树脂基玻璃纤维复合材料吸湿对性能影响及其机理研究

研究了树脂基玻璃纤维增强复合材料吸湿过程及其机理。通过对玻璃纤维复合材料吸湿后相关性能的测试,了解了复合材料的吸湿行为,以及吸湿行为对相关性能的影响。研究认为树脂基体及界面的吸湿行为对材料整体性能影响很大,宏观表现为力学性能、热性能等明显下降。研究结果表明纤维复合材料吸湿性不仅取决于树脂基体,与纤维及界面均有关系。     

Crashworthiness of various random chopped carbon fiber reinforced epoxy composite materials and their strain rate dependence

The ACC (Automotive Composite Consortium) is interested in investigating the use of random chopped fiber reinforced composites as crash energy absorbers primarily because of the low costs involved in their manufacture thus making them cost effective for automotive applications. Although many scientists have investigated the energy absorption characteristics in various continuous fiber reinforced composite materials and their dependence on strain rate, there is very little literature available on the energy absorption and crushing characteristics of random chopped fiber reinforced composite materials and their strain rate dependence. Therefore, the primary goal was to determine the crashworthiness of various random chopped carbon fiber composite material systems. To meet this goal, first an experimental set up was developed for discerning the deformation behavior and damage mechanisms that occur during the progressive crushing of composite materials. The three different random chopped carbon reinforced epoxy composite material systems studied were P4, HexMC, and CCS100. Quasi‐static progressive crush tests were then performed on these random chopped carbon fiber composite plates to determine their crashworthiness. In addition, an attempt was made to investigate and characterize the strain rate effects on the energy absorption of a random chopped carbon fiber P4 composite. The specific energy absorption was found to increase with increasing loading rate from 15.2 to 762 cm/min. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1477–1486, 2006     

Effects of hygrothermal aging on the thermomechanical properties of a carbon fiber reinforced epoxy sheet molding compound: An experimental research

Carbon fiber sheet molding compounds (C-SMCs) are discontinuous fiber reinforced composite materials. Among them, epoxy-based C-SMCs are becoming relevant materials due to their high thermomechanical performance and better formability than continuous fiber reinforced composites. The thermomechanical performance of epoxy resins and epoxy based continuous carbon fiber composites have shown to be influenced by hygrothermal aging. In this work, this influence is studied for an epoxy-based C-SMC. Epoxy-based C-SMC samples were hygrothermally aged by means of accelerated conditioning, exposing them to 65% relative humidity, and 80°C in a climatic chamber. The equilibrium moisture content, as well as the moisture diffusion coefficient has been determined. The thermomechanical properties of epoxy C-SMC have been analyzed by dynamic mechanical analysis, tensile, 3-point bending, and short beam tests in dry and aged samples. The results showed that epoxy C-SMC is affected by hygrothermal aging in the cases of moisture intake and its effects on T_g value, but interestingly, the hygrothermal aging did not generate any degradation effects in the mechanical response of epoxy C-SMC.     

Isolation and characterization of betel nut leaf fiber: Its potential application in making composites

Betel nut leaf fiber (BNLF) is a new finding as cellulosic filler for polymer composites. Its main constituents are 75% α‐cellulose, 12% hemicelluloses, 10% lignin, and 3% others matter, viscosity average molecular weight 132,000 and degree of crystallinity 70%. In the present work, BNLF reinforced polypropylene (PP) composites were prepared using heat press molding method. 5–20 wt% short length fiber is taken for getting benefits of easy manufacturing and the fiber was chemically treated with NaOH, dicumyl peroxide (DCP), and maleic anhydride‐modified PP (MAPP) to promote the interfacial bond with PP. The extent of modification of fiber was assessed on the basis of morphology, bulk density, moisture absorption, thermal, and mechanical properties of untreated fiber, treated fiber, and their reinforcing PP composites. The tensile and flexural strength of composites increase with the increase of fiber loading up to 10 and 20 wt%, respectively. It was also observed that Young's modulus and flexural modulus increase with fiber loading. The thermal degradation behavior of resulting composites was investigated. Among the various treated fibers, MAPP‐treated fiber composite showed best interfacial interactions as well as mechanical and thermal properties. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Einfluß der Faserbehandlung auf das Feuchteverhalten von glasfaserverstärkten Epoxidharzen

