Fiber Debonding Research Articles

Pengaruh Fraksi Massa Serat Terhadap Kekuatan Fatik Material Komposit Berpenguat Serat Tandan Kosong Kelapa Sawit

The present study was investigated the effect of fiber mass fraction on the tensile and fatigue strength of oil palm fiber reinforced composite and resin as the matrix. Fatigue test has been performed by using rotary bending fatigue machine. The specimens were made by press hand lay-up with matrix to fiber mass ratio was 90:10, 80:20 and 70:30 respectively. Fracture surface of fatigue specimens have also been observed by using digital camera to knowing the failure mode. The results showed that the tensile and fatigue strength and fatigue life increased with increasing the fiber mass fraction as seen in the S-N curve. The fatigue limit was found 0.27 MPa, 0.55 MPa, and 0.82 MPa for composites with 90:10, 80:20 and 70:30 of matrix to fiber mass ratio respectively. The observed failure modes were matrix cracking, fiber debonding, and fiber breaking.

Consistent application of periodic boundary conditions in implicit and explicit finite element simulations of damage in composites

This paper presents an implementation-dedicated analysis of Periodic Boundary Conditions (PBCs) for Finite Element (FE) models incorporating highly non-linear effects due to plasticity and damage. This research addresses fiber-reinforced composite materials modeled at micros-scale level using a Representative Volume Element (RVE), where its overall mechanical response is obtained via homogenization techniques. For the sake of clearness, a unidirectional ply with randomly distributed fibers RVE model is assumed. PBCs are implemented for implicit and explicit FE solvers, where conformal and non-conformal meshes can be used. The influence of applying PBCs in the reliability of the mechanical response under tension and shear loading is assessed. Furthermore, the Poisson effect and the consistency of damage and fiber debonding propagation through the periodic boundaries are reported as well as their impact on the homogenized results. Likewise, numerical aspects like computational performance and accuracy are evaluated comparing implicit- versus explicit-based solutions.

Interfacial Compatibility Evaluation on the Fiber Treatment in the Typha Fiber Reinforced Epoxy Composites and Their Effect on the Chemical and Mechanical Properties.

Natural fiber composites have been widely used for various applications such as automotive components, aircraft components and sports equipment. Among the natural fibers Typha spp have gained considerable attention to replace synthetic fibers due to their unique nature. The untreated and alkali-treated fibers treated in different durations were dried under the sun for 4 h prior to the fabrication of Typha fiber reinforced epoxy composites. The chemical structure and crystallinity index of composites were examined via FT-IR and XRD respectively. The tensile, flexural and impact tests were conducted to investigate the effect of the alkali treated Typha fibers on the epoxy composite. From the microscopy analysis, it was observed that the fracture mechanism of the composite was due to the fiber and matrix debonding, fiber pull out from the matrix, and fiber damage. The tensile, flexural and impact strength of the Typha fiber reinforced epoxy composite were increased after 5% alkaline immersion compared to untreated Typha fiber composite. From these results, it can be concluded that the alkali treatment on Typha fiber could improve the interfacial compatibility between epoxy resin and Typha fiber, which resulted in the better mechanical properties and made the composite more hydrophobic. So far there is no comprehensive report about Typha fiber reinforcing epoxy composite, investigating the effect of the alkali treatment duration on the interfacial compatibility, and their effect on chemical and mechanical of Typha fiber reinforced composite, which plays a vital role to provide the overall mechanical performance to the composite.

Seawater ageing effect on the mechanical properties of composites with different fiber and matrix types

The use of fiber-reinforced composites in marine applications such as components of tidal turbines and wave energy converters is becoming attractive because of their reduced weight and improved corrosion resistance. However, when these polymer matrix composite structures are exposed to seawater environment, degradation of material properties is produced affecting reliability. A deep understating of seawater ageing effect on composite structures is essential to ensure long-term performance and durability. A systematic investigation was conducted in this work to evaluate the effect of seawater ageing on mechanical properties of five different composites manufactured with two types of fiber fabrics (unidirectional glass and carbon) and three types of resin systems (epoxy, vinylester and polyester). The behavior of samples with and without accelerated seawater ageing and subjected to tensile, compressive, flexural and shear loading was evaluated. A significant strength reduction due to seawater ageing was observed on composites with epoxy and polyester matrices. Low strength and stiffness values of composites with vinylester matrix are in general observed; however, seawater ageing makes these properties increase slightly. Fracture surface examination by scanning electron microscopy revealed delamination, fiber debonding and resin crumbling due to seawater effect.

