Fiber-matrix Debonding Research Articles

Experimental Investigation on Mechanical Joint of Lontar (Borassus Flabellifer) Fiber Reinforced Polyester Composites under Static Flexural Test

This study has been conducted to investigate the flexural strength of Borassus Flabellifer Fiber/BFF reinforced polyester composite joint under static condition. Tests were carried out to study the flexural strength of double strap butt joint and single lap joint of BFF polyester composite. In addition, post observation of macroscope was used to map failure behavior. The results shown that the flexural strength of single lap joint is higher compared to double strap butt joint of BFF polyester composite. The larger cross-sectional area and the existence of gap area could be the main reason for lower flexural strength generated by double strap butt joint of BFF polyester composite. The failure of BFF polyester composite joints under flexural test indicated the brittle failure behaviour that fiber breakage was found to be the final failure mechanism which start with matrix cracking and fiber-matrix debonding failure mechanisms.

Tribological characterization of recycled basalt-aramid fiber reinforced hybrid friction composites using grey-based Taguchi approach

Fibers play an imperative role in determining the tribological behavior of reinforced friction composites. The objective of the present study is to develop recycled basalt and recycled aramid fiber reinforced hybrid friction composites with the addition of various fillers and optimize the tribological behaviors of the composites. The pin-on-disc test rig was used to conduct dry sliding wear following Taguchi’s L27 orthogonal array with process parameters of the applied load, sliding speed and the weight percentage of fiber content. Grey relational analysis was adopted for tribological parameters optimization, satisfying multiple performance characteristics. Analysis of variance was used to find the contribution of individual factors that affect tribological behavior. Optimal parameter combination for multi-response characteristics of the friction composite under investigation was applied a load of 15 N, sliding speed of 1 m s−1 and composite with 25 weight percent of fiber content. The results showed that addition of fiber content significantly increased wear resistance of the friction composites. Further, from the scanning electron microscopy images of friction and wear tested friction composites, plateau formation, fiber-matrix debonding, fiber pull out, cracks and damage on the matrix and various wear mechanism were identified.

Experimental study on milling performance of 2D C/SiC composites using polycrystalline diamond tools

The present paper concerns assessment of the milling machinability of 2D C/SiC composites using polycrystalline diamond (PCD) tools. Influences of milling parameters on cutting forces, surface integrity and machined defects were studied. Experimental results showed that cutting forces varied greatly in a milling circle due to the sudden changes of fiber cutting angle. As cutting speed increased, cutting forces and surface roughness decreased. Cutting forces and surface roughness both increased as feed rate increased. Fiber fracture, matrix damage and fiber-matrix debonding were three main material removal mechanisms during slot milling. Pits and cracks were main machined defects at ground surface, and they more easily happened at the intersection of woven yarns. Surface integrity of 90° fiber orientation was better than that of 0° fiber orientation. Machined defects of side edges had three types: fiber protrusion combined with surface damage, fiber protrusion and surface damage. Quantity and size of surface damage were much larger than fiber protrusion. Both of surface damage and fiber protrusion increased with the increase in feed rate. Higher cutting speeds could decrease the fiber protrusion of side edges evidently, however have minor influence on the surface damage.

Analysis and Identification of the Mechanism of Damage and Fracture of High-Filled Wood Fiber/Recycled High-Density Polyethylene Composites.

The damage and fracture of fiber reinforced polymer composites are vital constraints in their applications. To understand the mechanism of damage of wood fiber (WF) reinforced high density polyethylene (HDPE) composites, we used waste WF and recycled HDPE (Re-HDPE) as the raw materials and prepared high-filled WF/Re-HDPE composites via extrusion. The damage and fracture mode and failure mechanism of the composites with different WF contents (50%, 60%, and 70%) was studied under a three-point bending test by combining the acoustic emission (AE) technique and scanning electron microscope (SEM) analysis. The results show that AE technology can better assist in understanding the progress of damage and fracture process of WF/Re-HDPE composites, and determine the damage degree, damage accumulation, and damage mode. The damage and fracture process of the composites presents three main stages: the appearance of initial damage, damage accumulation, and destructive damage to fracture. The matrix deformation, fiber breakage, interface delamination, fiber-matrix debonding, fiber pull-out, and matrix cracking were the dominant modes for the damage of high-filled WF/Re-HDPE composites under bending load, and the AE signal changed in different damage stages and damage modes. In addition, the WF content and repeated loading had a significant influence on the composite’s damage and fracture. The 50% and 60% WF/Re-HDPE composites produced irreversible damage when repeated load exceeded 75% of the maximum load, while 25% of the maximum load could cause irreversible damage for 70% WF/Re-HDPE composites. The damage was accumulated owing to repeated loading and the mechanical properties of the composites were seriously affected.

