In order to evaluate the probability of detecting the flaw in the materials, it is studied how to measure and identify the cognitive capability of the human being with multiple modalities. Procedures for measurement of psychometric functions of a single attribute and joint probability of dual attributes in the inspection image data are proposed by the experiment of paired comparison under constant stimuli. The validity of the proposal methods was also verified by the examples of the experiments of single and dual attributes from the inspection sample data of mat FRP panel. From the results of these examples, the differences of the detection probabilities were illustrated by the features in single and multiple modalities such as the psychometric curves for each attributes, correlation matrix among attributes and so on.
A service load like random load has been analyzed by the rain flow method extensively. When the reliability of a structure is estimated, mean stresses on fatigue life are probably ignored because it is not easy to measure. The purpose of this study is to propose a practical estimation method of a structural reliability for fatigue under service loads by Miner's law. In addition, the fatigue tests to obtain S-N curve is carried out under constant amplitude loading. However, the each stress ratio of cyclic stress counted with rain flow method is different. In the proposed method, the effect of stress ratio has been considered by fatigue limit diagram with failure probability. On this diagram, the increment of cumulative cycle ratio ΔDpf for each cyclic stress can be calculated with failure probability by a computer program. The expected life Npf is defined as the period when Dpf reaches 1.0. If we assume the ergodicity of the sampling time T, Npf is T/Dpf. It gives fatigue life distribution, when a structure is under service loads. In conclusion, we have got a reliability curve of the structure for fatigue life. This curve can be obtained with service load or design stress easily by using our developed program. This proposed method is practical and the industrial applicability is wide.
Ceramic parts such as a combustor of gas turbine requires the design considering strength reliability, because ceramics are easily fractured by thermal stress due to rapid changes of temperature. Therefore, it is essential to estimate the thermal shock stress and is also necessary to control the cooling rate of ceramic parts. In this paper, the thermal stresses at trip and steady state in a ceramic combustor liner are analyzed numerically by using a simple ceramic cylinder model, which is heated from the inside and is cooled from the outside. The propability of failure of a ceramic cylinder subjected to thermal stresses both at trip and steady state is also analyzed theoretically. As a result, the thermal shock stress at trip decreases with the increase in cooling rate at steady state. However, because the thermal stress at steady state increases with the increase in cooling rate, the cooling rate at steady state should be optimized to minimize the propability of failure in the ceramic cylinder system, considering the thickness of cylinder.
The geological survey using boring is often performed to obtain information for geotechnical parameters. Therefore, a lot of survey dates for geotechnical characterizations on ground have been accumulated. However, these data have not been put to practical use. The authors have performed the estimation of spatial distribution of the geotechnical characterization by the use of these data and a new information processing technique replacing by the empirical method used by the expert. In this study, a precise spatial estimation approach using a new algorithm improved the SOM with considering soil information is proposed. The efficiency is demonstrated by an example for estimating the spatial characterization of N value using actual boring data.
In this study, an attempt is made to develop an analysis method for calculating Life-Cycle Cost (LCC) of Reinforced Concrete (RC) piers, paying attention to the difference of initial seismic performance. In order to evaluate the seismic performance, reliability index in service life is used by considering the deterioration of RC piers due to the corrosion. Through several numerical examples, the following conclusions were derived : 1) It is difficult to calculate LCC by considering only the initial seismic performance. 2) Paying attention to the corrosion of reinforcement, the service life of RC piers becomes longer as the longitudinal reinforcement ratio becomes larger. 3) It is obtained that the maintenance actions during service life greatly affect LCC minimization.
A practical approach for the reliability evaluation of structure under corrosive environment has been proposed and applied to an oil storage tank as an example. The failure of an oil tank was classified into two modes. One is fatigue fracture caused by the thickness reduction of bottom plate by uniform corrosion and the other is the leakage of contents from the pits caused by localized corrosion. For the evaluation of uniform corrosion, corrosion rate has been treated as a random variable and maximum stress distribution has been calculated by Monte-Carlo simulation. On the other hand, in case of localized corrosion, maximum pit depth has been evaluated by the simulation of pit growth. As a result, the effect of the leakage by localized corrosion becomes large when the uniform corrosion rate is comparatively slow. However, the risk caused by fatigue fracture increased rapidly when the uniform corrosion rate became large.
