Fiber Pull-out Mechanism Research Articles

Non-destructive AC impedance spectroscopy (ACIS) analysis to characterize the evolution of impact damage in UHPC

Ultra-high performance concrete (UHPC) widely serves as protection material owing to superior impact resistance. Rapid and effective assessment of impact damage level is crucial for ensuring structural safety. The non-destructive AC impedance responds sensitively to impact-induced microstructural changes, providing important information for understanding the damage development mechanism. Therefore, this paper intends to investigate the feasibility of AC impedance spectroscopy (ACIS) for UHPC impact damage detection. UHPC specimens with different types and volume fractions of steel fibers were prepared, subjected to multiple repetitive low-velocity hammer impacts to induce cumulative damage, and the impedance responses were simultaneously tested in the frequency range of 10 Hz-5 MHz. Additionally, the effects of steel fiber distribution characteristics and pull-out mechanism on the conductive path and impact resistance were explained through microstructural analysis and 3D reconstructed model. The results show that ACIS exhibits a strong correlation with impact damage, where the increment of the imaginary part can be used as an effective and sensitive indicator to achieve whole-process damage assessment. Compared to straight steel fibers, hooked-end and corrugated fibers greatly enhance the impact resistance of UHPC but cause a nonlinear response in impedance due to extracted deformations and orifice complexities. These findings demonstrate the potential application of ACIS for detecting impact damage in UHPC and warrant further investigation.

High-strength TiO2/TPU composite fiber based textiles for organic pollutant removal

Effective integration of nanostructured photocatalysts into polymer matrices is crucial for the broad practical application of fiber-based photocatalytic composite textiles. Herein, highly durable TiO2/TPU composite fibers with high TiO2 content (>30 wt. %) were prepared through wet spinning using 1D electrospun TiO2 nanofibers (TNFs). Due to the fiber reinforcement principle, the TNF/TPU composite fibers exhibited superior mechanical properties compared with pure TPU fibers. Furthermore, the TNF/TPU composite fibers with a ratio of 1:2 process impressive degradation efficiency for rhodamine B (RhB). The orientation of 1D TNFs and stronger interface between TNF and TPU matrices not only enable the excellent load sharing and transfer effects following fiber pullout and crack bridging mechanisms, but also improve photogenerated charge transfer efficiency, resulting in high strength and high photocatalytic activity. In addition, enhanced TNF exposure on the fiber is due to the hollow and porous structures of composite fibers, which is advantageous for photocatalytic degradation. Notably, when the RhB concentration exceeded 15 ppm, the TNF/TPU composite fibers exhibited higher degradation efficiency than the TNF powder. Therefore, TNF/TPU composite fiber–based textiles with high photocatalytic activity and strength are promising for overcoming the separation and recovery issues of nanostructured catalysts in practical wastewater treatment applications.

Investigation of recycled carbon fiber-reinforced ultrafine-grain carbon-matrix composites

To broaden the usefulness of recycled carbon fibers and develop the high value-added product, the recycled carbon fiber-reinforced carbon-matrix composites were prepared using ultrafine-grain coke as a filler and coal tar pitch as a binder via a liquid mixing process. A comprehensive study and investigation of the microstructures and properties of recycled carbon fibers and composites were conducted. It was found that the recycled PAN-based carbon fiber (rPCF) outperformed the recycled rayon-based carbon fiber (rRCF) in terms of fiber integrity and pitch-coated effect in the recycling and forming processes. By relieving thermal stress, lowering stacking pores, and inhibiting the growth of shrinkage pores, the rCF can promote the sintering of the green body. The flexural strength of rPCF-reinforced carbon-matrix composite (30.70 MPa) and rRCF-reinforced carbon-matrix composite (20.75 MPa) increased by 60.6% and 8.6% than that of pristine carbon-matrix composite (19.11 MPa), respectively. The difference in mechanical properties between rPCF-reinforced carbon-matrix composite and rRCF-reinforced carbon-matrix composite is attributed to the mechanical interlock mechanism and fiber pull-out mechanism. This work provides a propagable, affordable, and environment-friendly idea for recycling waste carbon fiber and producing recycled carbon fiber reinforced composites.

