Shigenori Egusa

Piezoelectric paints: preparation and application as built-in vibration sensors of structural materials

Piezoelectric paints were prepared using lead zirconate titanate (PZT) ceramic powder as a pigment and epoxy resin as a binder. The obtained paints were spread on the surface of an aluminium beam and cured at room temperature, thus forming the final thin films having thicknesses of 35–81 μm and PZT volume fractions of 25%–53%. The thin films were then poled under electric fields of up to 350 kV cm−1 at room temperature, and the resulting piezoelectric activity was evaluated from vibration measurements on the aluminium beam. Although not strictly quantitative, the piezoelectric activity of the thin film showed a tendency to increase with an increase in the film thickness and the PZT volume fraction. From the standpoint of the thin film application as built-in vibration sensors, the piezoelectric activity was confirmed to be high enough to determine the natural frequencies and mode shapes of the aluminium beam.

Piezoelectric paints as one approach to smart structural materials with health-monitoring capabilities

Piezoelectric paints have a potential to change a conventional structural material into an intelligent material system with health-monitoring capabilities such as vibration sensing and damage detection. Such paints were prepared using lead zirconate titanate (PZT) ceramic powder as a pigment and epoxy resin as a binder. The obtained paints were coated on aluminum test specimens, and were cured at room temperature or at 150 , thus forming the paint films having different thicknesses of 25-300 . These films were then poled at room temperature, and were evaluated with regard to the sensitivities as vibration and acoustic emission sensors in the frequency ranges of 0-250 Hz and 0-1.0 MHz, respectively. This paper mainly describes the effects of the film thickness and the cure temperature on the poling behavior of the PZT/epoxy paint film. This paper describes also the application of the paint film as a vibration modal sensor integrated into a structural material.

Mechanism of radiation-induced degradation in mechanical properties of polymer matrix composites

Four kinds of polymer matrix composites (filler, E-glass or carbon fibre cloth; matrix, epoxy or polyimide resin) and pure epoxy and polyimide resins were irradiated with 60Co γ-rays or 2 MeV electrons at room temperature. Mechanical tests were then carried out at 77 K and at room temperature. Following irradiation, the Youngs (tensile) modulus of these composites and pure resins remains practically unchanged even at 170 MGy for both test temperatures. The ultimate strength, however, decreases appreciably with increasing dose. The dose dependence of the composite strength depends not only on the combination of fibre and matrix in the composite but also on the test temperature. A relationship is found between the composite ultimate strain and the matrix ultimate strain, thus indicating that the dose dependence of the composite strength is virtually determined by a change in the matrix ultimate strain due to irradiation. Based on this finding, we propose a mechanism of radiation-induced degradation of a polymer matrix composite in order to explain the dose dependence of the composite strength measured at 77 K and at room temperature.

Anisotropy of radiation-induced degradation in mechanical properties of fabric-reinforced polymer-matrix composites

Four kinds of fabric-reinforced polymer-matrix composites (filler: E-glass or carbon fabric; matrix: epoxy or polyimide resin) were irradiated with60Coγ-rays or 2 MeV electrons at room temperature. Three-point bend tests were then carried out at 77 K and at room temperature in a 45° direction from warp to fill. Comparison of the degradation behaviour among these composites reveals that the glass-epoxy and glass-polyimide composites are quite similar to each other in the dose dependence of the ultimate interlaminar shear strength at each test temperature. This result suggests that the radiation damage at the fibre-matrix interface decreases the contribution of the chemical bond mode to the total bond strength at the interface, thus decreasing the composite shear strength with increasing dose. For the carbon-epoxy and carbon-polyimide composites, on the other hand, the shear strength at room temperature changes little even after irradiation up to 140 MGy, while the shear strength at 77 K decreases monotonically with increasing dose. These findings suggest that the fibre-matrix bond strength due to the friction force mode is quite insensitive to radiation, thus resulting in the dose-independent shear strength at room temperature. At 77 K, however, the friction force mode fails to function properly because of the brittleness of the matrix resin, and consequently the composite shear strength decreases with increasing dose owing to a resulting increase in the matrix brittleness.

Effects of neutron irradiation on polymer matrix composites at 5 K and at room temperature: I. Absorbed-dose calculation☆

Abstract The spatial distribution of absorbed dose in a composite specimen irradiated in the Intense Pulsed Neutron Source (IPNS) was calculated for four kinds of cloth-filled polymer-matrix composites (filler: E-glass or carbon fiber; matrix: epoxy or polyimide resin). This calculation was performed by taking into account the range of recoil particles and the array of fibers in the composite. The average ratio of the energy of recoil protons deposited in a matrix of a composite to that deposited in an infinite matrix is 0.55–0.79, depending on the IPNS neutron spectra and on the kinds of composite materials. For E-glass fiber composites which have a 10 B ( n , α ) 7 Li reaction taking place in the fiber, the average ratio of the energy of α and 7 Li particles deposited in the matrix to that deposited in an infinite fiber material is about 0.79. On the basis of these ratios, the conversion factor from total neutron fluence to absorbed dose for a matrix of a composite is calculated for composite materials irradiated in IPNS.

