Fiber-matrix Interfacial Shear Strength Research Articles

ON THE EFFECTS OF THE INTERPHASE ON THE DAMPING OF CFRP STRUCTURES: AN EXPERIMENTAL INVESTIGATION

The increased adoption of composite laminates in modern engineering requires advancement in the prediction of their dynamic behavior. Damping is a major design constraint in aerospace structures subjected to cyclic loads. While the effects caused by damping are well known, the mechanisms that cause it at the microscopic level are still unclear on a quantitative basis. Testing of these phenomena requires some difficulties to be overcome, like the contribution of spurious sources. The study focuses on the effects that the interphase has on the damping properties of carbon fiber-reinforced polymer (CFRP) composite structures. Three-phase models are employed to investigate the dependence of damping on the interphase mechanical properties, with a focus on the fiber-matrix interfacial shear strength. The experimental campaign confirms the attended results: in particular, a stronger interphase determines a lower damping of the structure.

Study on the interfacial bonding properties between alkali-treated bamboo fibers and high-performance seawater sea-sand concrete

In this paper, the interfacial bonding properties between alkali-treated bamboo fibers and the matrix in fiber-reinforced high-performance seawater sea-sand concrete (HPSSC) materials were investigated. The natural bamboo fibers were modified with NaOH solution, and the cellulose crystallinity, chemical composition, and microstructure of the bamboo fibers before and after modification were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The impact of alkali treatment on the water absorption and mechanical properties of bamboo fibers were evaluated by water absorption test and single fiber tensile test. In addition, the influences of NaOH concentration, treatment time, and embedded length on the interfacial bonding properties were analyzed by pull-out test. Subsequently, the bonding mechanism between the fibers and the matrix was revealed based on the SEM scans of the extracted fiber surfaces. The experimental results indicate that appropriate alkali treatment could significantly eliminate the non-structural substances on the surface of bamboo fibers, reduce the water absorption, and increase the cellulose crystallinity. This process made the bamboo fibers exhibit better stability and bonding performance while ensuring the initial mechanical properties. Moreover, various fiber embedded lengths have a significant impact on the pull-out behavior of bamboo fibers. The maximum pull-out force of bamboo fibers increased with the increase of embedded length, while the fiber-matrix interfacial shear strength decreased. Based on the experimental results, a theoretical model for the pull-out behavior of bamboo fibers was proposed, and the predicted results showed a strong correlation with the experimental results.

Effect of Silica Addition to Resin on Fiber Matrix Interfacial Shear Strength of Carbon Fiber Reinforced Polyamide Resin at High Temperature

Effect of Silica Addition to Resin on Fiber Matrix Interfacial Shear Strength of Carbon Fiber Reinforced Polyamide Resin at High Temperature

Effect of moisture content and carbon fiber surface treatments on the interfacial shear strength of a thermoplastic-modified epoxy resin composites

The effect of moisture absorption on the fiber-matrix interfacial shear strength (IFSS) between a polysulfone-modified epoxy matrix and silane surface-treated carbon fiber using a factorial experimental design was studied. Also, two conditions of relative humidity, 25%, and 95%, and likewise six combinations of interfacial adhesion level between the IM7 carbon fiber and the epoxy resin (diglycidyl ether of bisphenol A), modified with polysulfone (PSF) (8.75 wt.%), were studied. The results show that IFSS of the composites increased with both the carbon fiber surface treatments and the epoxy resin modification with PSF. Again, it was found the moisture content had a substantially detrimental effect on the IFSS. However, both the silane treatment and the (PSF) modification of the epoxy resin enhanced the composite's resistance to moisture attack. The ANOVA results showed that the three variables, matrix modification, fiber's surface treatment, and moisture content, were statistically significant. Furthermore, interactions fiber surface treatment–moisture content and fiber surface treatment–epoxy matrix were statistically significant and the interaction between fiber surface treatment and moisture content is as crucial as the polysulfone epoxy modification. It was also found that the silane-treated carbon fibers play a major role in preventing moisture attack to the composite.

