• Journal of Power System Engineering
• /
• v.10 no.2
• /
• pp.117-123
• /
• 2006

Woven fabrics composites are used as primary structural components in many applications because of their superior properties that offer high specific strength and stiffness. However, the complexity of the fabric structure makes understanding of their failure behavior very difficult. Also, laminate woven fabrics CFRP have unique failure mechanisms such as fiber bridging, fiber/matrix crack and so on. In particular, the delamination phenomenon of the composite materials is one of the most frequent failure mechanisms. So, we estimated interlaminar fracture and damage in composites using as ENF specimen by a 3 point bending test. And AE characteristics were examined for crack propagation on plain woven CFRP. We obtained the following conclusions from the results of the evaluation of the 3 point bending fracture test and AE characteristic estimation. AE counts of maximum crack length were obtained as $85.97{\times}10^4\;and\;93{\times}10^3\;for\;a_0/L=0.3$ and 0.6, respectively. Also the maximum amplitudes were over 80dB at both $a_0/L=0.3\;and\;0.6$. $G_{IIc}$ at that's $a_0/L$ ratio were obtained with $1.07kJ/m^2\;and\;3.79kJ/m^2$.

• Journal of Ocean Engineering and Technology
• /
• v.10 no.4
• /
• pp.75-83
• /
• 1996

Polymeric composites can be subjected to a wide variety of environmemtal conditions in practical use. One of most important conditions to be considered in the stuctural design using such materials is the miisture envirnment. Thus the moisture effect on interlaminar fracture toughness $G_IC$ and $G_IIC$ of CFRP(carbon fiber reinforced plastic) composed of carbon fibers and epoxy resin is studied in this paper. Specimens were first processed in 25, 50, $80^{\circ}C$ flesh water and $25^{\circ}C$ sea water for various periods of time. After that, the water absorption and fracture toughness tests were performed under laboratory atmosphere. As result, the specimen processed in $80^{\circ}C$ flesh water indicates the highest misture absorbing capability, the second in $50^{\circ}C$ flesh water, the third in $25^{\circ}C$ sea water, and the specimen in $25^{\circ}C$ flesh water does the lowest. The interlaminar fracture toughness $G_IC$ increases, approaches to the maximum, and decreases as the immersion time increases. In case of interlaminar $G_IIC$, the value of the specimen processed in $80^{\circ}C$ flesh water turns out to be higher than others. In addition, the scanning electron micrographs(SEM) of fracture surfaces were also examined in order to explain the mechanism of fracture.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.35 no.4
• /
• pp.410-420
• /
• 1999

The value of the mode I interlamina fracture toughness, GIC, is calculated by experimental compliance method, modified compliance method and beam theory. The value of the mode II interlamina fracture toughness, GIC, is evaluated by beam method, theory beam theory and compliance method. This paper describes the effect of load pint displacement rate and speicimen geometries for mode I and II interlaminar fracture toughness of glass fiber reinforced plastic composites by using double cantilever beam (DCB) and end notched flexure (ENF) specimen. For the load point displacement rate of increases whereas the value of 2,6 and 10 mm/min the value of GIC decrease as load point displacement rate increases whereas the value of GIC is found to be no significant effect. The value of GIC decreases as initial crack length increases. The fractured surface of the DCB and ENF samples are examined by scanning electron microscopy (SEM).

• Transactions of the Korean Society of Automotive Engineers
• /
• v.6 no.2
• /
• pp.80-91
• /
• 1998

In this paper, the estimation of dynamic interlaminar fracture toughness on fracture mode II in CFRP(carbon fiber reinforced plastics) laminates in made. Dynamic ENF(End Notched Flexure) apparatus used in this paper is manufactured by suing Split Hopkinson Pressure Bar. The static and impact load history in the CFRP specimen is measured by using manufactured dynamic ENF tester and 3-point bending test is carried out to find the load history. Also dynamic interlaminar fracture toughness can be found by using the J integral obrained from dynamic analysis in consideration of intertia-force effect.

• Journal of Ocean Engineering and Technology
• /
• v.16 no.4
• /
• pp.42-47
• /
• 2002

This paper describes the effect of loading rate, specimen geometries and material properties for Mode II interlaminar fracture toughness of hybrid composite by using end notched flexure(ENF) specimen. In the range of loading rate 0.5~2mm/min, there is found to be no significant effect of loading rate with the value of critical energy release rate( $G_{IIc}$). there is no dependence of the interlaminar fracture energy upon the specimen width over the specimen widths examined. The value of $G_{IIc}$ for variation of initial crack length are nearly similiar values when material properties are CF/CF and GF/GF, however, the value of $G_{IIc}$ are highest with the increasing intial crack length at CF/GF. The values of $G_{IIc}$ for variation material properties are higher with the increasing moulding pressure when moulding pressures are 307, 431, 585㎪. The SEM photographs show good fiber distribution and interfacial bonding of hybrid composites when the moulding is the CF/GF.e CF/GF.

