• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.83-86
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• 2003

동시경화조인트는 경화 시 복합재료로부터 흘러나오는 수지를 접착제로 사용하기 때문에 제조과정이 간편할 뿐 아니라 복합재료를 표면 처리할 필요가 없기 때문에 기존의 접착제에 의한 접합방법에 비해 장점을 지닌다. 최근 동시경화조인트에 관한 연구가 활발하게 진행되고 있으나 해석적인 방법을 통한 연구는 아직까지 미비하다. 실험적으로 연구된 결과를 보면 동시경화 조인트는 계면 모서리에서 파괴가 시작되어 계면을 따라 파괴가 진행된다. 그러므로 조인트의 계면 모서리에서의 응력집중계수에 관해 연구하는 것이 중요하다. 본 논문에서는 고유치 문제를 고려하여 복합재료와 강재료로 구성된 동시경화조인트의 계면 모서리에서 발생하는 응력 및 변위장을 결정하고, H-적분을 이용하여 응력집중계수를 구하는 방법을 제시하고자 한다.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.5
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• pp.409-417
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• 2003

Cure monitoring can be used to improve the quality and productivity of thermosetting resin matrix composite products during their manufacturing process. In this work, the sensitivity of dielectrometry was improved by adequate separation the efforts of sensor and externals on the measured signal. A new algorithm to obtain the degree of cure during dielectric cure monitoring of glass/polyester and glass/epoxy composites was developed by employing a function of both temperature and dissipation factor, in which five cure monitoring parameters were used to calculate the degree of cure. The decreasing pattern of dissipation factor was compared with the relationships between the degree of cure and the resin viscosity. The developed algorithm might be employed for the in situ cure monitoring of thermosetting resin composites.

• Composites Research
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• v.32 no.6
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• pp.349-354
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• 2019

The Aluminum conductor composite core consists of fast-curing thermosetting epoxy used as reinforcements and carbon fiber and glass fiber used as matrix. In this study, we have investigated fast curing epoxy cured products used for composite core(Aluminum Conductor Composite Core, ACCC). Tetrafunctional epoxy(PA 806) was used as a multifunctional epoxy, along with two kinds of curing agents, MNAn(5-Methyl-5-norbornene-2,3-dicarboxylic anhydride) and HHPA(Hexahydrophthalic Anhydride), to make an epoxy cured product and their properties were evaluated. Optimum conditions are confirmed by varying the content of curing accelerator in the selected epoxy and curing agent.

• Composites Research
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• v.14 no.2
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• pp.33-42
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• 2001

The cure kinetic equation fur 52-glass/polyester prepreg composites was established through DSC (differential scanning calorimetry). Using the established kinetic equation, the temperature distribution of the thick composite was calculated considering the change of heat transfer resistance due to resin impregnation of bleeder plies used. In order to reduce the overheat during cure of thick glass fiber composites, the cure cycle was modified by introducing the cooling and reheating steps. Then the thick glass composites were cured both by the conventional cycle without any cooling or reheating step and the modified cure cycle. The mechanical properties of the thick composites cured by the both cycles were tested by the short beam shear test and the Barcol hardness test, and then their results were compared.

• Composites Research
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• v.16 no.6
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• pp.33-40
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• 2003

The initial thermal degradation of polymer matrix composite is not observed easily. At the beginning of thermal degradation of polymer matrix composites, phase transformation such as chain scission, oxidation occur, and then micro delamination is produced in matrix and interface between matrix and fiber before blistering. Initial heat damage deteriorate mechanical properties of composites. We presented the detection method of the initial heat damage of composites conveniently using ultrasonic technique. Absorption coefficient and material velocity was measured with thermal degradation and degree of cure. The more thermal degradation was progressed, the more absorption coefficient was increased. When the cure temperature is more high, the absorption coefficient of cured composite is increased and material velocity is decreased. We concluded that cure temperature is more high, the defects such as void is increased and molecular structure cured at high temperature has cross-linking structure which is more absorb the ultrasonic waves.

• Composites Research
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• v.27 no.3
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• pp.90-95
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• 2014

Cure shrinkage during cure process of polymer matrix composites develope residual stress that cause some structural deformation, such as spring-in, spring-out and warpage. The carbon/epoxy prepreg used in this study is Hexply M21EV/34%/UD268NFS/IMA-12K supplied by Hexcel corp. Cure shrinkage and degree of cure measured by TMA(thermomechanical analyzer) and DSC(differential scanning calorimetry). Cure shrinkages are measured by TMA within a temperature range of $140{\sim}240^{\circ}C$ in a nitrogen atmosphere, and degree of cure determined by the heat of reaction using dynamic and isothermal DSC runs in argon atmosphere. As a result, the cure shrinkage is increased dramatically in a degree of cure range between 27~80%. the higher the cure temperature, the lower the degree of cure occurring to begin cure shrinkage.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.04a
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• pp.99-102
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• 1999

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.6
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• pp.39-45
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• 2002

In this paper, a finite element formulation was introduced for the three-dimensional cure simulation of composite structures. Based on the formulation, a three-dimensional finite element code was developed. Numerical examples found in the literatures were solved for code verification. Results from the present analyses agreed well with the measured cure-induced temperatures. Unlike in one or two dimensional analysis, temperature and degree of cure were able to be calculated at any point within composite structures in the present analysis. The finite element program can be used for the cure simulation of composite structures with arbitrary geometry under non-uniform autoclave temperature distribution.

• Polymer(Korea)
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• v.27 no.3
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• pp.189-194
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• 2003

Interfacial evaluation, damage sensing and cure monitoring of single carbon fiber/thermo setting composite with different curing processes were investigated using electro-micromechanical test. After curing, the residual stress was monitored by measurement of electrical resistance and then compared to various curing processes. In thermal curing case, matrix tensile strength, modulus and interfacial shear strength were higher than those of ultraviolet curing case. The shrinkage measured during thermal curing occurred significantly by matrix shrinkage and residual stress due to the difference in thermal expansion coefficient. The apparent modulus measured in the thermal curing indicated that mechanical and interfacial properties were highly improved. The reaching time to the same stress of thermal curing was faster than that of UV curing case.

• Composites Research
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• v.30 no.3
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• pp.202-208
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• 2017

Resin transfer molding (RTM) is a mass production process that allows the fabrication of composites ranging in size from small to large. Recently, fast curing resins with a curing time of less than about 10 minutes have been used in the automotive and aerospace industries. The viscosity of resin is bound up with the degree of cure, and it can be changed rapidly in the fast-cure resin system during the mold filling process. Therefore, it is advantageous to experimentally measure and evaluate the degree of cure because it requires much effort to predict the flow characteristics and cure of the fast curing resin. DMA and dielectric technique are the typical methods to measure the degree of cure of composite materials. In this paper, the resin flow and degree of cure were measured through the multi-channel dielectric system. A total of 8 channels of dielectric sensors were used and resin flow and degree of cure were measured and compared with each other under various pressure conditions.