Amorphous alloy ribbons have no crystalline structure and they have superiority in the electomagnetic and mechanical properties. Due to their useful electomagnetic property, the amorphous ribbons are widely used, nowadays, in the various products such as core of current transformers and electric motors. But we have a difficulty that the thickness of the amorphous ribbon is restricted within a certain value in order to realize the rapid quenching. Thus amorphous ribbons must be put together to some extent in order to use as mechanical components. In this study, a number of thin ribbons of Fe78B13Si9 amorphous alloy are piled up and bonded by an adhesive. Statistical fatigue properties of such multilayer composites are examined by performing fatigue tests and fatigue mechanisms are discussed.
A methodology of structural integrity analysis via convex model of uncertainty is presented for structures that are subject to the uncertain ground motion caused by earthquakes. The ground motion is represented in terms of a truncated Fourier series, and the Fourier coefficients are assumed to fluctuate uncertainly. The uncertain fluctuation of the coefficients is bounded within convex hulls so as to introduce a convex set representing the characteristic information of the earthquake, that is, the power spectrum. An undesirability index is adequately defined in order to indicate the degree of undesirability of structural integrity. The fluctuation of the undesirability index is submitted to first-order approximation with respect to the uncertain Fourier coefficients through finite element sensitivity analysis. The worst case, which produces the maximum value of the undesirability index during the observation period, is identified using the Lagrange multiplier method with equality constraints for the uncertain Fourier coefficients by the boundary of the convex hulls. The validity of the proposed formulation is proven through numerical examples using a planar portal frame that is subject to artificial and observed earthquake ground motions.
In the design of railroad train, main interests have been placed on stiffness, mass and strength. Therefore, great improvement has been achieved in functional point of view. For further development, however, it is necessary to provide a procedure for the decision-making in design process. For example, if design change such as geometry variation or material replacement occurs, it is required to evaluate the validity of the action. For this purpose, a rational procedure to assist the decision-making is needed. However, the research from this point of view has not been done sufficiently so far. In this paper, we attach importance to the decision-making performance in risk assessment. Though conventional risk assessment is used in the operational stage such as maintenance or inspection, it is investigated to apply the risk assessment in the design stage of railroad train. Specifically, the design of ceiling-shelf module is considered. By introducing the risk evaluation, not only the evaluation of function of single part but also the total performance for safety can easily be treated. Besides, uncertainty property is also able to be included in the assessment. After the formulation of risk assessment is stated, the application for several decision-making in ceiling-shelf module will be shown.
Since the experimental results of fatigue test show large scatter, the S-N curve should be determined after the evaluation of them. In the previous paper, we have proposed a decision method for the S-N curve based on the fatigue strength distribution. In the proposed method, we have applied bilinear regression model for the data in the stress level around the fatigue limit. However, the S-N curves for some materials don't show obvious knee point. In this case, curved regression models such as hyperbola regression model are available. In this paper, we improve the proposed method to be applicable for such types of materials. In the developed method, 8 types of regression models, which are proposed by the committees on fatigue and reliability engineering in JSMS, are available, In addition, we can also decide the best-fitted model using the correlation for the plots of normalized fatigue strength on the probability paper, which are used for the evaluation of the fatigue strength distribution The proposed method has been applied to the fatigue test data for some materials. As a result, it is recognized that the reasonable S-N curves are obtained.
By arranging the field maintenance database of steam turbines with operation history and by conducting probabilistic safety analyses, a quantitative risk assessment method was established. The method includes three steps: (1) event tree analyses of parts failures which require any maintenance action, (2) assignment of unreliability functions of operation time or start cycles for each item in those event trees, and (3) calculation of total risk function by summing up recovery costs multiplied by the unreliability functions obeying the event trees and comparison of the risk cost with preventive maintenance cost. Those three steps were applied to actual turbine components and the effectiveness of proposed method was demonstrated with a risk simulation analysis.
Embrittlement behavior of the duplex stainless steel in the intermediate temperature range (275 to 500°C) is one of the very serious problems for applying reliability assessment to practical pipes in a nuclear power plant. In this work, it is shown by formularization of embrittlement behavior with aging time that the increase in hardness due to embrittlement is governed by α contents of the duplex stainless steel. The formula as function of aging time and temperature, which can predict the embrittlement behaviors in the duplex stainless steel of arbitrary chemical compositions, is proposed by using the Scheffler's statechart diagram. For the purpose of estimating the structural reliability of a nuclear power plant, the formula can be used to predict the change of fracture toughness KIC with service term in the field probabilistically.
Recently, several immune network information models are proposed, and they are applied to process diagnosis as well as sensor fault diagnosis of cement process by Prof. Ishida. In this paper, a simple network model for the water supply system of waterworks is diagnosed using this immune network information model, and it is tried to find the cause of a sensor fault diagnosis and process faults diagnosis (water leak etc.). Through some numerical examples the effectiveness and applicability of immune network information model is shown.
Creep life prediction method has been investigated on 9-12Cr ferritic creep resistant steels in conjunction with region partitioning method of stress vs. time to rupture diagram. Region partitioning method of stress vs. time to rupture diagram has been discussed from a viewpoint of correspondence of breakdown observed in stress vs. time to rupture curves with both change in creep deformation behaviour and 0.2% proof stress. Good correspondence have been observed between breakdown in stress vs. time to rupture curve and the stress condition where the onset strain of tertiary creep stage is 0.012 and 1/2 of the 0.2% proof stress. It has been concluded that creep rupture data in the stress region less than 1/2 of the 0.2% proof stress should be used for a long-term creep life prediction by Larson-Miller parameter with a constant of 20.
