Fiber Debonding Research Articles

Improving mechanical, thermal, and erosive wear performance of natural bamboo fibers modified epoxy resin matrix composites

Natural bamboo fibers (BFs), which were treated by silane coupling agents, reinforced epoxy resin (EP)–based composite were synthesized. Effects of the coupling agents on the chemical structures of the BFs were characterized by Fourier Transform Infrared Spectroscopy. The mechanical properties, such as tensile strength, flexural strength, impact strength, and hardness of the BFs/EP-based composites were improved significantly, which could be attributed to the excellent strengthening effect of the BFs. Simultaneously, experimental investigations on the thermal behaviors of the BFs/epoxy composites were also presented, indicating that the thermal decomposition temperature of the polymer materials was lowered but the flame retardancy was improved. The bamboo fiber breakage and fiber split were also observed on the impact fracture surface of the composites, which indicate energy dissipation during fiber debonding and pullout process. Moreover, the erosive wear tests have also been carried out to analyze the erosive wear properties of the natural bamboo fibers which modified the epoxy matrix composites. The results indicate that the erosive wear resistance of the EP-based composite was improved greatly when the natural bamboo fibers content was 15 wt.%.

Effects of dynamic fibre failure in unidirectional composites

The stress redistribution around a broken fibre is a substantial issue in longitudinal strength analysis of unidirectional (UD) composites. Most investigated models are based on a regular fibre packings and classical shear lag theory (static failure) that considers pre-broken fibers, where the dynamic aspects of brittle fiber failure are not considered. In the present work, Representative Volume Elements with random fibre packings were modeled by means of 3D finite element analysis, and simulated considering the event of dynamic fibre failure. Significant effects were observed on the stress concentration factor (SCF) and ineffective load length which are related to the fibre debonding length and the volume of matrix damage-plasticity zones. Hence, it can be concluded that an accurate representation of the stress redistribution after a fibre breakage event requires consideration of dynamic effects.

LaPO4 coating on alumina-based fiber: Strength retention of fiber and improvement of interfacial performances

The characteristics of the interface are the key factors that determine the mechanical properties and fracture behavior of fiber-reinforced ceramic matrix composites. Design and preparation of coatings which can preserve fiber strength and maintain appropriate interfacial bonding strength are of great challenges. LaPO4 coating is a promising weak interface coating for oxide fiber reinforced oxide ceramic matrix composites. Through this coating, the toughening mechanism of the composite such as fiber pulling out and fiber debonding is triggered. The LaPO4 coating was deposited on the surface of alumina-based fibers by a solution precursor heterogeneous precipitation method. The effects of different precursors and different deposition temperatures on fiber strength were studied, and the mechanism of the strength degradation of the coated fiber was analyzed. It was found that the fibers coated with phytic acid precursor and deposited at 90 °C had the highest tensile strength compared to other coated fibers. The retention of strength is attributed to its loosely stacked coating. Besides, a single fiber pullout test was carried out to evaluate the effect of the coating on the interface of the composites. The results show that the composites coated by depositing citric acid precursor and phytic acid precursor at 90 °C can reduce the interfacial bonding strength by 32.5% and 46.7%, respectively compared to uncoated composites. This study has potential application value in the preparation of ceramic matrix composites used in oxidation and high temperature environments.

Influence of Cenosphere on Compression After Impact Strength of Glass Epoxy Laminates

Under controlled lab settings, two distinct laminates, one containing cenosphere and the other with neat resin, were evaluated for impact strength using a Fractovis impact machine, compression, and Compression After Impact (CAI) strengths through Tinus Olsen UTM. The GFRP laminates were prepared with 16 layers of glass fiber combined with epoxy resin reinforced Cenospheres at concentrations of 1, 3 and 5 wt%, according to ASTM specifications. The dominant failure mode controlling the specimen’s compression ultimate load resistance, and other failure modes of impacted specimens such like fiber pull-out and debonding, were found to be the effects of delamination using coupled coustic emission (AE) monitoring and compression tests. On specimens with a 3 wt% filler additive, there was a noticeable increase in strength. Both impacted and non-impacted samples exhibited significant compression ultimate load resistances, with the 3 wt% filler impregnated specimen having the maximum.