Effects of neutron irradiation on polymer matrix composites at 5 K and at room temperature: II. Degradation of mechanical properties☆

Abstract Neutron irradiation with a low flux of accompanying γ-rays in the Intense Pulsed Neutron Source was carried out at 5 K and at room temperature on four kinds of polymer matrix composites (filler: E-glass or carbon fiber cloth; matrix: epoxy or polyimide resin). The specimen irradiated at 5 K was warmed up to room temperature before the mechanical test was performed at 77 K. The Youngs modulus of these composites scarcely decreases even when a total neutron fluence is 3.0 × 10 18 n / cm 2 (2.1 × 10 18 n / cm 2 for E > 0.1 MeV) for the 5 K irradiation and 1.6 × 10 19 n / cm 2 (8.0 f 10 18 n/cm 2 for E > 0.1 MeV) for the room-temperature irradiation. The ultimate strength, however, decreases significantly at this neutron fluence for all the composites except the carbon/epoxy composite whose initial strength is comparatively low. Comparison of this result with that obtained for 60 Co γ-ray irradiation demonstrates that the radiation sensitivity of the glass/epoxy and glass/polyimide composites is 1.8–2.6 times higher towards neutrons than γ-rays. As to the irradiation temperature of 5 K and room temperature, no significant influence on the degradation efficiency of the composite strength is observed under the present conditions of mechanical test.

Application of piezoelectric paints to damage detection in structural materials

Piezoelectric paints were prepared using lead zirconate titanate (PZT) ceramic powder as a pigment and epoxy resin as a binder. The obtained paints were coated on aluminum plates and were cured at room temperature, thus forming the paint films having thicknesses of 25 to 300 /tm and a PZT volume fraction of 53%. These films were then poled at room temperature, and were evaluated with regard to the sensitivity as an acoustic emission sensor in the frequency range of 0-1.2 MHz. The paint film sensitivity obtained at a given poling field depends on the film thickness, even after being normalized by dividing by the film thickness. The current-voltage characteristic of the paint film reveals that the film-thickness dependence of the normalized sensitivity is interpreted in terms of the space-charge buildup at the PZT/epoxy interface during the poling process of the paint film.

Thickness dependence of the poling and current–voltage characteristics of paint films made up of lead zirconate titanate ceramic powder and epoxy resin

A specially prepared paint made up of lead zirconate titanate (PZT) ceramic powder and epoxy resin was coated on an aluminum plate and was cured at room temperature, thus forming the paint film of 25–300 μm thickness with a PZT volume fraction of 53%. The paint film was then poled at room temperature, and the poling behavior was determined by measuring the piezoelectric activity as a function of poling field. The poling behavior shows that the piezoelectric activity obtained at a given poling field increases with an increase in the film thickness from 25 to 300 μm. The current–voltage characteristic of the paint film, on the other hand, shows that the increase in the film thickness leads not only to an increase in the magnitude of the current density at a given electric field but also to an increase in the critical electric field at which the transition from the ohmic to space‐charge‐limited conduction takes place. This fact indicates that the amount of the space charge of electrons injected into the pain...

Mechanical properties of polymer matrix composites at 77 K and at room temperature after irradiation with 60Co γ-rays

Ten different polymer matrix composites were irradiated with 60Co γ-rays at room temperature, and were examined with regard to the mechanical properties at 77 K and at room temperature. The radiation-induced degradation of these composites is observed much more significantly in the ultimate strength and in the shear modulus than in the Youngs modulus. The radiation resistance of these composites depends primarily on the radiation resistance of matrix resins, which increases in the order diglycidyl ether of bisphenol A < tetraglycidyl| diaminodiphenyl methane < Kerimid 601. Comparison of the mechanical properties tested at 77 K and at room temperature demonstrates that the extent of radiation-induced decrease in the composite strength is appreciably greater in the 77 K test than in the room temperature test. Interpretation of these results is based on the competition between the two opposing effects due to the hardness and brittleness of matrix resins.

Characterization of carboxylated latices prepared by radiation-initiated emulsion polymerization. Comparison with chemically prepared latices

Abstract Copolymer latices of n-butyl methacrylate, 2-hydroxyethyl methacrylate, and acrylic acid were prepared with 60Co γ rays and the redox system of (NH4)2S2O8/NaHSO3 as initiator and with sodium dodecylsulfate as emulsifier at polymerization temperatures of 20 to 80°C. The resulting latices were characterized with regard to viscosity, particle size, distribution of acid groups, and electrolyte stability. The latices are more viscous when prepared with radiation than with the chemical initiator. The particle size increases with polymerization temperature for the radiation-prepared latices, whereas for the chemically prepared latices the tendency is reversed. The conductometric titration of acid groups reveals that the surface charge density is higher for the latices prepared with radiation than with the chemical initiator, giving the expectation that the radiation-prepared latices are more stable to the addition of electrolytes than the chemically prepared latices. The stability measurement by the stopped-flow method, however, gives a result contrary to the expectation, suggesting that not all the surface-bound acid groups are effective for the latex stabilization, and the effectiveness is low for the radiation-prepared latices. These findings should be interpreted in terms of a difference in the initiation method of emulsion polymerization and in terms of the resultant difference in the ionic strength of water phase as well as the presence of strong acid end groups derived from the decomposition of chemical initiators. As to the dependence of the latex stability on polymerization temperature, a tendency to increase with the temperature is observed for both types of initiation method. The computer simulation based on the DLVO theory suggests that this tendency is attributable mainly to the carboxyl groups produced by the hydrolysis during the polymerization for the chemically prepared latices, while for the radiation-prepared latices the same tendency should be ascribed to the increasing particle size with polymerization temperature.