In recent years, the blast furnace as a manufacturing process of steel material is in use. The coke is indispensable to obtain iron in the furnace. Each blast furnace company has been improving the structure and composition of the coke material for energy-saving and environmental conformity in iron production. The coke is used for the purpose of supply of the thermal energy by combustion and maintenance of the breathability in a furnace. In order to maintain the breathabiliy against sever loading condition in a blast furnace, high porosity and strength are required for the coke. In this research, the computational model simulating the coke is proposed using three-dimensional finite-element model considering its porosity. By using the model, the material properties of coke, that is the young's modulus, Poisson's ratio and compressive strength, are calculated and these values are discussed with the percolation factor of pore in the coke.

View full abstract

Appearance and subsequent behavior of lattice defects induced by coalescence between copper atom clusters are investigated by molecular dynamics method. Since mechanical properties of atomic-cluster-assembled structure are supposed to be largely dominated by interface phenomena, elementary knowledge on atomic rearrangement near the boundary is required. The Effective Medium Theory (EMT) is adopted as interatomic interaction of the present problem because of demand for sensitivity to surface energy and stacking fault energy. Main defects detected are stacking faults (SFs), i. e. planar spreading of local h. c. p. structures. Static energy of SF in the range of 30-90 mJ/m² is computed, which agrees well with experimental data. Transition in deformation mechanism of cluster is found by means of computational configuration, where approaching velocity between 0 K clusters varies from 20 to 1000m/s. In general, larger velocity results in flattened structure of clusters. High energy regime, where SF extends all over clusters, consumes kinetic energy at least 9-16 times as large as static energy of isolated SF. When slight orientation angle in-plane is applied to clusters before their adhering, the mismatch in angle is canceled by spontaneous rotation of clusters unless the orientation angle exceeds 15 degrees. On the other hand, larger difference in orientation angle prevents SF from occurring and moving. This degradation in amount of SF due to orientational mismatch is nicely predicted by considering Schmid factor, which is calculated from configuration of slip directions and clusters' approaching direction.

View full abstract

In this study, a multi-scale finite element modeling procedure, based on a crystallographic homogenization method, has been developed to estimate a macroscopic plastic properties, such like an anisotropic yield behavior and a plastic hardening evolution, caused by its microscopic plastic deformation. In this homogenization procedure, a particular scale value to specify the sizes of macro and microstructures has been introduced for physical understanding the compatibility between two scales. Especially, the micro crystal structure, which consists a unit cell to obey the periodicity of deformation, has consistency with a macrostructure deformation, and has been determined by employing the experimental observation results. ODF analyses to identify the texture of polycrystal structure were carried out through SEM and EBSD measurements. It is confirmed that this homogenized FE analysis code can predict a macroscopic anisotropic yield and inhomogeneous deformation in the microstructure.

View full abstract

The tensile tests of 2024-T 6 aluminum alloy reinforced by 2% and 10% SiC particles are conducted. The stress-triaxiality of the specimens is changed from 0.33 to 2.5 in 7 cases by changing the notch radius of the specimen. The effect of stress-triaxiality on viod volume fraction at final fracture by coalescence of micro voids is investigated using SEM (Scanning Electron Microscope) and 3-dimensional imaging analysis system. The experimental results show that the final void volume fraction at fracture changes by changing the stress-triaxiality and SiC particle volume fraction. The void diameter and depth also change by the SiC particle volume fraction and stress-triaxiality. Observation on fracture surface shows that the number of voids increases with decreases of the stress-triaxiality and SiC particle volume fraction.The effect of stress-triaxiality strongly affects on the fracture process of SiC 0%, pure matrix, and the effect of SiC particle volume fraction strongly affects on that of low stress-triaxiality condition specimens.

View full abstract

It is of importance to optimize the cross sectional shape of an extruded structural material, while no applicable mathematical method which directly reveals the solution has ever been proposed. The present studies discussed 2 D-modifying algorithms imposed on the direct solution obtained by the conventional 3 D topology optimization method to validate the extrusion shape. The algorithms were applied to a sample problem of optimizing a cross sectional shape of a truck rear bumper made of aluminum extruded material to satisfy the load conditions (span = 880 and 1500 mm having different stress concentration) with respect to the minimum bumper weight. The authors proposed three algorithms ; 1) to calculate the pure average density distribution over the extrusion axis on the cross section, 2) to employ the maximum density along the extrusion axis for each cross sectional position, and 3) to calculate the weighted average density distribution on the cross section considering the stress concentration. It was concluded that the expected solution as the extrusion shape can be obtained after its characteristics and yardstick suggested by algorithms 1) and 3), and that the algorithm 2) which is quite sensitive to the extent of stress concentration on the structure well suggests the detailed shape that should be under large stress concentration. Discussions on the characteristics suggested by the algorithms are of great value to introduce general information for optimizing the cross section of an extruded structure.