Investigation of the tensile performance and failure mechanism of carbon–aramid hybrid fibers/epoxy sandwich structure laminates using the UV-thermal synergetic curing mechanism: Experimentation and simulation

The tensile failure mechanism of carbon–aramid hybrid fibers/epoxy sandwich structure laminates was investigated by using experimental and finite element methods. Double curing agents, triarylsulfonium hexafluoroantimonates and triethylene tetramine with a mass ratio of 4:15 were introduced into the laminates. Sandwich structure laminates, with different proportions of hybrid fibers, were cured by UV-initiated anion/cationic dual curing technique. The results showed that the synergetic curing effects of two curing agents were observed under UV irradiation, leading to the better curing of the system, which further plays a positive influence on the mechanical performance. The tensile properties and failure mechanism of the laminates depended on the stacking sequence and fiber volume fractions of the layer structures. The interplay hybrid laminates, containing three alternate plies with fiber contents of 67.7 vol%, presented the optimal tensile performance, and its tensile strength and modulus were 0.82 GPa and 22.09 GPa, respectively. The fracture morphologies revealed that pull-out and debonding of fibers were the main failure mechanism of hybrid laminates. The performance of sandwich structure laminates was determined by the load-carrying capacity of carbon fiber and load-transferring capacity of the aramid fiber and adhesive. The finite element model based on experiments was established to simulate the stress state and failure mechanism of sandwich laminates. The results demonstrated that the stress was better transferred into carbon fibers from the aramid fibers and adhesive, and the relative error rate of maximum stress from finite element analysis and experimental results was less than 5%, which were in reasonable agreement with the experimental results.

Tensile loading rate effect on mechanical properties and failure mechanisms in open-hole carbon fiber reinforced polymer composites by acoustic emission approach

In this article, the effect of the tensile loading rate has been investigated on mechanical properties and failure mechanisms in open-hole carbon fiber reinforced polymer composites. For this objective, acoustic emission signals on standard specimens under tensile loading were acquired and analyzed by the wavelet packet transform (WPT) and the fuzzy C-Means (FCM) methods. Tensile tests were also performed on pure resin, pure fiber and composite samples, at different loading rates. Obtained results showed that by increasing the tensile loading rate, the maximum stress increased and the maximum strain decreased, in open-hole composite specimens. The frequency range of failure mechanisms including matrix cracking, the fiber breakage and debonding of fibers from the matrix was 100–250 kHz, 420–500 kHz and 250–420 kHz, respectively. In addition, debonding was the dominant failure mechanism in both WPT and FCM methods. Such results were also verified by scanning electron microscopy images.

Stress corrosion cracking and brittle failure in a fiber-reinforced plastic (FRP) insulator from a 400 kV transmission line in humid environment

Abstract A fiber-reinforced plastic (FRP) suspension insulator belonging to the Israel Electric Corporation (IECo) failed catastrophically on a 400 kV transmission line during service at the humid south Israeli coastline. The failure occurred during the summer of 2016 after 15 years of service. The suspension had a declared life expectancy of 30 years. The failure resulted in a local outage at a high cost. An investigation was commissioned. The insulator includes a FRP rod with a housing and weather-sheds made of silicon rubber (SiR); the FRP rod is fitted into a metal connector at its end. The fracture occurred 30–40 mm above the metal fitting/grading ring area near the first weather-shed. Macroscopically, the fracture surface was partially characterized by the features of brittle fracture mode in FRP, while the rest of the fracture surface featured severe fiber pullout and debonding. It was also possible to observe that a large crack in the SiR housing led directly to the fracture surface area that included stained and crushed fibers. EDS analysis revealed that the housing around the crack and the stained fibers themselves were polluted with a significant amount of nitrogen, in addition to other foreign pollutants. After surveying similar cases, it was strongly suggested that the source of nitrogen was nitric acid formed as a result of corona discharges on the insulator's surface. The acid caused the housing, fiber and resin to undergo corrosion. SEM imaging revealed fiber fracture surfaces with a morphology typical of stress corrosion cracking, showing that stress was part of the failure mechanism. The fracture of fibers and loss of resin led to a decrease in FRP rod strength and to failure.

