Fiber Pull-out Research Articles

Large deformation of cable networks with fiber sliding as a second-order cone programming

A new model for irreversible large deformations of fiber networks is developed. The fibers are considered as inextensible cables that slide relative to each other in the frictional junctions. This sliding is constituted by a rate-independent flow rule. The nonsmooth dissipation potential for each sliding system is defined as a product of the yield strength and the absolute value of the fiber sliding. The response of the cable segments is nonsmooth as well, since it shows asymmetry with respect to tension and compression. A principle of minimum incremental potential and a pure complementary energy principle are derived for the equilibrium incremental loading of the network at large deformations. They form a pair of primal and dual second-order cone programming problems with matching sets of displacement-based and force-based variables. These problems can be effectively solved by interior point methods that have many advantages compared to the gradient-based methods or dynamic relaxation. The model is extended by a simple mechanism of fiber pull-out resulting from fiber sliding at the free unconstrained ends. This can be used for the microstructural analysis of failure of needle-punched nonwoven materials.

Strengthening the fiber-cement matrix interface by introducing functional groups on fiber surface

Polypropylene (PP) fiber is widely used for reinforcing cement matrix to improve its cracking resistance, but the poor interaction between two materials caused localized cracks along the fiber thus adverse effect on the fiber reinforced composites. Thus, novel methods for strengthening the fiber-cement matrix interface were proposed in this study. Amidoxime and amine functional groups were successfully grafted onto PP fiber surface through a two-step chelating procedure. XPS, FTIR, iGC-SEA and TG were employed to characterize the modified fibers, and the results verified that the surface treatment significantly improved the surface roughness, specific surface area, hydrophily and thermostability of PP fiber. Moreover, single fiber pullout, uniaxial tensile and three-point bending were conducted to assess the efficiency of surface treatment in enhancing the bonding between fiber and cement matrix, as well as the tensile and flexural strength of composites incorporating PP fibers. The bonding strength was increased by 84.15%–90.08 % and the flexural strength at 28 days was increased by 23.7%–26.4 %. The change in PP fiber surface led to densified fiber-cement matrix ITZ, enhanced chemical bonding and mechanical interlocking thus stronger interaction between fiber and cement matrix. Overall, the proposed surface treatment method is of great potential to be used in producing high performance concrete due to its easy of application and high efficiency.

Carbon fiber pull-out analysis for composite materials by considering interface properties

ABSTRACT An improved shear-lag model is adopted in this paper to study the fiber pull-out by considering interface properties in a representative volume element (RVE). The surface roughness, represented by grooves distributed around the fiber, is introduced to analyze the influence of roughness on fiber pull-out comparing it with a round fiber. The influence of groove shapes is also discussed. The interfacial stiffness is introduced in the improved shear-lag model by the cohesive zone modeling to simulate a practical interface connection. To represent the residual stress in composites, a pressure load is added on the surface of the RVE to analyze its influence on the fiber pull-out. The results show that the proposed theory can accurately predict the stress distribution in the RVE. Furthermore, the maximum reaction force increases with an improvement in roughness and interfacial stiffness, while the pressure can improve the reaction force in the third stage of fiber pull-out process. The proposed theory can predict the stress field and fiber pull-out process accurately. It can improve the efficiency and effectivity of micro-experiment with the reference of theoretical results. The results obtained using the proposed theory in this research can also be useful for the design and analysis of composite materials.

Experimental analysis of 3D printed continuous carbon/glass hybrid fiber reinforced PLA composites: Revealing synergistic mechanical properties and failure mechanisms

AbstractThis study investigates the mechanical properties of continuous carbon/glass hybrid fiber‐reinforced polylactic acid (PLA) composites (HFRC) produced through the three dimensions (3D) printing process, comparing them with single carbon fiber‐reinforced PLA composites (CFRC). Initially, composite prepreg filaments are prepared using an impregnation device, followed by fabrication using a 3D printer. The mechanical performance results reveal a 13% increase in tensile strength for HFRC compared with CFRC. Due to differing elongation rates of carbon and glass fibers, HFRC exhibits two strength peaks, while CFRC demonstrates a 37% higher bending strength than HFRC. Scanning electron microscope images indicate that the tensile failure mechanism involves fiber brittle fracture and fiber‐matrix interface debonding, while the bending failure mechanism includes fiber pullout, fiber debonding, fiber cluster buckling, and interlayer interface failure.Highlights To realize the moldless rapid manufacturing of continuous hybrid fiber‐reinforced PLA composites. The stress–strain curves of single fiber‐reinforced composites and hybrid fiber‐reinforced composites are obviously different. Elucidating the effect of single fiber/hybrid fiber in composites on mechanical properties and failure mechanism according to micro‐morphology.

