Interlaminar fracture toughness of woven fabric composite laminates with carbon nanotube/epoxy interleaf films

The Mode I interlaminar fracture behavior of woven carbon fiber/epoxy composite laminates incorporating partially cured carbon nanotube/epoxy composite films has been investigated. Laminates with films containing carbon nanotubes (CNTs) in the as‐received state and functionalized with polyamidoamine were evaluated, as well as laminates with neat epoxy films. Double‐cantilever beam (DCB) specimens were used to measure G_Ic, the critical strain energy release rate (fracture toughness) versus crack length. Post‐fracture microscopic inspection of the fracture surfaces was performed. Results show that initial fracture toughness was improved with the amino‐functionalized CNT/epoxy interleaf films, but the important factor appears to be the polyamidoamine functionalization, not the CNTs. The initial fracture toughness remained relatively unaffected with the incorporation of neat epoxy and as‐received CNT/epoxy interleaf films. Plateau fracture toughness was unchanged with the use of functionalized CNT/epoxy interleaf films, and was reduced with the use of neat epoxy and as‐received CNT/epoxy interleaf films. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dynamic-mechancial response of graphita/epoxy composite laminates and neat resin

The dynamic mechanical properties of carbon-fiber-reinforced, epoxy-matric-composite laminates subjected to loading perpendicular to the plane of lamination and of neat epoxy resin are reported. The dynamic mechanical measurements were performed in the frequency range from 0.1 to 40 Hz and at temperatures between 20° and 200°C at deformation levels within the linear viscoelastic region by the use of a Dynastat apparatus. It is found that thein-phase and out-of phase stiffnesses superpose to form master curves covering a frequency range of 12 decades. By a suitable scaling procedure of the master curves, it is found that thein-phase stiffiness has tbe same shape and the out-of-phase stiffness has the same dispersion for all laminates irrespective of the stacking sequence and are nearly identical to those for neat epoxy resin, An empirical function for the relaxation modulus is developed that, when converted to dynamic modulus, gives a good overall agreement for both components of the dynamic stiffness as a function of frequency. Absorbed moisture is found to cause a reduction in thhe elevated temperature mechanical properties of a laminate due to a reduction in the glass-transition temperature of the resin. It is also found thatthemositure absorption is a reversible process, in the sense that the initially dry properties of the laminate are recovered afterredrying the wet sample.     

Temperature effect on interfacial bonding property of single‐carbon fiber/epoxy resin composite

The changes in interfacial fracture energy of three kinds of commercially sized carbon fiber (CF)/epoxy resin composites in the range from ambient temperature to 130°C were investigated using the single‐fiber fragmentation test to evaluate the heat resistance of the interphase. The effects of CF sizing on the interfacial bonding property were studied using desized CF/epoxy resin composites. Thermogravimetric analysis and differential scanning calorimetry of the combination of sizing and matrix were employed to investigate the role of sizing on the variations in the fiber/matrix interfacial property under elevated temperature. The interfacial fracture energy values of all the studied CF composites were found to decrease quickly during the initial stage of temperature rise and drop gradually at higher temperature. At elevated temperature, the desized CF composites had higher heat resistance than the corresponding sized fiber composites. The differences in the interfacial heat resistance among the three kinds of CF composites and the difference in the interfacial thermal stability between the sized and the desized fiber composites were related to different glass transition temperatures of the interphases. The interaction between sizing and the matrix and the chain motion of the crosslink structure of the interphase has been suggested to determine the interfacial heat resistance. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Repeated impact behavior of glass/epoxy laminates

The response of glass–epoxy composites to repeated impact for various impact energies ranging from 5 to 15 J was investigated. Specimens with two different stacking sequences were studied; [0/90/0/90]_S and [0/90/+45/−45]_S. In addition to the room temperature, impact tests were also performed at −40°C environmental test temperature for impact energy of 15 J. Contact force‐deflection and energy‐time curves at each test and the number of impacts to failure (N_f) were obtained for each experiment. Compression after impact (CAI) tests were also conducted to determine the residual load carrying capacity of the damaged specimens. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Mode II interlaminar fracture behavior of carbon bead‐filled epoxy/glass fiber hybrid composite

To investigate the effect of including carbon beads on the mechanical properties of epoxy resin, the fracture toughness of carbon bead‐filled epoxy was earlier evaluated using a CT (compact tension) specimens and Mode I fracture toughness was observed. Based on those results, in this study, the Mode II interlaminar fracture toughness of carbon bead filled epoxy/glass fiber hybrid composites was evaluated using end notch flexure (ENF) specimens. The hybrid composites showed increased Mode II interlaminar fracture toughness. The optimal bead volume fraction was around 15%.     