Dynamic crack propagation from a circular defect in a unidirectional carbon fiber reinforced plastic composite

A single-ply unidirectional IM7/8552 carbon fiber reinforced plastic composite with artificially introduced circular defects is subjected to dynamic tensile loading using a modified Kolsky tension bar. A high-speed X-ray phase contrast imaging method is integrated with the Kolsky bar setup to record the crack initiation from the defects and subsequent propagation in the material in real time during the tensile loading. The tensile loading was applied either in longitudinal (0° to fibers) or transverse (90° to fibers) direction of the specimens. Shear failure of the matrix and axial splitting along the loading/fiber direction were observed in longitudinal specimens to initiate from the edge of the artificial circular defects. Debonding of fiber and matrix was observed in transverse specimens, which initiated from the top and bottom edge of the hole. The dynamic tensile loading history during the crack propagation was recorded using a piezoelectric load cell and synchronized with the observed damage and failure processes.

Mode I and mode II delamination of a chopped strand mat E-glass reinforced vinyl ester composite

ABSTRACTThe objective of the present work is to investigate mode I and mode II delamination behaviour of chopped strand mat (CSM) E-glass reinforced vinyl ester (VE) composite. Double cantilever beam and end notched flexure tests were carried out to evaluate the mode I and mode II delamination, respectively. The fracture toughnesses were calculated using the experimental calibration method. Results showed that the average mode I and mode II fracture toughnesses were 185 and 2386 N m−1, respectively. Furthermore, the mode II–mode I ratio for this material was 12.9. This value was the highest when compared with other composite materials from the literature. Finally, through scanning electron micrographs, the dominant failure mechanisms were found to be matrix cracking, fibre debonding and fibre breakage. In addition, shear cusps were observed in mode II specimen, which signified the shearing between the layers.

Modeling on temperature-dependent first matrix cracking stress for fiber reinforced ceramics considering fiber debonding and residual thermal stress

The combined effects of temperature, fiber debonding and residual thermal stress on the first matrix cracking stress for fiber reinforced ceramic matrix composites were investigated. We analyzed the temperature-dependent stress fields in the fiber and matrix by using the modified shear-lag model, and developed a temperature-dependent interface debonding criterion. Then, based on the energy balance approach, a temperature-dependent first matrix cracking stress model considering the effects of fiber debonding and residual thermal stress was established. The model predictions were compared with the available experimental results, which shows good agreement between the theoretical predictions and experimental results. Moreover, the quantitative effects of fiber volume fraction, interface debonded energy and interface frictional shear stress on the first matrix cracking stress and fiber debonding length were analyzed in detail at different temperatures. This work not only helps understand the matrix cracking behavior of fiber reinforced ceramic matrix composites with general interfacial properties at high temperatures, but also provides a guidance for the material design.

Investigation of interfacial strength parameters in polymer matrix composites: Compatibility and reproducibility

Effects of various geometrical and physical factors, as well as the method of data reduction (analysis of experimental forceedisplacement curves) on the values of local interfacial strength parameters (local IFSS, td, and critical energy release rate, Gic) determined by means of a single fiber pull-out test are discussed. Experimental results of our pull-out tests on several fiberepolymer matrix systems showed that td and Gic weakly depended on geometrical factors. However, the pull-out test appeared to be sensitive to the conditions of specimen formation and testing, such as changing the nature of the contacting surfaces (fiber sizing) and the fiber pull-out rate. Of several methods of td and Gic Determination from a forceedisplacement curve, the most reliable and reproducible one is the approach based on the values of the maximum force recorded in a pull-out test and the interfacial frictional force immediately after fiber debonding.

An evaluation of damage development for CFRTP by conventional tows and spread tows using acoustic emission

Comparison of damage development of textile composites made by combination of two resin (Polyamide and Epoxy) and two kinds of fiber bundles (conventional tows and spread tows) is carried out. The quasi-static tensile tests were carried out with using DIC (digital image correlation) system to estimate the full field strain and AE (acoustic emission) sensors for measurement of the acoustic emission features. The CFRTP specimens were also investigated with optical microscope to clarify the difference of damage. Fig.1 shows characteristic damage of each CFRTP. The fiber debonding and delamination were shown in CF(with spread tows)/PA composites and the damage in weft yarn covered a wide range of test specimens. It is suggested that these features of damage were influenced with effect of fiber opening. This may also be explained by AE events. In weft yarn of CF(with conventional tows)/PA composites, we observed not only transverse crack but also clack which propagated parallel to loading direction. This type of crack was not found in other thermoplastic carbon composites such as CF/PPS described in the literature. From these results, we conclude that the damage development of textile composites is sensitive to the form of fiber bundles and the properties of the matrix.