Mechanical properties of unidirectional laminated hybrid SiC–Nextel™ 720 fiber-reinforced oxide matrix composites fabricated by a novel precursor infiltration and pyrolysis method

Unidirectional laminated hybrid SiC–Nextel™ 720 fiber-reinforced yttria-stabilized zirconia–mullite composites were fabricated by a novel precursor infiltration and pyrolysis method. The effect of annealing atmosphere (Ar and air) at 1200 °C on the mechanical properties and failure mechanism of the composites was investigated. The Ar-annealed composite had a superior flexural strength of 337.1 ± 5.7 MPa and a good fracture toughness of 13.3 ± 0.1 MPa m1/2, and exhibited non-brittle failure behavior. However, the Air-annealed composite had a poor flexural strength of 102.8 ± 0.8 MPa and a low fracture toughness of 5.3 ± 0.3 MPa m1/2, and it exhibited brittle failure behavior. Further analysis indicated that the presence of a considerable amount of residual carbon in the Ar-annealed composite effectively weakened the fiber/matrix interface by reducing the residual radial compressive stress and the interfacial coefficient of friction. The weak interface could trigger toughening mechanisms in the composite, such as fiber pullout and debonding, and crack deflection. The mechanical degradation of the Air-annealed composite was also associated with the slight damage of Nextel™ 720 and the oxidation of SiC fibers after exposure in a high-temperature air environment. The findings of this study provide guidance for designing new composites exhibiting high performance.

Laser structural training, artificial intelligence-based acoustic emission localization and structural/noise signal distinguishment in a thick FCEV fuel tank

Acoustic emission (AE) is present when transient elastic waves from structures are generated by various causes, such as structural cracks, fiber breakage, debonding of fibers and matrix, temperature changes, and fatigue. In AE-based structural health monitoring, the simple event counting method is unable to determine where AE occurs, so it is possible to discard a structure even if it is safe or not discard it when it is not safe. Much research on AE localization has been conducted to solve these problems. However, most of the methods have limitations with respect to isotropic material or near field conditions and cannot be applied when there is a change in the boundary conditions of the structure or obstacles. Thus, to solve these problems, a Q-switched laser capable of generating elastic waves has been used to scan and train the structures. Although this method worked effectively on thin specimens, a more advanced method is required for thick and complex structures, such as a fuel tank of a fuel cell electric vehicle (FCEV). Therefore, we propose a novel method based on artificial intelligence (AI) that can be applied to a real FCEV fuel tank fabricated with a filament winding composite. More specifically, this technique modulates the difference in characteristics between AE and laser-induced elastic waves in the frequency domain with AI. AE is simulated by a pencil lead break of the Hsu-Nielsen source. Then, AE localization is performed through cross-correlation in the time⋅frequency domains between a generated AE signal and modulated laser-induced signals obtained from AI. In addition, an experiment conducted to localize the AE that occurs at arbitrary points in real time confirms that AE localization can be performed within 2 s. Finally, an AI algorithm is proposed to distinguish between structural AE and unwanted noise to consider real-world applications and visualize the features of these two types of signals.

Investigations on effectiveness of transfer layer on specific wear rate and coefficient of friction during dry sliding of hybrid polymer matrix composites

AbstractThe formation of transfer layer especially in polymer‐based composites is unavoidable and essential to investigate the effectiveness of transfer layer under working conditions as it decides the material removal between mating parts. The main aim of the present work is to analyze the performance of transfer layer on specific wear rate (SWR) and coefficient of friction (COF) during dry sliding of hexagonal boron nitride (h‐BN)/prosopis juliflora (PJ) reinforced polymer matrix composite. The mechanical test results exhibited that 136.4%, 145.7%, and 106.2% improvement in hardness, tensile and flexural properties of the hybrid composites compared to pure epoxy. Pin on disc wear test results showed that 15 wt% of h‐BN and 5 wt% of PJ reinforced hybrid composite produced better wear performance of minimum COF as 0.0912 and SWR as 0.0000151 mm3/Nm. ANOVA analysis results showed that load is major contributing parameter on COF and SWR and their percentage of contribution as 25.40% and 79.38% respectively. Worn surface analysis revealed that the reason behind transfer layer formation and its effectiveness under sliding conditions. The major wear mechanisms are identified as micro cutting and micro plowing followed by matrix crack, fiber debonding, and fiber pull out.