Fracture toughness evolution and failure mechanisms of two-dimensional SiCf/SiC composites at temperatures up to 1500 °C in air

Silicon carbide fiber reinforced silicon carbide composites (SiCf/SiC) are of the few most promising materials for high-temperature structural applications. In this study, two-dimensional (2D) plain-woven SiCf/SiC composites were prepared by chemical vapor infiltration process and subjected to single-sided notched beam three-point bending tests from room temperature (RT) to 1500 °C in air. The temperature-dependent bending load–deflection curves and fracture toughness were obtained. The results show that the SiCf/SiC composites exhibit linear deformation characteristics initially, followed by nonlinear deformation behavior which become more pronounced with increasing temperature. The fracture toughness decreases in the range of RT to 1000 °C due to the evolution of components properties, and increases at 1200 °C due to the interface property degradation and fiber pull-out. Above 1200 °C, it decreases with increasing temperature owing to the serious high-temperature oxidation. Further, the failure mechanisms of the 2D plain-woven SiCf/SiC composites at different temperatures was analyzed through macro and micro analysis. The evolution of components properties affected by high temperature and oxidation as well as fiber pull-out play a leading role in fracture toughness of composites. The findings of this study provide important support for the mechanical behavior and failure mechanisms of SiCf/SiC composites at ultra-high temperatures in air.

Cracking of soft collagenous tissues under suture retention

Soft collagenous tissues consist of collagen fibers and soft matrix, such as skin, muscle, and heart valve, etc. Suture of the tissues is ubiquitous in surgery, which may cause fracture of tissues due to inevitably introduced defects. However, the cracking mechanism of soft collagenous tissues under suture retention remains elusive. Herein, we use bovine pericardium as a model tissue to study the suture related fracture considering various fiber orientations. Fracture tests reveal distinct toughness and fracture modes of the tissue depending on the fiber orientation, such as crack propagation and crack deflection. The maximum J-integral criterion has been established to predict the direction of crack propagation in the tissue. We further conduct suture retention test to evaluate the suture resistance of tissues, and find two different failure modes: fracture and cutting. Microscopic examination of the fracture surface demonstrates that the tissue can rupture with long fiber pullout, cut through matrix failure, or cut by a combination of fiber break and pullout. The cohesive element model is used to analyze the cutting mode. The predicted failure modes and force-displacement curves match well with experiments. This paper may provide guidance to surgical operations and benefit new artificial collagenous materials.

Evaluation of Performance of Cotton Fiber Reinforced Epoxy Composites

This experimental study explored the impact of varying weight proportions (5%, 10%, 15%, and 20%) of cotton fiber reinforcement in epoxy composites on compressive strength, Charpy impact strength, and water absorption characteristics. Concurrently, the interfacial properties were examined using Scanning Electron Microscopy (SEM). The inclusion of 15 wt.% cotton fiber notably enhanced compressive strength, displaying consistent improvement as cotton content increased until reaching 15 wt.%. Beyond this point, further increases yielded diminishing enhancements in compressive properties. EC20 demonstrated superior impact strength and energy absorption. Increased cotton concentrations improved impact properties due to the fibrous nature of cotton, enhancing energy dissipation and crack resistance within the epoxy matrix. Higher cotton content correlated with increased water absorption, aligning with cotton’s hydrophilic properties. The EC20 composite exhibited heightened water uptake and permeability, indicating the influence of elevated cotton concentrations. SEM analysis of fracture surfaces identified crucial features such as fiber pull-out, matrix cracking, interfacial debonding, and surface irregularities. These findings contribute significantly to understanding the inherent failure mechanisms in these composite materials.