Effects of styrene-isoprene copolymer glass fiber coatings on woven glass cloth epoxy composite performance

Woven glass-epoxy composites were prepared from mats that had been treated in a variety of ways. Fibers were coated with a commercial sizing, no sizing, and a surfactant coating. In addition, fibers were coated with styrene-isoprene copolymers at varying molar ratios using a novel technique termed admicellar polymerization. Dynamic contact angle measurements were used to quantify the effect of the different coating techniques on the fiber, while dynamic mechanical analysis (DMA) and flexural testing were used to characterize the cured composites. Wetting studies conducted with EPON 828 resin revealed no difference in wetting for the polymer-treated fiber compared to the commercially-treated fiber. Aqueous wetting results were consistent with a surfactant layer adsorbed on the polymer treated and surfactant treated fiber surface. DMA established that both the polymer and surfactant treatment depressed the alpha transition temperature of the composite and suggested an interpenetrating network existed at the fiber-matrix interface. Flexural strength testing showed the properties of the composites made from surfactant-treated and polymer-treated glass fibers were comparable to composites made from commercially-sized fibers and exceeded the flexural strength of the composite made from glass fibers without sizing.     

Fabrication and physicochemical properties of glass fabric–multifunctional epoxy resin composite

Polymer Bulletin - (2E,6E)2,6-Bis(4-amino benzylidene)cyclohexanone (BABC) was synthesized and used as a curing agent for tetrafunctional epoxy resin of bisphenol-C-formaldehyde (EBCF). Cured resin...     

5231环氧树脂体系/玻璃布复合材料性能研究

一种160℃固化的改性环氧树脂体系5231,该树脂体系粘性适中,具有良好的阻燃性和较高的抗滚筒剥离强度,其预浸料可与Nomex芳纶纸蜂窝直接共固化。另外,其玻璃布复合材料力学性能满足了技术指标要求,耐热性和耐湿热性良好,并已在飞机的结构件上得到应用。     

Preparation of emulsion‐type thermotolerant sizing agent for carbon fiber and the interfacial properties of carbon fiber/epoxy resin composite

A modified resin was synthesized through the reaction between dodecylamine and tetraglycidyldiaminodiphenylmethane (TGDDM), which was used as the film former of sizing agent for carbon fiber (CF). The sizing agents were prepared through phase inversion emulsification method. Fourier transform infrared spectroscopy (FTIR) was utilized to analyze the modified resin. Particle sizes of the sizing agents were tested to evaluate their stabilities. Differential scanning calorimetry (DSC) results demonstrated that the glass transition temperature (T_g) of the modified TGDDM is much higher than the T_g of the cured epoxy resin E‐44. The influences of the sizing treatment on CF were investigated by abrasion resistance, fluffs, and stiffness tests. The maximum abrasion resistance increased by 172.8%, compared with the abrasion resistance of the desized CF. Interlaminar shear strength (ILSS) results of the CF/TGDDM composites indicated that the interfacial adhesion between CF and matrix resin was greatly improved after CF was sized. The maximum ILSS value could obtain a 29.16% improvement, compared with the ILSS of the desized CF composite. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41882.     

碳纤维/环氧树脂复合材料的改性及改性机理

介绍了碳纤维/环氧树脂复合材料中碳纤维的增强机理.综述了纳米材料、聚合物对碳纤维/环氧树脂复合材料的改性进展,并总结了相应的改性机理.探索新型柔和的碳纤维表面处理技术以及对碳纤维表面接枝将是碳纤维/环氧树脂复合材料改性的发展方向.     