In this study, we use a combiend method of a classical molecular dynamics with the Tersoff potential and an ab-initio calculation based on density functional theory. This combination method can provide quantitative evaluation of the surface energy and surface stress of well-relaxed amorphous silicon in addition to its structure. Using this method, a surface energy of 1.05 ± 0.14 J/m2 and a surface stress of 1.5 ± 1.2N/m was obtained. This calculation also led to a new discovery of the microscopic characteristic of a-Si surfaces, which was not revealed through the use of an empirical potential. It was shown that there are two types of threefold coordinated atoms at the surface region; one with p3-like bonding and the other with sp2-like bonding. In addition, the investigation indicated that the microstructures of these coordination defects were different from those of threefold coordinated atoms observed in the bulk region.
The physical structure of oriented polyoxymethylene (POM) was studied, and the degree of crystallization and tensile modulus depending on stretching ratio were analyzed. The oriented films were obtained through 2-directional stretching using press elongation method. The stretching ratio reached to 6.0, and the tensile modulus increased from 2.5GPa to 4.5GPa. However, the degree of crystallization slightly decreased from 70% to 65%. The rupture elongation increased in the lower stretching region and reached its peak when the stretching ratio was 1.7%. The characteristics of the physical structure such as the degree of the crystallization and the orientation and dispersion of the lamella were analyzed by measuring the density and the X-ray diffraction. The crystal orientation observed by the X-ray diffraction pattern was isotropic, and the result was confirmed by microscopic photos. The crystallization was found out to be difficult under strong mechanical strength. After thermal aging under various temperatures, the degree of the crystallization increased from 63% to 67%. However, a degree higher than 67% could not be observed. The major factors of such a complicated phenomena seemed to be the higher rate and degree of crystallization of POM than those of PET.
The variation of dynamic viscoelasticity during isothermal crystallization of Nylon6 is investigated. The time dependence of the crystallinity evaluated from DSC (xH) is compared with that of the crystallinity defined by dynamic measurements (xG) as (Gt - G0)/(G∞ - G0) where Gt, G0 and G∞ are the moduli at concerning time, in the initial molten and fully crystallized states, respectively. The onset of the increase in xG is retarded as compared with xH, while xG becomes identical with xH in the later crystallization process. These features are commonly observed in Nylon6 and polybutene-1 varying significantly in viscoelasticity before crystallization as well as the size of spherulites. The relation between xG and xH is well explained by considering the morphological change of system resulting from the growth of spherulite domains.
Piezoelectric materials are widely used in industrial areas from the excellent characteristic of mechanical and electrical couplings such as the sensors and actuators. On the other hands, cavities, inclusions, and dislocations in the materials affect fracture and strength of materials. So it is important to analyze mechanical and electrical fields around these defects. In this paper, two-dimensional electro elastic analysis is performed for transversely isotropic piezoelectric materials containing multilayered elliptical inclusion under several singular loads. General solutions of this study are obtained by using the complex potential functions and conformal mapping technique. And several numerical examples are shown by graphical representation. The effects of some condition of singular loads are discussed.
Pure titanium is expected to be used in high-speed ships in light of its corrosion resistance, high specific strength, ability to reduce ship-dismantling costs, and recyclability. Titanium rudder forgings, each of which is an integrated combination of a rudder plate and a rudder stock, have been used for high-speed ships. Fatigue fractures have often been observed in the rudder stocks. In the context of these fractures, tensile and fatigue tests were performed using forgings with forging ratios of 2 and 4 and different grain sizes. Typical results obtained are summarized as follows : (1) 0.2% proof stresses in the tensile test agreed with the Hall-Petch equation; (2) their slope was approximately equal to that for low-carbon steels ; (3) S-N curves showed that forgings with a forging ratio of 4 were obviously superior in fatigue strength to those with a forging ratio of 2 ; (4) fatigue crack initiation was observed at grain boundaries between large grains, indicating that the decrease in fatigue strength is caused by an inhomogeneous microstructure; and (5) the forging ratio had an obvious effect on fatigue strength rather than on tensile properties.
