Steel making mill rolls usually contain shrinkage defects. The design of mill rolls is currently based on the empirically modified formulae. However, fatigue fractures of mill rolls from shrinkage defects have been experienced in service even based on the empirical design method. Many studies have shown that the effects of defects such as nonmetallic inclusions and graphite nodules on the fatigue strength can be effectively evaluated by paying attention to the geometrical parameter √(area), the square root of area of defects onto the plane perpendicular to the principal stress. Different from that of nonmetallic inclusions, shrinkage defects generally have extremely complex three-dimensional shapes, and accordingly the projection of their shapes onto the plane perpendicular to the principal stress is very irregular. In this study, the tension compression fatigue tests are carried out with the specimen materials cut out from a real mill roll. Based on the propagation properties of cracks emanating from shrinkage defects, the effective geometrical parameter √(area)_eff for complex shrinkage defects is defined. The rule for estimating the maximum √(area)_eff of shrinkage defects to be contained in a real roll by the statistics of extremes is proposed.

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In this paper, a method to predict the fatigue limit reliability of specimens with various surface roughness is proposed. First, the mechanical profile for fatigue limit is proposed. This is obtained from the ineffective crack length. Then the equivalent notch depth is proposed to treat a rough surface as a smooth surface with a notch. Next, a method to predict the fatigue limit reliability is discussed. As the surface roughness is expressed with the spectrum analysis, computational simulation is used to produce surface profiles. And stress analysis described in the first report is carried out for each specimen. Then a fatigue limit of an arbitrary metal specimen with an arbitrary small notch can be estimated. Moreover, rotating bending fatigue tests of 0.1% carbon steel with a complex surface are carried out. Then the experimental fatigue limit data is compared with the present estimated values. As results, the validity of the present meso-analysis is examined.

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Effect of surface treatment on fatigue behavior in gigacycle regime was investigated in order to clarify the duplex S-N curve characteristics. A cantilever-type rotating-bending fatigue tests were performed in laboratory air at room temperature using hour-glass-shaped specimen of high speed tool steel, JIS SKH 51 with four kinds of surface treatment conditions, such as grind-stone polishing, emery-paper polishing, electro-polishing and plasma-nitriding. The fatigue limit of surface failure mode depended on compressive residual stress value on specimen surface. On the other hand, no difference in fatigue life controlled by subsurface crack initiation was observed among four kinds of surface-treated specimen in high cycle region. Fatigue crack initiation site changed from the surface of untreated specimen to the subsurface of the specimen because of hardening and compressive residual stress with plasma-nitriding in the region of high-stress amplitude. It is suggested that the S-N curve corresponding to internal failure mode is as inherent in the material, as compared with that the S-N curve of surface failure mode is affected by surface conditions. It was pointed out through the detailed measurement of crack initiation area that the formation of GBF (granular-bright-facet) around an inclusion controls the internal failure in long-life fatigue regime.

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The finite element method (FEM) is useful for stress analysis and is used widely in general. However, it is still not necessarily easy to obtain the highly accurate values, of the stress intensity factors by FEM. Recently, a method for calculating the highly accurate values of the stress intensity factors hag been proposed by H. Nisitani, based on the usefulness of the stress values at a crack tip calculated by FEM. This method is called the crack tip stress method. The usefulness of this method has already been confirmed by the body force method in the cases of the homogeneous material. In this study, an extension of the crack tip stress method to the interface crack problems was made. Then the accuracy of the present analysis is discussed through the stress intensity factors obtained by the body force method. As the results, it was confirmed that the present analysis has the sufficient accuracy in the interface crack problems.

