were applied to characterize the surface properties of the fibers under investigation. Moreover, fiber-matrix interactions were assessed by single-fiber pullout from a cementitious matrix with respect to dopamine concentration and modification time. Compared to the unmodified reference sample, a noticeable increase in maximum pullout load, interfacial shear strength, and fiber pullout energy was achieved with the modified fibers. This was explained by the formation of active hydrophilic groups on the fiber surfaces, which groups enhance the fibers’ wettability and yield better interaction with the cementitious matrix. Furthermore, the modified fibers exhibit increased tensile strength, modulus of elasticity, and suitable stability in a highly alkaline environment as well.

The effect of alkali treatment on mechanical, morphological and thermal properties of date palm fibers (DPFs): Study of the interface of DPF–Polyurethane composite

This paper focuses on investigating the effect of alkali treatments on the bond characteristics of date palm fibers (DPFs) in a polyurethane (PU) matrix, including the bond strength, pullout energy. This kind of fiber treatment is generally used to improve the mechanical behavior of composites. Raw DPFs underwent a surface modification method by alkali treatment with different percentages of NaOH: 0 wt%, 2 wt%, 5 wt% and 10 wt%. All treatments were carried out under mild conditions without heating for 1 h. The Fourier transform infrared spectroscopy (FTIR), tensile properties, surface morphology and thermal gravimetry analysis (TGA) of treated DPFs were investigated. The experimental results showed that the alkali treatment can effectively remove non cellulosic materials and enhance the tensile strength of DPFs. In order to investigate on DPF-PU adhesion, the fiber pullout test was also carried out. It was found that the DPF-PU interfacial properties increased after the alkali treatment, especially fiber pullout energy. Indeed the optimal alkali concentration was reported at 5 wt% in terms of the bond characteristics, and, this is mainly due to the reduction of the amorphous parts of the fibers.

Fracture behaviour of steel fibre-reinforced concrete at a wide range of loading rates

Three-point bending tests on notched beams of steel fibre-reinforced concrete (SFRC) have been conducted using both a servo-hydraulic machine and a drop-weight impact device. The shape and geometry of the beams followed the RILEM recommendation, i.e., 150 mm × 150 mm in cross section, 700 mm in length, notch-depth ratio was around 1/6 and the span of the tests was kept constant 500 mm. The peak load and the fracture energy were measured over a wide range of loading rates (loading point displacement rates), spanning six orders of magnitude. Under low loading rates, from 10−3 mm/s to 100 mm/s, the tests were performed with the servo-hydraulic machine; from 102 mm/s to 103 mm/s, the drop-weight impact machine was used instead. The results show that the fracture energy and the peak load increase as the loading rate increases. Furthermore, such a trend is relatively mild under low rates. The gain of the fracture energy and peak load is around 10% compared with its quasi-static values. It could be attributed to viscous effects mainly originated by the presence of free water in voids and porous structures in the matrix, and the weak fibre pullout resistance. However, under high rates the increases in the fracture energy and the peak load are pronounced due to the inertia effect and the greater fibre pullout energy. The dynamic increase factors of the peak load and the fracture energy for the fastest loading rate are approximately 3.5 and 2.5, respectively.

Waste fibre–cement matrix bond characteristics improved by using silane-treated fibres

In this paper, the effects of silane treatment on the bond characteristics of fibre in a cementitious matrix, including the bond strength, pullout energy, etc., are presented. These fibres were obtained from recycling by crushing of a thermoset composite based on unsaturated polyester/glass fibre. The experimental results of the fibre pullout test under different conditions are reported. Silane treatment contents between 0% and 1% are used, and single fibre pullout tests are conducted to measure the bond characteristics of the fibre to the cementitious matrix. It is found that the silane treatment (VTMO) can effectively enhance the fibre–matrix interfacial properties, especially the fibre pullout energy. It is also concluded that in terms of the bond characteristics, the optimal silane content is 0.5%, given the conditions of this experimental program. Microstructural observation confirms the findings on the interfacial-toughening mechanism drawn from the fibre pullout test results.