Silane treatment for sisal fibers to improve the degradation resistance and interface with cement matrix

In order to improve the degradation resistance of sisal fibers in the alkaline cement matrix and enhance the fiber-matrix interface adhesion, silane treatment on fiber was studied. Four kinds of commonly used silane coupling agents were selected to modify the sisal fibers via the simple dip-coating method. Contact angle, water retention, and semi-immersion tests were performed on the sisal fibers to determine the influence of silane treatment on their hydrophilicity and barrier property. The interfacial bonding between the sisal fibers and cement matrix was studied by a self-designed fiber pull-out test. Furthermore, the degradation of sisal fibers embedded in cement matrix and sisal fiber reinforced cementitious composites (SFRCC) was evaluated based on the changes of mechanical properties with accelerated aging. The results indicate that silane treatment is an efficient approach to mitigate the degradation of SFRCC.

Enhanced high-temperature dimensional accuracy by fibers in silica ceramic cores prepared through vat photopolymerization 3D printing

3D printing technology provides new ways to complex-shaped ceramic cores forming inner structures in aero-engine blades, but its high-temperature dimensional accuracy is highly impacted by their volume shrinkage and creep deformation. Silica ceramic cores reinforced by mullite fibers were fabricated by 3D printing in terms of vat photopolymerization in this work. Due to the scraper paving the ceramic slurry in 3D printing, majority of the mullite fibers displayed orientation distribution inside the printing layers and decreased the bending strength as the fiber content was below 5 wt%. With 12.5 wt% of mullite fibers, some fibers showed disorder distribution and arranged to connect the interlayer cracks, therefore improving the strength by fiber pull-out. Even though the reinforcement effect of mullite fibers was inadequate, the porosity and leaching rate were significantly improved. Furthermore, the mullite fibers were beneficial to lower shrinkage during sintering and casting, and enhanced the creep resistance due to the high softening temperature, which resulted in enhanced dimensional accuracy.

Numerical simulation of the effect of projectile shape and size on the high-velocity impact of carbon fiber reinforced composite laminates

To investigate the impact response and damage mechanism of CFRP composite materials for high-speed trains under high-speed impact from foreign objects of different shapes and sizes, high-speed impact experiments and simulations were conducted on CFRP composite laminate at a velocity of 163 m/s. A finite element simulation model was established in Abaqus/Explicit. This model adopts the 3D-Hashin failure criterion considering strain rate effects to simulate the failure of fibers and matrix. Bonded elements with zero thickness were inserted along the fiber direction in the laminate to replicate the damage phenomena of fiber bundle debonding and pull-out. The effectiveness of the finite element model was validated by high-speed photography of the impact process and ultrasonic C-scan damage images recorded during the experiments. Based on this simulation model, the influence of projectiles of different shapes and sizes on the impact response of CFRP composite materials was studied. Projectiles of different shapes exhibit their own characteristics in terms of the time of peak force occurrence, manifestation, and characteristics of laminar damage. The peak force of the cylindrical projectile is 245.01% greater than that of the spherical one, while the conical projectile is 52.26% smaller than the spherical one. When the projectile size increases from 10 mm to 20 mm, the peak force of the spherical projectile, conical projectile, and cylindrical projectile increases by 79.67%, 120.12%, and 283.13% respectively. The total area of delamination in laminated plates is positively correlated with the size of the impacting body.

Measurement of tensile and shear strength of interfacial bonding in fiber reinforced soft composites combining experiments and simulation

Interfacial bonding strength plays a key role in the mechanical performance of fiber reinforced polymers. However, measurement of interfacial bonding strength in fiber reinforced soft composites (FRSCs) becomes a challenging issue, because the large deformation capability of soft matrix invalidates most of current testing methods. This paper demonstrates an advanced method combining experiments and simulation, which provides a convenient and reliable means to measure both tensile strength and shear strength of interfacial bonding for FRSCs. The specimen is made by embedding a fiber bundle in a soft plate for transverse tensile test. Various stress states along the fiber–matrix interface can be realized by controlling the inclination angle of fiber bundle to the stretching direction. Tensile strength and shear strength of interfacial bonding in FRSCs can be estimated based on the analysis of critical stress states. The comparison with the widely adopted fiber pull-out test indicates that the nominal shear strength obtained in pull-out test is severely underestimated.