Effects of Temperature on the Fibre Matrix Interfacial Shear Strength of Carbon Nanotube Grafted Carbon Fibre Reinforced Heat Resistant Resin

Transportation sector is required to reduce CO2 emissions as environmental problems are becoming more serious. Carbon fibre reinforced thermoplastic (CFRTP) are expected to be applied to the structural parts of automobiles and aircrafts because of their superior mechanical properties such as high specific strength, high specific stiffness and high recyclability. One of the problems in using CFRTP for the structural parts is heat resistance, and it is necessary to clarify the mechanical properties under their service environmental temperature. The tensile strength of CFRTP at high temperatures decreases with temperature rise. The fibre matrix interfacial shear strength is reported to be improved by grafting of carbon nanotubes (CNTs) on the surface of carbon fibre. In this study, in order to clarify the effects of temperature on the fibre matrix interfacial shear strength of CNTs grafted carbon fibre reinforced PPS resin, single fibre pull-out test was conducted. While the interfacial shear strength of CNT grafted-CF/PPS is higher than that of As-received-CF/PPS at 25 °C, no significant difference was found in the interfacial shear strength of As-received-CF/PPS and CNT grafted-CF/PPS at 80 °C.

Influence of Unsizing and Carbon Nanotube Grafting of Carbon Fibre on Fibre Matrix Interfacial Shear Strength of Carbon Fibre and Polyamide 6

Carbon Fibre Reinforced Thermoplastics (CFRTP) are expected to be applied to the automotive industry instead of CFRP which require curing time, due to the expected short production cycle time of CFRTP, which is using thermoplastic as a matrix. We reported that the grafting of carbon nanotubes (CNTs) on the carbon fibre improves the fibre matrix interfacial shear strength. In our process to graft CNTs on carbon fibre, chemical vapour deposition (CVD) method was used and Ni, which was used as the catalyst, was electrically plated onto carbon fibres. Since commercially available carbon fibre was sized, which may affect the plating behaviour of Ni, the effects of sizing agents on CNT deposition have to be clarified. In this study, Ni for catalytic metal was plated by electrolytic plating using a watt bath on spread PAN-based carbon fibre and unsized carbon fibre, and the influence of the sizing agent to the distribution of Ni was evaluated. The morphological observation of carbon fibre and single fibre pull-out test were conducted to clarify the influence of sizing agent on the CNT deposition and the interfacial shear strength between the CNT grafted carbon fibre and Polyamide 6 (PA6). Uniform distribution of small sized Ni particles can be obtained on unsized carbon fibre and uniform Ni particles results in uniform CNT distribution. The CNT grafted unsized carbon fibre showed higher interfacial shear strength with PA6 than that of sized carbon fibre.

Effects of Water Absorption on the Fiber–Matrix Interfacial Shear Strength of Carbon Nanotube-Grafted Carbon Fiber Reinforced Polyamide Resin

Carbon fiber reinforced thermoplastics (CFRTPs) are expected to be used for the structural parts of automobiles and aircraft due to their mechanical properties, such as high specific stiffness, high specific strength, short molding times and high recyclability. The fiber/matrix interface of the composite plays an important role in transmitting stress from the matrix to the reinforcing fibers. It was reported that grafting of carbon nanotubes (CNTs) on the carbon fiber can improve the fiber/matrix interfacial property. We have reported that CNTs, which are directly grafted onto carbon fiber using Ni as the catalyst by the chemical vapor deposition (CVD) method, can improve the fiber/matrix interfacial shear strength (IFSS) of carbon fiber/polyamide 6 (PA6). For practical use of CFRTPs, it is important to clarify the effects of water absorption on the mechanical properties of the composite material. In this study, the effects of water absorption on the fiber–matrix interfacial shear strength (IFSS) of carbon fiber reinforced polyamide resin and CNT-grafted carbon fiber reinforced polyamide resin were clarified by the single fiber pull-out test for specimens preserved in air, then in water for 24 h and re-dried after water absorption. The IFSS of carbon fiber/PA6 was significantly decreased by water absorption. In contrast, CNT-grafted carbon fiber/PA6 showed smaller degradation of the IFSS by water absorption.

