Influence of stereoisomerism of epoxy hardeners on fracture toughness of carbon fiber/epoxy composites

Dongjun Kwon,Minkyu Lee,Woong Kwon,Eunsoo Lee,Euigyung Jeong 한국탄소학회 2019 Carbon Letters Vol.29 No.5

Interfacial adhesion between carbon fiber and epoxy resin mostly determine the mechanical properties of the carbon fiber/ epoxy composites and the chemical structures of epoxy resin and hardener plays an important role. In this regard, stereoisomerism of epoxy hardeners, such as 3,3′ and 4,4′-DDS (diaminodiphenylsulfone), can have significant influence on the fracture toughness of the cured epoxy and related carbon fiber composites. Therefore, this study aims to investigate the influence of stereoisomerism of epoxy hardeners on fracture toughness of the carbon fiber/epoxy composites. Triglycidyl aminophenol (TGAP) are selected as epoxy resin and 3,3′- and 4,4′-DDS are selected as epoxy hardener. Wetting behaviors and fiber matrix adhesion of TGAP/DDS mixtures onto carbon fiber are investigated and fracture toughness (KIC) of TGAP/ DDS mixtures are also investigated. Then, the mode II fracture toughness test of the carbon fiber/TGAP/DDS composites are carried out to investigate the influence of hardener stereoisomerism on fracture toughness of the resulting composites. Wetting and fiber matrix adhesion to carbon fiber of TGAP/3,3′-DDS was better than those of TGAP/4,4’-DDS and KIC of TGAP/3,3′-DDS was also better than that of TGAP/4,4′-DDS. As a result of the synergistic effect of better wetting, fiber matrix adhesion, and fracture toughness of TGAP/3,3′-DDS, the mode II fracture toughness of the carbon fiber/ TGAP/3,3’- DDS composites was almost twice of that of the carbon fiber/ TGAP/4,4′-DDS composites. Based on the results reported in this study, stereoisomerism of the epoxy hardeners can influence the fracture toughness of the resulting composites as well as that of the resin itself. In other words, only small difference, such as the spatial arrangement of the molecular structure of epoxy hardeners can cause huge difference in the mechanical properties of the resulting composites.

Effects of oil absorption on the wear behaviors of carbon/epoxy woven composites

Jae-H. Lee,Jae-S. Lee,Kyong-Y. Rhee 한국탄소학회 2011 Carbon Letters Vol.12 No.4

Carbon/epoxy woven composites are prominent wear-resistant materials due to the strength, stiffness, and thermal conductivity of carbon fabric. In this study, the effect of oilabsorption on the wear behaviors of carbon/epoxy woven composites was investigated. Wear tests were performed on dry and fully oil-absorbed carbon/epoxy woven composites. The worn surfaces of the test specimens were examined via scanning electron microscopy to investigate the wear mechanisms of oil-absorbed carbon/epoxy woven composites. It was found that the oil absorption rate was 0.14% when the carbon/epoxy woven composites were fully saturated. In addition, the wear properties of the carbon/epoxy woven composites were found to be affected by oilabsorption. Specifically, the friction coefficients of dry and oil-absorbed carbon/epoxy woven composites were 0.25-0.30 and 0.55-0.6, respectively. The wear loss of the oilabsorbed carbon/epoxy woven composites was 3.52×10-2 cm3, while that of the dry carbon/epoxy woven composites was 3.52×10-2 cm3. SEM results revealed that the higher friction coefficient and wear loss of the oil-absorbed carbon/epoxy woven composites can be attributed to the existence of broken and randomly dispersed fibers due to the weak adhesion forces between the carbon fibers and the epoxy matrix.

Influence of stereoisomerism of epoxy hardeners on fracture toughness of carbon fiber/epoxy composites

권동준,이민규,권웅,이은수,정의경 한국탄소학회 2019 Carbon Letters Vol.29 No.5

Interfacial adhesion between carbon fiber and epoxy resin mostly determine the mechanical properties of the carbon fiber/epoxy composites and the chemical structures of epoxy resin and hardener plays an important role. In this regard, stereoisomerism of epoxy hardeners, such as 3,3′ and 4,4′-DDS (diaminodiphenylsulfone), can have significant influence on the fracture toughness of the cured epoxy and related carbon fiber composites. Therefore, this study aims to investigate the influence of stereoisomerism of epoxy hardeners on fracture toughness of the carbon fiber/epoxy composites. Triglycidyl aminophenol (TGAP) are selected as epoxy resin and 3,3′- and 4,4′-DDS are selected as epoxy hardener. Wetting behaviors and fiber matrix adhesion of TGAP/DDS mixtures onto carbon fiber are investigated and fracture toughness (KIC) of TGAP/DDS mixtures are also investigated. Then, the mode II fracture toughness test of the carbon fiber/TGAP/DDS composites are carried out to investigate the influence of hardener stereoisomerism on fracture toughness of the resulting composites. Wetting and fiber matrix adhesion to carbon fiber of TGAP/3,3′-DDS was better than those of TGAP/4,4’-DDS and KIC of TGAP/3,3′-DDS was also better than that of TGAP/4,4′-DDS. As a result of the synergistic effect of better wetting, fiber matrix adhesion, and fracture toughness of TGAP/3,3′-DDS, the mode II fracture toughness of the carbon fiber/ TGAP/3,3’-DDS composites was almost twice of that of the carbon fiber/ TGAP/4,4′-DDS composites. Based on the results reported in this study, stereoisomerism of the epoxy hardeners can influence the fracture toughness of the resulting composites as well as that of the resin itself. In other words, only small difference, such as the spatial arrangement of the molecular structure of epoxy hardeners can cause huge difference in the mechanical properties of the resulting composites.