A Multi-Scale Analysis of Unidirectional Carbon Fiber-Reinforced Polymer Composite

In this paper, a multi-scale computational analysis is conducted based on representative volume element (RVE) modeling and molecular dynamics (MD) simulation of a carbon fiber-reinforced polymer composite micropillar. The fiber distribution in the micropillar was obtained from a specimen manufactured for real micropillar mechanical testing. Based on the failure modes directly observed from the micropillar testing, the RVE model aims to capture the major failure mechanism, which is the fiber/matrix interface failure of the composite. In the finite element model, the properties of each individual phase, namely, the fiber and the matrix are first identified. Then, cohesive elements are incorporated into the interphase region between the fiber and matrix to capture the interphase debonding. Finally, the global stress–strain relation of the composites is obtained and compared to experimental results. A good correlation was found. Due to convergence difficulties associated with stiffness degradation, the simulation was performed in the commercial software ABAQUS/Explicit. A Molecular dynamics simulation is performed to investigate the stress–strain relation and shear strength of carbon fiber-reinforced polymer composites at nanoscale. The compressive strength and stiffness obtained from MD simulation were lower than that observed from experiments. Interface debonding is a critical failure mode, of which the failure strength is determined from fiber pull-out simulation. The results can be used in RVE simulation to deduce the interphase properties. The modeling method allows the detailed failure mechanisms of the composite microstructure to be captured and a correlation between the micro-properties and macro-properties of the material to be established.

Transformation of waste carbon fiber prepreg into sustainable composites: Application in the automotive industry components

AbstractCarbon fiber (CF) prepregs are employed in the manufacture of many different aeronautical structural and non‐structural components. Following the cure of the prepregs in molds, trimming is generally used to give the final shape to the components. Considering the aircraft's vast surface area and the use of multiple prepreg layers in each component, an extensive amount of carbon fiber prepreg is discarded. The unique characteristics of carbon fibers render this CF waste highly valuable and requires its efficient recycling. Cured waste CF prepregs were milled and processed in this research to produce chopped carbon fibers for use in the novel composite development. The matrix material used in the composites was selected as recycled polypropylene sourced from old surgical masks, which highlighted the sustainability of the developed composites. To enhance the quality of the fiber‐matrix interface and improve the impact resistance of the composites an anhydride‐grafted polyethylene (Fusabond) was employed in small quantities. From mechanical characterizations, synergistic effects of the fillers were observed. Besides, compositions containing CF and Fusabond are found more impact resistant than neat matrix. In addition, the use of carbon fibers increased fracture toughness of the matrix through various mechanisms including fiber bridging, fiber pullout, and matrix plastic deformation identified by scanning electron microscopy fractography. Thermomechanical characterizations using dynamic mechanical analysis revealed that carbon fiber raises the neat matrix's glass transition temperature. The developed materials are intended to be employed in the automotive industry to produce inner fender liners, with an optimal composition determined by an optimization research.Highlights Carbon fiber (CF) derived from aerospace fresh scraps significantly improved the mechanical properties of the polymer matrix. Anhydride‐grafted polyethylene incorporation remarkably enhanced the impact resistance of the polymer. CF demonstrated a bridge effect and improved the fracture toughness of the composites. The use of recycled CF presents encouraging prospects in the automotive industry for the production of inner fender liners.

Revealing low temperature-mechanical coupling failure mechanisms in CFRP laminates with in-situ observations

The number of layers and ply orientations determined the service performance of carbon fiber-reinforced polymer (CFRP) materials. Under low-temperature service conditions, the unclear weakening mechanism of mechanical properties of CFRP aggravates the failure risks of aerospace structures. In present work, the unclear correlation between layers with alternating orientations and the tensile-failure mechanisms of CFRP, the low temperature-mechanical coupling micromechanical behavior, and the failure mechanism of CFRP was experimentally revealed by using a horizontal testing instrument integrated with a low-temperature loading module and real-time optical imaging function. Based on various temperatures in a range from −40 °C to room temperature (RT) and two strain rates, the gradually decreasing trends of tensile strength, Young's modulus, and elongation after fracture with decreasing temperature are obtained. Three failure modes including fiber brittle fracture, fiber pull-out, and interface debonding are proposed to reveal the low temperature-mechanical coupling failure mechanism. Low-temperature asynchronous shrinkage of carbon fiber and epoxy resin promoted the transition from fiber brittle fracture to delamination at the interface. The proposed instrument could establish the approximatively actual service conditions involving low temperature and mechanical load.