Influence of polyethersulfone modification of a tetrafunctional epoxy matrix on the fracture behavior of composite laminates based on woven carbon fibers

In this study, the influence of poly(ethersulfone) (PES) as a modifying agent of a tetrafunctional epoxy matrix (TGDDM) on the mechanical behavior of composite laminates based on woven carbon fibers has been investigated. Dynamic mechanical experiments were performed on neat matrix resins and on their corresponding laminate composites. Mode-I and Mode-II fracture toughness tests for the bulk matrices and their composites, respectively, and also flexural and short beam shear tests (SBS) were carried out. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to investigate the morphologies obtained. A nanoscopic phase separation was obtained after PES addition, which was not able to stabilize the fracture process, leading, as a consequence, to a poor extent of improvement on fracture toughness properties. Polym. Compos. 25:480–488, 2004. © 2004 Society of Plastics Engineers.     

Photo-oxidation and photoprotection of the surface resin of a glass fiber–epoxy composite

The rapid photo-oxidation of the surface epoxy resin of a commercial seven-ply laminate (Scotchply 1009-26) is due principally to the epoxy novolac resin component. The photo-oxidation rate of this resin is eight times that of the other component, a bisphenol A epoxy resin. This rate depends on the conditions of cure, and photo-initiation occurs in part through aromatic carbonyl groups formed by oxidation of the methylene linkages of the novolac at the cure temperature (160–180°C). Inhibition of this thermal oxidation by vacuum cure or a chain-terminating antioxidant increases the photostability. Photoprotection of thin resin sections by the UV stabilizer 2-hydroxy-4-isooctoxybenzophenone and an epoxidized analog is assessed.     

Optimum consolidation of all‐polyester woven fabric‐reinforced composite laminates by film stacking

This study involves the examination of all‐polyester composites prepared using the two‐step consolidation of lamina and composites. The raw materials in this process are poly(ethylene terephthalate) (PET) plain woven fabric, used as reinforcement, and biodegradable polyester, used as a matrix. First, the all‐polyester laminae were produced at various consolidation temperatures (200, 210, 220, and 230°C) with a holding time of 1 min. Then, all‐polyester composites were prepared at various consolidation temperatures (200, 205, 210, 215, and 225°C) with a 3‐min holding time, using all‐polyester laminae consolidated at 220°C. This study established that proper lamina preparation is necessary for preparing a good composite, and a method is proposed that allows a wide processing window for composite preparation. The method is validated through the results of tensile, flexural, and Izod impact tests of lamina and composites. The optimum consolidation temperature observed was 220°C for all‐polyester lamina and 200–215°C for all‐polyester composites. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Tensile properties of glass microballoon‐epoxy resin syntactic foams

The effect of hollow glass particle (microballoon) volume fraction in the range of 0.3–0.6 on the tensile properties and fracture mode of syntactic foams is characterized in the present research. Sixteen types of syntactic foams have been fabricated and tested. Four types of glass microballoons, having 220, 320, 380, and 460 kg/m³ density, are used with epoxy resin matrix for making the syntactic foam samples. These foams contain 30, 40, 50 and 60% microballoons by volume. All types of microballoons have the same size but different wall thickness, which reflects as a difference in their density. It is observed that the tensile strength increases with a decrease in the volume fraction of microballoons. All types of syntactic foams showed 60–80% decrease in the tensile strength compared with that of the neat resin. The foams containing low strength microballoons showed lower tensile modulus compared with that of the neat resin, but the presence of high strength microballoons led to an increase in the tensile modulus of the composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1254–1261, 2006     

The hierarchical structure and flexure behavior of woven carbon fiber epoxy composite

The hierarchical structure and flexure behavior of woven carbon fibers epoxy composite were investigated in this work. First, the hierarchical structure of the composite is characterized on three levels: composite, ply, and yarn. Structura imperfections,

1 In this paper, “structural imperfections” is used to describe the inherent structural characteristics of the actual composite, which deviate from the theoretically ideal and perfect composites, control, that are used in composite theories.

such as, ply‐ply misalignment, ply‐ply offset, and resin pockets, are identified and described. Second, a four‐point bending arrangement is used to study the flexure properties of the composite. Additionally, in‐situ traveling microscope and acoustic emission (AE) techniques are utilized to gain insight to the failure proceses during flexure test. AE showed early stages of matrix cracking before visual observation, which makes it a valuable tool for early failure detection.     