Interfacial Shear, Tensile Strength and Young Modulus of Kenaf Fiber: The Effects from Different Settings of Alkali Treatment

The project explained about what happened to fiber matrix interfacial shear strength, fiber tensile strength and fiber Young modulus when different alkali treatment settings were applied. Kenaf fiber were exposed to different alkali concentration, immersion duration and immersion temperature. To determine the interfacial shear strength (IFSS), unsaturated polyester matrix was utilised to expose the properties. The effects of alkali treatment on sample mechanical properties were successfully evaluated, whereby the treated sample's IFSS showed slightly higher value compared to untreated kenaf fiber at all settings. Meanwhile, the IFSS value was increased at low alkali concentration and decreased with the increment of alkali concentration percentage. On the other hand, untreated kenaf fiber tensile strength and Young modulus average value was 632MPa and 40.65GPa respectively. It was also established that the sample's tensile strength was keep reducing after treatment at all settings. At 30 minutes constant immersion duration, the percentage of kenaf fiber tensile strength decrement was 42.57% when other treatment settings increased. Furthermore, a decline pattern was obtained in term of sample tensile strength and Young modulus when the alkali treatment increased at all settings.

Influence of Treatment against Decomposition and Water Absorption on Fiber Matrix Interfacial Shear Strength of Glass Fiber Reinforced PLA

Influence of Treatment against Decomposition and Water Absorption on Fiber Matrix Interfacial Shear Strength of Glass Fiber Reinforced PLA

Mechanical properties and strain monitoring of glass-epoxy composites with graphene-coated fibers

An engineered interphase can improve the mechanical properties of epoxy/glass composites simultaneously inducing a piezoresistive response. To prove this concept, E-glass fibers were coated with graphene oxide (GO) by electrophoretic deposition, while reduced graphene oxide (rGO) coated fibers were obtained by subsequent chemical reduction. The fiber-matrix interfacial shear strength (measured by the single-fiber fragmentation test) increased for both GO and rGO coated fibers. Unidirectional composites with a high content of both uncoated and coated fibers were produced and mechanically tested under various configurations (three-point bending, short beam shear and mode-I fracture toughness, creep). Composites with coated fibers performed similarly or better than composites prepared with uncoated fibers. Finally, composites with rGO coated fibers were tested for their piezoresistive response under both static and dynamic conditions. The electrical resistance changed proportionally to applied strain thus confirming the possibility of using composites with rGO coated fibers as strain sensors in load-bearing components.

An exploration of the relationship of chemical and physical parameters in the micromechanical characterisation of the apparent interfacial strength in glass fibre epoxy systems

This paper focuses on the cure shrinkage and the thermomechanical properties of an amine cured epoxy resin system and its adhesion to glass fibre. The fibre-matrix interfacial shear strength (IFSS) was characterized using the microbond test over a range of test temperatures and a range of amine:epoxy ratios. The apparent IFSS in this glass-epoxy system was shown to be strongly dependent on the testing temperature and the matrix stoichiometry. High levels of cure shrinkage were measured in the IFSS microdroplets which resulted in internal stresses causing significant levels of droplet deformation. The results presented here can be interpreted as providing further support for the hypothesis that a significant fraction of the interfacial stress transfer capability in epoxy composites can be attributed to a combination of residual radial compressive stress and static friction at the fibre-matrix interface.

Hydrogen bonds, interfacial stiffness moduli, and the interlaminar shear strength of carbon fiber-epoxy matrix composites

The chemical treatment of carbon fibers used in carbon fiber-epoxy matrix composites greatly affects the fraction of hydrogen bonds (H-bonds) formed at the fiber-matrix interface. The H-bonds are major contributors to the fiber-matrix interfacial shear strength and play a direct role in the interlaminar shear strength (ILSS) of the composite. The H-bond contributions τ to the ILSS and magnitudes KN of the fiber-matrix interfacial stiffness moduli of seven carbon fiber-epoxy matrix composites, subjected to different fiber surface treatments, are calculated from the Morse potential for the interactions of hydroxyl and carboxyl acid groups formed on the carbon fiber surfaces with epoxy receptors. The τ calculations range from 7.7 MPa to 18.4 MPa in magnitude, depending on fiber treatment. The KN calculations fall in the range (2.01 – 4.67) ×1017 N m−3. The average ratio KN/|τ| is calculated to be (2.59 ± 0.043) × 1010 m−1 for the seven composites, suggesting a nearly linear connection between ILSS and H-bonding at the fiber-matrix interfaces. The linear connection indicates that τ may be assessable nondestructively from measurements of KN via a technique such as angle beam ultrasonic spectroscopy.