Carbon fibre pullout under the influence of residual thermal stresses in polymer matrix composites

► The anisotropic property of carbon fibres has significant effect on thermal residual stresses. ► The residual thermal stress has a significant influence at frictional sliding stage of fibre pullout. ► The interfacial shear strength is not a constant and decreases with the fibre embedded length. ► The specific pullout energy increases with the embedded length. ► The specific pullout energy does not depend on the fibre radius. A single carbon fibre pullout from a polymer matrix under the influence of residual thermal stresses was numerically investigated in this paper. The finite element method was first applied to obtain the residual thermal stress components along the interface between the fibre and the matrix due to curing. Four typical carbon fibres, T300, AS4, T800HB-40B and IM7 with anisotropic properties embedded in epoxy matrix HY6010 were considered. A comparison study indicates that simplified isotropic fibre model would overestimate the compressive residual axial and interfacial radial stress by up to 30%. Therefore, the anisotropic material properties of the fibres should be considered in the theoretical study of carbon fibre pullout. The cohesive zone model was then used to study the single carbon fibre pullout test. The numerical results indicate that the residual thermal stresses have a significant influence on fibre pullout at the stage of frictional sliding after interfacial debonding, which leads higher specific pullout energy. The effects of interfacial bonding condition and the fibre geometry were investigated by a parametric study. An interesting finding is that the interfacial shear strength, which is defined as the ratio of the debonding force to the embedded area, is not a constant. It decreases with the increase in the fibre embedded length. In addition, the fibre pullout energy per unit interfacial area (specific pullout energy) increases with the embedded length due to the effect of residual thermal stresses and interfacial friction. But the specific pullout energy does not depend on the fibre radius, which means that reducing fibre radius alone would not enhance the fibre bridging effect.

Experimental Results of Polyester/Glass Fibers – Cementitious Matrix Bond Characteristics: Effect of Silane on Fibers

In this paper, the effect of silane treatment on the bond characteristics of fiber in cementitious matrix, including bond strength and pullout energy are presented. These fibres arise from recycling by crushing of thermoset composite based on unsaturated polyester/glass fiber. Various silane treatment contents ranging from 0% to 1% are used. This treatment by silane enhances the fiber–matrix interfacial properties, especially in fiber pullout energy. However, the bond strength was increased by 150% and the pullout energy was increased by 300%. It is also concluded that in terms of the bond characteristics, the optimal content of silane is 0.5%, given the conditions of the experimental program. The micro structural observation confirms the findings on the interfacial-toughening mechanism drawn from the fiber pullout test results.

Mechanical properties of concrete-reinforced fibres and powders with crushed thermoset composites: The influence of fibre/matrix interaction

This paper focuses firstly on the formulation and mechanical behaviour of concrete reinforced fibre and powder (CRFP). Secondly, we present the effect of silane treatment on the bond characteristics of the fibre–matrix of ultra-high-performance concrete (UHPC). The initial objective of the study was to optimize the incorporation of fibres and powders in high performance concrete (HPC). Two materials were investigated. The first involved replacing a volume of sand by an equivalent volume of fibres and powders. The second type was obtained by replacing an equivalent volume of silica fume with powders. Testing of the first material showed that the incorporation of fibres and powders by sand substitution increased the bending and tensile strength by 32%. In the second material, the substitution of silica fume by the powder led to an increase of 37% in flexural and tensile strengths.The second section of this paper focuses on silane-treated fibres. The experimental results on fibre pullout tests under different conditions are reported. Various silane treatment contents ranging from 0% to 1% were studied. Fibre pullout tests were conducted to measure the bond characteristics of fibres in the UHPC matrix. The treatment by vinyl trimethoxy silane (VTMO) can effectively enhance the fibre–matrix interfacial properties, especially the fibre pullout energy. It was concluded that in terms of the bond characteristics, the optimal silane content is 0.5% under these conditions.

