Interfacial Shear Strength Of Composites Research Articles

Dynamic enhancement induced by interface for additively manufactured continuous carbon fiber reinforced composites

Additive manufacturing (AM) has become one advanced manufacturing method for continuous carbon fiber reinforced polymer (CCFRP) composites, which is promising to work as aerospace materials. To promote their efficient design and extensive application, series of tensile and fiber-pullout tests were implemented to investigate the rate-dependent mechanical behavior and fracture mechanism. Both tensile strength and fracture strain significantly increase with the increase of strain rate in the studied range of 0.0001–1600 s−1. Fiber-pullout test also confirms that the interfacial shear strength of composites increases with the increasing loading rate. Dynamic enhancement is analyzed quantitatively, and it is mainly contributed by the rate-dependent behavior of fiber-matrix interface. Fracture analysis indicates the stronger interfacial bonding under dynamic loading, which is attributed to the impeded interfacial crack propagation by high strain rate. A constitutive model is built to predict the rate-dependent strength of CCFRP composites, and it fits well with the experimental results.

Flax fiber treatment by an alkali solution and poly(dopamine) coating: Effects on the fiber physico-chemistry and flax/Elium® composite interfacial properties

The use of natural fibers to reinforce polymer-based composites is gaining interest to replace conventional synthetic fibers due to their sustainability. In this frame, optimizing the adhesion between natural fibers and the polymer matrix is crucial to ensure high mechanical properties. To improve the adhesion between flax fiber and an acrylic-based thermoplastic resin, the combining of alkalization and poly(dopamine) (PDA) coating as fiber treatments has been investigated in this paper. It is found that applying an alkalization with sodium hydroxide (3 wt%, 2 h, 21 ± 2 °C), followed by dopamine polymerization (2 g/L, pH of 8.5, 24 h, 21 ± 2 °C) in the presence poly(ethylene imine) (600 g/mol, 1 g/L) as a polyelectrolyte, provides the highest increase in composite interfacial shear strength (+22.0 %) and interlaminar shear strength (+63.2 %) compared to the composite with untreated fibers. The results are discussed based on the fiber physico-chemical properties and composite interfacial aspects.

Heating De-fluorination derived radicals promoted interfacial grafting and enhanced Kevlar/Bismaleimide composites

Lack of stable, active reacting centers of fiber with bismaleimide (BMI) resin severely limited interfacial properties of composites. In this article, we found defluorination derived radicals under high temperature was able to participate into BMI resin curing reaction. X-ray Photoelectron Spectroscopy (XPS), In-situ Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis-Fourier Transform Infrared Spectroscopy-Gas Chromatography/Mass (TGA-GC/MS) Spectrometry hyphenated testing results of model molecules revealed decomposition process of fluorinated layer, and in-situ Electron Paramagnetic Resonance (EPR) captured alkyl radicals from defluorination. According to Differential Scanning Calorimeter results, above radicals were able to promote curing of BMI resin via radical coupling, which meant definite covalent combination between fluorinated aramid fiber and BMI matrix. Therefore, composite interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) simultaneously enhanced by 41.93% and 31.44% at maximum, respectively. Consequently, flexural properties of laminates also increased where flexural strength and flexural modulus respectively improved by 26.29% and 35.24%.

Latent active unit triggered crosslinking inside aramid fiber with improved transverse connection and composite properties

Weak transverse connection inside organic fiber limited its structural stability during processing and mechanical property in composite products. In this article, we utilized the latent activity of imidazole unit of aramid fiber, proved its spontaneous feasibility in open-ring reaction with epoxy-contained compound as anionic polymerization under suitable high temperature using in-situ Fourier Transform Infrared Spectroscopy (in-situ FTIR). Utilizing this in-situ polymerization inside fiber, crosslinked fiber linked between imidazole spots was obtained via simple penetrating bifunctional 1,3-Bis(Oxiran-2-Ylmethoxy)Benzene (RDGE) inside aramid fiber and heat annealing. Crosslinked fiber showed stable excellent mechanical strength, while the composite interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) respectively improved by 31.49% and 28.20% due to the suppressed axial peeling due to crosslinking enhanced transverse connection, and improved fiber surface wettability without any further surface modification. Besides, compressive strength of modified fiber reinforced composite also improved by 59.84%, while according to the digital images revealed the interfacial failure dominated compressive failure focused in the destroyed area, it was further founded that composite of aramid fiber with much lower bending stiffness than carbon fiber performed highly sensitive dependence with composite interfacial combination.