Expanded graphite nanoplatelets as coupling agents in glass fiber reinforced polypropylene composites

The interfacial adhesion between E-glass fibers and various types of nanomodified polypropylene (PP) matrices have been investigated on single-fiber model composites. In particular, an evaluation of the fiber–matrix interfacial shear strength was performed by the fragmentation tests on model composites prepared by using PP matrices containing various amounts (up to 7wt%) of expanded graphite nanoplatelets (xGnP).The presence of xGnP in the polymer matrix resulted in a remarkable increase of the interfacial shear strength values (up to a factor of about 6 for a 7wt% content of xGnP) if compared to neat PP. Moreover, wettability measurements in various liquids evidenced that the work of adhesion of the polymer matrix with respect to glass fiber, was improved by the presence of xGnP.

Effect of silane coupling agents on basalt fiber-epoxidized vegetable oil matrix composite materials analyzed by the single fiber fragmentation technique

The fiber–matrix interfacial shear strength (IFSS) of biobased epoxy composites reinforced with basalt fiber was investigated by the fragmentation method. Basalt fibers were modified with four different silanes, (3-aminopropyl)trimethoxysilane, [3-(2-aminoethylamino)propyl]-trimethoxysilane, trimethoxy[2-(7-oxabicyclo[4.1.0]hept-3-yl)ethyl]silane and (3-glycidyloxypropyl)trimethoxysilane to improve the adhesion between the basalt fiber and the resin. The analysis of the fiber tensile strength results was performed in terms of statistical parameters. The tensile strength of silane-treated basalt fiber is higher than the tensile strength of the untreated basalt fiber; this behavior may be due to flaw healing effect on the defected fiber surfaces. The IFSS results on the composites confirm that the interaction between the fiber modified with coupling agents and the bio-based epoxy resin was much stronger than that with the untreated basalt fiber. POLYM. COMPOS., 36:1205–1212, 2015. © 2014 Society of Plastics Engineers

Strengthening of CF/PEEK interface to improve the tribological performance in low amplitude oscillating wear mode

An attempt was made to improve the interfacial adhesion strength in carbon fabric/polyetheretherketone (CF/PEEK) composites using plasma modification of the carbon fiber surfaces. A static press method was used to fabricate CF/PEEK composites using unmodified and plasma modified carbon fibers. The influence of plasma treatment on fiber matrix interfacial shear strength was studied using a fragmentation test. The wear performance of composites was evaluated using low amplitude oscillation. A high limiting load was predicted for all modified composites. Scanning electron microscopy technique was used to support the wear trends among the composites and further investigations for underlying mechanisms.

Interfacial shear behavior of 3D composites reinforced with CNT-grafted carbon fibers

This paper presents the Molecular Dynamic (MD) models and the simulation results for the shear deformation process of an interface representative cell to develop an understanding of the roles of multi-walled carbon nanotube (MWNT) in enhancing fiber–matrix interfacial properties such as shear modulus and strength. Based on the MD results and the two simple formulae of rule of mixture, the shear modulus and strength of the carbon nanotube (CNT) grafted interface can be predicted. It is shown that there exists a good agreement between the predicted fiber–matrix interfacial shear strength with and without grafted CNTs and these measured from single-fiber micro bond test and single-fiber fragmentation test. The MD simulation also shows the MWNTs’ shear stress cross-section distribution is similar to that of a circular beam in shear with a non-zero shear stress on the neutral plane.

Strengthening of polypropylene–glass fiber interface by direct metallocenic polymerization of propylene onto the fibers

This work deals with the development of a new approach to improve the interfacial adhesion and properties of polypropylene–glass fiber composites. The chemical anchoring of the matrix polymer on glass fibers was improved by direct metallocenic polymerization of propylene onto the fibers surface. The experimental route involves an initial contact with methylaluminoxane (MAO) and hydroxy-α-olefin to generate the anchorage points on the fiber surface, followed by a propylene polymerization catalyzed by EtInd 2ZrCl 2 (metallocene)/MAO. During the polymerization reaction, polypropylene chains grow on the glass fiber surface. This reaction was studied for different hydroxy-α-olefin concentrations and its effectiveness was characterized by scanning electron microscopy (SEM) with X-ray disperse energy microanalysis. An evaluation of the fiber–matrix interfacial shear strength (ISS) was performed by single-fiber fragmentation tests on model composites. Depending on the hydroxy-α-olefin concentration, the surface treatment induced an increase of the ISS with respect of the untreated fibers by a factor ranging from 1.7 up to 2.1. The improved interfacial adhesion level was also confirmed by SEM observations of the morphology of the fiber–matrix region of cryogenic-fractured surfaces of composites.

