Yoshiki Okuhara

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.

Recovery characteristics of optical hydrogen sensor using Pd thin film: Behaviour of three-stage hydrogen desorption

The recovery behaviour of optical hydrogen sensor using Pd film has been investigated. The change in reflectance with hydrogen desorption indicated distinctive characteristics with three-stage curve which depended on thickness of the Pd film. Moreover, the distinction became clearer with increasing number of absorption-desorption cycles. These behaviours were related to the change in pressure concentration isotherm.

Damage Evaluation for Concrete Structures using Fiber Reinforced Composites as Self-Diagnosis Materials

Health monitoring techniques that utilize structural materials with the ability to diagnose their own condition, so-called self-diagnosis materials, have been under development. The authors have developed two types of electrically conductive fiber reinforced composite to diagnose cracks in concrete structures: a high sensitivity detection sensor and maximum strain memory sensor. Three points bending tests on pre-notched reinforced concrete beam under the cyclic loading is presented using these two self-diagnosis materials, with attention towards the relationship between crack width of the concrete beam and electric resistance. Moreover, effects of volume fraction of carbon particle on memorizing maximum strain are investigated. It has been proved that both self-diagnosis materials are highly effective to detect the cracks in the concrete. And present strain can be obtained by the proposed fiber reinforced plastic composites. Although volume fraction of carbon particle has significant influence on the characteristics of memorizing maximum strain, maximum strain of the concrete structures can be memorized using the appropriate self-diagnosis materials.

Near-infrared reflection from Al-doped ZnO films prepared by multi-target reactive sputtering

Thin films of aluminium-doped zinc oxide (ZnO:Al) as heat reflective coatings were prepared by multi-target reactive sputtering using metallic Zn and Al targets. An optimization of Al content and a reduction in oxygen partial pressure were crucial in increasing the carrier concentration Ne and the Hall mobility μ. The ZnO:Al film with the highest Ne achieved the shortest plasma wavelength λp of 1375 nm, which shifted the near-infrared reflectance spectrum closer to the visible region. The high μ reduced the optical absorption and enhanced the reflectance. Moreover, the multi-target system enabled intermittent doping of Al, which was applied to stack multilayers consisting of non-doped and Al-doped ZnO layers. A drop in the refractive indices n above λp for the ZnO:Al layers formed the periodic distribution of n in the thickness direction, which provided a high reflectance zone from 1000 to 1400 nm in wavelength.

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.

Influence of phase transformation in Pd hydride on the recovery characteristics of optical hydrogen sensors

The recovery characteristics of optical hydrogen sensor, using Pd film, have been investigated in order to clarify their distinctive behaviour showing three-stage curve. The obvious two peaks observed in differentiated reflectance as a function of elapsed time during hydrogen desorption were found to correspond to the phase boundaries of Pd hydride. The phase transformation determined by these peaks was consistent with that observed within situ X-ray diffraction analysis. Moreover, the change in resistivity with hydrogen desorption indicated distinctive recovery curve, which was also connected with the phase transformation. These results clarified that the hydrogen desorption obviously consisted of three-stage process, and the distinctive behaviour was due to the phase transformation of Pd hydride.

Fiber reinforced composites as self-diagnosis materials for memorizing damage histories

Electrically conductive fiber-reinforced composites have been designed in order to develop self-diagnosis materials with the ability to memorize damage histories. Irreversible resistance changes dependent on the strain histories of the composites were utilized to achieve this ability. Conductive fiber-reinforced plastics for memorizing maximum strain were prepared by adding carbon fibers or particles into the composites. Pre-tensile stresses in composites containing carbon fibers were found to effectively enhance their residual resistance and to significantly improve the limit of smallest detectable strains. The residual resistances of composites containing carbon particles connected by a percolation structure were found to depend strongly on the volume fractions of carbon particles; composites with high volume fractions of carbon displayed remarkable residual resistance without application of a pre-tensile stress. In order to memorize cumulative damage, composites consisting of a brittle titanium nitride ceramic wire laminated with glass fiber reinforced plastics were prepared. These composites were found to exhibit remarkable residual resistances that increased in proportion to the logarithm of the number of tensile cycles. These results suggest that a simple and low cost monitoring technique without real-time measurement system will be available in wide range of applications using these composites.

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.

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.