Fiber Bridging Research Articles

Characterization and properties of porous red mud–based geopolymer composites reinforced with carbon fiber powders

To obtain porous composites with high porosity and improved performance, porous geopolymer composites (CFP/RMG) were fabricated using alkali-excited red mud and carbon fiber powders (CFPs) using the foaming method. The synergistic effects of CFPs and H2O2 on the microstructure, pore structure, strength, and thermal properties of the porous samples were systematically investigated. CFPs were uniformly distributed on the pore walls of the samples. The total porosity decreased with CFPs and increased with H2O2, the density of CFP/RMG samples ranged from 0.57 ± 0.01 to 1.71 ± 0.05 g/cm3. The compressive strength of the composite samples increased from 0.54 ± 0.09 to 4.16 ± 0.24 MPa with an increase in CFPs from 0 to 12.5 wt%, and it decreased from 4.06 ± 0.23 to 0.47 ± 0.06 MPa with 1–5 wt% H2O2. Fiber bridging and fiber pullout contributed to the strength reinforcement of the whole composite. The porous composites also showed low thermal conductivity (0.176–0.680 W/(m·K)), which revealed that it had potential applications in the field of building materials in the future.

Enhancing interlaminar fracture toughness and shear strength of carbon fiber composite laminates via orientation of nickel-plated short carbon fibers in a magnetic field

This study aimed to enhance the interlaminar mechanical properties of carbon fiber composites by incorporating nickel-plated short carbon fibers (Ni@SCFs) between adjacent layers in a magnetic field. Herein, non-flocked composites, flocked composites with unoriented Ni@SCFs, and flocked composites with oriented Ni@SCFs using a magnetic field were fabricated to investigate the impact of fiber orientation on the mode I interlaminar fracture toughness (GIC) and interlaminar shear strength (ILSS) of the composite laminates. It was observed that Ni@SCFs were distributed at varying vertical angles between adjacent layers under the influence of the magnetic field. The areal density of oriented Ni@SCFs was systematically increased, resulting in notable enhancements in both initiation and propagation of GIC for flocked composites. At a flocking density of 6 g/m2, maximum values reached 533 J/m2 and 769 J/m2 respectively, representing a substantial increase of 52 % and 63 % compared to non-flocked composites. Additionally, the ILSS of flocked composites with oriented Ni@SCFs significantly improved to 55.83 MPa at a flocking density of 2 g/m2, indicating an increase of 27 % over non-flocked composites. The oriented Ni@SCFs played a crucial role in inhibiting crack propagation through the fiber bridging effect.

A semi-analytical method for determining the mode-I delamination R-curve and fiber bridging traction-separation law of Double-double laminates

Delamination, as one of the most prevalent failure modes of composites, was significantly influenced by the interface angles. In contrast to the limited combinations of interface angles found in traditional laminates, DD laminates, with unique sequence [±Φ/±Ψ]rT and diverse interface angles , urgently required extensive experiments and high-precision simulation analyses to delve into the complexities and unique properties of their interlayer performance. However, the calculation process of current method for determining the R-curve and the bridging traction-separation law was time-consuming. This study proposed a simplified semi-analytical method based on the Euler–Bernoulli beam theory that only required recording initial crack length, final crack length, initial compliance and final compliance. The method validation showed that the deviation between the results obtained from the semi-analytical method and the MBT method averaged no more than 2%. In addition, a tri-linear cohesive zone model based on the delamination fracture micro-mechanism was developed combining semi-analytical method. Both the initial load and ultimate load errors between the simulation and experimental results were within 5 N, showing the accuracy of the model and the semi-analytical method. This method provided a simple and effective way to study the delamination propagation behaviors of DD laminates.

