• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.219-223
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• 2001

The on-line cure monitoring during the cure process of composite materials is important for better quality and productivity. The dielectric sensor for cure monitoring consists of base film and electrodes. Because the characteristic of dielectric sensor for the on-line cure monitoring is dependent on the base material, width and number of electrode, etc, the dielectric sensor should be standardized. And the selection of base film material of sensor is very important. In order to prevent the measuring errors generated from the increase of environmental temperature, the base film material should have stable dielectric constant with respect to environmental temperature. In this study, the newly developed dielectric sensor for cure monitoring was designed and the dissipation factor which is function of degree of cure was measured using the sensor. The relationship between the dissipation factor and degree of cure with respect to environmental temperature was investigated.

• 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.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.797-803
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• 2001

The on-line cure monitoring of fiber reinforced thermosetting resin matrix composite material was performed for the better quality and productivity during manufacturing. Since the dissipation factor measured by dielectrometry method is dependent on the degree of cure and temperature of resin, in this study, a new method to obtain the degree of cure during on-line cure monitoring for glass/polyester composites was developed by employing a combination function of the temperature and the dissipation factor. Two sensor signals from a K-type thermocouple and an interdigitated dielectric sensor were processed during curing process under various cure cycles. The DSC (Differential Scanning Calorimetry) data was also used for the reference of degree of cure.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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• pp.1563-1572
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• 1995

The on-line cure monitoring during the cure process of fiber reinforced resin matrix composite material is important for the better quality and productivity. Among several cure monitoring methods, the dielectrometry that uses electrodes as its sensor is known to be the most promising method. In this study, the sensitivity of the dielectric sensor for the on-line cure monitoring was analyzed by finite element method and compared to the experimental results. Using the analytical results, the equation for the capacitance of the sensor was derived. Also, the optimal sensor design method was suggested after analyzing several different sensor shapes.

• Composites Research
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• v.14 no.1
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• pp.30-38
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• 2001

As fiber reinforced composite materials are widely used in aircraft, space structures and robot arms, the on-line cure monitoring during the cure process of the composite materials has become an important research area for the better quality and productivity. In this paper, the dielectric circuit of the Wheatstone bridge type for measuring the dissipation factor during cure of thermsetting resin matrix composite materials was designed and manufactured. Also, the dielectric sensor for the cure monitoring of high temperature cure composites was developed and tested. The residual thermal stresses of the dielectric sensor during high temperature cure were analyzed by the finite element method and its dielectric characteristics at high temperature cure were analyzed by the finite element method and its dielectric characteristics at high temperature were evaluated. The on-line cure monitoring of the BMI(Bismaleimide) resin was performed using the developed Wheatstone bridge type circuit and the high-temperature dielectric sensor.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.22-28
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• 2000

The fiber reinforced composite materials is widely used in aircraft, space structures and robot arms because of high specific strength and high specific modulus. The on-line cure monitoring during the cure process of the composite materials has become an important research area for the better quality and productivity. In this paper, the dielectric circuit of the wheatstone bridge type for measuring the dissipation factor was designed and manufactured. Also, the dielectric sensor for the cure monitoring of the high temperature composites was developed. The residual thermal stresses of the dielectric sensor were analyzed by the finite element method and its dielectric characteristics under high temperature were evaluated. The on-line cure monitoring of the BMI resin was performed using the wheatstone bridge type circuit and developed high-temperature dielectric sensor.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.3
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• pp.211-216
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• 2016

In several industrial fields, epoxy resin is widely used as an adhesive for co-curing and manufacturing various structures. Controlling the manufacturing process is required for ensuring robust bonding performance and the stability of the structures. A fiber optic sensor is suitable for the cure monitoring of epoxy resin owing to the thready shape of the sensor. In this paper, a fiber Bragg grating (FBG) sensor was applied for the cure monitoring of epoxy resin. Based on the experimental results, it was demonstrated that the FBG sensor can monitor the status of epoxy resin curing by measuring the strain caused by volume shrinkage and considering the compensation of temperature. In addition, two types of epoxy resin were used for the cure-monitoring; moreover, when compared to each other, it was found that the two types of epoxy had different cure-processes in terms of the change of strain during the curing. Therefore, the study proved that the FBG sensor is very profitable for the cure-monitoring of epoxy resin.

• Composites Research
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• v.16 no.4
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• pp.51-58
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• 2003

Since the reliability of adhesively bonded joints is much dependent on the curing status of thermosetting adhesive, the on-line cure monitoring during the cure of adhesively joints could improve the quality of adhesively bonded joints. In this work, the dielectric method which measures the dissipation factor of the adhesive during the cure of joints and converts it into the degree of cure of the adhesive was devised. The relation between the dissipation factor and the degree of cure of adhesive was investigated, which could eliminate the temperature effect on the dissipation factor that is a strong function of the degree of cure and temperature of adhesive. From the investigation, it was found that the dissipation factor showed a trend similar to the cure rate of the adhesive.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.37-41
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• 2005

The curing of thermoset resin is accompanied with the changes in chemical and physical properties. The cure monitoring techniques can be designed by tracing these property changes. This paper presents the cure monitoring technique with fiber optic sensors to detect the change of refractive index during the polymerization process of engineering epoxy resin. The fiber optic sensor system was developed to measure the reflection coefficient at the interface between the fiber optic and the resin. The correlation between the sensor output and the degree of cure was performed following Lorentz-Lorenz law. The isothermal data from the sensors are compared with the data from differential scanning calorimeter.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.2
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• pp.59-66
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• 2002

In this paper, we present the simulataneous monitoring of the strain and temperature during cures f various composite laminates using fiber Bragg grating/extrinsic Fabry-Perot interferometric (FBG/EFPI) hybrid sensors. Three types of graphite/epoxy composite were used : a undirectional laminate, a symmetric cross-ply laminate, and a fabric laminate. Two FBG/EFPI hybrid sensors were embedded in each laminate at different directions and different locations. We performed the real time monitoring of fabrication strains and temperatures at two points within the composite laminates during cure process in an autoclave. Throuhg these experiments, FBG/EFPI sensors proved to be an efficient choice for smart cure monitoring of composite structures.