The strength of glass fiber reinforced epoxy resins can be significantly reduced under exposure to moisture. Besides other factors, the interface between fiber and matrix plays an important role. It is responsible for a proper load transfer between fibers and matrix by coupling effects and significantly affects the moisture behavior of the composite. In the present study, glass fibers were treated with different sizes under defined conditions and embedded in three epoxy matrix systems. The composites were exposed to different moisture conditions. The change of the shear and impact behavior due to moisture was determined. It will be shown that the composites with coupling agent treated fibers are significantly more resistant to moisture than composites with poor fiber/matrix adhesion. Furthermore, it will be shown that also the binder plays an important role if the material is subjected to moisture.     

Effect of various water immersions on mechanical properties of roselle fiber–vinyl ester composites

In the present communication, the effect of water absorptions on mechanical properties of roselle fiber reinforced vinyl ester composites prepared by wet hand lay‐up method was studied. Water absorption tests were conducted by immersing composite specimens into three different water environments, namely distilled water, ground water, and sea water, which were at room temperature, for a period of 10 days. The water absorption behavior of composite was found to follow a non‐Fickian behavior. The maximum water absorption percent and diffusion coefficient were determined from the obtained water absorption curves. The scanning electron microscopy was used for the fractographic studies on the fractured surface of composite. The results show that composites exposed to sea water environment absorb more water absorption percent than that of other water environments. It was observed that the water absorption percent increased with increasing fiber loading. Mechanical properties of dry composite specimens were compared with wet composite specimens. Mechanical properties were found to decrease with an increasing percentage of water uptakes. POLYM. COMPOS., 36:1638–1646, 2015. © 2014 Society of Plastics Engineers     

Barrier properties for short‐fiber‐reinforced epoxy foams

The barrier properties of short‐fiber‐reinforced epoxy foam are characterized and compared with unreinforced epoxy foam in terms of moisture absorption, flammability properties, and impact properties. Compression and shear properties are also included to place in perspective the mechanical behavior of these materials. Compared with conventional epoxy foam, foam reinforced with aramid fibers exhibits higher moisture absorption and lower diffusion, while glass‐fiber‐reinforced foam is significantly stiffer and stronger. In addition, the polymeric foam composites studied present superior fire‐resistance compared with conventional epoxy foam systems. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3266–3272, 2006     

Comparison of mechanical performance and fracture behavior of gelatin composites reinforced with carbon fibers of different fiber architectures

Gelatin‐based composites reinforced, respectively, with continuous carbon fibers, short carbon fibers, plain woven carbon fibers, and carbon fiber felt were investigated. Tensile and shear strengths, and their changes with fiber volume fraction (V_f) of these four composites were compared. It was demonstrated that at all fiber levels, the composite containing continuous carbon fibers showed the largest strength, while the composite reinforced with carbon fiber felt exhibited the lowest strength of the four composites. The above results were analyzed by comparing the fracture surfaces of the four composites. SEM confirmed the great differences in fracture surfaces for composites of different fiber architectures. The presence of a large number of pores in the C_F/Gel composite was responsible for its lowest strength, and cracks within fiber tows caused the lower strength of the C_W/Gel composite when compared to its C_L/Gel counterpart. It was suggested that fiber architecture exerted a great effect on composite performance and the effect was dependent on the nature of the matrix material.     

Prediction of failure and fracture mechanisms of polymeric composites using finite element analysis. Part 2: Fiber reinforced composites

A robust finite element scheme for the micro‐mechanical modeling of the behavior of fiber reinforced polymeric composites under external loads is developed. The developed model is used to simulate stress distribution throughout the composite domain and to identify the locations where maximum stress concentrations occur. This information is used as a guide to predict dominant failure and crack growth mechanisms in fiber reinforced composites. The differences between continuous fibers, which are susceptible to unidirectional transverse fracture, and short fibers have been demonstrated. To assess the validity and range of applicability of the developed scheme, numerical results obtained by the model are compared with the available experimental data and also with the values found using other methods reported in the literature. These comparisons show that the present finite element scheme can generate meaningful results in the analysis of fiber reinforced composites.     

