A new piezoelectric ceramic fiber containing a metal core was produced by the extrusion method. The insertion of a metal core is significant because the fiber's strength can be supported by the metal core which also serves as an internal electrode. A new smart board was designed by mounting these piezoelectric fibers into the surface of a CFRP composite. This smart composite board was able to both detect, and suppress vibrations.

View full abstract

In order to investigate the fracture mechanism in fatigue of nickel-based superalloy at elevated temperature, rotating bending fatigue tests were carried out for Inconel 718 at 500°C and 600°C up to 10⁸ cycles. At both temperatures, fatigue fracture initiated from the subsurface of specimens in the long life region, though the origin of fracture was on the surface of specimens in the short life region. As a result, S-N curves showed a two-step shape. Although surface cracking was observed even in the long life region at elevated temperatures, similar results as observed at room temperature, surface cracks ceased propagating after extending to approximately 20-30μm at elevated temperatures. Meanwhile, intergranular cracking was observed at the origins of subsurface fracture, which was found to be nucleated in the early stage of fatigue.

View full abstract

We analyze the stress field near an interface edge of an elastic-creep bi-material with and without an additional constraint layer by finite element method. The focus is on the effect of material thickness on the stress field. The results reveal that the creep J-integral, J^*, on a path in a creep zone near the interface edge, which characterizes the intensity of the singular stress field, time-dependently decreases and becomes constant in the large-scale creep condition. For thin creep materials, J^* increases proportionally with an increase of the thickness, while it saturates when the thickness becomes about a quarter of the material width. The normalized creep J-integral by the creep material thickness is the general parameter of the stress intensity near the interface edge for the thin films. In unconstrained bi-material, the time to reach the steady state is independent of creep material thickness; however, the one in constrained bi-material increases as the thickness decreases.

View full abstract

Slip deformation in symmetric-type bicrystal models subjected to tensile load is investigated by a finite element crystal plasticity analysis code. Accumulation of geometrically necessary dislocations (GNDs) and statistically stored dislocations (SSDs) are studied in detail. Some results of the analysis show local strain hardening of slip systems and activity of secondary slip systems with accumulation of GNDs on primary slip system in the form of band. Mechanism of local strain hardening of primary slip systems in symmetric-type bicrystals is discussed from the viewpoint of dislocation interaction between primary and secondary slip systems and effects of high density pattern formation of GNDs on primary slip system.

View full abstract

This paper deals with the optimization problem of material composition for minimizing the stress intensity factor of radial edge crack in thick-walled functionally graded material (FGM) circular pipes under steady-state thermomechanical loading. Homogenizing the FGM circular pipes by simulating the inhomogeneity of thermal conductivity by a distribution of equivalent eigentemperature gradient and the inhomogeneity of Young's modulus and Poisson's ratio by a distribution of equivalent eigenstrain, we present an approximation method to obtain the stress intensity factor of radial edge crack in the FGM circular pipes. The optimum material composition for minimizing the stress intensity factor of radial edge crack is determined using a nonlinear mathematical programming method. Numerical results obtained for a thick-walled TiC/Al₂O₃ FGM circular pipe reveal that it is possible to decrease remarkably the stress intensity factor of radial edge crack by setting the optimum material composition profile.

View full abstract

Fracture tests have been performed for both millimeter-sized and micro-sized specimens prepared from a Fe-3 mass%Si alloy single crystal, and the size effects on fracture behavior have been considered. Notch plane was set to be (100), which is a cleavage plane of this material, and notch direction was set to be [010] for both type of specimens. For millimeter-sized specimens, cleavage fracture occurred during introducing a fatigue pre-crack. In contrast, the micro-sized specimens were fractured by ductile manner. This phenomenon is discussed based on the plastic zone at crack tip and the ligament size. The results obtained in this investigation provide important information for designing actual MEMS devices.

View full abstract

In recent years, the metal forming industries are rapidly and continuously growing and causing sound and waste pollution. Therefore, the reduction of environmental pollution is extremely important. In terms of waste pollution, in this study, the lubricant used in the application of the deep drawing process was considered. In this research, the author explored method for the realization of the reduction of the amount of lubricant used in order to resolve the above issue. Namely, the die was slotted in order to continuously apply lubricants in the process of the drawn part fabrication. Furthermore, the optimization of the amount of lubricant used was also investigated. On the basis of the results, the author clarified that the slotted die method is effective in realizing the reduction of the amount of lubricant used in the deep drawing process.

View full abstract

Deep drawing process is an important process adding values to flat sheet metals in many industries. An important concern in the design of a deep drawing process generally is formability. This paper aims to present the connection between formability and inverse analysis (IA), which is a systematical means for determining an optimal blank configuration for a deep drawing process. In this paper, IA is presented and explored by using a commercial finite element software package. A number of numerical studies on the effect of blank configurations to the quality of a part produced by a deep drawing process were conducted and analyzed. The quality of the drawing processes is numerically analyzed by using an explicit incremental nonlinear finite element code. The minimum distance between elemental principal strains and the strain-based forming limit curve (FLC) is defined as tearing margin to be the key performance index (KPI) implying the quality of the part. The initial blank configuration has shown that it plays a highly important role in the quality of the product via the deep drawing process. In addition, it is observed that if a blank configuration is not greatly deviated from the one obtained from IA, the blank can still result a good product. The strain history around the bottom fillet of the part is also observed. The paper concludes that IA is an important part of the design methodology for deep drawing processes.

View full abstract

In this research, TiO₂ photocatalyst was immobilized on borosilicate glass powder. The immobilization was carried out by mixing the TiO₂ and borosilicate powders and then calcined at 600 to 800 °C for 1 h. XRD and SEM analysis showed uniform coating of the TiO₂ particles on glass powder surface. The TiO₂-coated glass powder showed good photocatalytic activity for methylene blue decomposition. The coated glass powder calcined at 650 °C showed highest activity. The reaction rate constant of the prepared catalyst, TiO₂ and TiO₂-P25 powders were 0.0111, 0.0341 and 0.0539 min^-1, respectively. Photocatalytic activity decreased when the catalysts were re-used as a result of TiO₂ particle detachment from the glass powder surface.

View full abstract

The industrial use of various kinds of rubber-like (hyper-elastic) material is rapidly increasing and growing in importance, especially in automobiles, trains, and machinery⁽¹⁾. In the past, rubber engineers and designers have predicted the behavior of rubber-like materials using analytic methods for limited problems or approximate methods for general problems. Yet, with the progress of digital computers, finite element methods⁽²⁾, represented by the Mooney-Rivlin model, are now widely used to analyze hyper-elastic as well as isotropic materials.
The conventional method used to evaluate the properties of rubber-like materials is the least square method (LSM), however, this method has a low precision and involves a tedious pre-solving process. Accordingly, this study proposes a simple yet powerful method for estimating the properties of rubber-like materials using a successive zooming genetic algorithm (SZGA). The proposed method results in dependable and precise rubber-like properties for various Mooney-Rivlin models based on simply changing the objective function. To demonstrate the effectiveness of the proposed method, it is compared with Haines & Wilson's method (LSM) and other commercial packages.

View full abstract