Microstructure and mechanical properties of carbon graphite composites reinforced by carbon nanofibers

Chen Yixing,Tu Chuanjun,Liu Yanli,Liu Ping,Gong Pei,Wu Guangning,Huang Xia,Chen Jian,Liu Tianhua,Jiang Jizhou 한국탄소학회 2023 Carbon Letters Vol.33 No.2

Renewed interest in the reinforced carbon graphite composites has intrigued the community in the advanced materials fields. In this work, we present a simple carbon nanofibers reinforced carbon graphite composites synthetic method by incorporating mixture of coal tar pitch, synthetic graphite, pitch coke and the dispersion liquid of carbon nanofibers via liquid-phase mixing process. The impact of carbon nanofiber utilization on the microstructures and mechanical properties of carbon graphite composites are studied systematically. The covalent surface modification of carbon nanofibers effectively improves its microstructure and thereby promotes the carbon graphite composites’ dispersion behavior. We propose that a small amount of carbon nanofibers could promote the carbonization process of carbon graphite composites, facilitating the densification of carbon graphite composites and reducing the undesired open porosity. The amount of 0.7 wt % of carbon nanofiber concentration allows the enhancement of bend and compressive strength of carbon graphite composites up to 36.50 MPa and 60.46 MPa, increased by 167.9% and 146.9% compared with the pure carbon graphite composite, respectively. Our findings can be rationalized due to the improvement in the mechanical strength of carbon graphite composites could be attributed due to pull-out of carbon nanofibers from the matrix and bridging effect across the crack pores within the matrix.

Characterization of hybrid carbon nanotubes/carbon fibers-reinforced composites: effect of carbon nanotube content on thermal and mechanical properties of the composites

함은광,최웅기,김영근,서민강 한국공업화학회 2014 한국공업화학회 연구논문 초록집 Vol.2014 No.1

Since the hybrid composites have mechanical properties better than metal composites, these have been required in aerospace, sporting goods, daily necessities, and etc. In this work, the effect of carbon nanotube content on thermal and mechanical properties of carbon nanotubes/carbon fibers-reinforced composites was investigated. The polymer resins used were epoxy and vinyl ester. Carbon nanotube content was added up to 1.0wt% in carbon fibers-reinforced composites. Thermal and mechanical properties of the composites were studied by thermal conductivity, tensile strength, interlaminar shear strength, and impact strength measurements. Morphologies of Carbon fibers-reinforced composites were measured by SEM and TEM.

Fabrication of carbon nanotubes dispersed woven carbon fiber/epoxy composites and their damping characteristics

Kim, Hee Chul,Kim, Eun Ho,Lee, In,Byun, Joon Hyung,Kim, Byung Sun,Ahn, Seok Min SAGE Publications 2013 Journal of composite materials Vol.47 No.8

<P>Damping characteristics of carbon nanotubes dispersed woven carbon fiber/epoxy composites were investigated. The composites were fabricated by an advanced resin film infusion prepreg manufacturing process based on the calendaring process using three-roll mill. Through this advanced process, well-dispersed nanocomposites containing high weight percent (up to 7 wt%) of carbon nanotubes was achieved. It was confirmed through the scanning electron microscopic images of the carbon nanotubes dispersed composites. Damping characteristics of the specimen were measured by the impact vibration test of the composites beam specimens. Considerable improvement of damping characteristics was observed in the carbon nanotubes dispersed composites, and structural damping increased as the weight percent of carbon nanotubes was increased. Damping ratio was improved up to 12.3% (at the 1st natural frequency) and 16.1% (at the 2nd natural frequency), especially in the 7 wt% carbon nanotubes dispersed specimen. Tensile test was performed to investigate the effects of carbon nanotubes on the tensile properties. The tensile stiffness of carbon nanotubes dispersed composites was similar with the conventional composites; however, tensile strength was degraded.</P>