Flexural progressive failure mechanism of hybrid 3D woven composites: Combination of X-ray tomography, acoustic emission and digital image correlation

This paper presents the hybrid effect on the bending progressive damage of three-dimensional (3D) angle-interlock woven composites. Three types of 3D angle-interlock specimens, carbon, hybrid (Carbon/UHMWPE) and UHMWPE, of the warp and weft orientations are experimentally tested via three-point bending method. X-ray micro-computed tomography (Micro-CT), acoustic emission (AE) and digital image correlation (DIC) techniques are combined to evaluate the damage initiation/evolution of hybrid 3D woven composites. Results indicate that hybrid structures have significant effects on the mechanical behaviors, damage models and failure mechanisms. Furthermore, the dominant failure mechanisms of hybrid 90° specimens are delamination, fiber fracture matrix cracking and debonding, whereas those of hybrid 0° specimens are matrix cracking and fiber matrix debonding.

Effect of Fiber Shape on the Tribological, Mechanical, and Morphological Behaviors of Sisal Fiber-Reinforced Resin-Based Friction Materials: Helical, Undulated, and Straight Shapes.

In this paper, we aim to evaluate the tribological, mechanical, and morphological performance of resin-based friction composites reinforced by sisal fibers with different shapes, namely helical, undulated, and straight shapes. The experimental results show that the shape of the sisal fibers exerts a significant effect on the impact property of the composite materials but no obvious influence on the density and hardness. The friction composite containing the helical-shaped sisal fibers exhibits the best overall tribological behaviors, with a relatively low fade (9.26%), high recovery (98.65%), and good wear resistance (2.061 × 10−7 cm3∙N−1∙m−1) compared with the other two composites containing undulated-shaped fibers and straight-shaped fibers. The impact fracture surfaces and worn surfaces of the composite materials were inspected by scanning electron microscopy, and we demonstrate that adding helical-shaped sisal fibers into the polymer composites provides an enhanced fiber–matrix interface adhesion condition and reduces the extent of fiber debonding and pullout, effectively facilitating the presence of more secondary plateaus on the friction surface, which are responsible for the enhanced tribological and mechanical properties. The outcome of this study reveals that sisal fibers with a helical shape could be a promising candidate as a reinforcement material for resin-based brake friction composite applications.

Interfacial reactions and mechanical properties of SiC fiber reinforced Ti3SiC2 and Ti3(SiAl)C2 composites

In this paper, SiC fiber (SiCf) reinforced Ti3SiC2 and Ti3(SiAl)C2 composites were fabricated by spark plasma sintering at 1250 °C and 1300 °C for 10 min, respectively. The interfacial reactions between fibers and matrix, as well as the mechanical properties of the two composites, were investigated. XRD, SEM and TEM were used to characterize the phase compositions and microstructures of the as-synthesized composites. The results showed that no interfacial reaction occurred between SiCf and Ti3SiC2 matrix, while it occurred between SiCf fiber and Ti3(SiAl)C2 matrix. In the latter case, the interfacial reaction layer was mainly composed of SiC, TiC, and TiSi2 phases, and its thickness was about 1.2 μm. Besides, due to the introduction of SiC fibers, both bending strength and fracture toughness of two composites were improved. Based on the investigation of crack propagation, it was proposed that the main strengthening and toughening mechanism was crack bowing for SiCf/Ti3(SiAl)C2 composite, while was fiber pullout, fiber debonding, and residual thermal stress for SiCf/Ti3SiC2 composite.

