• Composites Research
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• 제15권5호
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• pp.14-18
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• 2002

본 논문에서는 정수압 환경에서 파괴인성 측정을 위한 일인자방법의 적용성을 검토하기 위해 단일방향 및 준등방성으로 적층된 $\textrm{[}0^{\circ}\textrm{]}_{88}$$\textrm{[}0^{\circ}/\pm/45^{\circ}/90^{\circ}\textrm{]}_{11s}$의 탄소섬유/에폭시 적층복합재에 있어 네 단계 정수압에 대해 탄성일인자를 층간 분리 길이의 함수로 결정 정수압 및 적층각이 탄성일인자에 미치는 영향을 검토하였다. $\textrm{[}0^{\circ}\textrm{]}_{88}$ 경우에는 0.1 MPa, 70MPa, 140MPa, 200MPa의 정수압력을 적용하였으며 $\textrm{[}0^{\circ}/\pm/45^{\circ}/90^{\circ}\textrm{]}_{11s}$에서는 0.1MPa, 100MPa, 200MPa, 300MPa의 정수압력을 적용하였다. 결과로서 탄성일인자는 정수압 및 두 경우 적층각에 의해 영향을 받지 않음을 알 수 있었다. 또한 탄성일인자는 층간분리가 증가함에 따라 선형적으로 감소함을 알 수 있었다.

• 대한기계학회논문집A
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• 제22권3호
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• pp.540-544
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• 1998

Compliance calibration method is frequently used to determine $G_IC$ from the DCB composite specimen. However, the method requires at least 4 to 5 fracture test (loading-unloading) records. In this study, $G_IC$ of unidirectional graphite/epoxy DCB composites was determined from the elastic work factor approach which uses a single fracture test record. In order to inspect the validity of the elastic work factor approach, $G_IC$ determined from the elastic work factor approach was compared to that of determined from the compliance calibration method. It was shown that $G_IC$ determined from the elastic work factor approach was comparable to that determined from the compliance calibration method. That is, the elastic work factor approach can be used to determine $G_IC$ of unidirectional graphite/epoxy DCB specimen from a single fracture record.

• 대한기계학회논문집A
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• 제20권9호
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• pp.2792-2799
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• 1996

It was shown in the previous study that the numerically derived elastic work factor for CLS specimen was independent of fiber direction for a unidirectional case. Also, it was proposed the elastic work factor could be used to determine energy release rate from a single test record. In the present study, elastic work factor was derived from a simple beam theory to investigate its dependence on material property and geometric condition. Also, the elastic work factor of CLS specimen was applied experimentally to determine critical energy release rate in order to prove its validity determining critical energy release rate from a single specimen. For this purpose, critical energy release rate determined using the elastic work factor was compared with that determined by the compliance method. The results showed that while elastic work factor is affected by $t_2/t_1$ and $L_2/L_1$ it is independent of fiber angle for a unidirectional case. It was also found that critical energy release rates determined by both methods are comparable each other, thus elastic work factor approach can be used to determine energy release rate from a single test specimen.

• 대한기계학회논문집A
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• 제23권11호
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• pp.1952-1959
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• 1999

The work factor approach, so-called single specimen technique could be used to determine energy release rate from a single test record for unidirectional CLS specimen. In the present study, the work factor approach was extended to determine the mixed-mode fracture toughness of multi-directional graphite/epoxy laminated composites. Multi-directional CLS specimens were used for fracture tests. The stacking sequences used for the lap and the strap were $[90_2/0_2]_s/[0_4/90_4]_s$ and $[0/\pm45/0]_s/[0_2/\pm45_2/0_2]_2$, respectively. For both cases, the fracture toughness determined from the work factor approach was compared with that determined from the compliance method. It was found that both methods produced fracture toughness within a maximum 15% difference for each stacking sequence. The fractography analysis also showed that the fiber bridging occurred for$[0/\pm45/0]_s/[0_2/\pm45_2/0_2]_2$ case while it did not occur for $[90_2/0_2]_s/[0_4/90_4]_s$ case.