炭黑/环氧树脂复合材料导电行为的研究

分别采用不同的混合分散方法制备炭黑/环氧树脂(CB/EP)复合材料(CB牌号为F101、XE2,EP牌号为E-54、E-51和E-44),研究了制备工艺、CB用量和CB结构等对复合材料导电性能的影响。结果表明:不同方法制得的复合材料体积电阻率的大小依次为机械混炼法离心混合法超声分散法;CB/EP复合材料的导电性能随CB用量增加而显著提高,并且F101/E-54、XE2/E-54复合材料体系均表现出明显的导电渗流行为;CB结构对复合材料的导电性能影响较大,F101/E-54、XE2/E-54复合材料体系的导电渗流阈值分别为3.85%、0.47%。     

Compression behavior of woven glass/epoxy specimens using a new end‐loaded hybrid specimen

A new compression specimen was applied to woven glass/epoxy laminates. The specimen consists of epoxy layers cast on the sides of the laminate to prevent buckling. Thin‐sheet aluminum ends enable alignment and avoid crushing under end loading, which does not require any special fixture. The compression stress–strain behavior of the laminate was obtained from the specimens by discounting the previously measured stress–strain curve of the epoxy backings. Despite the higher scatter in compression tests, the average modulus was practically identical to the tensile modulus. Moreover, failure occurred away from the ends in nearly all of the specimens tested. The average compressive strength was 84% of the tensile strength and consistent with the flexural strength measured in four‐point bending tests. The present compression specimen could, therefore, become an interesting alternative to the more elaborate standard test methods available. Nevertheless, this new compression testing approach needs further evaluation involving application to other materials. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Comparison of mechanical and ballistic performance of composite laminates produced from single‐layer and double‐layer interlocked woven structures

Textile structures have become quite popular as reinforcement materials in composite laminates due to their high impact‐damage tolerance and energy absorption ability. The impact performance of textile composites is not only affected by the type of fiber/matrix but also by the fabric structure used as reinforcement. The aim of this study was to compare the mechanical and ballistic performance of composite laminates reinforced with single‐layer and double‐layer interlocked woven fabrics. Kevlar^®−29 multifilament yarn was used for preparation of all the fabric structures and epoxy resin was used as the matrix system. The composites were produced using a hand lay‐up method, followed by compression molding. The mechanical and ballistic performance of composites reinforced with single‐layer and double‐layer interlocked woven fabrics was investigated in this study. The energy absorption and mechanical failure behavior of composites during the impact event were found to be strongly affected by the weave design of the reinforcement. The composites reinforced with double‐layer interlocked woven fabrics were found to perform better than those comprising single‐layer fabrics in terms of impact energy absorption and mechanical failure. POLYM. COMPOS., 35:1583–1591, 2014. © 2013 Society of Plastics Engineers     

碳纤维湿法缠绕用环氧树脂基体研究

以TDE-85树脂和AFG-90树脂为主体树脂,混合芳香胺为固化剂,研究了一种适合于碳纤维复合材料湿法缠绕成型的树脂配方。结果表明,该树脂的黏度低(＜550 mPa·s)、适用期长,其浇铸体具有优异的力学性能,其拉伸强度为107 MPa,拉伸模量为4．09 GPa,弯曲强度为161 MPa,弯曲模量为3．88 GPa,断裂伸长率超过6%。用其制备的T-700碳纤维缠绕复合材料界面粘接好,NOL环层间剪切强度达到66．8 MPa,拉伸强度达到2．44 GPa。     

Research on the mechanical properties prediction of carbon/epoxy composite laminates with different void contents

The influence of the porosity on the static mechanical strength of the carbon fiber fabric reinforced epoxy composites laminates was investigated. The tensile, compressive, bending, and interlaminar strength test on the CFRP laminates with porosity of 0.33% and 1.50% were conducted and simulated by a finite element analysis model. The article proposes the failure criterion of the static mechanical strength of the fabric fiber reinforced composites based on the improved Hashin failure criterion that is suitable for the undirectional composite laminates. The basic composite strength parameters are used to evaluate the mechanical properties of CFRP laminates with different porosities. A finite element analysis model is established by using software ABAQUS™ combined with the sudden stiffness degradation model. The experiment results show that the tensile, compressive, bending, and interlaminar strength decrease with the increasing porosities. The tensile, compressive, bending, and interlaminar strength of the fabric carbon fiber reinforced epoxy composites laminates are simulated accurately by the finite element model. POLYM. COMPOS., 14–20, 2016. © 2014 Society of Plastics Engineers