Additive manufacturing of high-performance CCF/SiC composites under dual protection

In this work, chopped carbon fibre reinforced silicon carbide (CCF/SiC) composites were fabricated by selective laser sintering (SLS) combined with reaction melt infiltration (RMI), using the SiC interface and pyrolytic carbon layer as a dual protection to protect the CCF from the erosion of molten silicon. The pyrolytic carbon layer encapsulates the CCF@SiC and the outer carbon preferentially reacts with silicon to form a β-SiC layer, which hinders the reaction of liquid silicon to CCF. Moreover, the fine-crystal β-SiC generated by the Si–C reaction optimizes the microstructure and enhances the mechanical performance of CCF/SiC composites. The CCF under the dual protection maintains its original high strength and high modulus, and the toughness of the CCF/SiC composites is significantly improved through the fibre debonding and fibre pull-out mechanism. The bending strength and toughness of CCF/SiC composites are 265.2 MPa and 3.5 MPa m1/2, respectively. The insights gained from this study contribute to a better understanding of microstructural engineering in SLS&RMI-fabricated CCF/SiC composites. This paves the way for future breakthroughs in composite material design and low-cost manufacturing for extreme environments.

Fabrication and compressive performance of novel lightweight C/SiC honeycomb for ultrahigh stability structures

As for high resolution satellite application field, novel C/SiC honeycomb sandwich structure is the first to propose and develop on account of such many attractive properties as excellent ultrahigh dimensional stability in thermal and moisture coupling environment, lightweight and high load-bearing. Three types of C/SiC honeycomb sandwich structures were fabricated for the first time as opto-mechanical structure in satellite. The innovative interlayer-crosslinking method to weave the continuous carbon fiber fabric of honeycomb core was proposed. The compressive properties of novel C/SiC honeycomb sandwich structures were investigated. Meanwhile, the damage mechanism for sandwich structures were analyzed by non-destructive testing. The results showed that the innovative fabrication processing possessed the capability to prepare high quality C/SiC honeycomb, which was shown from the volume and distribution of pores in the X-ray tomography. The compression modulus and strength of the C/SiC honeycomb reached 927 MPa and 10.76 MPa, and showed better rigidity and higher strength compared with classical honeycombs. Two main types of cracks wall were found in the C/SiC honeycomb, i.e., the horizontal ones in the wall with t thickness and the inclined ones in the wall with 2 t thickness. The outstanding compressive performance was attributed to the high mechanical property of ceramic-matrix composite with fiber pull-out mechanism. The exceptional lightweight capacity was inherited from the low bulk density of honeycomb structure ranged from 0.08 g/cm3 to 0.15 g/cm3. This study can help for the development of lightweight materials for opto-mechanical structure in aerospace optical remote sensing technology.

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

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

Mechanical properties and phase-transformation behavior of carbon nanotube-reinforced yttria-stabilized zirconia composites

The mechanical properties and phase transformation behavior of carbon nanotube (CNT) reinforced 3 mol% yttria-stabilized zirconia (3YSZ) composites prepared by spark plasma sintering are reported for CNT contents between 0 and 7 wt%. CNTs are shown to improve the fracture toughness of the material by a combination of fiber pull-out and crack-bridging toughening mechanisms. Stress release by these mechanisms results in a smaller proportion of the YSZ matrix transforming from the tetragonal to monoclinic phase, reducing the microcracking that would otherwise result from cumulative volume expansion associated with this well-known phase transformation process. This produces a material with high fracture toughness without compromising hardness, thereby providing superior mechanical reliability. The high fracture toughness (7.0 MPa∗m1/2) of the 7 wt% CNT/3YSZ composite makes it an attractive material for high-impact, high-temperature applications such as environmental barrier coatings.

