Modeling tensile response of fiber‐reinforced polymer composites using discrete element method

An advanced discrete element method (DEM), coupled with imaging techniques, of the tensile response of carbon fiber‐reinforced composite materials is presented in this article. DEM was developed using the image‐based shape structural model to determine the composites' elastic modulus, stress–strain response, and tensile strength. The developed model utilizes the microfabric micromechanical discrete element modeling technique. Clusters of very small bonded discrete elements were used to model the two composite constituents (matrix and reinforcement). The microparameters of each discrete element were determined from the macrocharacteristics of each constituent. The results from the developed model were compared with the results from an experimental case study. The results obtained from DEM simulations are within the coefficient of variation of the experimental values. The comparison indicates that the image‐based DEM micromechanical model accurately determines the elastic modulus and tensile strength of the molded carbon fiber‐reinforced polymer composite. POLYM. COMPOS., 34:877–886, 2013. © 2013 Society of Plastics Engineers     

Analytical and experimental evaluation of elastic properties of vacuum assisted resin infusion molded polymer composites with eight‐harness woven fiber mats

An analytical and experimental evaluation of elastic properties of composite materials under tensile load is presented in this paper. The analysis focuses on composite materials molded by vacuum assisted resin infusion molding (VARIM). The molded composite structure consists of AS4‐8 harness carbon fiber mats and a high‐temperature polymer (5250‐4‐RTM). The analytical model presented is adapted and formulated using optical microscopy observations of cross sections of samples molded by VARIM. Effects of resin degree of cure, fiber undulation, and resin rich areas between fiber bundles are addressed in the model. An experimental case study is presented to evaluate the accuracy of the adapted analytical model. The evaluation shows a reasonable agreement between the experimental and analytical results. POLYM. COMPOS., 29:63–71, 2008. © 2007 Society of Plastics Engineers     

Process development and characterization of spraying carbon nanofibers over fabrics for reinforcing polymer composites

Process development and characterization of spraying carbon nanofibers (CNF) over carbon fiber fabrics for reinforcing polymer composites are presented in this study. The molded composite structure consists of a high‐temperature polymer reinforced with carbon fiber fabrics sprayed with different dosages of carbon nanofibers. The materials were molded using vacuum assisted resin transfer molding process. Tensile testing and scanning electron microscopy (SEM) were used to characterize the molded materials. The results show that the tensile strength and modulus were both improved over the molded materials without CNF. Spraying CNF with a dosage of an 8 µg/mm² of the used fabrics helped to increase the tensile strength by 12%. The tensile modulus increased by 28% with a CNF dosage of 16 µg/mm². Uniform distribution of CNF was observed under SEM in the molded composites. POLYM. COMPOS., 35:1629–1635, 2014. © 2013 Society of Plastics Engineers     

Processing and properties of solution impregnated carbon fiber reinforced polyethersulfone composites

Carbon fiber reinforced polymer composites are attractive because of their high stiffness and strength‐to‐weight ratios. In order to fully utilize the stiffness and strength of the reinforcement fiber, it is necessary to bring the polymer matrix and the reinforcement fiber together with homogeneous wetting. In this paper, a solution processing technique and the mechanical properties of carbon fiber reinforced polyethersulfone composites were investigated. The polymer was dissolved in cyclopentanone and fed onto a continuous carbon fiber tow using a drum winder. The solution‐processed composite prepregs were then layed up and compression molded into unidirectional composite panels for evaluation. The composite samples showed uniform fiber distribution and reasonably good wetting. The longitudinal flexural modulus was as high as 137 GPa, and longitudinal flexural strength 1400 MPa. In addition, the effects of polymer grade and processing conditions on the mechanical properties of the composites were discussed. It is suggested that the transverse properties and interlaminar fracture toughness could benefit from higher polymer matrix molecular weight. A careful design in the spatial distribution of the molecular weight would be necessary for practical applications.     