Measuring effective interfacial shear strength in carbon fiber bundle polymeric composites

Adhesion in composite materials is often quantified using the single fiber fragmentation (SFF) test. While this method is believed to provide accurate values for the fiber–matrix interfacial shear strength (IFSS), these may not accurately reflect the macroscopic mechanical properties of specimens consisting of tows of thousands of tightly spaced fibers embedded in a resin matrix. In these types of specimens, adhesion may be mitigated by fiber twisting and misalignment, differences in the resin structure in the confined spaces between the fibers and, most importantly, by any incompleteness of the fiber wetting by the resin. The present work implements fiber band fragmentation (FBF) testing to obtain effective interfacial shear strengths, whose values reflect the importance of these factors. The fiber fragmentation in these specimens is tracked through the counting and sorting of acoustic emission (AE) events occurring during the tensile testing of the specimen and yields the average critical fiber fragment length. AE results, in conjunction with stress-strain data, show that fiber breakage events occur at acoustic wavelet amplitudes substantially greater than those generated by fiber/matrix debonding. Kelly–Tyson analysis is applied, using the measured critical fiber fragment length together with known values for the fiber diameter and tensile strength to yield the effective IFSS. FBF tests are performed on carbon fiber/poly(vinyl butyral) (PVB) dog-bone fiber-bundle systems, and effective IFSS values substantially lower than those typically reported for the single fiber fragmentation testing of similar systems are obtained, suggesting the importance of multi-fiber effects and incomplete fiber wetting.

Flax fiber surface modifications: Effects on fiber physico mechanical and flax/polypropylene interface properties

This study arises on the opportunities of using flax fibers as reinforcement for polypropylene (PP) matrix composites. For this purpose, untreated flax fiber bundles obtained by a retting process have been used. For improving compatibility between flax fiber bundles and PP matrix, fiber surface treatments such as maleic anhydride, maleic anhydride polypropylene copolymer, and vinyltrimethoxy silane have been carried out. On the other hand, alkali treatment has also been carried out for fiber modification. The effect of surface modification on tensile properties of single fibers and also on fiber-matrix interfacial shear strength (IFSS) has been analyzed. Finally, both optical microscopy and atomic force microscopy have been used for characterizing flax fiber microstructural features. The current study completes previous results to elucidate the influence of treatments on fiber surface and flax fiber-PP interface. POLYM. COMPOS. 26:324–332, 2005. © 2005 Society of Plastics Engineers.

The influence of silane coupling agent composition on the surface characterization of fiber and on fiber-matrix interfacial shear strength

It is well known that the fiber-matrix interface in many composites has a profound influence on composite performance. The objective of this study is to understand the influence of composition and concentration of coupling agent on interface strength by coating E-glass fibers with solutions containing a mixture of hydrolyzed propyl trimethoxysilane (PTMS) and n -aminopropyl trimethoxysilane (APS). The failure behavior and strength of the fiber-matrix interface were assessed by the single-fiber fragmentation test (SFFT), while the structure of silane coupling agent was studied in terms of its thickness by ellipsometry, its morphology by atomic force microscopy, its chemical composition by diffuse reflectance infrared Fourier transform (DRIFT), and its wettability by contact angle measurement. Deposition of 4.5 ‐ 10 m 3 mol/L solution of coupling agent in water resulted in a heterogeneous surface with irregular morphology. The SFFT results suggest that the amount of adhesion between the glass fiber and epoxy is dependent not only on the type of coupling agent but also on the composition of the coupling agent mixture. As the concentration of APS in the mixture increased, the extent of interfacial bonding between the fiber and matrix increased and the mode of failure changed. For the APS coated glass epoxy system, matrix cracks were formed perpendicular to the fiber axis in addition to a sheath of debonded interface region along the fiber axis.