In-plane mechanical behavior and failure mode of a 2D-SiC/SiC composite under uniaxial dynamic compression

Dynamic and quasi-static in-plane compression failure process of a 2D-SiC/SiC composite were explored in this paper. Specular Reflection Method (SRM) was introduced to capture the real-time high-resolution images of the SiC/SiC composite in tests. The fracture surfaces of the subject composite under dynamic and quasi-static loading show different angles with loading direction. Dynamic fracture surface results showed a larger angle with the loading direction, with fiber breakage without debonding. However, in the quasi-static tests fracture surface showed a small angle with the loading direction, with fiber debonding and fiber bundle buckling. Scanning electron microscope (SEM) characterization of fragments obtained after experiments were used to characterize the deformation mechanisms of the 2D-SiC/SiC composite. Although both shear deformation and delamination were found under quasi-static and dynamic loading, shear deformation dominated the failure process of specimens during dynamic compression. Two microscopic fracture modes were concluded from the failure process of quasi-static and dynamic loadings. The strength of the fiber-matrix interface significantly influenced the fracture modes. Finally, an effort was made to simulate the dynamic failure process of SiC/SiC composite using the topological structure of a full-size specimen.

Modeling matrix multicracking development of fiber‐reinforced ceramic‐matrix composites considering fiber debonding

AbstractIn this paper, the effect of fiber debonding on matrix multicracking development of different fiber‐reinforced CMCs is investigated using the micromechanical approach. The Budiansky–Hutchinson–Evans shear‐lag model is adopted to analyze the fiber and matrix stress distributions of the damaged composite. The fracture mechanics approach is used to determine the fiber/matrix interface debonding length. Combining the critical matrix strain energy criterion and fracture mechanics fiber/matrix interface debonding criterion, the stress‐dependent matrix multicracking development is analyzed for different fiber volume fraction, fiber/matrix interface properties and matrix cracking characteristic stress. The experimental matrix multicracking development of unidirectional C/Si3N4, SiC/Si3N4, SiC/CAS, SiC/CAS‐II, SiC/SiC, SiC/Borosilicate and mini‐SiC/SiC composites are predicted.

Clustering effect on damage mechanisms in open-hole laminated carbon/epoxy composite under constant tensile loading rate, using acoustic emission

In the present research, damage mechanisms in the open-hole laminated carbon/epoxy composite have been investigated using the acoustic emission method. For such objective, standard specimens, made of the pure resin, the pure fiber and composites, were tested under tensile conditions, at a constant loading rate. Then, the clustering effect was studied in order to know which damages (debonding, fiber pull-out, delamination, matrix cracking and fiber breakage defects) occurred in the material. For the analysis of acoustic emission signals, wavelet packet transform and fuzzy C-means methods were applied to data. Obtained results indicated that the frequency range for matrix cracking, the fiber breakage, the fiber pull-out, debonding of fibers from the matrix and the delamination was obtained as 100–250 kHz, 420–500 kHz, 250–320 kHz, 320–380 kHz and 380–420 kHz, respectively. Scanning electron microscopy images showed that the dominant damage was qualitatively related to debonding, the fiber pull-out and the delamination, which had a proper agreement with obtained results from the analysis of acoustic emission signals.

Influence of SiC fiber on thermal cycling lifetime of SiC fibers /YSZ thermal barrier coatings by atmospheric plasma spraying

The initiation and propagation of cracks under thermal stresses easily is one of the problems limiting the thermal cycling lifetime of thermal barrier coatings (TBCs). In order to improve the thermal cycling lifetime, SiC fibers were introduced to yttria stabilized zirconia (YSZ) coating deposited on In738LC substrate by atmospheric plasma spray (APS). Phase composition, thermal cycling behaviors and fiber toughening mechanisms of coatings were systematically investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal cycling test. Results showed that the thermal cycling lifetime and fracture toughness of SiC fibers/YSZ coatings could reach 442 ± 13 and 1.54 ± 0.19 MPa m respectively, which were 1.6 times and 1.3 times higher than that of conventional TBCs. There are two stages of fiber reinforced during thermal cycling, and the first is crack deflection and termination, the second is fiber debonding, pull-out, breakage and bridging. Meanwhile, SiC fibers could prevent the stress-activated ZrO2 martensitic transformation by reducing the stress in the lattice.

