Fiber Pull-out Mechanism Research Articles

EFFECT OF NANOSILICA CONTENT ON LONGITUDINAL AND TRANSVERSE TENSILE PROPERTIES OF UNIDIRECTIONAL KENAF COMPOSITE

Nowadays, continuous natural fibre reinforced polymer nanocomposites have attracted substantial attention among researchers due to various benefits possesses by the natural fibres. Kenaf fibre has become one of the high potential candidates to replace synthetic fibres in polymer composite. Kenaf fibre exhibits good strength and modulus properties, low density, non-abrasive during processing and biodegradable. This study is aimed to evaluate the effect of nanosilica on longitudinal and transverse tensile properties of unidirectional (UD) kenaf composite. The UD kenaf composite samples were prepared based on three different nanosilica content; i.e. 5, 13 and 25 wt.%. The samples were prepared using filament winding and vacuum bagging techniques. The 0o and 90o tensile tests were conducted in accordance to ASTM standard D3039 in order to obtain longitudinal and transverse tensile properties of unmodified and nanosilica-modified kenaf composites. The fracture surfaces of the specimens were observed using scanning electron microscope in order to identify fracture mechanisms involved during tension. The results showed that the addition of nanosilica reduced longitudinal tensile Young’s modulus, strength and failure strain of the kenaf composite. SEM micrographs revealed incomplete resin wetting and fibre pull-out mechanism at high nanosilica content that contributed to premature failure of the kenaf composites. However, it was found that the addition of nanosilica improved transverse tensile properties of kenaf composites since these properties were mostly governed by the properties of the matrix. A stiffer matrix improved the transverse tensile modulus and strength of kenaf composites.

Injection Molded Sustainable Biocomposites From Poly(butylene succinate) Bioplastic and Perennial Grass

Biocomposites from poly(butylene succinate) (PBS) and perennial grass (miscanthus fibers) were successfully prepared by extrusion and injection molding methods with different fiber loadings. The tensile strength of uncompatibilized PBS/miscanthus composites was much lower compared to that of neat PBS. Unlike tensile strength, the flexural and impact strengths were significantly enhanced after incorporation of miscanthus fibers into the PBS matrix. The enhanced flexural strength was attributed to the reinforcing effect of miscathus fibers. The fiber pull-out mechanism is likely responsible for the observed impact strength improvement. Addition of 5 wt % maleic anhydride (MAH) grafted PBS (MAH-g-PBS) into PBS composites showed a significant improvement in tensile and flexural strength compared to the corresponding uncompatibilized composites and neat matrix. For example, the PBS composites with 50 wt % miscanthus fiber and 5 wt % MAH-g-PBS resulted in 22, 139, and 47% improvements in tensile, flexural, and ...

The effects of SiC precursors on the microstructures and mechanical properties of SiCf/SiC composites prepared via polymer impregnation and pyrolysis process

SiCf/SiC ceramic matrix composites (CMC) are considered to be promising candidates for potential structural and functional usages in several strategic engineering applications. In the current work, SiCf/SiC were fabricated by seven repeated polymer impregnation and pyrolysis (PIP) cycles using three types of polycarbosilane (PCS) precursors. SMP-10 had the highest ceramic yield of 81.7% and the lowest melting temperature (room temperature). The CMC prepared using these precursors had high relative density and strength. Due to the fiber pull-out mechanism during fracture, the stress–strain curves displayed a jagged failure behavior. The maximum four-point bending strength of 305MPa was obtained from the CMC made with the NaBond precursor. Several pieces of evidence were provided to reveal the strength deterioration of the NaBond-CMC material at 1500°C in Ar atmosphere.