Immersion Temperature Effects on the Water Absorption Behavior of Hybrid Lignocellulosic Fiber Reinforced-Polyester Matrix Composites

Although economic, ecological, processing and property considerations suggest that it is very attractive to use lignocellulosic fibers as reinforcement in polymer matrix composites, moisture can strongly and deleteriously affect their properties. In this work the water absorption behavior of sisal/cotton, jute/cotton and ramie/cotton hybrid fabric reinforced composites is evaluated. The effect of the temperature of immersion, fiber volume fraction, and predrying of the fabrics before their incorporation onto the composites are evaluated. Sisal was shown to be the most hygroscopic of the fibers analyzed, and its presence leads to higher values of the maximum water content and of the diffusion coefficient of sisal/cotton reinforced composites. Under the range of temperatures analyzed (30–60°C) the volume fraction of the fibers, rather than the temperature itself, was shown to be the main parameter governing water absorption. Predrying usually lowers maximum water content, although for sisal/cotton reinforced composites a reverse trend was observed for the composites with higher volume fractions. This behavior was again attributed to the higher hydrophilic behavior of sisal fibers.     

Effects of hygrothermal aging on the thermal–mechanical properties of vinylester resin and its pultruded carbon fiber composites

Hygrothermal aging was carried out on vinyl ester (VE) resin cast and its pultruded carbon fiber reinforced composite (CF/VE) by immersing them in distilled water at 65 and 95°C. Hygrothermal aging effects on the samples were studied in terms of thermal–mechanical properties, as well as moisture absorption behavior, interfacial adhesion, and transverse mechanical properties. Moisture absorption behaviors of the VE casts and the CF/VE composites were characterized as Fickian behavior. Dynamic mechanical thermal analysis (DMTA) tests showed that the tan δ peak temperatures of the VE casts and CF/VE composites decreased with immersion time at 65 and 95°C. Moreover, there existed a splitting in the tan δ peaks at 95°C, which was reversible and could be recovered by dehydration. Three‐point flexural test indicated that flexural strengths of both the VE casts and the composites decreased by hygrothermal aging with a trend related to their moisture absorption behaviors, while flexural modulus of the composites was less affected. The ILSS of the CF/VE composites was also depressed by deterioration in interfacial adhesion, which was proved by the interfacial adhesion parameters, A and α. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Short‐beam and three‐point‐bending tests for the study of shear and flexural properties in unidirectional‐fiber‐reinforced epoxy composites

The bending properties of composite materials are often characterized with simply supported beams under concentrated loads. The results from such tests are commonly based on homogeneous beam equations. For laminated materials, however, these formulas must be modified to account for the stacking sequence of the individual plies. The horizontal shear test with a short‐beam specimen in three‐point bending appears suitable as a general method of evaluation for the shear properties in fiber‐reinforced composites because of its simplicity. In the experimental part of this work, the shear strength of unidirectional‐glass‐fiber‐reinforced epoxy resin composites was determined in different fiber directions with the short‐beam three‐point‐bending test. Also, the elastic constants and flexural properties of the same materials were determined from bending experiments carried out on specimens in the 0, 15, 30, 45, 60, 75, and 90° fiber directions with high span–thickness ratios. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 63–74, 2004     

吸湿介质对碳纤维增强铸型尼龙复合材料的吸湿行为及力学性能的影响

本文对碳纤维增强铸型尼龙(CF／MC 尼龙)复合材料在不同吸湿介质中的吸湿行为进行了研究。结果表明，对于纤维体积分数为10％的碳纤维增强铸型尼龙复合材料(10％CF／MC尼龙复合材料)，随着吸湿介质的PH值减小，它的吸湿率增大。同时，经过吸湿后，10％CF／MC尼龙复合材料的弯曲强度有明显的下降。随着吸湿介质的PH值减小，试样的弯曲强度下降。使用环境扫描电子显微镜观察在10％HCl溶液中吸湿的试样的剪切断口形貌，得到的结果与吸湿实验的结果一致。     

