Thermal barrier coating (TBC) had been already applied to the hot section parts of gas turbines, such as a bucket and a combustor. It is thought that TBCs are in dispensable for the gas turbines along with cooling technology. It is now desired to give higher durability to TBCs so as to endure higher combustion temperature. The object of this study is to clearify the oxidation behavior of Atmospheric Plasma Spraying TBC at high-temperature. The experimental results showed that the oxidation layer was formed mainly of alumina at the interface between the yttria stabilized zirconia top-coating and MCrAlY bond-coating. There was a tendency that the oxide layer growth increased with increasing heating temperature and heating time. It was also indicated that the oxide layer growth followed a 0.45 power time law. The Arrhenius type temperature dependence for the rate constant of oxide layer growth was confirmed. Finally, the long time estimation of oxide layer growth behavior was conducted by the simulation analysis.
Thermal barrier coating (TBC) had been already applied to the hot section parts of gas turbines, such as a bucket and a combustor. It is thought that TBCs are in dispensable for the gas turbines along with cooling technology. It is now desired to give higher durability to TBCs so as to endure higher combustion temperature. The object of this study is to clearify the sintering behavior of Atmospheric Plasma Spraying zirconia TBC at high-temperature. The experimental results showed that the shrinkage of plasma sprayed zirconia coating became remarkable above 1300K. There was a tendency that the shrinkage increased with increasing heating temperature and heating time. It was also indicated that the linear shrinkage followed a 2/5 power time law. The Arrhenius type temperature dependence for the sintering rate constant was confirmed. Finally, the shrinkage stress behavior induced by the sintering was made clear by the simulation analysis.
The quantitative estimation of the failure stress of a gadolinium orthosilicate (Gd2SiO5, hereafter abbreviated as GSO) single crystal due to thermal shock was investigated. A cylindrical test specimen was heated in a silicone oil bath, then subjected to thermal shock by pouring room temperature silicone oil. Cracking occurred during cooling. The heat conduction analysis was performed to obtain temperature distribution in a GSO single crystal at cracking, using the surface temperatures measured in the thermal shock cracking test. Then the thermal stress was calculated using temperature profile of the test specimen obtained from the heat conduction analysis. It is found from the results of the thermal stress analysis and the observation of the cracking in test specimens that the thermal shock cracking occurs in a cleavage plane due to the stress normal to the plane. Three-point bending tests were also performed to examine the relationship between the critical stress for thermal shock cracking and the three-point bending strength obtained from small-sized test specimens.
Spall damage analyses are conducted in the framework of continuum damage mechanics with special emphasis on the 3-dimensionality and the effect of void volume fraction on the spall process. The evolution equation of a scalar damage variable taking account of the nucleation and growth of spherical voids, and the elastic-viscoplastic constitutive equations extended to damaged materials are incorporated into the commercial hydrocode MANJUSRI-3D. The axisymmetric two-dimensional analyses of the plate-impact tests on OFHC copper plates are performed to examine the effect of the ratio of the target radius to its thickness and that of the volumetric strain related to the void development on the relation between volumetric strain and hydrostatic pressure.
This paper presents the applicability of an estimation method for the experienced maximum load and displacement responses by small load increment. For the expansion of the proposed method, three reinforced concrete column specimens were tested under dynamic loading and a comparatively large scale specimen was tested under static reversed cyclic loading. The test results indicated that the relationships between the secant stiffness under the small load increment and the equivalent secant stiffness corresponding to the maximum experienced response were represented by a logarithmic function. They also indicated that the relationships between the displacement caused by small load increment and the experienced maximum displacement of the damaged columns were expressed by an exponential function. From the test results the applicability of the proposed method were examined. As a result, it was found that the proposed method was applied to specimens under dynamic loading and comparatively large scale specimens under static reversed cyclic loading. However, furthermore experimental and analytical studies are needed to establish a more reliable estimation method.
The reinforced concrete structures have been considered durable for a long time. But recently, it has been reported that they are deteriorated by alkali-silica reaction and/or reinforcement corrosion and so on. In the deterioration mechanism, water existing in concrete can be one of the main factors. Silane, which is one of hydrophobic impregnants, is applied on concrete to control water in concrete. In this paper, the effect of silane was evaluated by mass change, strain, and halfcell potential. Silane performed better for controlling the expansion of concrete by alkali-silica reaction and the reinforcement corrosion by chloride ion. However, when an excessive amount of reactive potential and/or chloride was included in concrete, it was difficult to restrain the deterioration in a long term. Silane was most effective when an water content in concrete was 85% and the concentration of silane solution was 40%.
In order to clarify the fatigue crack propagation characteristics at a cryogenic temperature of the equiaxed Ti-6Al-4V alloy, fatigue crack propagation tests were carried out at 77K and 298K. Microscopic observations were also made on the longitudinal section and fracture surface of specimens. The fatigue crack propagation rate at 77K was smaller than that at 298K, especially in the low propagation rate region, where the crack closure level was higher as compared to that at 298K. The crack propagation characteristics in terms of the effective stress intensity factor range at 77K and those at 298K were close to each other. A marked crack bifurcation was seen in the low propagation rate region at 77K. Transmission electron microscopic observations revealed that a high-density dislocation structure existed in the close neighbor of crack route, and cracks propagated mainly across α-grains accompanied with small branch cracks. Although the fracture surface morphologies at these two temperatures were almost the same, the plateau in the low propagation rate at 77K was smoother as compared to that at 298K.