碳纤维改性HA/PMMA生物复合材料力学性能的研究

采用原位合成与溶液共混相结合的方法,制备了短切碳纤维增强纳米羟基磷灰石(HA)/聚甲基丙烯酸甲酯(PMMA)生物复合材料。研究了碳纤维的含量和长度对HA/PMMA复合材料结构和力学性能的影响。采用万能材料试验机和扫描电子显微镜对复合材料的力学性能及断面的微观形貌进行了测试和表征。结果表明:碳纤维在HA/PMMA复合材料中分布均匀,有效提高了复合材料的力学性能;碳纤维含量为4%时,复合材料的拉伸强度、弯曲强度、压缩强度和弹性模量等均达到最大值;复合材料的断裂伸长率随碳纤维含量的增加而减小;当碳纤维含量一定时,随其长度的增加,复合材料的拉伸强度、弯曲强度和弹性模量均增加,但断裂伸长率降低。     

On the longitudinal compressive strength prediction of unidirectional laminated composites based on an improved model

The compressive failure of unidirectional (UD) composite laminates is investigated using an improved model. Most of the existing models to predict the compressive strength of UD composites are either based on microbuckling or kinking of fibers. However, the failure mechanism analysis based on the SEM microscopy observations of failed specimens shows that the two mechanisms are responsible for the failure simultaneously when kinking occurs following the microbuckling of fibers. Therefore, the fiber microbuckling and fiber kinking models are combined to predict the compressive strength of UD T300/QY8911 composite laminate. Furthermore, this study proposes a new model for the stiffness of the foundation determination, making the predicted microbuckling strength closer to its real value. Also the effects of parameters presented in the prediction formula on the compressive strength are discussed, and it is found that the Young's modulus of matrix is the most important parameter. The predicted compressive strength using the improved model with combined modes shows a very good agreement with the experiment measurement. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Characterizing elastic properties of carbon nanotube‐based composites by using an equivalent fiber

Effective elastic properties for carbon nanotube (CNT)‐reinforced composites are obtained through a variety of micromechanics techniques. An embedded CNT in a polymer matrix and its surrounding interphase is replaced with an equivalent fiber for predicting the mechanical properties of the CNT/polymer composite. Formulas to extract the effective material constants from solutions for the representative volume element under three loading cases are derived based on the elasticity theory. The effects of an interphase layer between the nanotubes and the polymer matrix as result of effective interphase layer are also investigated. Furthermore, this research is aimed at characterizing the elastic properties of CNTs‐reinforced composites using Eshelby–Mori–Tanaka approach based on an equivalent fiber. The variations of mechanical properties with tube radius, interphase thickness, and degree of aggregation are investigated. It is shown that the presence of aggregates has stronger impact than the interphase thickness on the effective modulus of the composite. This is because aggregates have significantly lower modulus than individual CNTs. POLYM. COMPOS., 2013 © 2013 Society of Plastics Engineers     

深潜壳体用高模量树脂基体的研究——基体模量对复合材料抗压抗剪性能的影响

制备了高模量树脂基单向复合材料，测试了单向复合材料的纵向压缩性能和平面剪切性能。研究了基体模量对单向复合材料抗压强度及复合材料平面剪切性能的影响，结果表明：单向复合材料的抗压强度与基体模量成线性比例关系，随基体模量的提高而提高，复合材料的平面剪切性能与基体模量基本上呈线性关系，平面剪切强度亦随基体模量的提高而提高。以模量达５．３６ＧＰａ的环氧树脂作为复合材料的树脂基体制备的，单向玻璃纤维增强复合材料其抗压强度高达１．２９５ＧＰａ，碳纤维增强的复合材料抗压强度高达１．３７２ＧＰａ，与普通环氧树脂的单向复合材料相比，分别提高了５５％和４５．８％；复合材料的平面剪切强度达６４．５ＭＰａ，比普通环氧树脂复合材料的平面剪切强度提高了４４．３％，满足了深潜壳体对复合材料抗压强度的要求。     