Modified mode I fracture toughness calculation method for composite laminate with large scale fiber bridging

Experimental investigation and theoretical analysis have been carried out in this study to assess the application limitation of the current ASTM D5528 method for Mode I fracture toughness calculation of composite laminate with fiber bridging. It is revealed that additional toughening effect introduced by the fiber bridging is not fully considered in the current method and consequently there are uncertainties associated with the fracture toughness calculated by the current ASTM method. Based on the same principle used in the development of the original ASTM method, a modified method is proposed to extend the applicability of the current method. The modified method is verified with mechanisms based cohesive zone modelling and numerical simulations of the Mode I delamination double cantilever beam tests. The significant improvement of the prediction results compared with experimental results by the modified method over the current method demonstrated its applicability for Mode I delamination fracture toughness calculation of composite laminates with large scale fiber bridging.

Enhancing interfacial performance and fracture toughness of carbon fibre reinforced thermoplastic composites

Enhancing the interlaminar fracture toughness of composites significantly improves their load bearing capacity and structural integrity over longer service life by improving their resistance to delamination. The effect of hybrid toughening of Elium-based thermoplastic composites involving polydopamine (PDA), multi-walled carbon nanotubes (MWCNTs) sizing, and polyphenylene sulfide (PPS) veil interlayers was investigated to observe the mechanical response using 3-point bending, interlaminar shear strength, and Mode I fracture toughness tests. The enhancement of fibre–matrix adhesion contributed to improvements in both flexural strength and interlaminar shear strength, while additional toughening mechanisms, such as PDA bridging, PPS pull-out and breakage, and fibre bridging, enhanced the Mode I interlaminar fracture toughness by 218%.

Health monitoring of bonded joints through electrical measurements

The aim of this research work is to explore the possibility of continuously monitoring the presence of damage in bonded joints through electrical measurements. Initially, an analytical model for estimating the crack length based on the electric resistance increase measured across the bond area is presented. The model is successfully validated through finite element analyses and experimental tests on single lap joints made of a conductive adhesive and aluminium or carbon/epoxy adherends. For the last case, the model is extended to account for damage scenarios where a residual conductivity is present across crack faces, due, for instance, to fibre bridging. Eventually, a procedure for predicting the crack length and the stiffness reduction in bonded joint based on electrical measurement is developed.

Enhancement of concrete performance and sustainability through incorporation of diverse waste carpet fibres

Carpet fibres have demonstrated the potential to mitigate early-age cracking and improve tensile properties in concrete. However, a detailed analysis of the varied types of standard carpet fibres in reinforced concrete has been lacking. This study aims to bridge this gap by investigating the performance of concrete reinforced with widely used waste carpet fibres, namely Nylon, Polypropylene, Polytrimethylene terephthalate, and Polyester. The study employs fibres at 0.3 % and 0.5 % volume fractions with a 12 mm length. The research examines mechanical properties, shrinkage and cracking behaviour, pore structure, microstructure, and the ITZ. Results show that 0.3 % fibre volume yielded optimal performance based on GRA analysis. All fibre types reduced shrinkage compared to the control with no fibres. Nylon T1 at 0.3 % achieved a 22.3 % reduction at 90 days. Furthermore, fibre inclusion enhanced flexural and splitting tensile strengths up to 12 % and 39 % respectively due to fibre bridging, pore refinement, and reduced porosity. Notably, individual fibre mechanical properties influenced concrete performance significantly. Hydrophilic fibres exhibited a thinner 10 µm ITZ compared to 15 µm for hydrophobic fibres, contributing to denser interfacial regions and improved bonding. This study demonstrates the potential of carpet fibre-reinforced concrete as a sustainable solution, offering enhanced mechanical properties, shrinkage mitigation, and effective utilization of carpet waste, addressing critical issues in construction and waste management sectors.