Effect of Compositional Parameters on the Characteristics of C-SiC-$B_4C$ Composites

Aggarwal, R.K.,Bhatia, G.B.,Saha, M.,Mishra, A. Korean Carbon Society 2004 Carbon Letters Vol.5 No.4

Carbon-ceramic composites refer to a special class of carbon based materials which cover the main drawbacks of carbon, particularly its proneness to air oxidation, while essentially retaining its outstanding properties. In the present paper, the authors report the results of a systematic study made towards the development of C-SiC-$B_4C$ composites, which involves the effects of compositional parameters, namely, carbon-to-ceramic and ceramic-to-ceramic ratios, on the oxidation behaviour as well as other characteristics of these composites. The C-SiC-$B_4C$ composites, heat-treated to $1400^{\circ}C$, have shown that their oxidation behaviour at temperatures of 800~$1200^{\circ}C$ depends jointly on the total ceramic content and the SiC : $B_4C$ ratio. Good compositions of C-SiC-$B_4C$ composites exhibiting zero weight loss in air at temperatures of 800~$1200^{\circ}C$ for periods of 4~9 h, have been identified. Composites with these compositions undergo a weight gain or a maximum weight loss of less than 3% during the establishment of a protective layer at the surface of carbon in a period of 1~6 h. Significant improvement in the strength of C-SiC-$B_4C$ composites has been observed which increases with an increase in the total ceramic content and also with an increase in the SiC : $B_4C$ ratio.

Role of Interface on the Development of Microstructure in Carbon-Carbon Composites

Dhakate, S.R.,Mathur, R.B.,Dhami, T.L.,Chauhan, S.K. Korean Carbon Society 2002 Carbon Letters Vol.3 No.4

Microstructure plays an important role in controlling the fracture behaviour of carbon-carbon composites and hence their mechanical properties. In the present study effort was made to understand how the different interfaces (fiber/matrix interactions) influence the development of microstructure of the matrix as well as that of carbon fibers as the heat treatment temperature of the carbon-carbon composites is raised. Three different grades of PAN based carbon fibres were selected to offer different surface characteristics. It is observed that in case of high-strength carbon fiber based carbon-carbon composites, not only the matrix microstructure is different but the texture of carbon fiber changes from isotropic to anisotropic after HTT to $2600^{\circ}C$. However, in case of intermediate and high modulus carbon fiber based carbon-carbon composites, the carbon fiber texture remains nearly isotropic at $2600^{\circ}C$ because of relatively weak fiber-matrix interactions.

Oxidation Resistant SiC Coating for carbon/carbon Composites

Joo, Hyeok-Jong,Lee, Nam-Joo,Oh, In-Seok 한국탄소학회 2003 Carbon Letters Vol.4 No.1

In this study, densified 4D carbon/carbon composites were made from carbon fiber and coal tar pitch through the process of pressure impregnation and carbonization and then followed by carbonization and graphitization. To improve the oxidative resistance of the prepared carbon/carbon composites, the surface of carbon/carbon composites was coated on SiC by the pack cementation method. The SiC coated layer was created by depending on the constitution of pack powder, and reaction time of pack-cementation. The morpology of crystalline and texture of these SiC coated carbon/carbon composites were investigated by XRD, SEM/EDS observation. So the coating mechanism of pack-cementation process was proposed. The oxidative res istance were observed through the air oxidation test, and then the optimal condition of pack cementation was found by them. Besides, the oxidative mechanism of SiC formed was proposed through the observation of SiC coated surface, which was undergone by oxidation test.

Mechanical Properties of Unidirectional Carbon-carbon Composites as a Function of Fiber Volume Content

Dhakate, S.R.,Mathur, R.B.,Dham, T.L. Korean Carbon Society 2002 Carbon Letters Vol.3 No.3

Unidirectional polymer composites were prepared using high-strength carbon fibers as reinforcement and phenolic resin as matrix precursor with keeping fiber volume fraction at 30, 40, 50 and 60% respectively. These composites were carbonized at $1000^{\circ}C$ and graphitised at $2600^{\circ}C$ in the inert atmosphere. The carbonized and graphitised composites were characterized for mechanical properties as well as microstructure. Microscopic studies were carried out of the polished surface of carbonized and graphitised composites after etching by chromic acid, to understand the effect of fiber volume fraction on oxidation at fiber-matrix interface. It is found that the flexural strength in polymer composites increases with fiber volume fraction and so does for the carbonised composites. However, the trend was found to be reversed in graphitised composites. In all the carbonized composites anisotropic region has been observed at fiber-matrix interface which transforms into columnar type microstructure upon graphitisation. The extension of strong and weak columnar type microstructure is function of fiber volume fraction. SEM microscopy of the etched surface of the sample reveal that composites containing 40% fiber volume has minimum oxidation at the interface, revealing a strong interfacial bonding.