Response to internal pressure shock and hoop strength of SiCf/SiC cladding

This study investigated the mechanical behavior of silicon carbide fiber-reinforced silicon carbide matrix (SiCf/SiC) cladding using expanding plug tests at 0.5 and 2 mm/min. A three-stage mechanical response for SiCf/SiC was observed, with significant differences in Stage 3 between specimens tested at different rates. Specimens tested at the slower rate (0.5 mm/min) exhibited a characteristic hoop strength of 112.4 MPa and homogeneous destruction behavior, indicative of uniform stress distribution. In contrast, the hoop stress in SiCf/SiC became unsteady at the faster rate (2 mm/min), leading to cracking at a lower nominal proportional limit stress (PLS), structural instability, non-uniform fiber pull-out, and a lower characteristic hoop strength of 92.4 MPa. This suggests that similar phenomena might occur at higher loading rates during internal pressure shock. Therefore, considering the application of SiCf/SiC, to conduct hoop strength testing at faster rates was recommend, such as 2 mm/min.

False banana fiber reinforced geopolymer composite – A novel sustainable material

A new geopolymer composite material was produced using low-calcium fly ash and false banana plant fiber. The effect of fiber content and length on the mechanical and microstructural properties of the resulting composite material was investigated. Results showed that the addition of alkali-treated false banana fiber significantly improved the compressive and splitting tensile strength of the composites. In particular, incorporating a 10 mm length fiber at a 1.4 % volume fraction increased compressive and splitting tensile strength by 31 % and 33 %, respectively, when compared to the pure geopolymer paste specimens. Furthermore, unlike the neat geopolymer paste specimens, all composites failed gracefully. In addition to this, FTIR absorption peaks and SEM micrographs demonstrated that alkali treatment effectively changes fiber morphology and chemical characteristics. Additionally, fiber pull-out, fiber bridging, and fiber fracture were identified as energy-absorbing mechanisms responsible for increasing the mechanical properties of the composites. In general, the results showed that using natural false banana fiber as reinforcement enhances the mechanical properties of geopolymer composites, making them a more environmentally friendly alternative to synthetic fibers in composite production.

Cure Behaviour and Tensile Properties of Pineapple Leaf Fibre Reinforced Natural Rubber Composites

Short natural fibres replace synthetic fibres as filler in natural rubber (NR) as they are environmentally beneficial and sustainable. This study investigates the cure behaviour and tensile properties of pineapple leaf fibre (PALF) reinforced NR composites at various fibre contents. The fibre contents are varied at 0, 10, 20 and 30 parts per hundred rubber (phr). PALF reinforced NR composites are prepared using a two-roll mill. Surface morphology of tensile fractured specimens is examined using scanning electron microscopy (SEM). The results demonstrated that the optimum cure time decreases significantly with greater fibre content. The hardness value increases gradually with increasing filler content. The stress-strain graphs show an increasing trend in stress at higher fibre content particularly at low strain regions. On the contrary, the tensile strength reduces when the fibre content is increased up to 30 phr. SEM analysis reveals that the fibre-matrix adhesion is considerably poor due to the fibre pullout phenomenon observed. It is indicated that higher fibre content could be possibly reinforced to NR to achieve high deformation stress at incredibly low strain regions.

Physicomechanical, water absorption and thermal properties and morphology of Paederia foetida fiber–Al2O3 powder hybrid‐reinforced epoxy composites

