• Composites Research
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• v.15 no.5
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• pp.7-13
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• 2002

The piezoelectric thin film sensor has good characteristics to observe the impact responses of composite structures. The capabilities for monitoring impact behavior of Gr/Ep laminates subjected to damage-induced impact using the PVDF(polyvinylidene fluoride) film sensor were examined. For a series of low-velocity impact tests from low energy to damage-induced energy, simulated sensor signals were compared with measured signals and the PVDF film sensor. Local impact damages(matrix cracking and delamination) were found at three impact tests, but the measured signals agreed well with the simulated sensor signals based on the linear relationship between the impact forces and the PVDF film sensor signals. And the inverse technique was applied to reconstruct the impact forces using the PVDF film sensor signals. Most of reconstructed impact forces had good agreement with the measured forces. The comparison results showed that the local damage due. to low-velocity impact didn't disturb the global impact responses of composite laminates and the reconstruction of impact forces from PVDF sensor signals wasn't affected by the local damage.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.5
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• pp.445-454
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• 2003

Health monitoring is a major concern not only in the design and manufacturing but also in service stages for composite laminated structures. Excessive loads or low velocity impact can cause matrix cracks and delaminations that may severely degrade the load carrying capability of the composite laminated structures. To develop the health monitoring techniques providing on-line diagnostics of smart composite structures can be helpful in keeping the composite structures sound during their service. In this study, we discuss the signal processing techniques and some applications for health monitoring of composite structures using piezoceramic sensors and fiber optic sensors.

• Composites Research
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• v.16 no.6
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• pp.41-47
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• 2003

Composites are widely used for aircraft, satellite and other structures due to its good mechanical and thermal characteristics such as low coefficient of thermal expansion(CTE), heat-resistance, high specific stiffness and specific strength. In order to use composites under condition of high temperature, however, material properties of composites at high temperatures must be measured and verified. In this paper, material properties of T700/Epoxy were measured through tension tests of composite specimens with an embedded FBG sensor in the thermal chamber at the temperatures of RT, $100^{\circ}$, $200^{\circ}$, $300^{\circ}$, $300^{\circ}$. Through the pre-test of an embedded optical fiber, we confirmed the embedding effects of an optical fiber on material properties of the composites. Two kinds of specimens of which stacking sequences are [0/｛0｝/0]$_{T}$. and [$90_2$/｛0｝/$90_2$]. were fabricated. From the experimental results, material property changes of composites were successfully shown according to temperatures and we confirmed that fiber Bragg grating sensor is very appropriate to strain measurement of composites under high temperature.

• 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.

• 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.

• Journal of the Korean Electrochemical Society
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• v.21 no.4
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• pp.80-87
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• 2018

Safety issues in Li-ion battery system have been prime concerns, as demands for power supply device applicable to wearable device, electrical vehicles and energy storage system have increased. To solve safety problems, promising strategy is to replace organic liquid electrolyte with non-flammable solid electrolyte, leading to the development of all-solid-state battery. However, relative low conductivity and high resistance from rigid solid-solid interface hinder a wide application of solid electrolyte. Composite electrolytes composed of organic and inorganic parts could be alternative solution, which in turn bring about the increase of conductivity and conformal contact at physically rough interfaces. In our study, composite electrolytes were prepared by combining poly(ethylene oxide)(PEO) and $Li_7La_3Zr_2O_{12}$ (LLZO). The crystallinity, morphology and electrochemical performances were investigated with the control of LLZO contents from 0 wt% to 50 wt%. From the results, it is concluded that optimum content and uniform dispersion of LLZO in polymer matrix are significant to improve overall conductivity of composite electrolyte.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.11
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• pp.1-8
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• 2005

In this paper, we present design and prototyping of a low-cost, integrated multi-functional micro health sensor chip that can be used or embedded in widely consumer devices, such as cell phone and PDA, for monitoring environmental condition including air pressure, temperature and humidity. This research's scope includes basic individual sensor study, architecture for integrating sensors on a chip, fabrication process compatibility and test/evaluation of prototype sensors. The results show that the integrated TPH sensor has good characteristics of ${\pm}\;1\%FS$ of linearity and hysteresis for pressure sensor and temperature sensor and of ${\pm}\;5\%FS$ of linearity and hysteresis But if we use 3rd order approximation for humidity sensor, full scale error becomes much smaller and this will be one of our future study.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.124-133
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• 2007

In our research, we focused on the FBG sensor system which is one of the fiber optic sensor system. The FBG sensor system is used for structural measurements. The problem of FBG sensor is very thin and weak. The methods that can protect FBG optical fiber sensor front outside forces such as the impacts are investigated. The FBG sensor embedded in the fiber reinforced composites which can replace the reinforcing steel bars in concretes can be applied to the concrete structures by embedding to the composite materials. The progresses in tensile strength of FBG sensor embedded in the reinforcing FRP bars in the concrete structures compare to plain FBGs were observed and the good long term durability is expected.

• Journal of Sensor Science and Technology
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• v.10 no.1
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• pp.42-51
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• 2001

In this study, the effects of embedded optical fibers on the static properties under tensile load and dynamic properties under fatigue load of composite laminates were investigated by experimental tests and finite element analysis. Based on the results, it can be concluded that the embedded optical fiber sensors do not have significant effects on the structural integrity of the smart composite structures except when the sensors are embedded perpendicular to the adjacent reinforcing fibers under fatigue loading. An intensity-based optical fiber sensor was embedded in the crossply composite laminates to monitor the fatigue damage by detecting the stiffness changes of the laminates. The result of this experiment has shown that the intensity-based optical fiber sensor has large potential to monitor the fatigue damage of composite structures by detecting the stiffness changes of the structures with simple and inexpensive instruments and without complex post-processing of measured signals. In addition, the optical fiber sensor showed good resistance to fatigue loading and wide sensing ranges of stiffness.

• Journal of Sensor Science and Technology
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• v.7 no.4
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• pp.285-292
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• 1998

Shape Memory Alloy(SMA) has been used in many engineering fields because of its good characteristics of actuator. For example, SMA wire can be embedded easily in the polymer composite laminate and then be used as actuator for structural control. Since the strain have a significant influence on the electrical resistance of SMA wire, It is a possible to use the SMA wire as a sensor of such physical quantities. In this study, the possibility for the application of Ni-Ti SMA wire as a sensor embedded within a composite laminate is investigated.