Mechanical behaviour of jute fibre-reinforced polyester composite: Characterization of damage mechanisms using acoustic emission and microstructural observations

The present work deals with the mechanical characterization of a woven jute fabrics reinforced polyester resin composite. Two stacking sequences were considered: [0]8 and [+45/−45]2S. In-situ acoustic emission technique, X-ray computed tomography (X-ray CT) and post-mortem microscopic observations were used to characterise the damage mechanisms and to follow their evolutions during uniaxial tension. The microstructural analysis and X-ray CT revealed the following damage modes for the two lay-ups: fibre-matrix debondings which constitute the dominant mechanism, matrix crackings and fibre breakages and pull-outs. The acoustic emission data were processed using an unsupervised pattern recognition technique which combines principal components analysis and k-means optimized by a genetic algorithm. Both temporal and frequential features of acoustic emission signals were considered. The Laplacian score and dendrogram were used to determine the relevant and uncorrelated descriptors for clustering. Three clusters of events were obtained and the waveforms of each one were examined. Furthermore, the frequency contents of signals of each cluster were accurately investigated using power density spectrum and smoothed pseudo Wigner-Ville time-frequency distribution and the discrepancies between clusters are highlighted. Cluster 1 (Cl 1) characterized by signals of low frequency and intermediate amplitude, cluster 2 (Cl 2) characterized by signals of higher frequency and an amplitude similar to that of Cl 1 and cluster 3 (Cl 3) characterized by signals of higher amplitude. A correlation between the clusters and the damage mechanisms was established by means of interrupted tensile tests: Cl 1 is assigned to the matrix cracking, Cl 2 to the fibre-matrix debonding and Cl 3 to the fibre breakage and pull-out. The kinetic of evolution of each damage mode was monitored for the two stacking sequences.

Low-Velocity Impact Characterization of Fiber-Reinforced Composites with Hygrothermal Effect

Abstract In this article, low-velocity impact characteristics of UHN125C carbon fiber/epoxy composite, including unidirectional (0°), cross-directional (0°/90°), and quasi-isotropic layups, were experimentally measured. The effect of the fiber orientation angle and stacking sequences on impact force and induced strain were measured via an instrumented drop-weight apparatus with special concern for the moisture absorption effect. Dried specimens were immersed in distilled water for a certain period of time to absorb water for intermediate and saturated moisture content. It was observed that the impulse was reduced with the increase in moisture content; on the other hand, strain increased with moisture, as measured by DBU-120A strain-indicating software (MADSER Corp., El Paso, TX). Impact damage is widely recognized as one of the most detrimental damage forms in composite laminates because it dissipates the incident energy by a combination of matrix damage, fiber fracture, and fiber-matrix debonding. Therefore, it is extremely important to know the impact strength of a structure, especially for applications in industries such as aerospace, ship design, and some other commercial applications. The use of composite materials in engineering applications is increasing rapidly because they have higher strength-to-weight ratios than metals. The strength, stiffness, and, eventually, the life of composite materials are affected more than conventional materials by the presence of moisture and temperature. Thus, it is necessary to analyze the response of composites in a hydrothermal environment.

Study of mechanical behaviour of eulaliopsis binata fiber reinforced polymer composite

Abstract In this investigation a new unexplored potential non-wood natural fiber, eulaliopsis binata (short fiber) is taken as reinforcement with epoxy as matrix material to examine the potential of the fiber as a reinforcement material. The incorporation of short eulaliopsis binata (sabai) fiber with different weight percentage (5,10,20,30,40) contributed towards enhancement of the mechanical properties of the composite. The modulus of elasticity, modulus of rupture, impact strength, hardness was found to be optimum for the composite with 30% weight fraction of fiber. The addition of fiber beyond 30% fiber fraction leads to fiber agglomeration, poor bonding at fiber matrix interface causing deterioration of mechanical strengths of the composite. The SEM analysis reveals fiber pullout, fiber-matrix debonding, micro crack propagation is found to be some of the primitive causes for the failure of composite under study.