Nonisothermal transient filling simulation of fiber suspended viscoelastic liquid in a center‐gated disk

The present study numerically investigates a fiber orientation in injection‐molded short fiber reinforced thermoplastic composite by using a rheological model, which includes the nonlinear viscoelasticity of polymer and the anisotropic effect of fiber in the total stress. A nonisothermal transient‐filling process for a center‐gated disk geometry is analyzed by a finite element method using a discrete‐elastic‐viscous split stress formulation with a matrix logarithm for the viscoelastic fluid flow and a streamline upwind Petrov–Galerkin method for convection‐dominated problems. The numerical analysis result is compared to the experimental data available in the literature in terms of the fiber orientation in center‐gated disk. The effects of the fiber coupling and the slow‐orientation kinetics of the fiber are discussed. Also, the effect of the injection‐molding processing condition is discussed by varying the filling time and the mold temperature. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Influence of PP fiber and SBR latex on the mechanical properties of crumb rubber mortar

This article presents a new kind of rubber mortar modified by polypropylene fiber (PP fiber) and styrene‐butadiene rubber latex (SBR latex). The mechanical properties of this crumb rubber mortar were investigated in the research, including the compressive strength, flexural strength, flexural toughness, and flexural elasticity modulus. The test results showed that the flexural toughness index of the rubber mortar was seen to enhance by about 50–100% with the addition of PP fiber and SBR polymer latex. Due to the addition of PP fiber and SBR latex, the flexural elastic modulus of rubber mortar could further reduce by 4–27%. The three‐phase composite dispersion model of this rubber mortar was put forward. Furthermore, it was observed from scanning electron micrograph that the interfacial transition zone between the rubber particles and cement paste was enhanced by the SBR latex, and the interleaving of polymer films and rubber particles strengthen the flexibility and toughness of the mortar. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40591.     

Low Cost and Rapidly Processed Randomly Oriented Carbon/Carbon Composite Bipolar Plate for PEM Fuel Cell

The objective of the present work is to develop carbon/carbon (C/C) composite bipolar plate at low cost with rapid processing time by a novel process. Carbon/carbon composite was developed using exfoliated carbon fiber reinforcement, isroaniso as primary matrix precursor, and resole type phenolic resin as secondary matrix precursor. Randomly oriented hybrid carbon fiber (T‐800 and P‐75) reinforced hybrid carbon matrix composite was fabricated. The slicing and channel forming were carried out using simple and conventional machines. The competency of the material was investigated by characterizing and analyzing density, scanning electron miscroscopy (SEM), compressive strength, compressive modulus, flexural strength, tensile strength, impact strength, hardness, electrical conductivity, thermal conductivity, coefficient of thermal expansion, permeability, and corrosion current. The C/C composite bipolar plate with exfoliated carbon fibers offered bulk density 1.75 g cm⁻³, tensile strength 45 MPa, flexural strength 98 MPa, compressive strength 205 MPa, electrical conductivity 190 (through‐plane) and 595 S cm⁻¹ (in‐plane), and thermal conductivity 24 (through‐plane) and 51 W m⁻¹ K⁻¹ (in‐plane). Further, single cell test was performed to evaluate the effectiveness of the C/C composite bipolar plate in the PEM fuel cell and the performance was compared with the commercial graphite bipolar plate at different operating temperatures.     