Study on interface toughening mechanism based on modified PBO fiber for CFRP/ plastic honeycomb sandwich structure

CFRP (carbon fiber reinforced composites)/honeycomb sandwich structures are widely used in aerospace, automotive, and high-speed rail industries due to their excellent mechanical properties and lightweight characteristics. This study investigates the impact of three designed toughened interfaces on the three-point bending performance of honeycomb structures. The results show that introducing a multiscale toughened interface made of poly(p-phenylene benzobisoxazole) (PBO) fibers grafted with polydopamine (PDA) and multi-walled carbon nanotubes (CNT) increases the peak load and post-peak load of the sandwich structure by 49.7 % and 51.9 %, respectively, and the absorbed energy by 92.4 %. This toughened interface adjusts the stress relationship between the panel, interface, and honeycomb, altering the deformation process and crack propagation mode of the sandwich structure. The micro-nano fibers form fiber bridging at the interface, changing the crack extension mode between the interfaces, transforming the delamination from a single debonding to the combined action of plate core debonding and honeycomb core buckling. Additionally, experimental results show that PBO fibers treated with PDA and CNT exhibit significantly improved surface roughness, Surface area per unit mass, wettability, and tensile strength, which delay and prevent crack propagation at the interface, effectively reducing panel debonding at the bonded joints.

Microstructure evolution and mechanical behavior of foamed cement-based tail backfills under varying fiber types and concentrations.

Industrial solid waste (mine tailings) management has emerged as the key universal ecological challenge as a result of the unceasing creation of rising waste by-products. Employing tailings makes mine fill production economical and assists resolve disposal problems. Foamed cement-based tailings backfill (FCTB) is a mine fill consisting of tailing, cement, water, and foaming agents. It provides certain advantages such as lightweight, good fluidity, and thermal insulation yet is relatively weak in strength. Additionally, FCTB's strength properties can be intensely improved by adding fibers. A total of three diverse fibers: polypropylene (PP), glass (G), and basalt (B) as well as dodecyltrimethylammonium bromide (DTAB) as a foaming agent were used to prepare fiber-reinforced foamed cementitious tailings backfill (FR-FCTB). The mechanical properties, energy evolution, ductility, and microstructure of FR-FCTB were elaborately investigated by uniaxial compression tests (UCS) and SEM. Laboratory findings demonstrate the reinforcing effect of three fibers on FCTB specimens: glass > polypropylene > basalt. FR-FCTB showed the best strength features as a fiber content of 0.3% was adopted in FCTB. At this time, the UCS performance of glass fiber-reinforced FCTBs was 0.85MPa increased by 18.1%. The addition of fibers can increase the fill's energy storage limit, slow down the discharge of elastic strain energy within the backfill, and enhance the fill's ductility and toughness. The ductility factor evaluates the degree of deterioration of filling in terms of post-peak drop, with all FR-FCTB values being greater than CTB. FR-FCTB's chief hydration product is the C-S-H gel. Fiber's bridging effect significantly rallies crack extension and thus fill's strength features. Lastly, the study's main results are instructive for the industrial application of FR-FCTB used in metallic mines.

Hybrid fiber reinforced ultra-high performance coal gangue geopolymer concrete (UHPGC): Mechanical properties, enhancement mechanism, carbon emission and economic analysis

The low carbonization of ultra-high performance concrete (UHPC) has become a hot topic for sustainable development in the construction industry. Calcined coal gangue was used as aggregate and binder to prepare ultra-high performance coal gangue geopolymer concrete (UHPGC) in this paper. The hybrid reinforcement effect of steel fibers, calcium carbonate whiskers (CW), and carbon nanotubes (CNTs) on UHPGC was studied in the experiment. The results indicated that when the mixing ratio of straight steel fibers and hooked-end steel fibers was 2:1, the 28 d-compressive strength of UHPGC reached 145.94 MPa. However, excessive hooked-end steel fibers deteriorated the reinforcement effect of adjacent fibers and reduced the mechanical properties of UHPGC. CW and CNTs had a more significant improvement in the flexural properties of UHPGC. The bridging effect of CNTs and CW dispersed the stress on the matrix and delayed the formation and development of micro-nano cracks. Meanwhile, CNTs and CW improved the fiber bridging energy dissipation, thereby improving the flexural properties of UHPGC. The UHPGC had the highest flexural strength and flexural deflection of 13.59 MPa and 4.12 mm, respectively. The UHPGC prepared in this paper had lower carbon emissions and economic costs compared to traditional UHPC. Overall, this study provided valuable references for the resource utilization of coal gangue and the multi-scale strengthening and toughening of UHPGC.