Behavior of Non-Shear-Strengthened UHPC Beams under Flexural Loading: Influence of Reinforcement Depth

This study was carried out in order to study the flexural behavior of fiber-reinforced ultra-high-performance concrete (UHPC) containing hybrid microsteel straight fibers and natural fine aggregates under four-point flexural loading. The experimental results revealed that the fiber pullout mechanism had a progressive pullout (collapse) mode. A highly flexural crack developed when the fiber pulling mechanism was explicitly triggered, leading to the failure of most beams. The maximum load in beams reinforced by 1.2, 1.6, and 2.0% exceeded that in beams without longitudinal reinforcement by 56, 73, and 94%, respectively. Further, bar reinforcements at 125, 115, 95, 85, and 75 mm depths led to increases of 56, 55, 73, 96, and 94% in beam load capacity, respectively. In addition, bar reinforcement at 115, 95, 85, and 75 mm depths reduced the beams’ ductility by 40, 23, 35, and 39% compared to those with 125 mm depth. All studied UHPC beams had an uncracked phase that extended to a curvature of about 7.5 × 10−6 rad, which occurred at about 10 kNm. The use of the design of experiments was exploited in this investigation to develop a prediction model for the ultimate moment capacity of UHPC beams. This prediction model took into account the sectional and material properties of UHPC beams. To carry out this analysis, a database of 25 beams, developed by other investigators, as well as the present authors, was utilized. With a mean prediction-to-test ratio of 0.92, this prediction model had a reasonable performance capacity. In turn, this model was used to generate isoresponsive surface contours that could be used for UHPC beam design.

Tiny yet tough: Maximizing the toughness of fiber-reinforced soft composites in the absence of a fiber-fracture mechanism

Tiny yet tough: Maximizing the toughness of fiber-reinforced soft composites in the absence of a fiber-fracture mechanism

Achieving synergy of load-carrying capability and damage tolerance in a ZrB2-SiC composite reinforced through discontinuous carbon fiber

Achieving synergy between load-carrying capability and excellent damage tolerance is one of the most concerned issues in the ultra-high temperature ceramic field. Herein, ZrB2-SiC-Cf composite with homogenous architecture was constructed by a novel pressure filtration and slurry infiltration accompanied by low-temperature hot pressing. The composite exhibited a typical non-brittle fracture feature owing to crack deflection, crack bifurcation and fiber pull-out mechanisms, resulting in a reliable specific flexural strength of 75 MPa/(g/cm3) and superior work of fracture of 672 J/m2.

Creep Mechanisms in Precracked Polypropylene and Steel Fiber–Reinforced Concrete

Recently, fiber-reinforced concrete (FRC) creep behavior has become a much addressed topic, and the main gap found in the literature is whether cracked FRC is stable in the serviceability limit state. Therefore, this work aims to investigate the creep behavior of steel and polypropylene (PP) FRC by analyzing the growth of the crack opening displacement over time in prismatic specimens subjected to sustained bending. Sustained load tests were also performed on FRC constituents and on the fiber matrix interface in order to evaluate individually their long-term response, and to understand their contribution in bending. Based on a model proposed, the rotation in a plastic hinge located in the crack area could be calculated considering the three mechanisms evaluated—fiber pullout, concrete compression, and shrinkage. It could be concluded that the fiber pullout mechanism plays a primary role in creep deformation in precracked elements subjected to sustained bending loads.

Fractographic analysis of scarf repaired carbon/epoxy laminates submitted to tensile strength

This study presents the main fractographic aspects and failure modes involved on the fracture of scarf repaired laminates submitted to tensile test, using scanning electron microscopy (SEM) technique. A detailed analysis of the fractographic aspects was carried out correlating them to the failure modes, the local crack propagation, and the mechanical performance of the scarf joint. SEM analyses showed cohesive failure of the adhesive film associated with a strong mechanical anchoring between the adhesive and the laminate, as well as a good patch ply consolidation on the adhesive interface, showing the joining mechanism efficiency. Fiber pull-out mechanism associated with the translaminar fracture, combined with intralaminar fracture were the predominant failure modes observed in the parent laminate and in the patch repaired region, evidencing the complexity on crack growing in woven fabric composite materials. Fractographic analyses provide evidences that justify the good mechanical behavior of the repaired laminates that is attributed to high interfacial shear strength of the scarf joint and overall good quality of the repair manufacturing process.