Progressive Micromechanical Modeling for Pullout Energy of Hooked-end Steel Fiber in Cement-based Composites

A progressive micromechanical damage-plasticity formulation is proposed to analyze the single hooked-end steel fiber pullout energy from the surrounding cement-based matrix within the context of hooked-end steel fiber-reinforced cementitious composites (HSFRCC). As the hooked-end steel fiber has a unique fiber geometry, its fiber pullout energy from the cement-based matrix consists of the interfacial fiber-matrix debonding, the frictional sliding and pullout energy, and the elastoplastic deformation energy of the steel fiber hooked end. The aforementioned energy components are analytically derived first, and the superposition principle is subsequently employed to obtain the total energy dissipation during the fiber pullout process. Good agreement is obtained for comparisons between the experimental results of single hooked-end steel fiber pullout tests and the proposed analytical predictions. This satisfactory verification supports the validity and applicability of the proposed damage-plasticity energy prediction formulation, and suggests the applicability of this methodology to further investigation on micromechanical fracture energy prediction of HSFRCC during flexural macro-cracking.

Effect of silica fume on steel fiber bond characteristics in reactive powder concrete

In this paper, the effect of silica fume on the bond characteristics of steel fiber in matrix of reactive powder concrete (RPC), including bond strength, pullout energy, etc., are presented. The experimental results on steel fiber pullout test of different conditions are reported. Various silica fume contents ranging from 0% to 40% are used in the mix proportions. Fiber pullout tests are conducted to measure the bond characteristics of steel fiber from RPC matrix. It is found that the incorporation of silica fume can effectively enhance the fiber–matrix interfacial properties, especially in fiber pullout energy. It is also concluded that in terms of the bond characteristics, the optimal silica fume content is between 20% and 30%, given the conditions of the experimental program. The microstructural observation confirms the findings on the interfacial-toughening mechanism drawn from the fiber pullout test results.

Tensile strength and rupture energy of hybrid poly(methylvinylsiloxane) composites reinforced with short PET fibers and wollastonite whiskers

In this paper, the tensile strength and rupture energy of hybrid poly(methylvinylsiloxane) composites reinforced with short PET fibers and wollastonite whiskers have been studied. It was observed that for a fixed fiber volume fraction, the tensile strength and rupture energy of the hybrid composites first decreased and then increased with wollastonite whisker volume fraction. Analyses of the fiber efficiency factor for the strength and rupture energy of the composites indicated that the fiber pull-out force and pull-out energy were changed as a result of the incorporation of wollastonite. The hybrid reinforcing mechanism is also discussed in this paper.

Fracture resistance of unfilled and calcite-particle-filled ABS composites reinforced by short glass fibers (SGF) under impact load

Abstract Acrylonitrile-butadiene-styrene (ABS) terpolymer, unfilled and filled with calcium carbonate (calcite) particles, was used as a matrix for reinforcement with short glass fibers (SGF). All of the materials were prepared by injection molding and the fibers in the specimens were oriented preferentially in the flow direction (i.e. the axial direction of the specimens). The composites were studied with respect to the work of fracture (WOF), here the notched Charpy impact energy, determined by the Charpy V-notch impact test. The fracture surfaces of the composites were studied by scanning electron microscopy. The total WOF theory for short-fiber-reinforced composites was used to evaluate the interface energy and the matrix fracture work, whereby the fiber fracture work was neglected because of the brittleness of glass fibers, only a small amount of broken fibers being observed experimentally. It was shown that the interface energy is much higher than the matrix fracture work in the presence of fibers. The results showed that the reduction in WOF caused by adding SGF to pure ABS resin matrix is the consequence of a significant reduction in the matrix fracture work; on the other hand, the incorporation of SGF into calcite-filled ABS resulted to some extent in an increase in the WOF, this is being due to the relatively large interface energy contribution to the WOF of the composite. Moreover, it was observed experimentally that the treated case showed a higher WOF for SGF/ABS composites than for the as-received case, whereas this was not observed for hybrid SGF/calcite/ABS composites. This behavior was explained in terms of the changes in fiber length distribution by using the total WOF theory and the fiber pull-out energy theory. Furthermore, it was pointed out that when investigating the influence of the fiber/matrix interface on the WOF of short-fiber composites, the fiber length distribution must be taken into consideration.