Compressive Behaviour and Failure Mechanisms of GFRP Composite at High Strain Rates

Experimental investigations into the compressive behavior of glass fiber reinforced polymer (GFRP) composite at high strain rates were carried out using a split Hopkinson pressure bar (SHPB) setup. The GFRP laminates were made from E-glass fibers and epoxy resins by vacuum assisted compression molding machine. The results of the compressive tests indicated that the mechanical behavior of the GFRP composite depends highly on the strain rate. The compressive peak stress, toughness and Young's modulus of the GFRP composite increased with the increase of strain rate, while the strain level at the initial stages of damage was shortened with the increase of strain rate. In addition, the dynamic deformation behavior and failure process of the specimens were observed directly by using a high-speed camera. Following the experiments, the fracture morphologies and damage modes were examined by scanning electron microscopy (SEM) to explore the possible failure mechanisms of the specimens. The results showed that multiple failure mechanisms appeared, such as matrix crack, fiber-matrix debonding, fiber failure and shear fracture.

Multi-stage mechanical behavior and failure mechanism analysis of CFRP/Al single-lap bolted joints with different seawater ageing conditions

This paper aims to investigate the mechanical response behavior of CFRP/Al single-lap bolted joints in marine environment. The joints with four interference fit sizes (0%, 0.42%, 2.14% and 3.02%) were prepared, and fully and half immersed in 3.5% sodium chloride solution with a controlled temperature of 30 °C for four months. Single-lap bearing tests were carried out to evaluate the mechanical behavior and failure mode of the CFRP/Al bolted joints after seawater ageing. Scanning electron microscope (SEM) was used to analyze the environmental damage and failure mechanism of structures. The results show that the critical load-bearing capacity and the maximum friction force at the overlap gradually decreased with the increasing of ageing time, and it was more serious in half immersion ageing environment compared with full immersion. The interference fit significantly improved the mechanical properties of joints, especially for 2.14% interference fit. Environmental damage such as pitting, delamination and fiber-matrix interface debonding was all aggravated with the increasing ageing time but suppressed by interference fit. In addition, the failure modes of structures were bearing failure and shear-out failure of CFRP, and the failure mechanism was delamination for unaged structures, the interlayer shear damage for aged structures.

A combined experimental/numerical investigation on hygrothermal aging of fiber-reinforced composites

This work investigates hygrothermal aging degradation of unidirectional glass/epoxy composite specimens through a combination of experiments and numerical modeling. Aging is performed through immersion in demineralized water. Interlaminar shear testes are performed after multiple conditioning times and after single immersion/redrying cycles. Degradation of the fiber-matrix interface is estimated using single-fiber fragmentation tests and reverse modeling combining analytical and numerical models. A fractographic analysis of specimens aged at 50°C and 65°C is performed through X-ray computed tomography. The aging process is modeled using a numerical framework combining a diffusion analysis with a concurrent multiscale model with embedded hyper-reduced micromodels. At the microscale, a pressure-dependent viscoelastic/viscoplastic model with damage is used for the resin and fiber-matrix debonding is modeled with a cohesive-zone model including friction. A comparison between numerical and experimental results is performed.

Fiber-reinforced polymer composites test specimen design for selected damage mechanisms

Fiber-reinforced polymer composites yield a range of microscopic damage mechanisms even under apparently “simple” load cases, e.g. quasi-static uniaxial tensile tests to failure. Even reducing the fiber-reinforced polymer composite to a single fiber embedded in a matrix will produce several different damage types under quasi-static tensile loading. These are fiber breaks and simultaneous fiber–matrix debonding as well as friction between fiber and debonded matrix, and sometimes, additional matrix cracks. Acoustic emission monitoring of mechanical load tests on material specimens or components is often used to identify the occurrence of damage and attempts at locating the source and identifying the damage mechanism or type in a wide range of materials. The complex damage behavior of fiber-reinforced polymer composites poses a challenge in that respect. Therefore, various approaches (e.g. pattern recognition or neural networks) have been developed to identify the different microscopic damage mechanisms from acoustic emission signals obtained from various load tests. For improved understanding of the damage mechanisms in fiber-reinforced polymer composites as well as for validating the procedures for identifying the types of mechanisms, fiber-reinforced polymer specimens showing a “single dominant damage mechanism”, i.e. occurring in significantly larger number than all others, at least in certain stages of damage accumulation or in localized volume elements, can be designed. The contribution discusses and classifies selected examples of single dominant damage mechanism for fiber-reinforced polymer composites and their application.

