• Journal of Power System Engineering
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• v.10 no.2
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• pp.117-123
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• 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 $1.07kJ/m^2\;and\;3.79kJ/m^2$.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.2
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• pp.80-91
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• 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
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• v.10 no.4
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• pp.75-83
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• 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.

• Composites Research
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• v.22 no.2
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• pp.43-48
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• 2009

For the practical use of improved interlaminar fracture toughness by interleaving carbon non-woven tissue (CNWT), intelaminar fracture toughnesses of CFRP laminates with CNWT having different weights were experimentally investigated. A suitable weight of interleaved CNWT in CFRP laminates was discussed with Mode I and Mode II tests. Mode I and Mode II interlaminar fracture toughnesses (GIC and GIIC) were obtained by DCB and ENF tests. Six kinds of specimens with CNWT were prepared. The weights of CNWT per square meter for six types of specimens are $8g/m^2,\;10g/m^2,\;12g/m^2,\;16g/m^2,\;20g/m^2$, and $24g/m^2$, respectively. The mean GIC and GIIC values of six kinds of specimens were not substantially different from one another. Compared with the CFRP specimen, the mean GIC values of six kinds of specimens were slightly decreased. But the mean GIIC values increased tremendously at least twice by interleaving CNWT. It seems that there is no interrelationship between the interlaminar fracture toughnesses (GIC and GIIC) and the interleaving CNWT weights. Consequently, it would be desirable to use the CNWT of $8g/m^2$ among the six kinds of CNWTs to take advantage of the interlaminar fracture toughness improved by interleaving CNWT, because the CNWT of $8g/m^2$ is a lightweight and low-priced material.

• Composites Research
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• v.13 no.2
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• pp.72-80
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• 2000

Effect of graphite powder addition on the mechanical properties of carbon fiber reinforced carbon composites (C/C composites) was investigated. Greenbody (G/B) with 0~30wt.% graphite powder addition to phenol resin was prepared and carbonized at $1000^{\circ}C$ to make C/C composites. Flexural strengths of 20wt.% graphite powder additions showed maximum values in the both case of G/B and C/C composites. But, at the graphite addition over 20wt.%, there was negative effect due to the matrix inhomogeneity. Flexural strength of cured resin without graphite Powder was higher than that with graphite. However, flexural strength of carbonized resin with graphite increased three times as much as that of carbonized resin without graphite. Because the addition of graphite powder effects the restraint of shrinkage after carbonization and the deflection of crack path. In Mode II ENF test, energy release rates($G_{II}$) of G/B and C/C composites with the 20w1.% addition of graphite were both increased. But, the addition of graphite was more effective to the increase of $G_{II}$ in C/C composites than that in G/B.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.5
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• pp.491-497
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• 2015

This paper reports an experimental study for evaluating the effect of temperature on the mode I, mode II and mixed-mode interlaminar fracture toughness of adhesive joints with a curved cross-section of filament-wound dome-separated composite pressure vessel. Mode I and mixed-mode interlaminar fracture toughness were evaluated using DCB specimens, while mode II interlaminar fracture toughness was determined using ENF specimens. $[{\pm}10^{\circ}]_6$, $[{\pm}27^{\circ}]_6$ and ($[{\pm}10^{\circ}]_3/FM73/[{\pm}27^{\circ}]_3$) winding specimens with the curved cross-section were considered. In-situ temperature environments were simulated with a range of $-30^{\circ}C-60^{\circ}C$ using an environmental chamber and furnace. Experimental results on the effect of temperature indicate that interlaminar fracture toughness tends to be high at low temperature and is degraded with increase in temperature. For specimen types, it was found that interlaminar fracture toughness of $[{\pm}10^{\circ}]_3/FM73/[{\pm}27^{\circ}]_3$ winding specimens considered as adhesive joints of dome and helical part was higher than other specimens.

• Composites Research
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• v.26 no.2
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• pp.141-145
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• 2013

The mode II interlaminar fracture toughness was evaluated for CFRP laminates with different types of nonwoven tissues and the source of increased mode II interlaminar fracture toughness was examined by SEM analysis in this paper. The interlaminar fracture toughness in mode II is obtained by an end notched flexure test. The experiment is performed using three types of non-woven tissues: 8 $g/m^2$ of carbon tissue, 10 $g/m^2$ of glass tissue, and 8 $g/m^2$ of polyester tissue. On the basis of the specimen with no non-woven tissue, interlaminar fracture toughness on mode II at specimens inserted with non-woven carbon and glass tissues and polyester tissues increases as much as 166.5% and 137.1% and 157.4% respectively. The results show that mode II interlaminar fracture toughness of CFRP laminates inserted with nonwoven tissues increased due to the fiber bridging, fiber breakage, and hackle etc. by SEM analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.519-525
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• 2009

In this study a cohesive zone model was used to simulate the delamination phenomena which occurs by a successive crack initiation and propagation in composite laminates. The cohesive zone model was incorporated to the classical finite element method via cohesive element formulation and then implemented into the user-subroutine UEL of a commercial finite element program Abaqus. To validate the formulation and implementation of the cohesive element the finite element results were compared with the experimental data of double cantilever beam and end notched flexure tests. The numerical results well agree with the experimental load-displacement curves. Also the effect of the elastic stiffness and the size of the cohesive element on the global load-displacement curves were studied numerically. To minimize the mesh-dependency of the crack propagation path and eliminate the zig-zag patterns in the load-displacement curve, cohesive elements should be refined at the crack-tip.

• Composites Research
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• v.29 no.2
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• pp.45-52
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• 2016

An understanding of the failure mechanisms of the adhesive layer is decisive in interpreting the performance of a particular adhesive joint because the delamination is one of the most common failure modes of the laminated composites such as the fiber metal laminates. The interface between different materials, which is the case between the metal and the composite layers in this study, can be loaded through a combination of fracture modes. All loads can be decomposed into peel stresses, perpendicular to the interface, and two in-plane shear stresses, leading to three basic fracture mode I, II and III. To determine the load causing the delamination growth, the energy release rate should be identified in corresponding criterion involving the critical energy release rate ($G_C$) of the material. The critical energy release rate based on these three modes will be $G_{IC}$, $G_{IIC}$ and $G_{IIIC}$. In this study, to evaluate the fracture behaviors in the fracture mode I and II of the adhesive layer in fiber metal laminates, the double cantilever beam and the end-notched flexure tests were performed using the reference adhesive joints. Furthermore, it is confirmed that the experimental results of the adhesive fracture toughness can be applied by the comparison with the finite element analysis using cohesive zone model.