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This paper deals with a stress concentration problem of an ellipsoidal inclusion of revolution in a bimaterial body under tension. The problem is formulated as a system of singular equations with Cauchy-type or logarithmic-type singularities, where unknowns are densities of body forces distributed in the r-and z-directions in bimaterial boodies having the same elastic constants of those of the given problem. I order to satisfy the boundary conditions along the ellipsoidal boundary, four fundamental density functions proposed in the previous paper are used. Then the body force densities are approximated by a linear combination of fundamental density functions and polynomials. The present method is found to yield rapidly converging numerical results for stress distribution along the boundaries of both the matrix and inclusion even when the inclusion is very close to the bimaterial interface. Then, the effect of bimaterial surface on the stress concentration factor is discussed with varying the distance from bimaterial interface, shape ratio, and elastic ratio.

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An experimental method for evaluating the interface strength of a micro-component on a substrate is developed using a modified Atomic Force Microscopy (AFM). The diamond tip is dragged along the surface of a silicon (Si) substrate with a micro tungsten (W) piece (length: 5 μm, width: 5μm. thickness: 0.1μm), and the lateral as well as the vertical load and displacement are continuously monitored during the test. After the tip hits the W piece, the lateral load, F₁, increases in almost proportion to the lateral displacement, δ₁. The F₁-δ₁ curve exhibits the non-linearity near the peak load, and the piece is abruptly separated from the substrate along the interface. The additional tests, where the load is interrupted before the interface failure, reveal that the non-linearity is attributed to the plastic deformation on the contacted zone. It is also elucidated that the zone is small in comparison with the scale of the W piece. Then, the apparent fracture stress of the interface between W and Si, τ_c, is evaluated as about 58 MPa regardless of the vertical force and the lateral displacement rate.

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This paper studies the crack initiation and propagation behavior of three types of solders. Hollow cylinder tube specimens of Sn-37 Pb, Sn-93.5 Pb-1.5 Ag and Sn-7.5 Bi-2 Ag-0.5 Cu solders were torsionally fatigued at 313 K at a Mises strain rate of 0.5%/s. Crack initiation and propagation behavior was observed by a replication method. Cracks were initiated in the life ratio less than 0.05, so that the crack propagation was the main fatigue damage process. Main cracks propagated in the maximum shear direction for Sn-37 Pb and Sn-93.5 Pb-1.5 Ag but in the maximum principal direction for Sn-7.5 Bi-2 Ag-0.5 Cu. The main crack propagation was uniquely correlated with the life ratio, independent of the strain range and types of solders. Combining this correlation with Manson-Coffin rule, an equation that describes the relationship between crack length, plastic strain range and number of cycles was discussed. The equation evaluated the remaining life by knowing crack length and plastic strain range.

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In order to obtain the transformation plasticity coefficient, three-point bending system is employed and the large deflection due to transformation plasticity in bending is analyzed under the simplified assumption that transformations occur uniformly across the cross section of the beam. It is shown that the deflection due to transformation plasticity is similar to that of elastic deformation and a simple relation is also derived between the ratio of the maximum deflection to the elastic one and material constants (transformation plasticity coefficient K and Young's modulus E). Experiments are carried out for a slender bar specimen, which is loaded in the three point bending system, and the austenized specimen is cooled down so that martensite transformation accompanied by transformation plasticity occurs and the profile and the maximum value of the deflection of the specimen are measured. The measured profiles of deflection agree very well with the thoretical result and it proves the validity of the proposed method. The transformation plasticity coefficient is also identified by the proposed method.

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This paper describes a novel method identifying the number and positions of cracks. Using the ECT signal obtained by two-dimensional scanning as a picture image, a template matching method with help of genetic algorithms is applied to predict the number and positions of cracks. The present method employs a superposition of crack signals and a nonlinear scaling technique of a signal profile on crack length which are verified by numerical simulation. The number and positions of cracks are predicted sufficiently.

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Porous material with photocatalytic characteristics was developed and tested for air clarification and water purification application by using the spark plasma sintering process. In this paper. the aggregate type porous material is made by using titanium oxide which also has photocatalyst function. The sintered material has porous structure with the volumetric porosity of about 56∼70%. The titanium oxide crystal structure of the sintered material changes from the anatase type to the rutile type according to the temperature range from 1173 to 1223 K, respectively. Also, the decolorization test for the methylene blue solution is performed by using the sintered porous material. It has been confirmed that in the anatase type new material photocatalyst functioning is better accomplished than the rutile type.