Enhanced tensile properties of aluminium matrix composites reinforced with graphene encapsulated SiC nanoparticles

Due to a high propensity of nano-particles to agglomerate, making aluminium matrix composites with a uniform dispersion of the nano-particles using liquid routes is an exceptionally difficult task. In this study, an innovative approach was utilised to prevent agglomeration of nano-particle by encapsulating SiC nano-particles using graphene sheets during ball milling. Subsequently, the milled mixture was incorporated into A356 molten alloy using non-contact ultrasonic vibration method. Two different shapes for graphene sheets were characterised using HRTEM, including onion-like shells encapsulating SiC particles and disk-shaped graphene nanosheets. This resulted in 45% and 84% improvement in yield strength and tensile ductility, respectively. The former was ascribed to the Orowan strengthening mechanism, while the latter is due primarily to the fiber pull-out mechanism, brought about by the alteration of the solidification mechanism from particle pushing to particle engulfment during solidification as a consequence of high thermal conductive graphene sheets encapsulating SiC particles.

Mechanical Properties of Natural Jute Fabric/Jute Mat Fiber Reinforced Polymer Matrix Hybrid Composites

Recycled needle punched jute fiber mats as a first natural fiber reinforcement system and these jute mats used as a core needle punched with recycled jute fabric cloths as skin layers as a second natural fiber reinforcement system were used for unsaturated polyester matrix composites via modifying the hand lay-up technique with resin preimpregnation into the jute fiber in vacuum. The effect of skin jute fabric on the tensile and bending properties of jute mat composites was investigated for different fiber weight contents. Moreover, the notch sensitivity of these composites was also compared by using the characteristic distance d o calculated by Finite Element Method (FEM). The results showed that the tensile and flexural properties of jute mat composites increased by increasing the fiber weight content and by adding the jute fabric as skin layers. On the other hand, by adding the skins, the characteristic distance decreased and, therefore, the notch sensitivity of the composites increased. The fracture behavior investigated by SEM showed that extensive fiber pull-out mechanism was revealed at the tension side of jute mat composites under the bending load and by adding the jute cloth, the failure mode of jute mat was changed to fiber bridge mechanism.

비구속 삽입된 직물 섬유를 이용한 샌드위치 쉴드의 초고속 충격 해석

본 연구에서는 우주 파편들과의 초고속 충돌로부터 우주 구조물을 보호하기 위한 새로운 하이브리드 복합재료 쉴드가 제안되었다. 제안된 쉴드의 유한요소 모델을 구성하고, 에너지 흡수율을 예측하기 위해서 유한 요소 해석을 수행하였다. 최종모델의 해석에 앞서 각 구성 요소인 알루미늄 판, PMMA 판 그리고 중간층인 직물 섬유의 해석이 먼저 수행되었으며, 각 요소의 유한요소 모델의 타당성이 검증되었다. 해석에 사용된 재료 물성은 고 변형률 속도에서의 재료 물성들을 예측하여 사용하였으며, 해석 결과 개별 요소의 에너지 흡수율이 직물섬유를 제외하고는 잘 맞음을 확인하였다. 이후 하이브리드 복합재료 쉴드의 유한 요소 모델을 구성하였고, 직물섬유의 구속 조건을 고정과 비 구속의 두 가지로 나누어 해석을 수행하여 비교하였다. 이를 통해서 비구속 삽입된 섬유를 이용한 하이브리드 쉴드가 섬유 풀아웃 현상이 잘 구현되었고, 이로 인해 에너지 흡수율이 향상 될 수 있음을 최종 확인하였다. 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, PMMA plate, and intermediate layer of fabric was performed, verifying the finite element model of each component. The material properties used in the analyses 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 restrained and unrestrained 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.

High Performance Fiber Reinforced Cement Composites with Innovative Slip Hardending Twisted Steel Fibers

This paper provides a brief summary of the performance of an innovative slip hardening twisted steel fiber in comparison with other fibers including straight steel smooth fiber, high strength steel hooked fiber, SPECTRA (high molecular weight polyethylene) fiber and PVA fiber. First the pull-out of a single fiber is compared under static loading conditions, and slip ratesensitivity is evaluated. The unique large slip capacity of T-fiber during pullout is based on its untwisting fiber pullout mechanism, which leads to high equivalent bond strength and composites with high ductility. Due to this large slip capacity a smaller amount of T-fibers is needed to obtain strain hardening tensile behavior of fiber reinforced cementitious composites. Second, the performance of different composites using T-fibers and other fibers subjected to tensile and flexural loadings is described and compared. Third, strain rate effect on the behavior of composites reinforced with different types and amounts of fibers is presented to clarify the potential application of HPFRCC for seismic, impact and blast loadings.

