Hiroaki Yanagida

Development of conductive FRP containing carbon phase for self-diagnosis structures

The electrical properties of fiber reinforced plastics (FRP) have been investigated in order to develop structural materials with a damage diagnosis function. Electrical conductivity was achieved by adding carbon particles or carbon fiber as a conductive phase into the FRP. The composites containing carbon particles connected by a percolation structure were found to have advantages in terms of response of conductivity to small strains and the size of the detectable strain range, compared to composites containing carbon fiber. A part of the resistance change in the elongated composites containing carbon particles remained after unloading despite deformation being predominantly elastic. This residual resistance was found to depend largely on morphology of the carbon particles and orientation of the glass fiber. A distinct residual resistance was observed in composites containing spherical carbon particles (carbon black) and glass fibers aligned at an angle of 0 degrees with respect to the tensile direction. Electrical time domain reflectometry (ETDR) was used to locate the damaged region in multilayer composites containing CFRP and GFRP. The position of local damage in the multilayer composites was clearly located to a precision of within 20 mm.

Application of self-diagnosis FRP to concrete pile for health monitoring

The function and performance of the self-diagnosis composites embedded in concrete blocks and piles were investigated by bending tests and electrical resistance measurements. Carbon powder (CP) and carbon fiber (CF) were introduced in glass fiber reinforced plastics composites to obtain electrical conductivity. The CP composite has commonly good performances in various bending tests of block and pile specimens, comparing to the CF composite. The electrical resistance of the CP composite increases in a small strain to response remarkably micro-crack formation at about 200 μ strain and to detect well to smaller deformations before the crack formation. The CP composite posses a continuous resistance change up to a large strain level near the final fracture of concrete structures reinforced by steel bars. It has been concluded that the self-diagnosis composite is fairly useful for the measurement of damage and fracture in concrete blocks and piles.

Self-diagnosis function of FRP containing electrically conductive phase

The electrical characteristics of fiber reinforced plastics (FRP) composites have been investigated in order to develop the self-diagnosis function suitable for health monitoring of structural materials. The electrical conductivity was achieved by adding carbon particles or fiber as a conductive phase into FRP. The self-diagnosis function of the composites was evaluated by the measurement of change in electrical resistance as a function of stress or strain in tensile tests. The resistance of carbon fiber in the composite slightly changed at a small strain level and increased nonlinearly with the applied stress due to the fracture of carbon fiber. The conductive FRP composite containing carbon particles had high sensitivity and linear response of the resistance in a wide strain range. In the cyclic loading tests, the phenomenon of residual resistance was observed at an unloading state in the composites with carbon particles. The residual resistance increased with an applied maximum strain, showing that the composite with carbon particles possesses the function to memorize the applied maximum strain or stress. These results indicate that the FRP composite containing carbon particles has a promising possibility for simple diagnosis of dynamic damage and for damage hysteresis with high sensitivity.

Application of the self-diagnosis composite into concrete structure

The function and performance of the self-diagnosis composites embedded in mortar/concrete blocks and concrete piles were investigated by bending tests and electrical resistance measurements. Carbon powder (CP) and carbon fiber (CF) were introduced in glass fiber reinforced plastics composites to obtain electrical conductivity. The CP composite has commonly good performances in various bending tests of block and pile specimens, comparing to the CF composite. The electrical resistance of the CP composite increases in a small strain to response remarkably micro-crack formation at about 200 (mu) strain and to detect well to smaller deformations before the crack formation. The CP composite possesses a continuous resistance change up to a large strain level near the final fracture of concrete structures reinforced by steel bars. The cyclic bending tests showed that the micro crack closed at unloading state was able to be evaluated from the measurement of residual resistance. It has been concluded that the self- diagnosis composite is fairly useful for the measurement of damage and fracture in concrete blocks and piles.

Gas Detection Utilizing the Interface of a CuO/ZnO Thin Film

The gas sensing function of the interface of CuO (p-type semiconductor) and ZnO (n-type semiconductor) thin films was investigated. Films were prepared by sputtering and the junction showed rectified I–V characteristics originating from the interface of the semiconductors. An array pattern was made in the films ( channels of ∼10 μm were formed ) by photolithography so that the interfaces of the semiconductors could be exposed to the atmosphere. These exposed junctions showed current increases at a p-n forward bias when flammable gases (CO, H2) were introduced. In the temperature range from 100°C to 250°C, the current increase was observed at 0.5 to 1.0 V bias, and at room temperature it occurred at a higher bias than 2.0 V. Little change was observed at a p-n reversed bias. The sensitivity (ratio of the current with and without flammable gas) and gas selectivity were different depending on the applied bias and the heat treatment temperature.

17.1 Intelligent Ceramics—Design and Development of Self-Diagnosis Composites Containing Electrically Conductive Phase

The electrically conductive composites having continuous structure of conductive particles with the continuous or network structure were designed and fabricated in the fiber-reinforced plastics (FRP) and the ceramics-matrix composites (CMCs). These self-diagnosis functions were evaluated from the measurement of resistance changes with applied strain in normal or cyclic loading tests. The practicability of the function was examined in bending tests for mortar specimen embedding FRP. Percolation phenomena with the second phase of various aspect ratios were also studied by two-dimensional computer simulation. The self-diagnosis functions of the CMC were evaluated by simultaneous measurements of stress and electrical resistance change as a function of applied strain in four-point bending tests. The chapter investigates the two-dimensional computer simulation to design percolation structure of the second phases with different aspect ratios. That is to clarify the relation between formation of percolation structure, the morphology, and the configuration of the second phase.

Computational modeling and design for continuous conductive structures in self-diagnosis composite

We have successfully developed the computer simulation technique of modeling and design for continuous conductive structures in the self-diagnosis composite. The Monte Carlo (MC) method has been used for the simulations of the microstructures at the array of two or three dimensional lattices. The simulation results were analyzed and discussed in relation to microstructural parameters such as particle size, content, aspect ratio, etc. The computer simulation gave us important and quantitative information to obtain continuous structure of the particles dispersed in a matrix phase.

Self-diagnosis function of fiber-reinforced composite with conductive particles

The electrically conductive fiber reinforced plastics (FRP) and ceramics matrix composites (CMC) have been designed and fabricated in order to introduce the self-diagnosis function which means the combination of reinforcement and damage diagnosis function into structural materials. The electrical conductivity was achieved by adding conductive fiber or particles into these composites. The composites with percolation structure consisting of carbon particles were found to have the advantages in response of conductivity to a small strain and in detectable strain range, comparing to the composites containing carbon fiber. A part of resistance change in the elongated composites with carbon particles remained after unloading despite its elastic deformation. The residual resistance increased with increasing applied maximum strain, showing that the composite possesses the function to memorize the previous maximum strain. The CMC materials containing TiN particles as a conductive phase indicated not only the fine response of resistance to slight deformation but also the increase in residual resistance during cyclic deformation at a constant load, suggesting that the composite have the ability to diagnose a cumulative damage through measurements of the residual resistance. These results suggest that the self-diagnosis functions peculiar to these composites are suitable for health monitoring techniques for many structural materials.