Toughening carbon fibre composites at cryogenic temperatures using low-thermal expansion nanoparticles

Matrix cracking of carbon fibre reinforced polymer composites at super cold temperatures, such as liquid hydrogen temperature, is a major issue for lightweight fuel storage, because the microcracks induced by the high thermal residual stresses in the matrix can cause fuel leaks and degrade the structural integrity of the storage vessel. Herein, we report a new method of toughening carbon fibre composites using nanomaterials of low-thermal expansion, i.e., nano-silica (nSiO2) and nano-cupric oxide (nCuO), at cryogenic liquid nitrogen temperature (~196 °C). In addition to their low coefficients of thermal expansion, these two nanoparticles are sufficiently small to avoid the filtering effect of carbon fibres during resin infusion process. The surfaces of nCuO are functionalized by a polydopamine coating to enhance their bonding with the epoxy resin and the cross-linking density of the epoxy resin. Results from tension and fracture toughness tests of an epoxy modified with these nanoparticles reveal that PDA-coated nCuO are more effective than their un-coated counterpart and nSiO2 in increasing the mechanical and fracture properties of epoxy nanocomposites at both room and cryogenic temperatures, tripling the fracture toughness values. More importantly, PDA-coated nCuO demonstrate significant improvements in the initiation and propagation fracture toughness of angle-ply carbon fibre composite ([±35°]8) by 113% and 46% respectively at the cryogenic temperature. The underlying toughening mechanisms are identified using scanning electron microscope as being fiber peel-off, debonding, and striation in the matrix. These exceptional improvements stem from the higher interfacial residual thermal stress at cryogenic temperature due to their low thermal expansion properties, which in turn promotes crack branching that increases the energy dissipation of the matrix.

Debonding damage detection of the CFRP-concrete interface based on piezoelectric ceramics by the electromechanical impedance method

Debonding in carbon fiber reinforced polymer (CFRP)-strengthened RC structures might always carry the risk of structural collapse. Several studies have focused on the debonding detection of CFRP-strengthened RC structures by nondestructive methods, which represents some limitations. Therefore, an electromechanical impedance (EMI) method based on piezoelectric ceramic (PZT) was applied to detect damage at the CFRP-concrete interface. First, different simulated interfacial defects in a CFRP sheet-wrapped concrete column were detected, and the feasibility of the method was validated. Then, the debonding process of a CFRP plate strengthened RC beam under four-point loading was monitored by the EMI method. Two damage indices, the root mean square deviation (RMSD) and the mean absolute percentage deviation (MAPD), were used to quantify the degree of damage at the CFRP-concrete interface. It is verified that these two damage indices obtained from the EMI method can clearly capture the process of damage development. Moreover, compared to the wave-based method, the EMI method is more sensitive to incipient concrete and debonding damage, which confirms the practicability of the EMI method for on-site applications.

Interfacial microstructure and strengthening mechanisms of Cf/Mg composite with double-layer interface

In order to overcome the interfacial incompatibility of carbon fiber reinforced magnesium matrix (Cf/Mg) composites, a double-layer interface (ZrO2–MgO) is designed in this work. Carbon fiber was modified with ZrO2 coating by sol-gel process. Microstructural examination reveals that MgO layer forms on the surface of ZrO2 coating by ZrO2 reacting with Mg during the composite fabrication. Such double-layer interface could inhibit Al4C3 and hence prevent fiber damage. Meanwhile, the wettability was improved for the reaction between ZrO2 and Mg. Thus the tensile strength of ZrO2-Cf/AZ91D composite was 68.0% higher than that of the unmodified one. Due to the fiber bundle pull-out, debonding and crack deflection, the toughness of Cf/Mg composite with double-layer interface is increased simultaneously.