Effect of fiber volume fraction,fiber length and fiber tow size on the energy absorption of chopped carbon fiber–polymer composites

Composite materials have the potential to reduce the overall cost and weight of automotive structures with the added benefit of being able to dissipate large amounts of impact energy by progressive crushing. To identify and quantify the energy‐absorbing mechanisms in candidate automotive composite materials, modified test methodologies were developed for conducting progressive crush tests on flat‐plate composite specimens. The test method development and experimental setup focused on isolating the damage modes associated with the frond formation that occurs in dynamic testing of composite tubes. The Automotive Composites Consortium (ACC) is interested in investigating the use of chopped carbon fiber–reinforced composites as crash‐energy absorbers primarily because the low costs involved in their manufacture make them cost‐effective for automotive applications. While many in the past have investigated the energy‐absorption characteristics in various continuous fiber–reinforced composite materials, no literature is available on the energy‐absorption and crushing characteristics of chopped carbon fiber–reinforced composite materials. Hence quasi‐static progressive crush tests were performed on composite plates manufactured from chopped carbon fiber (CCF) with an epoxy resin system using compression‐molding techniques, and the effect of material parameters (fiber volume fraction, fiber length, and fiber tow size) on energy absorption was evaluated by varying them during testing. Of the parameters evaluated, fiber length appeared to be the most critical material parameter determining the specific energy absorption of a composite material, with shorter fibers having a higher specific energy absorption than longer fibers, possibly because of the increased concentration of stress raisers in the shorter fiber specimens, resulting in a larger number of fracture‐initiation sites. The combination of material parameters that yielded the highest energy‐absorbing material was identified. The test observations and trends established from this work would help support the development of low‐cost energy absorbers for the automotive industry. POLYM. COMPOS. 26:293–305 2005. Published 2005 Society of Plastics Engineers.     

Shear properties and load–deflection response of cross–ply glass–epoxy composite short–beams subjected to three‐point‐bending tests,and the effect of moisture absorption

The extensive use of composites in aerospace, chemical, marine, and structural applications leads to exposure to humidity and water immersion. Hence, there is a need to study the effect of moisture absorption on the mechanical properties of composite materials, especially the matrix dominated properties, such as the interlaminar shear strength (ILSS). The horizontal shear test with a short‐beam specimen in three‐point‐bending is used as a general method of evaluation for the shear properties in fiber‐reinforced composites because of its simplicity. In this work, the ILSS of cross‐ply glass‐epoxy resin composites is determined in seven different fiber directions with short‐beam three‐point‐bending tests, before and after moisture conditioning. It is found that moisture absorption reduces ILSS and stiffness of the examined composites whereas it leads to larger failure deflections. It is also found that the direction of fibers strongly affects the load–deflection response and the ILSS of the dry and conditioned specimens. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The effect of hybridization on mechanical properties of woven kenaf fiber reinforced polyoxymethylene composite

The challenges of using natural fibers in polymer composites include high moisture uptake and poor interfacial bonding with thermoplastic matrix. In this study, the effect of hybridization was investigated to address the challenges of high moisture uptake and balanced mechanical properties in natural fiber reinforced polymer composites. Polyethylene terephthalate fiber (PET) was used in woven kenaf reinforced POM due to its hydrophobic characteristics. The results of tensile test showed that the tensile strength of the interwoven POM/kenaf/PET hybrid composite when tested along kenaf fiber direction, increased from 72 to 85 MPa due to increase in fiber content. Similarly, the tensile strength of the interwoven POM/kenaf/PET hybrid composite increased from 67 to 75 MPa. However, the flexural strength of the interwoven POM/kenaf/PET hybrid composite dropped from 160.1 to 104.9 MPa while that of woven POM/kenaf composite dropped from 191.4 to 90.3 MPa. The interwoven hybrid composite also showed significant improvement in impact strength compared to the woven POM/kenaf composite. The water absorption of the woven POM/kenaf composite dropped by approximately 30% due to hybridization with PET fiber. The results confirmed that hybridization with PET fiber significantly improved the tensile and impact properties of the woven composite and increased its resistance to moisture uptake. POLYM. COMPOS., 35:1900–1910, 2014. © 2014 Society of Plastics Engineers     