Effect of Carbon Fiber Surface Microstructure on Composite Interfacial Property Based on Image Quantitative Characterization Technique.

The surface roughness (Ra) and composite interfacial property of carbon fiber (CF) are considered to be mainly affected by the microstructure of the CF surface. However, quantitative characterization of the CF surface microstructure is always a difficulty. How the CF surface microstructure affects the interfacial property of CF composites is not entirely clear. A quantitative characterization technique based on images was established to calculate the cross-section perimeter and area of five types of CFs, as well as the number (N), width (W) and depth (D) of grooves on these CF surfaces. The CF composite interfacial shear strength (IFSS) was tested by the micro-droplet debonding test and modified by the realistic perimeter. The relationship between the groove structure parameter and the Ra, specific surface area and composite interfacial property was discussed in this article. The results indicated that the CF cross-section perimeter calculated by this technique showed strong consistency with the CF specific surface area and composite interfacial property. At last, the composite interface bonding mechanism based on defect capture was put forward. This mechanism can be a guiding principle for CF surface modification and help researchers better understand and establish interface bonding theories.

Pre-use interfacial shear strength prediction for fiber-reinforced thermosetting composites based on stress-impedance effect of ferromagnetic microwires

A new rapid evaluation method of composite interfacial shear strength (IFSS) on basis of impedance parameter utilizing the glass-coated cobalt-based ferromagnetic microwire (GCM) with sensitive stress-impedance effect is proposed. The intrinsic properties analysis and surface modification of GCM were performed to improve the sensitivity of stress-impedance effect and meet the application requirements in composites. The correlation between impedance increments and interfacial stress is investigated for GCM composites with different resin embedded lengths through experimental verification and finite element simulation. The impedance increment of microwire shows a high degree of dependence on IFSS of GCM/resin systems, which is mainly associated with the local interfacial stress from the resin. Based on this correlation mechanism and IFSS measured by microdroplet debonding test, IFSS of composites with different resin matrix were successfully calculated from the impedance parameter, and the interfacial bonding of resin matrix could be distinguished and sorted as relatively superior or inferior conveniently and rapidly. In comparison with the sophisticated, lengthy and expensive interface mechanical tests after the manufacture of fibers and resin, the pre-use efficient interfacial assessing of resin matrixes only using GCM shows potential to screen resin matrix with excellent interfacial properties towards advanced fiber-reinforced thermosetting resin matrix composite.

Improved interfacial shear strength of CF/PA6 and CF/epoxy composites by grafting graphene oxide onto carbon fiber surface with hyperbranched polyglycerol

The interfacial properties between carbon fiber (CF) and polymer matrix are critical to the performance of CF reinforced composites. Herein, we reported a new method of tailoring the interfacial properties by grafting graphene oxide (GO) onto the CF surface with hyperbranched polyglycerol (HPG), which could improve the interfacial shear strength (IFSS) and heat resistance of CF/PA6 and CF/epoxy (EP) composites. A large number of hydroxyl groups were introduced onto CF surface by using HPG as a new coupling agent, which improved the grafting amount of GO, the polarity, wettability and surface energy of CF. The IFSS of composites at different temperature was investigated by microbond test. The results showed that after introducing GO into the interface, the IFSS of CF reinforced PA6 and epoxy composites increased by 44% and more than 30%, respectively. Moreover, the IFSS of GO modified CF/EP1 composites at 85°C was only 9.1% lower than that at 25°C. In addition, the IFSS of the CF/PA6 and CF/EP2 composites could be kept stable when the ambient temperature was lower than the melting point or glass transition temperature of the resin matrix. Finally, the interfacial enhancement mechanism was further analyzed in details.

Mussel-Inspired Co-Deposition of Polydopamine/Silica Nanoparticles onto Carbon Fiber for Improved Interfacial Strength and Hydrothermal Aging Resistance of Composites.

A novel and effective strategy was first proposed for the codeposition of a mussel-inspired nanohybrid coating with excellent wettability onto the surface of carbon fibers (CFs) by simultaneous polymerization of bioinspired dopamine (DA) and hydrolysis of commercial tetraethoxysilane (TEOS) in an eco-friendly one-pot process. Mussel-inspired nanohybrids could be adhered onto the surface of CFs firmly. The novel modification could afford sufficient polar groups and significantly improve fiber surface roughness and energy without decreasing fiber intrinsic strength, which were advantageous to promote interfacial compatibility and wettability between CFs and matrix resin. As a result, the interfacial shear strength of composites increased to 48.21 ± 1.45 MPa compared to that of untreated composites 29.47 ± 0.88 MPa. Meanwhile, the nanohybrid coating increased significantly composites’ hydrothermal aging resistance. The efficient strategy shows a promising and green platform of surface functionalization of CFs for preparing advanced polymer composites arising from broadly mechanical-demanding and energy-saving usages.