The fibre pull-out energy of misaligned short fibre composites

A theoretical study on the fibre pull-out energy has been carried out for short fibre-reinforced composites. Two probability density functions were introduced for modelling the fibre-length distribution and the fibre-orientation distribution. By taking into account the effect of snubbing friction between fibres and matrix at the fibre exit point during fibre pull-out, and that of the fracture stress of fibres obliquely crossing the fracture plane (i.e. the inclined strength of fibres), the fibre pull-out energy of composites has been derived as a function of fibre-length distribution and fibre-orientation distribution, as well as interfacial properties. The previously existing fibre pull-out energy theories can be deduced from the present model. The effects of fibre-length distribution, fibre-orientation distribution, interfacial properties, snubbing-friction coefficient and parameter A for determining the inclined strength of fibres on the fibre pull-out energy, have been studied in detail. The present study provides the necessary information as to which fibre-length distribution, fibre-orientation distribution and interfacial property are required to achieve a desired fibre pull-out energy and hence a desired composite toughness. High-strength fibres, a large fibre-volume fraction and a large fibre diameter for a comparatively large mean fibre length, are shown to be favourable for achieving a high fibre pull-out energy.

The effect of crack orientation on the fracture properties of composite materials

The fracture properties of a composite material reinforced with discontinuous fibers depend on how the fibers are oriented with respect to the crack plane. If the fibers are randomly oriented, their fracture contribution is independent of the crack orientation. In the more usual case, fibers possess a biased-orientation distribution, and fracture properties such as fiber pull-out energy or fiber crack bridging do depend on the crack orientation. Simple methods are given for finding These methods are demonstrated for the pull-out energy of poorly bonded fibers. The results clearly show the variation of pull-out energy with crack orientation. The proposed methods are presented as an “enabling technology”, and are sufficiently general to permit application to other fracture properties.

Mechanism of impact energy absorption for [formula omitted] metal-matrix composites

The impact energy absorbed by fiber pull-out and debonding of carbon-aluminum ( C Al ) metal-matrix composites during the impact process has been investigated by theoretical calculations and experimental verification. The theoretical calculations are basically consistent with the experimental results. A self-made small-scale drop-weight impact transient recording machine was used to study the impact fracture process of composite precursor wires in different interfacial bonding states, and the elastic and plastic impact energies determined from the impact curves. It was found that the plastic energy absorbed in the impact fracture process is basically due to fiber pull-out. A part of the plastic energy may be absorbed by debonding between fiber and matrix, but it is less than about 10% of the fiber pull-out energy. Plastic energy, as well as total impact energy, are closely related with the interfacial bonding strength and can be improved by decreasing the interfacial bonding strength.

Fracture Energy for Short Brittle Fiber/Brittle Matrix Composites With Three-Dimensional Fiber Orientation

Adding brittle fibers to a brittle matrix can create a composite that is substantially tougher than the monolithic matrix by providing mechanisms for energy dissipation during crack propagation. A model based on probabilistic principles has been developed to calculate the increased energy absorption during fracture for a brittle matrix reinforced with very short, poorly bonded fibers. This model, previously developed for planar fiber orientations, is extended to consider the three-dimensional fiber orientations that may occur during composite fabrication. The fiber pull-out energy is assumed to dominate other fracture energy terms, and simple parametric studies are performed to demonstrate the effect of fiber orientation, fiber length, fiber diameter, and fiber-matrix interfacial shear stress. In particular, the fiber orientation effects may be grouped into an effective “orientation parameter.” The model predictions compare satisfactorily with the limited data available, and offer a conceptual framework for considering the effect of changing the physical variables on the fracture energy of the composite.