Prediction of fatigue limit for unidirectional carbon fibre/epoxy composites

A micromechanics model is used for the prediction of the fatigue limit of unidirectional carbon fibre/epoxy composite materials. The model is based on the hypothesis that failure of a fibre will result in fibre/matrix debonding of the broken fibre. The associated debond crack tip stress fields will raise the stress in the neighbour fibres as the debond crack tips move along the broken fibre and can thus cause failure of the neighbouring fibres. The fatigue limit is defined from the maximum applied cyclic stress that does not induce failure of any neighbour fibres. Effects of microscale mechanical properties are investigated. The model predicts that the fatigue limit, expressed in terms of stress, increases with fibre volume fraction until 50-60 %, whereafter the fatigue limit decreases with increasing fibre volume fraction. With other parameters held fixed, the fatigue limit increases with increasing interfacial frictional sliding shear stress and with decreasing interfacial fracture energy.

Synthesis of Heterocyclic Aramid Fiber Based on Solid‐Phase Cross‐Linking of Oligomers with Reactive End Group

AbstractLow compressive strength of aramid fiber is one of the major obstacles for its application in advanced composite materials. In this study, poly‐(benzimidazole‐terephthalamide) (PABI) fibers are fabricated by solid‐phase cross‐linking of corresponding oligomers end‐capped with norbornene anhydride (NA). Concentration of the spinning solution increases and apparent viscosity is reduced significantly through this method, which improves its processability. Reactivity and thermal stability of the NA group are measured by in situ Fourier transform infrared (FTIR) and thermogravimetric analysis and it shows high reactivity at 360 °C and adequate thermal stability under 400 °C. Results of solubility test and dynamic mechanical analysis indicate cross‐linking degree increases with decrease of molecular weight of the corresponding oligomer. Results of both 2D wide angle X‐ray diffraction and polarized FTIR illustrate orientation will be affected by cross‐linking and it decreases with the increase of cross‐linking degree. PABI fibers fabricated through this method can maintain outstanding mechanical properties and compressive strength is improved by 67% at most. Interestingly, interfacial shear strength of PABI fibers is improved by nearly 20% and damage between skin–core layers after debonding of fiber and resin is not observed.

Thermal and Mechanical Properties of Bamboo Fiber Reinforced Epoxy Composites.

Bamboo fibers demonstrate enormous potential as the reinforcement phase in composite materials. In this study, in order to find suitable NaOH concentration for bamboo fiber treatment, bamboo fibers were treated with 2 wt.%, 6 wt.% and 10 wt.% NaOH solutions for 12 h, respectively. We determined that 6 wt.% NaOH treated bamboo fibers were optimal for the fabrication of bamboo fiber composites by single fiber tensile test, single fiber pull-out test, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The short length bamboo fibers treated with 6 wt.% NaOH solutions were well dispersed in the epoxy matrix by a new preparation method. The effect of fiber content and fiber length on the mechanical behavior of bamboo fiber reinforced epoxy composites was investigated. The results confirmed that fracture toughness and flexural modulus of the composites monotonically increased with fiber length and content. However, for all samples, composites showed negligible difference on the flexural strength. The fracture surfaces of the composites were observed by SEM, revealing that fiber breakage, matrix cracking, debonding, and fiber pull out were major failure types. In addition, thermogravimetric analysis (TGA) was carried out to investigate the thermal behavior of both bamboo fibers and composites.

Characterization of concrete matrix/steel fiber de-bonding in an SFRC beam: Principal component analysis and k-mean algorithm for clustering AE data

Steel fibers have been used in concrete structures to increase the tensile strength and ductility of concrete. Fibers bridging cracks reduce micro cracking and improve post-cracking strength in concrete. Propagation of damage in a fiber reinforced concrete member occurs by concrete matrix cracking and widening of these cracks, which is accompanied by de-bonding of steel fibers from the concrete matrix. Fiber de-bonding is the main factor affecting the post-peak behavior of these members. Therefore, distinguishing the matrix cracking and fiber de-bonding mechanisms is important in nondestructive structural health monitoring methods. This study is focused on characterizing steel fiber/matrix de-bonding events apart from concrete matrix cracking sources in acoustic emission (AE) method. Two reinforced concrete beams, one of which included steel fibers within the concrete matrix, were tested under three point bending and monitored by AE. Afterwards, Principal Component Analysis (PCA) was applied to AE data and the failure mechanisms were clustered for characterization of steel fiber/matrix de-bonding. Finally, different AE features of these clusters were evaluated and applicable AE parameter distributions, which are useful to clarify steel fiber de-bonding mechanisms, were revealed.