Chemical grafting of salicylaldehyde onto carbon fiber for enhancing interfacial strength of silicone resin composites

AbstractChemical grafting of salicylaldehyde onto the surface of carbon fibers (CFs) via the bridging 3‐aminopropyltriethoxysilane was reported to improve interfacial properties of composites. Surface microstructures, compositions, wettability, and surface energy of CFs before and after modification were studied. Single‐fiber tensile strength (TS) was also determined to evaluate the damage degree brought by using the grafting strategy to the fiber intrinsic strength. The interfacial shear strength of composites was characterized to confirm interfacial compatibility and adhesion between CFs and matrix resin. Antihydrothermal aging experiments were also carried out to evaluate their environmental stability. As a result, the introduced salicylaldehyde molecules could increase polar functional groups, roughness, and interfacial wettability of CFs, and thus enhance interfacial strength as well as the hydrothermal aging resistance of the resulting composites significantly. Such sharp improvements could be due to the increases of interfacial compatibility, mechanical interlocking, and chemical bonding at the interfacial region via the formation of salicylaldehyde‐modified interface. Meanwhile, the modification procedure does not decrease fiber TS.

The adhesive strength of fiber reinforced nano clay/epoxy matrix by drag-out test

Clay nanoparticles are widely available and inexpensive natural resources with many features such as a large specific surface high mechanical.As a result, they have attracted more than special attention, in particular for the fiber reinforcement materials based onpolymers.The morphology and reactivity of clay nano-reinforcements can be set by varying the weight fraction of nanoclay in the epoxy matrix. The composite interfacial shear strength, which reflects the load transfer efficiency between the fiber and the matrix determined by drag-out test for glass fiber or carbon fiber reinforced nanoclay epoxy matrix at room temperature cured. clay-based with advanced mechanical properties relies on scale control molecular properties between clay and polymer matrix. The degree of layer exfoliation was shown by scanning electron microscopy and X-ray diffraction measurements.

Effect of Water Temperature on Interfacial Shear Strength of Resin Particles Added CFRTP

In this study, interfacial shear strength of resin particles added carbon fiber/maleic acid anhydride grafted polypropylene under water temperature was investigated. Water temperature range was from room temperature to 80 oC. The maximum immersion time was 24 hours. Micro debonding tests of non and resin particles added composites were conducted. Fracture surface of resin particles added composite were observed by Scanning Electron Microscope (SEM). As a result, interfacial shear strengths of non particles added composite monotonously decreased with an increase of water temperature. Interfacial shear strength of resin particles added composite was higher than that of non resin particles added composite under all water temperatures except for 50 oC. From SEM observation, large resin particles on surface of carbon fiber after water immersion at 50 oC were found. And, many matrices and large resin particles on surface of carbon fiber after water immersion at 80 oC were found. Therefore, interfacial shear strength of composite was improved because resin particle addition prevented water penetration into the interface between fiber and matrix under water immersion less than 50 oC. And, interfacial shear strength of composite was probably improved by anchor effect of resin particle under water immersion at 80 oC.

Achieving Higher Strength and Sensitivity toward UV Light in Multifunctional Composites by Controlling the Thickness of Nanolayer on the Surface of Glass Fiber.

The interphase between fiber and matrix plays an essential role in the performance of composites. Therefore, the ability to design or modify the interphase is a key technology needed to manufacture stronger and smarter composite. Recently, depositing nanomaterials onto the surface of the fiber has become a promising approach to optimize the interphase and composites. But, the modified composites have not reached the highest strength yet, because the determining parameters, such as thickness of the nanolayer, are hardly controlled by the mentioned methods in reported works. Here, we deposit conformal ZnO nanolayer with various thicknesses onto the surfaces of glass fibers via the atomic layer deposition (ALD) method and a tremendous enhancement of interfacial shear strength of composites is achieved. Importantly, a critical thickness of ZnO nanolayer is obtained for the first time, giving rise to a maximal relative enhancement in the interfacial strength, which is more than 200% of the control fiber. In addition, the single modified fiber exhibits a potential application as a flexible, transparent, in situ UV detector in composites. And, we find the UV-sensitivity also shows a strong correlation with the thickness of ZnO. To reveal the dependence of UV-sensitivity on thickness, a depletion thickness is estimated by a proposed model which is an essential guide to design the detectors with higher sensitivity. Consequently, such precise tailoring of the interphase offers an advanced way to improve and to flexibly control various macroscopic properties of multifunctional composites of the next generation.