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Global optimization method for continuous design variables called as generalized random tunneling algorithm is proposed. Many global optimization methods have been proposed for the unconstrained optimization problem which is to find global minimum subject to the side constraints only. Proposed method is called as "generalized" random tunneling algorithm because this method can treat the inequality (behavior) constraints as well as the side constraints. Generalized random tunneling algorithm consists of three phases. That is, minimization phase, tunneling phase, and constraints phase. The characteristics of mathematical programming and heuristic approaches are included in the proposed method. Without using penalty function to consider the inequality constraints, global optimum which may lie in the boundary of constraints is easily found by generalized random tunneling algorithm. The effectiveness and validity of proposed method have been examined through several numerical examples.

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We propose a new method for topology optimization, which is free from numerical instabilities such as checkerboard patterns and mesh-dependency, without introducing any additional constraint parameters. This aim is accomplished by the introduction of finite element approximation for continuous material distribution in a fixed design domain. That is, the continuous distribution of microstructures, or equivalently design variables, is realized in the whole design domain in the context of the homogenization design method (HDM), by the discretization with finite element interpolations. By virtue of this continuous FE approximation of design variables, discontinuous distribution like checkerboard patterns disappears without any filtering schemes. We call this technique the method of continuous approximation of material distribution (CAMD) to emphasize the continuity imposed on the "material field". Two representative numerical examples are presented to demonstrate the capability and the efficiency of the proposed approach against the numerical instabilities.

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Fracture-dislocation of proximal interphalangeal (PIP) joints caused by impact loadings is one of the common injuries in finger joints. The influence of thickness of articular cartilage on the impulsive stress in PIP joints is studied using the dynamic finite element method in the present paper. As the thickness of cartilage decreases, the concentration of equivalent stress is observed in the cartilage. The maximum principal stress is tension in the subchondral bone of the middle phalanx and does not change much with the thickness of cartilage. The thin cartilage layer causes the decrease of the minimum principal stress in the subchondral bone and consequently leads to the concentration of equivalent stress. The influence becomes remarkable when the thickness is reduced to a quarter of normal thickness, indicating that the risk of failure is higher when the cartilage has worn out.

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When a static load is applied to a brittle material beam, the beam fractures at the fixed end. However, such a phenomenon does not necessarily occur in the case of dynamic load. In dynamic load the fracture behavior changes with the situation of the stress wave propagation, the material properties and the shape of beam. In this research, an impact fracture behavior of free end of cantilever beam made of plaster is analyzed using the Discrete element method (DEM). This method is able to analyze the discontinuous fracture behavior of the plaster beam. The analytical results are compared with the experimental results presented previously by the authors. From the results, the impact fracture mechanism of brittle material beam, that is the condition of the crack initiation and propagation, is considered.

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It is useful to propose a new algorithm to analyze the complicated optimization problems by imitating the functions of living things. In this study, it is object to propose new optimization method using the microcosm which is model of natural ecosystem. The microcosm in this paper is constituted by considering a bone forming ecosystem that the interaction of each cell is clear and able to be regarded as ecosystem. By combining the proposed microcosm and GA, the optimization problems are analyzed. The problems to search a minimum point in the multiple-peak function, and to search the plane structure of the minimum value subjected to a load are analyzed. Moreover, the validity of design solution is checked for the several design conditions.

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Property of polycrystalline piezoelectric material is strongly affected by its crystal orientation distribution, because the crystal lattice has a strong anisotropy. In our previous study, a multi-scale finite element analysis code based on crystallographic homogenization method has been proposed to predict macroscopic piezoelectric properties. It can analyze the microscopic behavior in keeping a compatibility with the macroscopic response. In this study, the microscopic behaviors of piezoelectric materials under macroscopic uniform mechanical/electrical loading were analyzed. At first, the microscopic piezo-electroelastic responses of polycrystals are evaluated by employing the statistical procedure. Next, those heterogeneous behaviors were characterized by symmetrized dot pattern (SDP) method. Finally, the availability of these multi-scale characterization methods were confirmed.