Comprehensive Characterization of Industrially Discarded Cymbopogon Flexuosus Stem Fiber Reinforced Unsaturated Polyester Composites: Effect of Fiber Length and Weight Fraction

ABSTRACT Industrial biowaste used as reinforcing materials for polymer composites has attained paramount importance. In this work, biowaste such as Cymbopogon flexuosus stem fiber (CFSF) was reinforced with unsaturated polyester. The results confirmed the enhancement of the mechanical properties with an increase of up to 30 wt.% fiber content and fiber length up to 40 mm. However, further addition declines the properties due to debonding of fiber with the matrix as identified by SEM analysis carried out in fractured specimens. It was also observed that the incorporation of CFSF decreased the rate of water absorption and increased the composite thermal stability.

Interpreting acoustic energy emission in SiC/SiC minicomposites through modeling of fracture surface areas

The relationship between acoustic emission (AE) and damage source areas in SiC/SiC minicomposites was modeled using insights from tensile testing in-scanning electron microscope (SEM). Damage up to matrix crack saturation was bounded by: (1) AE generated by matrix cracking (lower bound) and (2) AE generated by matrix cracking, and fiber debonding and sliding in crack wakes (upper bound). While fiber debonding and sliding exhibit lower strain energy release rates than matrix cracking and fiber breakage, they contribute significant damage area and likely produce AE. Fiber breaks beyond matrix crack saturation were modeled by two conditions: (i) only fiber breaks generated AE; and (ii) fiber breaks occurred simultaneously with fiber sliding to generate AE. While fiber breaks are considered the dominant late-stage mechanism, our modeling indicates that other mechanisms are active, a finding that is supported by experimental in-SEM observations of matrix cracking in conjunction with fiber failure at rupture.

Single diamond scribing of SiCf/SiC composite: Force and material removal mechanism study

SiC fiber-reinforced SiC ceramic matrix (SiCf/SiC) is an advanced high-temperature material widely used in the heat-resistant componets of the aerospace engine and nuclear reactor, which are generally precisely ground to achieve the designed dimensional and geometrical tolerances. This research investigates the scribing force and material removal mechanism of 2.5D woven SiCf/SiC with the flat and sharp diamond grits, which present the new dressed and worn grinding wheel. The results show that the sharp grit has larger wear on the cutting edge and generates lower force than that of the flat grit at the same scribing depth and groove cross-section area. In both sharp and flat grits, the SiC matrix is mainly removed by the fracture cracks, peeling off, fiber exposure and powdering. In transverse diamond scribing of the SiCf, the fiber debonding and shear breakage are dominant removal feature for the flat grit scribing. Two additional removal patterns, the ductile scratch and fiber cracking, are observed for the sharp grit. In parallel diamond scribing of the SiCf, the shear and bending fractures in the cut-in and cut-out points are two key material removal modes, respectively, especially in the fiber woven structure. This research provides a fundamental understanding of interaction force and the material removal process of SiCf/SiC in grinding.

Mode I and Mode II interfacial fracture energy of SiC/BN/SiC CMCs

Quantifying the mixed mode fracture toughness of interfaces in ceramic matrix composites (CMCs) is crucial for understanding their failure. In this work we use in situ micromechanical testing in the scanning electron microscope to achieve stable interfacial crack propagation in Mode I (Double Cantilever Beam) and Mode II (Push out) and measure the corresponding fracture resistances. We use this approach to measure the interfacial fracture resistance in SiC/BN/SiC CMCs and compare it to the fracture energy of the fibres. During in-situ testing, fracture paths can be observed while data is acquired simultaneously. We clearly observe debonding at the BN-fibre interface (i.e. inside adhesive debonding). The critical energy release rate of the BN-fibre interface for Mode I and II (GIc ≈ 2.1 ± 1.0 J/m2 and GIIc ≈ 1.2 ± 0.5 J/m2) are equivalent and is lower than that measured for the fibre using microscopic DCB tests (GIc ≈ 6.0 ± 2.0 J/m2). These results explain the generalized fibre debonding and pull out observed in the fracture of these CMCs. By enabling direct observation of crack paths and quantifying the corresponding fracture energies, we highlight possible routes for the optimisation and modelling of the new generation of CMC interphases.