CDPM2F: A damage-plasticity approach for modelling the failure of strain hardening cementitious composites

For the use of micro-mechanics based constitutive models for fibre reinforced strain hardening cementitious composites in finite element simulations of structural components, it is required to link the crack opening at the scale of fibres to the cracking strain at the scale of structural components. We aim to establish this link by incorporating a micro-mechanics based fibre bridging stress crack opening law into a macroscopic damage-plasticity approach, which we call CDPM2F. The model is implemented in the open-source finite element program OOFEM. The model produces mesh-insensitive results and its response agrees well with experimental results for failure in tension, shear and compression reported in the literature.

Unveiling the impact of short fibre reinforcement and extrusion properties on microstructure of 3D printed polycarbonate composites

In the evolving realm of additive manufacturing, this study investigates the microstructural and mechanical implications of short fibre reinforcement within Polycarbonate (PC) composites fabricated via material extrusion (MEX). The research specifically examines the roles of extrusion temperature, extrusion multiplier and fibre content on void content and fibre alignment, with a focus on their influence on inter-bead strength and overall print quality. Through a combination of high-resolution micro-CT scanning and mechanical testing, the study reveals that an increase in the extrusion multiplier significantly enhances fibre-bridging up to 47 % and inter-bead adhesion up to 237 % depending on the fibre content. It also traces an optimal fibre content threshold that maximizes benefits of fibre bridging, thereby bolstering the mechanical properties of the material. The comprehensive analysis demonstrates that precise control over the extrusion parameters as well as filament quality are crucial for exploiting the full potential of fibre reinforcement in 3D printed structures. This research advances our understanding of MEX in fabricating short fibre-reinforced composites, offering novel insights for tailoring material properties to meet the demands of high-performance applications.

Bond behavior between highly ductile fiber-reinforced concrete (HDC) and deformed rebar under repeated and post-repeated monotonic loading

This paper tested nine groups of six specimens each to investigate the bond behavior between deformed steel reinforcing bars and highly ductile fiber-reinforced concrete (HDC) under repeated and post-repeated monotonic loading considering different compressive strengths, flexural toughnesses, fiber volume contents and cover thicknesses. The results indicate that fiber bridging of cracks allowed the bonds in the HDC specimens to exhibit more ductile failure mode and greater energy dissipation capacity than those in conventional concrete. Furthermore, an increase in compressive strength or cover thickness improved the bond strength, whereas excessive flexural toughness was detrimental to further improvement in the bond strength and energy dissipation capacity. Finally, the residual bond strength increased by 95.03 % as the fiber volume content increased from 1 % to 2 %. Specimens with insufficient flexural toughness and cover thickness exhibited the deterioration in their bond strength and residual bond strength, with the former degrading more than the latter. After repeated loading, the stiffness of the primary ascending branch of the monotonic bond stress–slip curve significantly increased, whereas that of descending branch generally decreased. These results were applied to derive an equation for the bond strength between deformed bars and the HDC in which they are embedded under post-repeated monotonic loading.

The Effect of Chopped Carbon Fibers on the Mechanical Properties and Fracture Toughness of 3D-Printed PLA Parts: An Experimental and Simulation Study