The fracture criterion of notched FRP plates based on the concept of stress concentration and the similarity of stress distribution near the notch root is investigated experimentally. An experimental method is presented for examining the fracture strength of notched FRP plates under static loads. The investigation is accomplished by obtaining experimental data on the tension and bending tests of a glass fiber-reinforced polycarbonate plates containing blunt and shallow notches. For sharp-notched specimens, the stress distributions near the notch root are the same in all specimens, for which both the maximum elastic stress and notch-root radius are equal to each other. Therefore, the maximum elastic stress at fracture is determined by the notch-root radius only. On the other hand, for blunt-notched specimens the situation is much more complex. The experimental results were discussed in terms of a combination of the maximum elastic stress, notch-root radius and the width of notch section. Applying the fracture criterion derived here, the experimental results for blunt-notched specimens can be clearly explained.
Tensile strength of monofilament carbon fibers was investigated for different gauge lengths ranging from 2 to 100mm. In the tensile tests, the fiber diameter was determined as the minimum diameter d3 at both ends and the center of gauge section by using an optical microscope. Weibull analysis of the data and the effective volume model for tensile strength of carbon fiber showed that the shape parameter a was not constant for different gauge lengths and the effective volume model could not be applied effectively to the results. It was found that these were caused by the fact that the diameter was never constant along a carbon fiber. Consequently, in this study, it was aimed to derive the distribution of tensile strength σ0 based on the true minimum diameter d0 along the gauge length. In order to do this, two dimensional distribution of d3 and d0 was derived from the data of diameter measured at every 0.1mm along a single fiber of 100mm assuming the normal distribution. Combining this distribution of d3 and d0 with the distribution of tensile strength σ3 based on the diameter d3, the distribution of strength σ0 was derived analytically, and calculated using the numerical values of included parameters. The distribution of σ0 obtained for the respective gauge lengths mutually agreed very well and could be represented by a single normal distribution, showing the validity of the present analysis.
A new process to open continuously reinforcing fiber tow was proposed. It consists of a roll part for its preliminary opening and a pneumatic part based on a novel principle for its main opening. This process was successfully applied to carbon and glass fiber tows. Three methods for evaluating the degree of tow opening were also proposed and applied to the evaluation of these opened tows. The following results were obtained: In the new combined method, filaments within tow are separated from the state adhered by a sizing agent in the roll part, and the tow is widely opened by the pneumatic part. Thus, much more widely opened tow can be obtained by the combined method, as compared with any of the singular process. The effects of the number of filaments within tow, the breadth/thickness ratio of tow, the compactness caused by sizing, and the diameter of single filament on the opening degree of carbon fiber and glass fiber tows were also clarified.
The technology for opening tow was applied to the opening of reinforcing fiber tow for thermoplastic composites. The effect of its opening on the impregnation behaviors of matrix resin was inveatigated in comparison with those for unopened tow through experiments and theoretical calculations. On-line measurement of void volume change during compression molding for carbou fiber/nylon 6 composite was carried out. Micro-scopic observation on the cross-section of parts fabricated at several molding time and measurement of transverse bending strength of these parts were also conducted. Based on the theoretical model presented previously, the void volume changes for several molding conditions were simulated under a certain assumptive void pressure-change. All these results show consistently that the tow opening makes the impregnation of matrix resin into the reinforcing fiber much easier.
A method is proposed for determining the orientation functions of fibers of isotropic materials such as glass and gamma alumina in FRP sheets and nonwoven mats. The method consists of (1) measurement of the anisotropy of inplane dielectric constant of a sheet sample with polarized microwave, (2) theoretical estimation of the difference between the dielectric constants parallel and perpendicular to the fiber direction of a perfectly oriented sheet, and (3) determination of the mean orientation angle and orientation function of the fiber from the results of (1) and (2). Regarding the second process (2), three of theoretical models which have been reported are examined and compared with experimental data of unidirectional glass/air and glass/epoxy and are found to be equally suitable. The orientation functions obtained for laminates of continuous fibers of glass and gamma alumina are in agreement with the theoretical values calculated from the stacking structure within 5% deviation. Orientation functions are also determined on FRP sheets and nonwoven mats of short glass fiber and the anisotropies in modulus of elasticity and in ultrasonic propagation velocity are calculated from them. The differences between the calculated values and the directly measured values are less than 10%.
The on-line monitoring system for single edge crack was developed based on the direct current multi-terminal potential drop method. The multi-terminal potential drop method means that many electrodes for measuring potential difference are distributed on one side of plate-like structure, the several combinations of potential difference ratio give the crack length, the crack position and the side on which the crack exists. Thus the algorythm for detection of single edge crack based on the multi-terminal potential drop method was programmed as an on-line monitoring system. The developed system was verified using single edge cracked specimens made of stainless steel, carbon steel and copper. The verification test results showed that the crack length could be detected with an accuracy of ±1.0mm even for a shallow crack, the crack position between electrodes could be detected within about ±1.0mm. Then the multi-terminal potential drop method system is considered to be very much effective as an online monitoring system.
The neutron diffraction method was applied to measure the loading stress in each constituent phase of an aluminum alloy composite reinforced by silicon carbide (SiC) particles. Under uniaxial loading, the longitudinal strain measured by the neutron method increased proportionally to the applied stress, while the transverse stress decreased with the applied stress in both materials. The phase stress of the aluminum matrix and SiC particles measured by the neutron method as a function of the applied stress agreed well with the theoretical prediction by Eshelby model. The X-ray diffraction method was also applied to measure the loading and residual stresses in the same materials. The residual stress was compression for both Al and SiC phases in the composite. The diffraction elastic constants of the monolithic aluminum alloy obtained from the X-ray method are very close to those determined by the neutron method and calculated by Kröner's model. The increase in the phase stress in each phase of the composite due to uniaxial tensile loading is nearly equal to the value measured by the neutron method. The macrostress calculated from the phase stress by using the rule of mixture was equal to the applied stress.