Optimized toughness of short fiber-based composites: The effect of fiber diameter

The effect of fiber diameter change on the toughness of short fiber polymer-based composites is studied by assuming that the main energy absorption upon fracture is the fiber pull-out mechanism. An expression is derived for a characteristic fiber length, ℓ ∗ , distinct from the critical length, above which an increase in fiber diameter always yields an increase in composite toughness. Experimental validation is provided through impact testing of composites made of short polyethylene terephthalate fibers in a polypropylene matrix.

To Study the Effect of Surface Roughness and Embedded Length in Steel-Polyester Composite

Fabrication properties are strongly influenced by the proportions and properties of matrix and reinforcements. The chemical and strength characteristics of the interface between fibers and matrix are particularly important in determining the properties of the composites. The interfacial bond strength has to be sufficient for a load to be transferred from the matrix to the fibers if the composite is to be stronger. To get good interfacial bonding surface treatment, chemical method and temperature must be considered. To study the interface/interphase, it was primarily decided to prepare and test a pull-out specimen. The pull-out test was carried out for different specimens to study the effect of fiber surface roughness and embedded length of the fiber. It was carried out for different specimens, and the pattern of load v/s displacement pattern was observed. One or more peaks in the ascending part of the curve were found which shows that the debonding process is stepwise for steel polyester composite. The CAD/FEA tool was used to simulate a fiber pull-out mechanism, and the results obtained had a deviation of 5% to 8% with the experimental displacements.

Load–deflection performance of partially prestressed concrete T-beams with steel fibres in partial and full depth

A total of twelve partially prestressed concrete T-beams were cast without and with fibres in partial and full depth. These beams were tested to assess the effect of fibre addition in different zones in the cross-section, namely, flange, web or the entire cross-section, on the load–deflection performance of the flexure critical beam specimens. An attempt has been made to predict the load–deflection characteristics of the beam specimens utilising the tension softening effects in the stress–strain behaviour of fibre-reinforced concrete. The proposed model accounts for the interaction of the matrix with the fibre pull-out mechanism. The details of the constitutive material properties used and the proposed layer-based analysis are presented in this paper. Comparisons with test data show good agreement.

Effect of Microstructure on the Tensile and Fracture Properties of Sisal Fiber/Starch-based Composites

In this study, the effect of microstructure on the tensile and fracture properties of injection molded biocomposites consisting of starch-based matrix and short sisal fibers has been investigated. Tensile tests are carried out on samples cut in longitudinal (L) and transverse (T) directions with respect to the melt flow direction. An increasing trend in Young’s modulus and tensile strength with fiber content is found, irrespective of the sample orientation. In addition, this reinforcing effect is more pronounced for L samples with many fibers mainly oriented longitudinally to the loading direction. Quasistatic fracture tests are also performed on SENB specimens with cracks propagating both parallel and perpendicular to the melt flow direction. The stress intensity factor is found to increase with fiber content, and it also depends on fiber orientation. The observed trend in fracture toughness with fiber content and microstructure is explained in terms of the fiber pullout mechanism. Puncture tests are carried out for all compositions. Injection molded composites exhibit higher values of total fracture energy than neat matrix. Furthermore, fiber orientation induces different patterns in the damage zone. Finally, several theoretical models are used in this study to predict the elastic properties of these composites.