Shear behaviors and failure mechanisms of 2D C/SiC pins prepared by chemical vapor infiltration

Connecting and fastening large-scale all-C/SiC airfoils to the fuselage of hypersonic vehicle requires C/SiC fasteners of high-performances under the re-entry environment. In this paper, 2D C/SiC pins prepared by chemical vapor infiltration (CVI) were sheared off to demonstrate their strength sensitivity to the nonuniform microstructures, such as porosity and ply orientation. Results showed that their average shear strengths increase linearly from 85.8 to 134.8 MPa as their average total porosity decreases from 23.2% to 14.5%. The shear strengths of 2D C/SiC pins are almost the same as the in-plane shear strengths of 2D C/SiC composites, under the condition that both have identical total porosity. In contrast, the variances of the pin shear strength are much higher than the in-plane shear strength, which is mainly ascribe to the effects of the loading angle between the shear plane and the ply orientation. The porosity of the 2D C/SiC pin is the main microstructural factor influencing the pin shear strength. Matrix shear cracking, debonding between matrix and fibers, crack deflection along fibers and interlayer sliding are the main shear failure mechanisms. Due to the secondary bending deformation, the interlayer sliding and the corresponding fiber pull-out mechanisms dominate the final ductile fracture behavior.

Impact of hybrid composites based on rubber tyres particles and sugarcane bagasse fibres

The paper describes the impact behaviour of hybrid composites made of sugarcane bagasse fibres and disposed rubber particles. The analysis was carried out using a full factorial design (25) on samples subjected to drop-tower testing. The effects of the bagasse fibre treatment, length and weight fraction were considered, as well as the rubber particles size and their amount. Higher weight fractions of coarse rubber particles led to an enhancement of the absorption. Sustained chemical treatments of the bagasse fibres provided an increase of the composites stiffness, reducing therefore the energy absorption. In contrast, higher energy absorption was obtained in composites made with untreated bagasse because of the enhanced fibre pull-out mechanism.

Hybrid Effect of Twisted Steel and Polyethylene Fibers on the Tensile Performance of Ultra-High-Performance Cementitious Composites.

The hybrid effect of twisted steel (T) fibers with an aspect ratio of 100 and polyethylene (PE) fibers with four different aspect ratios of 400, 600, 900, and 1200 on the mechanical performance of ultra-high-performance cementitious composite (UHPCC) was investigated. This involved a total of 17 different sample types at an identical fiber volume fraction of 2% being made and subjected to compressive and tensile loads. Samples were made by replacing 0.5%, 1.0%, 1.5%, and 2.0% of T fibers with four different types of PE fibers. In addition, the pullout behaviors of fibers at cracked sections and the cracking behaviors of specimens were evaluated in order to determine the effect of the pullout mechanism of each fiber on the overall tensile performance. Test results indicate that the compressive strength decreased in proportion to the amount of PE fibers, regardless of their aspect ratio. The fiber hybridization had a great synergetic effect, successfully improving the tensile strength and strain capacity of UHPCCs; this effect was dependent on the aspect ratio of the PE fibers. Finally, the cracking behaviors were determined to be more related to the fiber type and pullout mechanisms than the tensile strength or strain capacity of UHPCCs.

Effects of glass fiber reinforcement and thermoplastic elastomer blending on the mechanical performance of polylactide

Abstract The purpose of this study was to investigate how optimum mechanical properties (strength-modulus-toughness) of inherently very brittle polylactide (PLA) could be obtained by reinforcing with E-glass fibers (GF) and blending with thermoplastic polyurethane elastomer (TPU). Composites and blends were compounded by twin-screw extruder melt mixing, while specimens were shaped by injection molding. SEM analyses revealed that 15 wt% GF and 10 wt% TPU domains, alone and together, could be uniformly distributed in the PLA matrix leading to significant improvements in properties. Mechanical tests indicated that use of TPU blending alone resulted in enormous increases in the ductility and fracture toughness values, while GF reinforcements led to significant increases in strength and elastic modulus values. When GF and TPU were added together, it was observed that crack deflection, debonding and fiber pull-out toughening mechanisms of GF reinforcements were as effective as the rubber toughening mechanism of TPU blending.