The incorporation of fiber reinforcements into polymer matrices has emerged as an effective strategy to enhance the mechanical properties of composites. This study investigated the tensile and fracture behavior of 3D-printed polylactic acid (PLA) composites reinforced with chopped carbon fibers (CCFs) through experimental characterization and finite element analysis (FEA). Composite samples with varying CCF orientations (0°, 0°/90°, +45°/−45°, and 0°/+45°/−45°/90°) were fabricated via fused filament fabrication (FFF) and subjected to tensile and single-edge notched bend (SENB) tests. The experimental results revealed a significant improvement in tensile strength, elastic modulus, and fracture toughness compared to unreinforced PLA. The 0°/+45°/90° orientation exhibited a 3.6% increase in tensile strength, while the +45°/−45° orientation displayed a 29.9% enhancement in elastic modulus and a 29.9% improvement in fracture toughness (259.12 MPa) relative to neat PLA (199.34 MPa√m). An inverse correlation between tensile strength and fracture toughness was observed, attributed to mechanisms such as crack deflection, fiber bridging, and fiber pull-out facilitated by multi-directional fiber orientations. FEA simulations incorporating a transversely isotropic material model and the J-integral approach were conducted using Abaqus, accurately predicting fracture toughness trends with a maximum discrepancy of 8% compared to experimental data. Fractographic analysis elucidated the strengthening mechanisms, highlighting the potential of tailoring CCF orientation to optimize mechanical performance for structural applications.

Reconstruction and prediction of Mode-I cohesive law using artificial neural network

Cohesive zone model (CZM) is a widely used tool for simulating both static and fatigue damage propagation for bonded area in composite materials. Under static loading, the damage propagation behavior is governed by a cohesive law (CL), the shape of which is an important property especially when non-linear damage mechanisms such as fiber bridging is involved. In this work, a CZM driven by artificially neural network (ANN) for simulating mode-I damage propagation is proposed, where the traction-separation relationship is calculated by a multi-layer perceptron (MLP). More importantly, a reconstruction method is proposed to extract the CL through the training of the neural network using a simple load-displacement (P–U) relation of a double cantilever beam (DCB) as the only inputs, without the need to measure the crack opening displacement (COD). The proposed method is first validated using finite element generated virtual experimental data with various CL shapes before being applied to experimental data, where good correlations are obtained, proving the effectiveness of the proposed method.

Optimizing the Tensile Strength of Weld Lines in Glass Fiber Composite Injection Molding.

Weld line defects, commonly occurring during the plastic product manufacturing process, are caused by the merging of two opposing streams of molten plastic. The presence of weld lines harms the product's aesthetic appeal and durability. This study uses artificial neural networks to forecast the ultimate tensile strength of a PA6 composite incorporating 30% glass fibers (GFs). Data were collected from tensile strength tests and the technical parameters of injection molding. The packing pressure factor is the one that significantly affects the tensile strength value. The melt temperature has a significant impact on the product's strength as well. In contrast, the filling time factor has less impact than other factors. According to the scanning electron microscope result, the smooth fracture surface indicates the weld line area's high brittleness. Fiber bridging across the weld line area is evident in numerous fractured GF pieces on the fracture surface, which enhances this area. Tensile strength values vary based on the injection parameters, from 65.51 MPa to 73.19 MPa. In addition, the experimental data comprise the outcomes of the artificial neural networks (ANNs), with the maximum relative variation being only 4.63%. The results could improve the PA6 reinforced with 30% GF injection molding procedure with weld lines. In further research, mold temperature improvement should be considered an exemplary method for enhancing the weld line strength.

Experimental study and analytical modeling of tensile performance of ultra-high-performance concrete incorporating modified recycled aggregates

Incorporating recycled aggregates (RA) into Ultra-High-Performance Concrete (UHPC) is pivotal for the sustainable development of high-performance construction materials. This study investigates the enhancement of RA through two methods: low-concentration acid treatment and sodium silicate treatment, focusing on improving physical properties and microstructural integrity. Experimental designs encompassed varying types of modified RA (URA, T1RA, T2RA), RA replacement rates (0%, 25%, 50%, 100%), and two steel fiber shapes (SSF and HSF), resulting in twenty-one distinct axial tensile specimen formulations. The study reveals substantial improvements in modified RA's physical properties, effectively mitigating internal microcracks and pores. Modified RA significantly bolstered UHPC-RA's tensile strength, notably when chemically strengthened, underscoring its efficacy in enhancing RA quality. However, escalating RA content correlated with diminished mechanical indices like tensile strength and toughness, attributed to reduced specimen quality. Digital Image Correlation (DIC) accurately forecasted crack locations, highlighting the minimal influence of modified RA and fiber bridging on specimen failure modes. A comprehensive theoretical model incorporating RA deterioration and hooked steel fiber anchorage predicted tensile behaviour, offering vital insights for designing UHPC-RA systems.