The role of interfacial interactions on the mechanical properties of banana fibre reinforced phenol formaldehyde composites

Banana fibre has been modified with silane treatments, acetylation, cyanoethylation, latex treatment and mercerization to improve the interfacial bonding with phenol formaldehyde (PF) resin. Scanning electron microscopy was used to study the morphology of the banana fibre. The tensile properties of the modified fibre were compared with the untreated fibre and it was found that the tensile strength and modulus of the fibre were decreased by all the treatments except cyanoethylation. Tensile, flexural and impact performance of phenol formaldehyde composites reinforced with various treated fibres were analyzed and compared with that of untreated fibre composite. The tensile and flexural properties of the fibre-reinforced composites were found to be increased by all the modifications except latex coating. Incorporation of heat-treated, vinyl silane-treated and acetylated fibre-reinforced PF composites was found to have higher impact strength than that of untreated fibre/compsites. The tensile fractographs of the composites were studied by scanning electron microscopy to analyze the fibre/matrix interaction, fibre pull-out and fracture mechanism of the composites.

Micro-mechanical approximation to the stress field around an inclined fiber of FRCC

Matrix spalling or crushing is one of the important mechanisms of fiber-matrix interaction of fiber reinforced cementitious composites (FRCC). The fiber pullout mechanisms have been extensively studied for an aligned fiber but matrix failure is rarely investigated since it is thought not to be a major affect. However, for an inclined fiber, the matrix failure should not be neglected. Due to the complex process of matrix spalling, experimental investigation and analytical study of this mechanism are rarely found in literature. In this paper, it is assumed that the load transfer is concentrated within the short length of the inclined fiber from the exit point towards anchored end and follows the exponential law. The Mindlin formulation is employed to calculate the 3D stress field. The simulation gives much information about this field. The 3D approximation of the stress state around an inclined fiber helps to qualitatively understand the mechanism of matrix failure. Finally, a spalling criterion is proposed by which matrix spalling occurs only when the stress in a certain volume, rather than the stress at a small point, exceeds the material strength. This implies some local stress redistribution after first yield. The stress redistribution results in more energy input and higher load bearing capacity of the matrix. In accordance with this hypothesis, the evolution of matrix spalling is demonstrated. The accurate prediction of matrix spalling needs the careful determination of the parameters in this model. This is the work of further study.

Computer Modeling and FEA Simulation for Composite Single Fiber Pull-Out

Using state-of-the-art computer-aided technologies, particularly CAD and integrated CAD/FEA technique to model and simulate the composite, the single-fiber pull-out problem is presented. The capability and effectiveness of using enabled CAD to generate solid modeling based composite fiber/matrix heterogeneous assembly and its application with the seamless integration of CAD/FEA to simulate fiber pull-out mechanisms and effects of material and geometric variation on stresses in fiber and matrix are demonstrated. The CAD/FEA model predictions are compared with an analytical solution. Parametric studies of fiber pull-out problems with different stiffness ratios of fiber and matrix, and with irregular fiber cross-sections, for which solutions are difficult to obtain analytically, are also presented.

Fiber pullout processes and mechanisms of a carbon fiber reinforced silicon nitride ceramic composite

Details of fiber pullout processes and mechanisms are addressed for a carbon fiber reinforced silicon nitride ceramic composite. The energy for fiber pullout, γpo, is experimentally measured by the work-of-fracture technique using test specimens with a circumferential notch. A precise determination of the distribution of pullout fibers combined with the experimental results of the pullout energy provides an important insight into the micromechanical processes and mechanisms of the composite fracture. Various energy dissipation processes associated with the composite fracture, the frictional interface shear stress, the Weibull modulus of the reinforcing fibers, and composite designs for improved toughening are discussed.

The role of fiber morphology on the creep behavior of discontinuous-fiber-reinforced composites

The role of the geometrical parameters of the fibers and effects of fiber distribution in the matrix on the creep deformation behavior of 20% discontinuous-fiber-reinforced composite were numerically investigated, including the debonding and fiber pull-out mechanisms. During the analyses, it is assumed that the matrix deforms with a power-law creep relationship and the fibers are rigid. The debonding behavior at the interface was stimulated in terms of a cohesive zone model which describes the decohesion by both normal and tangential separation. The results indicate that, for a given fiber geometry and distribution parameters in the matrix, an increase in the interfacial strength or an increase in the work of separation per unit area of interface reduces the creep rates. For even very weak interface characteristics, it is possible to achieve lower creep rates and delayed interface failure by suitable selection of the geometrical parameters of fibers and by controlling the distribution of fibers in the matrix. The role of applied stress direction and formation of a more ductile phase between the fibers and the matrix in the overall creep behavior were also elucidated.