AbstractHybridization of natural fibers with ceramic materials for reinforcing composites allows the optimization of the properties of these materials. For this reason, the present study aims to investigate physical, mechanical, water absorption, swelling and thermal properties as well as morphological characteristics of a hybrid Paederia foetida fibers–alumina powder (PFs–Al2O3)‐reinforced epoxy composite. Epoxy resin served as the matrix, while PFs and Al2O3 were employed as reinforcement. Five types of composites were fabricated using the hot‐pressing technique. The corresponding ratios of PFs:Al2O3 volume fractions (%) considered here were 0:40 (SFA), 10:30 (SFB), 20:20 (SFC), 30:10 (SFD) and 40:0 (SFE). The results reveal that the density of the hybrid PFs–Al2O3 composites decreased for increasing volume fractions of PFs: from 2.173 g cm−3 of SFA to 1.042 g cm−3 of SFE. The highest values of tensile strength (i.e. 49.085 MPa), tensile elastic modulus (i.e. 1.431 GPa) and impact strength (24 kJ m−2) were obtained for the SFD composite material with 30% volume fraction of PFs and 10% volume fraction of Al2O3: this happened because interface bonds between PFs, Al2O3 and epoxy phases achieved their optimal configuration. Overall, mechanical properties of the hybrid PFs–Al2O3‐reinforced epoxy composites were superior to those of composites reinforced only by PF fibers or only by Al2O3. Water absorption and swellability reached their maximum values at the steady state occurring after tested samples remained immersed in water for 820 h. The SFE composite reinforced only by PFs presented the highest water absorption and swelling (i.e. 6.034% and 5.81%, respectively) while for all other hybrid composites (SFD, SFC and SFB) these two quantities remained below 5%. Density and volume fraction of voids of hybrid PFs–Al2O3‐reinforced composites were consistent with the corresponding properties of the composites reinforced only by Al2O3 or PFs. SFD was also the most thermally stable material. Scanning electron microscopy observations of fractured surfaces indicated that the microstructure of the PFs–Al2O3‐reinforced epoxy composites presents several voids, fiber pullouts and transverse fibers, which together optimize the mechanical response of the composite material. Remarkably, the SFD composite material was highly competitive with the most recently developed hybrid composites employing natural reinforcements. © 2024 Society of Industrial Chemistry.

Nanohybridization Effects on Impact Behavior of Basalt/Glass Fiber Reinforced Epoxy Hybrid Nanocomposites

Basalt fiber-based composites have received greater attention from manufacturers and researchers recently for use in a variety of structural applications, owing to their high strength-to-weight ratio, high stiffness, and excellent mechanical properties. The main objective of the current research is to examine the impact behavior of hybrid basalt/glass fiber reinforced composites that have been altered by the addition of MWCNTs and SiO2 (Nano silica) to the epoxy matrix as per the ASTM standards. All of the composites were created using Manual lay-up method followed by Compression molding using novel symmetric stacking sequence configurations of B/GG/BB/GG/BB/GG/B fibers with nanoparticles at weight percentages of 0%, 1% (0.5% MWCNTs + 0.5% SiO2) 2% (1% MWCNTs + 1% SiO2) and 3% (1.5 % MWCNTs + 1.5% SiO2). The homogeneous dispersion of nanoparticles in the epoxy matrix was achieved by ultrasonicator and magnetic stirrers. The maximum value of Izod impact strength was recorded as 203 kJ/m2 for the composite filled with 2 wt. % of nano-fillers. In comparison to the composite containing no fillers, the composite adding 2 wt. % showed a 24% improvement from 167 to 203 kJ/m2 in Izod impact resistance. It was observed that increasing the weight percentage of fillers in composites causes insufficient interfacial interaction between the matrix and fibers, thereby decreasing their impact resistance. The load transmission between the matrix and fibers is increased by the presence of MWCNTs/SiO2 at the fiber/matrix interface, which also improves the fracture toughness. According to images obtained by Scanning Electron Microscopy of the fracture surfaces of impact-tested specimens, the major reasons for failure include fiber/matrix deboning, fiber breaking, fiber fracture and fiber pull-out.

Effect of Water Absorption and Stacking Sequences on the Tensile Properties and Damage Mechanisms of Hybrid Polyester/Glass/Jute Composites.

The aim of this work is to analyze the effect of water absorption on the mechanical properties and damage mechanisms of polyester/glass fiber/jute fiber hybrid composites obtained using the compression molding and vacuum-assisted resin transfer molding (VARTM) techniques with different stacking sequences. For this purpose, the mechanical behavior under tensile stress of the samples was evaluated before and after hygrothermal aging at different temperatures: TA, 50 °C, and 70 °C for a period of 696 h. The damage mechanism after the mechanical tests was evaluated using SEM analysis. The results showed a tendency for the mechanical properties of the composites to decrease with exposure to an aqueous ambient, regardless of the molding technique used to conform the composites. It was also observed that the stacking sequence had no significant influence on the dry composites. However, exposure to the aqueous ambient led to a reduction in mechanical properties, both for the molding technique and the stacking sequence. Damage such as delamination, fiber pull-out, fiber/matrix detachment, voids, and matrix removal were observed in the composites in the SEM analyses.