Optimization of stress wave propagation in a multilayered elastic/viscoelastic hybrid composite based on carbon fibers/carbon nanotubes

The hypothesis of incorporating carbon nanotubes (CNTs) into the interfacial layers of fiber‐reinforced polymer composites fiber‐reinforced Polymers (FRPs) to enhance their mechanical properties and mitigate the stress wave propagation during a blast event is investigated. A numerical model is developed to simulate the stress wave propagation in a laminated elastic/viscoelastic FRP. Coupled with multiobjective optimization paradigms, the optimal CNTs contents in the interfacial layers are determined to minimize the stress‐to‐strength ratio in each layer. A case study demonstrating the design of a five‐layered FRP subjected to a blast event is presented. The simulation revealed that the viscoelastic properties of the matrix material contribute significantly to the energy dissipation during stress wave propagation. It is shown that addition of 0.69% CNTs by volume to the epoxy interface significantly enhances the ability of composite to resist blast loading. Results were compared with a standard model that assumes only elastic behavior. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Structure and properties of UHMWPE fiber/carbon fiber hybrid composites

Ultrahigh molecular weight polyethylene (UHMWPE) fiber/carbon fiber hybrid composites were prepared by inner‐laminar and interlaminar hybrid way. The mechanical properties, dynamic mechanical analysis (DMA), and morphologies of the composites were investigated and compared with each other. The results show that the hybrid way was the major factor to affect mechanical and thermal properties of hybrid composites. The resultant properties of inner‐laminar hybrid composite were better than that of interlaminar hybrid composite. The bending strength, compressive strength, and interlaminar shear strength of hybrid composites increased with an increase in carbon fiber content. The impact strength of inner‐laminar hybrid composite was the largest (423.3 kJ/m²) for the UHMWPE fiber content at 43 wt % to carbon fiber. The results show that the storage modulus (E′), dissipation factor (tan δ), and loss modulus (E″) of the inner‐laminar hybrid composite shift toward high temperature remarkably. The results also indicate that the high‐performance composite with high strength and heat resistance may be prepared by fibers' hybrid. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1880–1884, 2006     

Effect of macromolecular coupling agent on the property of PP/GF composites

Silane‐grafted polypropylene manufactured by a reactive grafting process was used as the coupling agent in polypropylene/glass‐fiber composites to improve the interaction of the interfacial regions. Polypropylene reinforced with 30% by weight of short glass fibers was injection‐molded and the mechanical behaviors were investigated. The results indicate that the mechanical properties (tensile strength, tensile modulus, flexural strength, flexural modulus, and Izod impact strength) of the composite increased remarkably as compared with the noncoupled glass fiber/polypropylene. SEM of the fracture surfaces of the coupled composites shows a good adhesion at the fiber/matrix interface: The fibers are coated with matrix polymer, and a matrix transition region exists near the fibers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1537–1542, 1999     

Effect of filler addition and strain rate on the compressive strength of silica styrene‐butadiene rubber‐filled epoxy composites

The compressive failure of nanoparticle silica and styrene‐butadiene rubber (SBR)‐filled epoxy composites has been investigated. Significant increase in compressive strength, compressive modulus, work of yielding, and work of fracture was noted for the cases of composites containing low weight fraction of silica and SBR. The compressive strength is about 4–10 times of the tensile strength for composite material containing different weight percent of SBR. Increase in compressive yield strength and decrease in compressive ultimate strength have been observed with crosshead speed 0.1–100 mm/s over all weight content of SBR and silica. The material shows increased elastic region with increasing crosshead speed. This indicates that the material is expected to behave more elastically and less plastically over all the crosshead speeds. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Study on the Mechanical,Rheological, and Morphological Properties of Short Kevlar™ Fiber/s-PS Composites

This article deals with oxy-fluorinated short Kevlar^TM fiber reinforcement and its effect on the dynamic, mechanical, and rheological properties of the syndiotactic polystyrene composites. The composites were prepared using a twin-screw extruder at 20 rpm and the resulting composite was molded under injection molding. The study shows that the addition of oxy-fluorinated Kevlar^TM fiber into the syndiotactic polystyrene matrix significantly affects the dynamic mechanical properties of the composite by appreciably increasing storage modulus. Rheological properties reveal a significant enhancement of viscosity of the treated composite, due to the formation of a strong interface between fiber and matrix. Oxy-fluorinated fiber incorporation leads to improved tensile strength, elastic modulus, and impact strength of the resulting composite as a result of better fiber-matrix adhesion at the interface.     