In contrast on microcrystalline diamond film, nanocrystalline diamond film has a flat and smooth surface. Therefore, nanocrystalline diamond film is desirable in application field of tribology. In this study, the nanocrystalline diamond film and the microcrystalline diamond film were deposited on pure titanium using CH4/H2 MPCVD method. The diamond film deposition was carried out under the deposition temperature of approximately 1173K and the deposition pressure of 8.0kPa. CH4 concentration was changed from 0.5mol% to 5mol%. The deposition time was changed from 4h to 12h. The diamond film surface was observed by scanning electron microscopy (SEM). In the laser Raman spectra, the sharp peak of sp3-bonded carbon was attributed to 1332cm-1 at microcrystalline diamond films. The band near 1140cm-1 was related to the feature of nanocrystalline diamond film. Diamond films were also analyzed using X-ray diffraction. It is confirmed from XRD profile that (111) and (220) exists in the nanocrystalline diamond film. Surface roughness of diamond films decreased with increasing CH4 concentration. But, the surface roughness of diamond films was close to approximately 50nm when CH4 concentration was changed from 2mol% to 5mol%. It was confirmed that the nanocrystalline diamond film can be deposited by CH4/H2 MPCVD method under CH4 concentration from 2mol% to 5mol%.
Biodegradable resins, having low environmental loads, are expected to have wide application in the future because they can decompose easily into carbon dioxide and water in certain environments. New functional materials could be created by modifying the biodegradable resins to include higher functions using thin-film coating or other processes. From this point of view, we formed titanium thin films on the surfaces of polyactic biodegradable resins by vacuum deposition and ion beam mixing to clarify the optimum thin film coating conditions. The thin-film layers were chemically analyzed and their conductance characteristics and adhesion strengths evaluated in relation to the biodegradable resins used to produce the thin films. We confirmed that the combined method of ion beam mixing and vacuum deposition was suitable for creating thin-film coatings on the surfaces of polyactic biodegradable resins. The thin films obtained by the combined method were found to have chemical compositions, conductivities, and adhesion strengths that would permit practical use.
Many studies have been made to develop artificial tracheas with good biocompatibility and mechanical performance. We have designed a new type of mesh-type artificial tracheas. The basic frame of the specimens was composed of a mesh cylinder and stent attached to the outside of the cylinder. We have demonstrated from the mechanical tests that artificial tracheas with ring-type stents are stiffer than those with spiral-type stents. Artificial tracheas with arc-shaped shaped stents are half as stiff as artificial tracheas with whole ring stents. We have compared the mechanical properties of mesh-type artificial tracheas with nylon ring stents and those of canine tracheas, and have found the proper number of rings per unit length for the mesh-type artificial tracheas.
The present paper is aiming to examine the tribological properties of Mg-Al-Zn alloy, AZ91. Especially, effect of precipitate morphology on tribological properties, such as wear rate and coefficient of friction, was systematically investigated for cast material. Accelerated aging treatment was carried out at temperatures ranging from 150°C to 300°C for 100 hours after solution-treatment at 413°C for 48 hours. A pin-on-disc wear testing machine was used to evaluate tribological properties at room temperature under dry condition, in which an SUJ2 steel disc was used as the counterface. Vickers hardness after the accelerated aging treatment of AZ91 alloy was about HV80 to HV90. Since the hardness of AZ91 was approximately eight times smaller than that of SUJ2, the dominant wear mechanism was assumed to be abrasive wear. However, the composition of wear debris, rise in temperature during wear tests, change in hardness near the wear surface and macroscopic flow of specimens indicated that the adhesive wear also contributed to the wear properties when the size of precipitates were small or the spacing between precipitates were large. It was suggested that the contribution of adhesive wear increased the wear rate and the coefficient of friction. It was concluded that the wear resistance of AZ91 alloy under dry condition would be improved by densely dispersing the precipitates with sufficiently large size, e.g., precipitates with its length of about 1mm that were observed in materials aged at 200°C.
The objectives of this study are to investigate the basic mechanical properties of TEEK polyimide-foam and TEEK-filled aramid honeycomb core-materials for sandwich structures and to compare their mechanical properties with those of AIREX R82 and ROHACELL WF foam core-materials. Compression, tension, and plate-shear tests provided their stress-strain relationships, elastic modulus, and strength. The test results are compared and discussed. The major results obtained are : (1) Filling the aramid honeycomb cells with TEEK can improve the basic mechanical properties of an aramid honeycomb core-material, in particular making them higher than the values expected from the principle of superposition for compression tests and equal to the values expected from superposition for plate-shear tests. (2) The basic mechanical properties of the TEEK-filled aramid honeycomb are superior to those of AIREX R82 110 and equivalent to those of ROHACELL WF 110, where the three materials have equal densities. (3) The basic mechanical properties of TEEK are inferior to those of AIREX R82 60 and ROHACELL WF 51, when materials with equivalent densities are compared. (4) TEEK-filled aramid honeycomb has high potential as a new core-material for aerospace sandwich structures.