The effect of fiber bridging on mode I fatigue delamination propagation—Part II: Cohesive zone model

AbstractThis is Part II of a series of two papers in which the effect of fiber bridging on fatigue delamination propagation is assessed. In Part I, unidirectional double cantilever beam specimens composed of the carbon fiber‐reinforced polymer prepreg AS4/8552 were tested by means of fatigue cycling. Fiber bridging in beam specimens composed of unidirectional plies causes the apparent fatigue delamination curves to exhibit growth which is slower than that for the case when fiber bridging does not occur. Generally, fiber bridging does not occur in laminate structures. In Part II of this study, a cohesive zone model (CZM) is developed and used to carry out finite element analyses to simulate the experiments. The CZM is employed to quantify and eliminate the contribution of fiber bridging to the fatigue delamination growth curves. In this way, more realistic results are obtained. These results are compared to an upper bound curve determined in Part I.

Effects of nano-silica on fracture properties and mechanism analysis of basalt fiber reinforced concrete

The reinforcing effect of basalt fibers (BFs) on the performance of concrete mainly relies on the bridging effect of fibers, while recently, it has been shown that nano-silica (NS) may further enhance this effect. In this paper, three-point bending fracture tests were carried out on BF reinforced concrete (BFRC) to determine the optimal BF condition (i.e. volume content and length). Based on this optimal condition, the effect of NS content on the fracture performance of BFRC was examined from macroscopic and microscopic perspectives. The results indicate that the optimal BF condition for yielding the best concrete performance was 0.2 % volume content and 6 mm fiber length. Based on this condition, NS at 1 % mass content could improve its fracture performance to the best extent. Specifically, the crack initiation toughness, unstable fracture toughness and fracture energy were 1.83 MPa·m0.5, 3.35 MPa·m0.5 and 364.42 N/m, respectively, which were improved by 5.58 %, 15.93 % and 4.97 % compared to BFRC. NS mainly affects the crack propagation mode of BFRC by enhancing the fiber bridging effect or altering the way BFs play a bridging role. NS at an appropriate mass content can delay the occurrence of cracks and improve the deformation ability of BFRC.

Fracture and multiple-cracking modelling of strain-hardening cementitious composites

Strain-hardening cementitious composites (SHCC), composed of short fibres embedded within brittle matrix, exhibit distinctive pre-peak strain-hardening characteristics and remarkable tensile ductility. The fracture and failure process of SHCC, involving both hardening and softening stages as a result of matrix multiple micro-cracking and strain localization, is highly complex and poses a significant challenge for numerical modelling. In the present paper, a novel numerical framework, characterized by the bi-layer superposed cohesive zone strategy, is developed for the numerical modelling of fracture and multiple cracking of SHCC, at both the material scale and structural scale. The developed model is based on diffused cohesive interface model, but with adaptions to consider fibre bridging mechanism. The crack interface is simulated by two cohesive elements sharing the same nodes: one for the matrix-cohesion effect and the other for the fibre-bridging effect. Cohesive constitutive relations of matrix cohesion and fibre bridging are carefully assigned. The proposed model is first validated on the material scale through a uniaxial tension test. With the aid of a random material field, multiple-cracking phenomenon and stress fluctuation are successfully predicted by the model. The model is then applied to the structural fracture modelling, where four case studies, including both pure mode I and mixed mode fracture, are performed. The size effect and boundary effect on the fracture behaviour are well captured by the numerical modelling. The model proposed in the current work has the potential to be extended to the multiple cracking modelling of other materials.