Peridynamic analysis of fibre-matrix debond and matrix failure mechanisms in composites under transverse tensile load by an energy-based damage criterion

Reliable simulation methods and failure criteria are required during the sizing of fibre reinforced plastics (FRPs). Peridynamics (PDs) is a promising numerical method to predict the evolution and interaction of damages. In the current text a novel energy-based failure criterion for linear peridynamic solid (LPS) materials is implemented and applied to the micromechanical damage of FRP structures. The novel criterion promises a more realistic reproduction of failure modes for ductile materials, a reduced mesh dependency and only requires physically measurable parameters. The results of the novel criterion are compared to a reference criterion and are evaluated against experimental observations.

Micromechanical Modeling of Fiber-Matrix Debonding in Unidirectional Composites

Micromechanical Modeling of Fiber-Matrix Debonding in Unidirectional Composites

Experimental and numerical investigation on the mechanical characteristics of polyethylenimine functionalized graphene oxide incorporated woven carbon fibre/epoxy composites

The synergistic effects of polyethyleneimine functionalized graphene oxide (PEI-FGO) on the static and dynamic mechanical properties of the carbon fibre reinforced epoxy composites were investigated in detail. The functional groups of PEI-FGO, especially the NH2, experienced strong molecular interaction with the epoxy resin, and increased the load carrying capacity of the matrix, and the corresponding overall mechanical strength of the composites. The tensile and flexural strength of the 0.3 wt% PEI-FGO incorporated CF/epoxy composites was improved by ∼ ((58–62) and (65–70)) %, respectively as compared to the base CF/epoxy composites. The numerical analysis via Finite Element Method of the prepared composites was carried out to validate the experimental results. The numerical models showed linear behavior in the stress-strain diagram, whereas the experimental results expressed non-linear behavior, due to the fibre-matrix de-bonding. The effects of temperature and frequency on the dynamic mechanical properties of the prepared composites were meticulously studied. The broadening of the tan δ curve with increasing frequency also signified that PEI-FGO affects the molecular motions of the epoxy network.

Combined effect of water uptake and temperature on wood polymer composites

ABSTRACTWood polymer composites are materials frequently used for outdoor applications, since they can operate under a large range of temperature and moisture conditions. The present work investigates the combined effect of water soaking and temperature (ranging from 10 up to 40 °C) on wood flour filled high density polyethylene. Water soaking tests have revealed that the percentage of absorbed water at the saturation plateau increases with temperature due to the induced stiffness reduction of the polymeric matrix. This hypothesis has been confirmed by scanning electron microscopy analyses, which has allowed to observe the filler–matrix interface and to measure the wood flour particle size. In addition, instrumented Charpy impact tests have shown a strong toughness reduction as a consequence of fiber–matrix debonding induced by particle swelling, which worsens with temperature. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46674.

Damage characterization and fatigue modeling of CFRP subjected to cyclic loading

Fatigue damage evolution in CFRP is characterized by variation of local transverse strain from digital image correlation (un-notched) and temperature variation from infrared thermography (notched). The damage evolves over 2–3 stages. Matrix cracks and fiber matrix debonding are observed in ±45°, 90° and 0° plies in stage I. Fiber fracture is observed in 0° plies only in stage II of the un-notched specimen. It is present even in stage I for notched specimens. In notched specimens, extensive fiber fracture is observed in −45°, 90° and 0° plies in stage II due to higher local stresses. Fiber fracture causes a larger rate of increase in local temperature. A three parameter cumulative damage model is used for predicting the damage evolution and fatigue life. Predictions were good for tension–compression tests in unnotched specimens, but inadequate for compression-compression tests. While using temperature for damage characterization in notched specimens, additional parametrization is required.