Highly improved Uv resistance and composite interfacial properties of aramid fiber via iron (III) coordination

The poor Uv stability and weak interfacial adhesion are considered as the bottleneck problems for further application of aramid fiber. Herein, a new strategy, Fe3+ coordination, was reported for aramid fiber to simultaneous improve its Uv resistance and composite interfacial shear strength. Fe3+ was introduced onto aramid fiber by coordinating with benzimidazole unit of fiber structure. It can reach a doping capacity of as high as 1516ug/g fiber, and the fiber surface is saturatedly covered with Fe3+. The chemical structure of Fe3+-benzimidazole brings about strong metal-enhanced fluorescence emission effect, which, in turn, greatly raises its Uv stability. Owing to the Fe3+ coordination, the tensile strength of Fe-coordinated fiber could preserve as high as 96% after Uv irradiation, compared with 73% of untreated fiber. Meanwhile, the introduction of Fe3+ improves the surface polarity of aramid fiber and consequently leads to the increase of the composite interfacial shear strength by 39%. It is believed that the Fe-coordinated fiber integrates the advantages of easy production, cost-effective and increased Uv stability, as well as high composite interfacial adhesion, and can be used as promising enhancement for the advanced composite material in harsh environment.

Interface controlled micro- and macro- mechanical properties of aluminosilicate fiber reinforced SiC matrix composites

Novel Nextel™ 440 aluminosilicate fiber reinforced SiC matrix composites, with/without chemical vapor deposited carbon interphase were fabricated by polymer derived ceramic process, and they were studied by a combination of micro- and macro- mechanical techniques such as nanoindentation, micropillar splitting, fiber push-in, digital image correction and high temperature three point bend tests. Specifically, micropillar splitting test was firstly employed to measure in-situ the localized fracture toughness. The results revealed that the carbon interphase can effectively hinder the interfacial reactions between Nextel™ 440 fiber and SiC matrix, thus remarkably weakening the composite interfacial shear strength from ∼293MPa to ∼42MPa, and enhance the composite fracture toughness from ∼1.8MPa√m to ∼6.3MPa√m, respectively. This is mainly a consequence of weak interface that triggers crack deflection at the fiber/interphase interface. Finally, this novel composite showed stable mechanical properties in vacuum at temperature range from 25°C to 1000°C.

Enhancing the fracture resistance of carbon fiber reinforced SiC matrix composites by interface modification through a simple fiber heat-treatment process

A simple method to significantly increase the toughness of carbon fiber reinforced SiC matrix composites is presented. The method is based on the heat treatment of Toray T300 carbon fibers in vacuum, leading to the in-situ formation of carbon coatings on the fiber surface that optimizes the interfacial strength in carbon fiber reinforced SiC matrix composite. The formation mechanism of the in-situ coatings was studied by transmission electron microscopy, and the effects of the in-situ carbon interphase on the interfacial property and fracture resistance of the composites were comprehensively assessed by combining transmission electron microscopy, fiber push-in and macro mechanical testing. The results reveal that the in-situ coating was originated from the pyrolysis of the proprietary sizing of the T300 fibers, that was crystallized during thermal treatment, maintaining a low oxygen content. For this reason, the resulting coating can effectively hinder the interfacial reactions in carbon fiber reinforced SiC composites, and remarkably weaken the composite interfacial shear strength from 105 ± 10 MPa to 30 ± 5 MPa. Due to the introduction of in-situ carbon interphase, the toughness of the carbon fiber reinforced SiC composite increased significantly from 1.7 ± 0.3 MPa m1/2 to 21.3 ± 0.7 MPa m1/2, triggered by toughening mechanisms such as crack deflection and fiber pullout.