Micromechanical model of crack growth in fiber-reinforced ceramics

A model based on the micromechanical mechanism of crack growth resistance in fiber-reinforced ceramics is presented. The formulation of the model is based on the small-scale geometry of a macrocrack with a bridging zone, in this case the process zone, which governs the resistance mechanism. The effect of a high toughness of the fibers on the retardation of the crack advance, and the significance of the fiber pullout mechanism on the crack growth resistance, are reflected in this model. The model allows one to address such issues as the influence of fiber spacing, fiber flexibility, and fiber—matrix friction. Two approaches were used. One represents fracture initiation and concentrates on the development of the first microcrack between fibers. An exact closed-form solution has been obtained for this case. The second case deals with the development of an array of microcracks between fibers forming the bridging zone. An implicit exact solution is formed for this case. In both cases, a discrete fiber distribution is incorporated into the solution.

Influence of Fiber and Interfacial Properties on Fracture Behavior of Fiber‐Reinforced Ceramic Composites

The fracture and fracture resistance behaviors of zirconmatrix composites uniaxially reinforced with either uncoated or BN‐coated silicon carbide fibers are studied by performing experiments in three‐point flexure and by analyzing results analytically using a cohesive crack model that incorporates crack bridging and fiber pullout mechanisms. A comparison of experimental results with the model predictions demonstrates good agreement. This analytical approach is then used in a parametrical study to demonstrate the role of fiber and fiber‐matrix interfacial properties on the mechanical behavior of fiber‐reinforced ceramic‐matrix composites. Material parameters that enhance ultimate strength and ductility or toughness are elucidated.

The mechanism of fiber—matrix interactions in carbon—carbon composites

The condition of the carbon fiber surface is of great importance in determing the mechanical properties of a carbon—carbon (CC) composite. The presence of functional groups on the fiber surface and roughness of the surface control to a great extent the tensile strength, fracture toughness and interlaminar shear strength. A compromise has to be made between a weak interfacial bond which improves fracture toughness by the debonding and fiber pull-out mechanism, but results in a low tensile strength and a strong interfacial bonding which leads to a catastrophic failure. Thus fiber—matric interactions have to be studied in order to determine the correlation between the conditions of the carbon fiber surface and the mechanical properties of C-C composites. This paper demonstrates the use of surface treatments and de-treatments to optimize the mechanical properties of C-C composites. Oxygen plasma and nitric acid treatments were used to introduce the surface functional groups and to alter the surface morphology. An argon plasma de-treatment was used to reduce the surface functionality. A correlation between the carbon surface modifications and the mechanical properties of C-C composites is discussed with the emphasis on the fundamental understanding of the fiber-matrix interactions.

Micromechanical Model of Crack Growth in Fiber Reinforced Brittle Materials

AbstractA model based on the micromechanical mechanism of crack growth resistance in fiber reinforced brittle matrix composites is presented. The formulation of the model is based on a small scale geometry of a macrocrack with a bridging zone, in this case the process zone, which governs the resistance mechanism. The effect of high toughness of the fibers in retardation of the crack advance, and the significance of the fiber pullout mechanism on the crack growth resistance, are reflected in this model. The model allows one to address issues such as influence of the fiber spacing and fiber-matrix friction.Two specific cases are analyzed. One represents the fracture initiation and concentrates on the development of the first microcrack between fibers. The second case deals with the development of an array of microcracks forming the bridging zone. In both cases a discrete fiber distribution is assumed. The analysis is based on an exact solution of the corresponding. boundary value problem.