All-cellulose composite laminates prepared from pineapple leaf fibers treated with steam explosion and alkaline treatment

Pineapple leaf fibers with diameters of 43 ± 0.1 µm were treated by two different approaches: the alkaline treatment and the combination of the steam explosion and alkaline treatment. The observations revealed the steam explosion process efficiently provided 3.4 µm diameter fibers with a less amount of lignin and a higher proportion of cellulose, compared with the alkaline-treated fibers. The steam-exploded fibers showed higher crystallinity and more thermal stabilities than the alkaline-treated fibers. No structural change from cellulose I to cellulose II was detected from both treated pineapple leaf fibers. Subsequently, all-cellulose composite laminates were prepared from these two types of treated pineapple leaf fibers mats. The higher tensile strength and modulus were obtained from the steam-exploded pineapple leaf fibers composite laminates due to larger surface areas of the fibers interacted with the cellulose matrix. Fracture morphology of the composites was studied after tensile deformation. The combination mechanism of fiber breakage and fiber pull-out deformation was observed from the steam-exploded pineapple leaf fibers composite laminates, whereas only fiber pull-out mechanism was found from the alkaline-treated pineapple leaf fibers composite laminates. The fiber width and amounts of the matrix filling in pores in a mat were found to dominate the mechanical properties of the all-cellulose composites.

Pull-out behavior of different fibers in geopolymer mortars: effects of alkaline solution concentration and curing

Reinforcing geopolymer materials with fibers can enhance tensile and flexural strengths and fracture toughness. The bond between fiber and geopolymer matrix is a critical factor that needs to be investigated to optimize the performance of the fiber reinforced composite. In this study, single fiber pull-out tests are conducted on steel and polypropylene fibers embedded in geopolymer matrices; in addition, OPC mortars are tested as control condition. The following parameters are investigated: fiber type (i.e. steel and polypropylene) and shape, concentration of alkali solution in the geopolymer matrix, and curing conditions. Bond-slip performance, failure modes, and slip resisting mechanisms of different matrices and fibers are compared and discussed. The fiber deformation ratio, a novel parameter, is introduced to quantitatively investigate the effect of fiber shape on the mortar performance. In case of steel fibers, the geopolymer-fiber composite performs better for lower fiber deformation ratios, where the full fiber pull-out mechanism can be exploited. For higher deformation ratios, the strong bearing forces developed, combined with the high adhesion strength of the geopolymer-steel fiber interface, lead to more brittle failure mechanisms, such as fiber breakage or matrix failure, as observed in end-deformed and length-deformed steel fibers, respectively.

Dynamic analysis of fiber pullout mechanism in cementitious composites under harmonic pullout displacement: analytical approach

Fiber pullout from the concrete matrix is a main characteristic damage mechanism which is observed in cementitious composites, like textile reinforced concrete and fiber reinforced cement composites, and it affects their mechanical behavior under static and dynamic loads. In this paper, an appropriate analytical model of the fiber pullout mechanism is proposed and closed-form analytical solutions are provided under a dynamical excitation of prescribed harmonic pullout displacements at the fiber tip. The constitutive behavior of the matrix-fiber interface is provided by considering the damage behavior, where an elastic damage material model of the interface is employed. For comparison purposes, derived solutions from corresponding Finite-Element simulations of the fiber pullout mechanism are provided and compared with the obtained analytical solutions.

Computational analysis of a sandwich shield with free boundary inserted fabric at high velocity impact

In this paper, a novel hybrid composite shield to protect space structures from hypervelocity impact of micrometeoroid and space debris is proposed. The finite-element model of the proposed shield was constructed and finite-element analysis was conducted to approximate the energy absorption rate. Before the final model analysis, analysis of each component including the aluminum plate (front plate), PMMA plate (rear plate), and intermediate layer of fabric was performed, verifying the finite-element model of each component. The material properties used in the analysis were predicted material property values for high strain rates. The analysis results showed that, other than the fabric, the energy absorption rate of each component was in agreement. Afterwards, the finite-element model of the hybrid composite shield was constructed, where it was analyzed for the constrained and unconstrained fabric boundary condition cases. Through the finite-element analysis, the fiber pullout mechanism was realized for the hybrid shield with free boundary inserted fabric, and it was observed that this mechanism led to energy absorption increase.