A thermal cyclic fatigue testing method for a hot gas tubular filter proposed by Matsushima, et al. simulates the stress state in the filter during reverse pulse cleaning by blowing air. The filter is composed of two layers, one is a thick inner layer made of silicon carbide with coarse pores and the other is a thin outer layer made of mullite with fine pores. In this paper, we presented a new technique for analyzing temperature distributions in a filter in cold blowing air on the assumption that a Biot number could express a heat loss inside the filter caused by blowing air. Temperature and stress distributions in the filter were analyzed numerically on condition that the filter was exposed to high temperature flue gas and received thermal shock by cyclic blowing air. Residual stresses after sintering were also analyzed. The results revealed that the stresses were greatly affected by the thickness of the mullite layer, there were considerable tensile residual stresses in the mullite layer, and the thicker layer of silicon carbide had higher thermal shock stresses on the inner surface of the filter.
Compressive residual stress is qualitatively known to have a strong effect of deceleration of crack propagation rate and hence improvement of fatigue strength. In fretting fatigue a fatigue crack generally initiates in the very early stage of fatigue life, which is therefore mainly dominated by the fatigue crack propagation life. This paper investigated the quantitative effects of residual stress on fretting fatigue crack propagation and fretting fatigue strength using aluminum alloy specimens with and without WPC treatment, which can induce residual stress in the specimen surface layer. It was found that the compressive residual stress in the surface layer decelerates the crack propagation rate, while it has no obvious effect on the crack initiation. A simple quantitative method for evaluating the effect of the residual stress on crack propagation has been proposed. It was found that both the effects of residual stress on fretting fatigue crack propagation and fatigue live could be quantitatively evaluated according to the proposed method. Moreover, based on the method proposed, the estimation of the increase of fretting fatigue strength due to residual stress agrees well with the experimental results.
In the present study, damage behavior in the adhesive layer of adhesive butt joints bonded with rubber-modified epoxy was investigated by using an anisotropic damage theory. In the experiments, the stress-strain curves of the bulk specimens and the adhesive layer in the butt joints were measured by loading-unloading tests at a relatively low strain rate. The values of damage parameter D1 in the maximum principal stress direction were obtained from the measured stress-strain curves for the specimens. The relation between D1 and the strain energy density given to the specimens was investigated in order to compare the damage behavior of the butt joint and bulk specimens. From the results, it was found that the strain energy density of the specimens given until they break increased with rubber contents, but their damage behaviors were almost the same. It was also found that the strain energy densities of the specimens at their fracture were almost the same but the damage parameter D1 of the butt joint specimen was higher than that of the bulk specimen over the full range of strain energy.
In this study, residual stress was generated in several structural ceramics by sintering and grinding, then estimated using the Vickers indentation method. First, we investigated the appropriate pretreatment for measuring fracture toughness (basis value, KC), while prevently any influence of residual stress. This is important in estimating residual stress using the Vickers indentation method. Based on that value, the residual stress in Al2O3 and Si3N4 ceramics was estimated by the Vickers indentation method. Next, several problems in estimating residual stress using the indentation method on ZrO2 ceramics were discussed focusing on phase transformation. Results show that residual stress in Al2O3 and Si3N4 can almost be eliminated by annealing the specimen after hand grinding. Consequently, it is thought that this treatment method is effective for determining the basis value KC. The estimated residual stress value on Al2O3 and Si3N4 obtained by the Vickers indentation method at 98N corresponded closely to the values obtained by X-rays. Compared with Al2O3 and Si3N4, residual stress in ZrO2 estimated by the indentation method was larger than that found by the X-ray method. This is assumed to be the influence of phase transformation.
Residual thermal stresses in the electrolyte of the anode-supported planar SOFC were measured using the X-ray diffraction method. The cell tested was fabricated by co-sintering screen printed 8YSZ electrolyte on NiO/YSZ substrate at 1500°C. The thickness of the electrolyte and the anode were about 30μm and 2mm, respectively. To estimate the residual stress precisely, the synchrotron radiation was used as an excellent X-ray source. The wavelength of the radiation beam used for the stress measurements was λ=0.154nm, and (531) and (620) planes were selected for the diffracting planes. The estimated residual stress in the electrolyte of the anode-supported cell was a compressive stress of about 600-720MPa at room temperature. In addition to the stress measurements, the residual stress distribution in the cell was simulated using the finite element method. The calculated principal stress in the electrolyte at room temperature was close to that estimated by the stress measurement.
The effect of morphology of fiber on mechanical properties of short fiber-reinforced composite was investigated. Test piece of the composite was prepared by hot pressing the mixture of powdery materials (calcium carbonate and thermosetting resin) containing the short fiber (aramid fiber). Aramid fibers were fibrillated by milling treatment and were used for reinforcement. The mechanical properties of the composites were evaluated by the fracture energy calculated by the load-displacement curves of 3-point bending test and the wear rate of abrasion test. To estimate the fiber-reinforced region in the composite, the occupied volume of the fiber was calculated by the morphology parameter of the fiber based on image analysis. The effective fiber morphology for the fracture and the wear resistance of composite was discussed on the basis of the occupied volume of the fiber.