Peak frequency analysis via wavelet transform for impact damage mechanisms in woven composites

Impact damages have been a major concern in the design of laminated composite structures since the damages mainly occur within the materials in a very short time. In this article, impact induced damage mechanisms of woven composites were investigated by means of novel SHPB-AE coupled tests. A step-consisting new methodology was developed; first, damage mechanisms of woven composites were determined by peak frequency analysis via wavelet transform (WT); second, the extraction of a range of acoustic emission (AE) parameters was achieved from AE energy, duration, and amplitude on the basis of peak frequency analysis; finally, the quantification of damage mechanisms was accomplished through a normalized cumulative AE count. In order to confirm the features of damage, the microscopic characterization of damage mechanisms was performed for the materials. As a result, the determination of impact damage mechanisms in tested composite materials was possible by peak frequency analysis via WT along with waveform and intensity examinations. In addition, the mechanisms could be identified by confirming the progress-based distribution and band formation of peak frequencies. AE parameter ranges were also extracted in terms of amplitude, duration, and energy according to the damage mechanisms. The damage process of the woven composites under impact loading began in the matrix and immediately caused fiber breakage to occur. Subsequently, multiple damage mechanisms were shown, such as fiber-matrix debonding, fiber pull-out, severe deformation and rupture in Kevlar fiber tips. The proposed methodology for the novel SHPB-AE coupled test of woven composites therefore showed an effective way to figure out in situ information on the damage under impact loading.

Highly boosting the interlaminar shear strength of CF/PEEK composites via introduction of PEKK onto activated CF

Due to poor wettability and low reactivity, the interfacial adhesions between CF and PEEK matrix are relatively weak, significantly affecting mechanical performances of composites, especially the interlaminar shear strength. This study focuses on improvement of fiber-matrix interfacial interactions for CF/PEEK composites via introducing interfacial layers of polyertherketoneketone (PEKK) on activated CF. This method takes advantage of hydrogen bond between PEKK and activated CF, as well as good compatibility between PEKK and PEEK. As a result, interlaminar shear strength, flexural strength and modulus of CF/PEEK composites increased by 70%, 37% and 48%, respectively. SEM observations on fractured surfaces of composites indicated that dominant failure mechanisms shifted from fiber-matrix debonding to deformation of interfacial layers and breakage in resin. This modification method is easy to handle and can be applied to produce large size of composite materials containing continuous CF or CF fabrics, showing potentials in industrial applications.

High residual mechanical properties at elevated temperatures of carbon fiber/acetylene-functional benzoxazine composite

It is always of great practical significance to develop carbon fiber (CF) reinforced polymer composites with high residual mechanical properties at elevated temperatures for aerospace engineering structures, etc. In this work, the CF reinforced composite based on acetylene-functionalized benzoxazine (AFBEN) was manufactured by the resin transfer moulding (RTM) technology. The mechanical properties at elevated temperatures (150–350 °C) are first and systematically examined for the as-prepared CF/AFBEN composite. Differential scanning calorimetry and rheological characteristics are employed to evaluate the adaptability of AFBEN for the RTM process. Dynamic mechanical and thermogravimetric properties of the CF/AFBEN composite are also investigated to evaluate the thermal stability. The results display that the mechanical strengths of the CF/AFBEN composite exhibit the high residual rates of ca. 90% at 250 °C and over 60% at 350 °C compared to the mechanical properties at room temperature. The fracture mechanisms at room and elevated temperatures are studied and the fracture behavior of the CF/AFBEN composite is shown to transform from fiber-matrix interfacial debonding to resin matrix failure as the temperature increases. Consequently, the as-prepared CF/AFBEN composite show great potentials for practical applications in aerospace engineering structures, etc. due to its high residual mechanical properties at elevated temperatures and the ease of the RTM processing.

Modeling of natural fiber reinforced composites under hygrothermal ageing

In this paper, we focus on the mechanical performance of fibers naturally derived from plants as reinforcement of a composite structure. A nonlinear constitutive model for the whole hygrothermal ageing process of natural fiber reinforced composites is established. This theoretical model accounts for large elastic and inelastic deformation, diffusion of water molecules and hydrolysis reaction. Based on the non-equilibrium thermodynamic framework, the Helmholtz free energy functions and the corresponding dissipation laws are established. The effects of matrix cracking, fiber-matrix interfacial debonding and change in the microstructure of natural fibers are all considered in this theoretical model. And the competition between the loss and the recovery of mechanical properties of natural fibers is investigated. Moreover, this theoretical model is applied to analyze the elastic response of natural fiber reinforced composites and the influence of ageing temperature is discussed. The obtained theoretical results are compared with corresponding experimental data and it is shown that the present theoretical model is capable of describing the evolution of elastic moduli of composite samples and their temperature dependence during the whole hygrothermal ageing process.