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The thermally induced fracture problem for a piezoelectric laminate having a crack under uniform electric and temperature fields is considered. The crack is oriented normal to the interfaces of the laminate. For the case of a crack which ends at the interface between the piezoelectric layer and the elastic layer, the order of the stress singularity around the tip of the crack is obtained. The Fourier transform technique is used to formulate the problem in terms of a singular integral equation. The singular integral equation is solved by using the Gauss-Jacobi integration formula. Numerical calculations are carried out, and the main result presented are the variation of the energy density factors as functions of the geometric parameters and the electrical boundary conditions of the layered composites.

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In this study, the impact response of a coated piezoelectric half-plane containing a crack perpendicular to the boundary is considered. The Laplace and Fourier transform techniques are used to formulate the problem in terms of a singular integral eauation. The singular integral equation is solved by using the Gauss-Jacobi integration formula. Both the cases of an internal crack and a terminated crack are studied. Numerical calculations are carried out, and the effects of the geometric parameters on the dynamic stress intensity factor and the dynamic energy density factors are shown graphically.

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In an attempt to develop piezoelectric sensors and actuators for smart boards, complex piezoelectric fibers with metal core were fabricated by hydrothermal method. The insertion of metal core was significant in view that the fragility of ceramics can be overcome and electrodes are not required in the use as sensors and actuators. In order to evaluate the sensing and actuating abilities of these new-type fibers, a cantilever structure was constructed by embedding the fiber into the surface layer of CFRP composite board. As a result of a vibration test of this CFRP board by an electromagnetic vibrator, it was found that the fiber has an obvious sensor function, since electric charge was output from the fiber in proportion to the vibration amplitude. On the contrary, it is also evident that the fiber can function as actuators, since the CFRP board was vibrated by applying an AC voltage between the metal core and CFRP matrix.

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Microstructures of polycrystalline Al₂O₃, Zro₂ and Al₂O₃-ZrO₂ ceramics were modeled as two-dimensional heterogeneous bodies composed of geometric Al₂O₃ and ZrO₂ grains. The crystallographic 3D-directions of each grain were assumed to be randomly distributed. Elastic properties of grain were derived from elastic stiffnesses, c_ij, of single crystal Al₂O₃ and ZrO₂. In calculation, some square plates with a unit thickness were cut from the initial grain models. A simulation method was developed to predict homogenized elastic moduli of models using a finite element method. An influence of the microstructural model size on apparent elastic moduli was examined. Next, actual microstructural models that were traced the SEM micrographs of samples were used in same calculation. And then, the optimum model size was determined by comparing calculated elastic moduli to experimental data measured by a pulse-echo method. As a result, the scattering of apparent elastic moduli, such as Young's modulus, of both models including Al₂O₃ grains varies narrowly with increasing model size. While, the deviation of apparent elastic moduli for actual model is wider than that of geometric model on the same model size. The number of Al₂O₃ grains within the optimum model size was found to be about more than 400, in which the scattering of apparent elastic moduli is below the ±1% deviation of the mean value of model samples.

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A simple method is presented for measuring the Young's modulus of a ceramic fiber, which is clamped horizontally as a cantilever beam and deforms due to its own weight. The Young's modulus is calculated from the deflection at the cantilever tip according to the equation for large deflection of a cantilever beam with uniformly distributed load. The validity, of this measurement method is demonstrated by comparing the test results at room temperature with those of tensile test on ceramic fiber specimens. For both testing methods, the measured values agreed within 6%. SiC fibers were tested at elevated temperatures up to 1000°C. It is shown that Young's modulus of the fibers decreases with increase in temperature.

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