• Journal of the Korean Society of Safety
• /
• v.15 no.4
• /
• pp.1-7
• /
• 2000

In this paper, an investigation was performed on the ModeII dynamic interlaminar fracture toughness of unidirectional CFRP laminates. The stacking sequences used in this experiment are two kinds of [$0_20$] and [$0_{10}F_20_{10}$]. In the experiments, Split Hopkinson's Bar test was applied to dynamic and notched flexure test. The Mode II fracture toughness of each unidirectional CFRP was estimated by the analyzed deflection of the specimen and J-Integral with the measured impulsive load and reactions at the supported points. As an experimental results, the specimen [$0_{10}F_20_{10}$] appears greater than that of [$0_20$] for the J-integral and displacement velocity at a measuring point within the range of experiment.

• Journal of Advanced Marine Engineering and Technology
• /
• v.25 no.5
• /
• pp.1140-1147
• /
• 2001

This paper describes the effect of various molding pressure for Mode I. Mode II interlaminar fracture toughness of carbon fiber reinforced plastic composites by using double cantilever beam(DCB), end notched flexure(ENF) and end loaded split(ELS) Specimen. The value of $G_{IC}$, $G_{IIC}$ as a function of various molding pressure is almost same at 307, 431, 585 kPa, however it shows highest value under 307kPa molding pressure, The SEM photographs show good fiber distribution and interfacial bonding of composites when the molding pressure is the 307kPa.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2000.11a
• /
• pp.110-114
• /
• 2000

The Interlaminar fracture behavior of hybrid composite with non-woven carbon tissue was investigated under Mode I (DCB) and Mode II (ENF) loading condition. Hybrid composites were manufactured by means of inserting a non-woven tissue between prepreg layers. Two kinds of specimens were prepared from [0]$_{24}$ and [$0_{12}/0_{12}$]. Where, the symbol "/" means that a non-woven carbon tissue was located at 0/0 mid-plane of the specimen. The interlaminar fracture toughness of hybrid composites was compared with that of CFRP. The fracture surfaces of the specimens were observed using optical microscope and SEM, and the failure mechanism was discussed. The hybrid laminates, which are made by inserting non-woven carbon tissue between layers, were shown to be effective to remarkably improve Mode II fracture toughness.toughness.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.12 no.4
• /
• pp.43-49
• /
• 2003

This research work has been carried out for finding J-integral in mode II of CFRP(carbon fiber reinforced plastics) laminate plates based on the classical bar theory in dynamic conditions with consideration of the effect of inertia forces, eventually to lead to finding the dynamic inter-layer fracture toughness. Dynamic inter-layer fracture toughness was found by a self-made ENF(End Notched Flexure) experimental apparatus using Split Hopkinson's Bar(SHPB), and also observed the variation of the fracture toughness haying different resin contents and fiber arrangements of CFRP specimen([$0_3^{\circ}/90_3^{\circ}/0_6^{\circ}/90_3^{\circ}/0_3^{\circ}$], [$0_{20}^{\circ}$], [$0_5^{\circ}/90_{10}^{\circ}/0_5^{\circ}$]). As an experimental result, in either cases of quasi-static or dynamic load condition, the critical load and the inter-layer fracture toughness increased sharply depending on the increase of resin contents. Therefore, it could, be concluded that the effect by resin contents is the major factor determining the inter-layer fracture toughness in the CFRP laminate plates.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.19 no.3
• /
• pp.326-333
• /
• 2010

In this study, DAQ and TRA modules were applied to the CFRP single specimen testing method using AE. A method for crack identification in CFRP specimens based on k-mean clustering and wavelet transform analysis are presented. Mode I on DCB under vertical loading and mode II on 3-points ENF testing under share loading have been carried out, thereafter k-mean method for clustering AE data and wavelet transition method per amplitude have been applied to investigate characteristics of interfacial fracture in CFRP composite. It was found that the fracture mechanism of Carbon/Epoxy Composite to estimate of different type of fractures such as matrix(epoxy resin) cracking, delamination and fiber breakage same as AE amplitude distribution using a AE frequency analysis. In conclusion, the presented results provide a foundation for using wavelet analysis as efficient crack detection tool. The advantage of using wavelet analysis is that local features in a displacement response signal can be identified with a desired resolution, provided that the response signal to be analyzed picks up the perturbations caused by the presence of the crack.