Interfacial Shear Strength of Glass Fiber Reinforced Polymer Composites by the Modified Rule of Mixture and Kelly-Tyson Model

Four types of commercial grade glass fiber reinforced thermoplastics (GFRP) were used in this study. Polymer matrices included polycarbonate (PC), polyoxymethylene (POM), polypropylene (PP) and polyamide 6 (PA6). The contents of GF were 10%, 20% and 40%. The GFRP were fabricated to dumbbell specimens by injection molding machine. Tensile strength of the GFRP composites was carried out by tensile testing. Theoritical caluculation of interfacial shear strenght was analyzed using a modified rule of hybrid maixture (MRoHM) strength equation according to the orientation and direction of glass fiber reinforcing. The fiber orientation was characterized from the fractured surface observation by scanning electron microscope and optical microscope. The tensile strength of GFRP composites increased with incresing glass fiber contents. However, the declination of tensile strength from the prediction was attributed to the reduction of glass fibers length and fiber orientation in GFRP composites. It is interesting to report that the interfacial shear strength of GFRP composites was calulated according to the MroHM and the Kelly-Tyson model, which the interfacial shear strength of the composites increased with incresing glass fiber contents.

The interfacial strength and fracture characteristics of ethanol and polymer modified carbon nanotube fibers in their epoxy composites

Carbon nanotube (CNT) fibers spun from CNT arrays were used as the reinforcement for epoxy composites, and the interfacial shear strength (IFSS) and fracture behavior were investigated by a single fiber fragmentation test. The IFSS between the CNT fiber and matrix strongly depended on the types of liquid introduced within the fiber. The IFSS of ethanol infiltrated CNT fiber/epoxy varied from 8.32 to 26.64MPa among different spinning conditions. When long-molecule chain or cross-linked polymers were introduced, besides the increased fiber strength, the adhesion between the polymer modified fiber and the epoxy matrix was also significantly improved. Above all, the IFSS can be up to 120.32MPa for a polyimide modified CNT fiber, one order of magnitude higher than that of ethanol infiltrated CNT fiber composites, and higher than those of typical carbon fiber/epoxy composites (e.g. 60–90MPa). Moreover, the composite IFSS is proportional to the tensile strength and modulus of the CNT fiber, and decreases with increasing fiber diameter. The results demonstrate that the interfacial strength of the CNT fiber/epoxy can be significantly tuned by controlling the fiber structure and introducing polymer to optimize the tube–tube interactions within the fiber.

Relationship Between Interfacial Shear Strength and Interfacial Tension of Silicone/Quartz Glass Fiber Composites

In this paper, the surface tension components of three silicone resins were determined with an advanced contact angle technique, which was composed of dynamic cycling contact angle and axisymmetric drop shape analysis (ADSA). The interfacial properties of three silicone/quartz glass fiber composites were measured through interfacial shear strength (IFSS) testing experiment. It was found that the Lifshitz–van der Waals component was the main surface tension component for all of the silicones. There is a perfect linear relationship between the interfacial tension and the IFSS. With the increase of the Lifshitz-van der Waals component, the interfacial tension and the IFSS of composites increased. Therefore, the Lifshitz-van der Waals component is the most important parameter for explaining the interfacial shear property of silicone/glass fiber composites.

Effect of Morphology of ZnO Nanowire Arrays on Interfacial Shear Strength in Carbon Fiber Composites

AbstractZnO nanowire arrays are grown on carbon fiber to enhance the interface strength of a polymer matrix composite without degrading the base fiber and in-plane strength of the composite. The morphology of the nanowire array is controlled during growth to create nanowires with different aspect ratios to elucidate the structure-property relations of the interphase. Nanowires are shown to double the composite interfacial shear strength at an intermediate nanowire length, indicating that an optimal point exists and the interface can be engineered to maximize the interfacial enhancement. Furthermore, the observed effect of the morphology on interface strength indicates that the bond between the ZnO nanowire array and the carbon fiber is quite strong, more than twice as strong as the interaction between the matrix and control fiber.

Statistical strength of unidirectional composites and the effect of the interfacial shear strength

A microscopic statistical analysis of the longitudinal tensile failure of unidirectionally fibre-reinforced composites has been performed. On the basis of the random critical-core probability model, in conjunction with the results of a stress-concentration analysis with interfacial damage between fibres and matrix, the strength-distribution function and failure criterion for composites with the effect of the interfacial shear strength are derived and the relationship between the tensile strength and interfacial shear strength of composites is obtained. The present results provide an important theoretical basis for the optimum design of composite microstructure. The correctness and reasonableness of the present methods and results are validated by existing experiments. Finally, the question of optimum interfacial bonding is discussed quantitatively.