Alkali Treatment of Screw Pine (Pandanus Odoratissimus) Fibers and Its Effect on Unsaturated Polyester Composites

Characteristics of Screw Pine fiber of species Pandanus Odoratissimus (PO fibers) and short PO fibers reinforced composite were studied. The results show that various alkali concentrations changed ability of PO fibers in absorptions of moisture, chemical compositions and cross-sectional area. The untreated and treated PO fibers were compounded with unsaturated polyester to evaluate their mechanical properties. The treated PO fiber composites exhibit high mechanical properties in comparison with untreated ones. SEM photographs revealed a different fracture surface between untreated PO fiber-reinforced composites and treated ones.     

Impact behavior of aramid fiber/glass fiber hybrid composites: The effect of stacking sequence

Aramid fiber/glass fiber hybrid composites were prepared to examine the effect of stacking sequence on the impact behavior of thin laminates. The effect of position of the aramid layer on the impact properties of hybrid composites was investigated using driven dart impact tester. The delamination area and fracture surface of hybrid composites were analyzed for correlation with impact energy. The addition of glass layer to aramid layer reduced the impact resistance of hybrid composite due to the restriction in the deformation of aramid layer. The position of aramid layer resulted in variations in the impact behavior of hybrid composites. When the aramid layer was at the impacted surface, the composite exhibited a higher impact energy. This was attributed to the fact that the flexible layer at the impacted surface in thin laminates can experience larger deformation. In three‐layer composites, the aramid fiber‐reinforced composite ( AAA ) exhibited the highest total impact energy due to high impact energy per delamination area (1EDA) in spite of low delamination area. Aramid fiber and glass fiber‐reinforced composites showed a different impact behavior according to the change of thickness. This was attributed to the difference in the energy absorption at interface between laminae.     

Carbon fiber‐reinforced gelatin composites. II. Swelling behavior

Carbon fiber‐reinforced gelatin composites have been prepared in our laboratory to obtain a novel biomaterial of improved mechanical properties. The swelling behavior (swelling rate, swelling kinetics, maximum solvent uptake, etc.) for both continuous carbon fiber‐reinforced gelatin composite (C_L/Gel) and short carbon fiber‐reinforced gelatin composite (C_S/Gel) are investigated. Experimental data show that the swelling process of the original gelatin and gelatin matrixes in both composites follows a second‐order kinetics. The swelling of the gelatin matrixes in both composites proceeds slower than that of the pristine gelatin, and depends on fiber form and fiber volume fraction (Vf). Results indicate that the presence of carbon fibers suppresses the swelling of the gelatin matrixes in both composites. It is found that the gelatin matrix in C_S/Gel possesses a smaller swelling rate and maximum solvent uptake than that in C_L/Gel. A mechanism governing these phenomena is discussed in this article. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 994–998, 2000     

Investigations on the performances of treated jute/Kenaf hybrid natural fiber reinforced epoxy composite

Natural fiber composite laminates are nowadays used in structural application such as aerospace, automobile and in sports goods because of their high strength to weight ratio and renewability. Hence the study of mechanical behaviors of natural fiber composites is very important in using these composite laminates for such specific applications. This project aims at identifying the mechanical properties of hybrid natural Jute/Kenaf fiber. The major drawbacks in natural fiber are its Resin incompatibility. Surface treatment of fiber is made to improve the interfacial bonding between the fiber and resin and to reduce the moisture absorption. Laminates are fabricated using Hand lay-up technique. Mechanical properties such as tensile, flexural, and Impact test for jute/kenaf hybrid laminates were obtained. Specimen preparation and Mechanical property testing were carried out as per ASTM standards. Micro structures of the different layer of hybrid specimens are scanned by the Scanning Electron Microscope.