Improved mechanical properties of basalt fiber/phthalonitrile composites modified by thermoplastic Poly(phthalazinone ether nitrile)s

Phthalonitrile resin is a potential high-performance composite matrix, its brittleness and weak interaction with fiber are the main obstacles to its wide application. High-performance thermoplastic poly(phthalazinone ether nitrile)s (PPEN) and poly(phthalazinone ether nitrile ketone)s (PPENK) have been used to toughen basalt fiber (BF) reinforced 4,4′-bis(3,4-dicyanophenoxy)biphenyl (BPh) composite. The curing kinetics for the BPh/PPEN and BPh/PPENK blends have been investigated using DSC. The structures and thermal properties of the cured BPh blends have been studied in detail. The effects of PPEN and PPENK on the mechanical properties of the modified BF/BPh composite have been assessed. The non-notched impact strength of BF/BPh/PPENK laminate can be up to 107.7 kJ/m2, which is 64.2% higher than that of the BF/BPh laminate. And the interlaminar shear strength of BF/BPh/PPEN laminate can reach 42.5 MPa, 134.8% higher than that of the BF/BPh laminate. Simultaneously, the fracture surface of the laminate showed that the thermoplastic PPEN and PPENK can significantly inhibit the delamination between the layers and the fiber pullout and debonding.

Fatigue life prediction of glass fiber reinforced epoxy composites using artificial neural networks

In this work, fiber-reinforced composites, consisting of glass fibers with an epoxy matrix, have been considered to assess their fatigue life under combined rotating bending loads. Rotating bending fatigue tests were performed under fully reversed loading cycles at an operating frequency of 10 Hz. Fatigue test results revealed that the fatigue life of glass fiber reinforced with epoxy (GFRE) matrix composite decreased with an increase in stress levels. In addition, an artificial neural network approach was used in this study to demonstrate the impact of stress levels on the fatigue strength and failure modes of GFRE composites. The neural network was trained by the Levenberg-Marquardt algorithm using MATLAB. The feasibility of artificial neural networks for modeling and predicting the fatigue behavior of GFRE composites was verified by the correlation results (R2 = 0.99857) between the experimental data and ANN outputs. Three failure modes viz. matrix cracking, interfacial debonding and interfacial splitting of fibers were observed under low and high cycle fatigue tests. Further, ANN was successful in classifying these failure modes using a conjugate gradient backpropagation algorithm with 100% accuracy.

Low‐velocity impact resistance and acoustic emission evaluation on mechanical failure of carbon fiber weft‐knitting‐reinforced composites

AbstractIn this study, the carbon fiber weft‐knitting (CFWK)‐reinforced composites were prepared and the deformation mechanism during acoustic emission (AE) and low‐velocity impact resistance. To fabricate CFWK composites, single‐sided 1 × 1 variable plain stitch, double‐sided interlock structure, and two inter‐ply and intra‐ply hybrid structures of the former two stitches were applied for reinforcements in epoxy films via hot‐pressing. Moreover, we evaluated the tensile and bending properties during AE and investigated the low‐velocity impact properties of CFWK‐reinforced composites to evaluate the failure mechanism of composites. Finally, we analyzed the effects of laminating numbers, ply angle, and fabric structure on the properties of CFWK‐reinforced composites. Results showed that the composites with 1 × 1 variable plain stitch reinforcement exhibited the highest tensile strength and bending strength (206.22 and 213.43 MPa, respectively) among the composites with a two‐layer structure. The tensile fracture strength of [0/90] laying was 35%–50% lower than that of [0/0] laying. In addition, the cluster analysis on AE signal frequency showed that fiber debonding was the main failure mode, accounting for 68% of the total debonding when stretching along the longitudinal direction of the two‐ply composite loop. Under the impact energy of 4 J, the maximum load of CFWK‐reinforced composites with three‐ply interlock increased by 275% compared to that of single‐ply composites. Furthermore, the three‐ply interlock CFWK‐reinforced composites were perforated under impact energy of 10 J.