Effect of temperature and aging on the mechanical properties of concrete: Part II. Prediction model

In Part I, empirical relationships between compressive strength and splitting tensile strength or elastic modulus with temperature and aging were proposed. This paper investigates new prediction models estimating splitting tensile strength and elastic modulus without knowing compressive strength. The prediction model is suggested on the basis of the equation that was suggested to predict compressive strength. The mechanical properties calculated by the model are compared with empirical results presented in Part I. To evaluate in-place applicability of the model, the empirical data on strength and elastic modulus of concrete cured at variable temperature are compared with the values estimated using the prediction model. The prediction model properly estimates the strength and elastic modulus of Types I and V cement concretes cured at constant and variable temperature conditions.     

Structure–property relationships in glass reinforced polyamide,part 2: The effects of average fiber diameter and diameter distribution

We present the results of an extensive study of the influence of average fiber diameter and the width of the diameter distribution on the performance of injection‐molded glass‐fiber reinforced polyamide 6,6. In the average fiber diameter range from 9 to 18 μm, dry‐as‐molded (DaM) composite unnotched impact and tensile strength decreased significantly. The composite notched impact performance and tensile modulus showed little dependence on fiber diameter. The influence of broadening the fiber diameter distribution by blending glass fiber samples of different average diameter was found to be particularly negative on the level of composite unnotched impact when compared at equal number average diameter. After hydrolysis treatment, the composite tensile strength and modulus exhibited a large drop compared to the DaM results. In contrast, the unnotched impact results became insensitive to fiber diameter after hydrolysis. The average level of unnotched impact after hydrolysis was sufficiently high to show an increase over DaM when the fiber diameter was above 14 μm. Residual fiber length correlated significantly with fiber diameter with a lower average length for thinner fibers. The interfacial shear strength was found to be in the range of 26–34 MPa for DaM composites. There was a highly significant inverse correlation between the DaM interfacial strength and the average fiber diameter. It is shown that results from both tensile and unnotched impact measurements can be brought back to single trend lines by using a Z average value for the average fiber diameter, which is more heavily weighted to the thicker fibers in the distribution. POLYM. COMPOS., 28:331–343, 2007. © 2007 Society of Plastics Engineers     

Mechanical and thermal properties of hierarchical composites enhanced by pristine graphene and graphene oxide nanoinclusions

Epoxy resin nanocomposites incorporated with 0.5, 1, 2, and 4 wt % pristine graphene and modified graphene oxide (GO) nanoflakes were produced and used to fabricate carbon fiber‐reinforced and glass fiber‐reinforced composite panels via vacuum‐assisted resin transfer molding process. Mechanical and thermal properties of the composite panels—called hierarchical graphene composites—were determined according to ASTM standards. It was observed that the studied properties were improved consistently by increasing the amount of nanoinclusions. Particularly, in the presence of 4 wt % GO in the resin, tensile modulus, compressive strength, and flexural modulus of carbon fiber (glass fiber) composites were improved 15% (21%), 34% (84%), and 40% (68%), respectively. Likewise, with inclusion of 4 wt % pristine graphene in the resin, tensile modulus, compressive strength, and flexural modulus of carbon fiber (glass fiber) composites were improved 11% (7%), 30% (77%), and 34% (58%), respectively. Also, thermal conductivity of the carbon fiber (glass fiber) composites with 4% GO inclusion was improved 52% (89%). Similarly, thermal conductivity of the carbon fiber (glass fiber) composites with 4% pristine graphene inclusion was improved 45% (80%). The reported results indicate that both pristine graphene and modified GO nanoflakes are excellent options to enhance the mechanical and thermal properties of fiber‐reinforced polymeric composites and to make them viable replacement materials for metallic parts in different industries, such as wind energy, aerospace, marine, and automotive. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40826.