View full abstract

The phenomenon of fatigue failure by the In-line flow-induced vibration was studied. A newly water-flow-induced vibration system was made and used to reproduce fatigue failure by flow-induced vibration. A medium carbon steel specimen was fixed to the experimental equipment. A small artificial hole was introduced onto the specimen surface. Fatigue crack initiated from the artificial hole. A small portable strain histogram recorder (Mini Rainflow Corder, MRC) developed in another project of the authors' team was used to acquire the service strain histogram at a critical point of the specimen and to measure the variation of natural frequency. Cumulative fatigue damage D defined by the Modified Miner Rule was calculated by using the strain histogram at the initial stage of test. The value of D was almost unity in the case of In-line vibration, while the values of D in the case of the Cross-flow vibration ranged from 0.2 to 0.8.

View full abstract

Cantilever-type rotating bending fatigue tests were carried out on bearing steels tempered at three different temperatures in order to clarify the strength level dependence of the long-life fatigue behavior. For the surface induced fracture, it was found that the fatigue limit tended to decrease with a decrease of the specimen hardness and it was related to the half value breadth which was a typical parameter of X-ray diffraction. On the other hand, the fatigue life in the interior inclusion induced fracture was improved as the hardness was decreased. Based on the fractography of the fracture surface, characteristic rough surface of fine granular area (FGA) was observed in the vicinity around the interior inclusion. Formation mechanism of this FGA was discussed from microscopic observations by TEM and SIM and X-ray diffraction patterns. Thus it was finally found that the martensite-lath was restructured as to give a number of microscopic subgrains and separation of the boundaries of these subgrains caused the fatigue crack producing the characteristic rough area of FGA.

View full abstract

The authors proposed a practical method for estimating the stress fields near a notch in a real structure under in-plane loading in the previous paper. In this method, boundary conditions of a region near a notch are determined reasonably, using the stress field expression and stress components by strain gages on the boundary. Therefore, in this method, precise estimation of the stress fields can be performed in real structure whose boundary conditions are hard to grasp. In this paper, we have developed this method so that it can be used for notches under anti-plane loading or both in-plane and anti-plane loading. A straight boundary near a notch and non-symmetric boundary conditions are investigated as factors lowering the estimation precision. Consequently, there is the angular limitation of a notch in application of this method. However estimation results accurate enough for practically were obtained in the most cases.

View full abstract

Electromagnetic acoustic transducers (EMATs) are developed for flaw detection in copper tubes. Longitudinal wave is propagated along length of the tubes. First, we use the square wave pulse, to find that the unidirectional transmission is possible with the array-type EMATs. Then, we apply the EMATs for U-bend tubes. Since low frequency components reflect at the U-bend section, the burst wave excitation is thus recommended. After finding the optimum excitation signal, flaw detection is executed. It is revealed that the flaw, which occupies 12% of the cross section, can easily be detected even in the U-bend tube, and that the flaw detectability is improved up to 3% by taking the correlation of the received signal with end reflected echoes. For straight pipe, the flaw occupying 1.5% of the cross section can be detected from 2 m distant.

View full abstract

Electrochemical impedance spectroscopy measurements under a smal alternating current were performed to investigate the electrochemical reactions on poly-crystalline nickel surfaces in nickel sulfamate electrolyte. The Nyquist diagrams exhibit the absence of inductive loops for the frequency range from 5MHz to 100 kHz. A condition for the existence of inductive loops derived in this study suggests that the electrocrystallization of Ni²⁺ions may take place in the slow reaction step Ni²⁺+e^-→ Ni⁺_adsand fast reaction step Ni⁺_ads+e^-→Ni. In addition, the reaction impedances are found to have two exponents that slightly deviate from the values predicted by a homogeneous charge-transfer reaction model.

View full abstract

An investigation has been carried out concerning the influence of water absorption on the impact fracture behavior and the residual strength after impact of CFRP/Aramid honeycomb core sandwich panels. Some specimens were manufactured by a hotpress molding method and others by an autoclave one. Low velocity impact tests were conducted using a falling weight tester. When the applied impact energy was higher than the threshold one, below which no damage of honeycomb core was introduced, the percentage of the absorbed energy became large. Although the SEM observation showed the degradation of the fiber/matrix interfacial strength by water absorption, no influence of water absorption on the impact induced delamination area was observed. The residual strength after impact was evaluated by compression test and four point bending test. Due to voids and poor adhesion between facing and core materials of the hotpress specimens, the residual compressive strength of the hotpress specimen was smaller than that of the autoclave one.

View full abstract

Although the dendrite arm spacing (DAS) seems to be a key parameter for mechanical properties of AC4CH aluminum casting alloy, it has not sufficiently been clarified. Especially, the relationship between impact tensile characteristics and DAS and the casting defect related to DAS has not been understood qualitatively. In this study, the influence of DAS on impact tensile properties of AC4CH aluminum casting alloy is investigated by means of a direct tension version of the split Hopkinson bar equipment. The effect of DAS on tensile properties is examined using the specimen which removed the defects by HIP treatment, and the effect of the defects is examined using the specimen with the defect without HIP treatment. As results, it can be confirmed that the tensile strength at high strain rates is linearly decreased with the increase in DAS. It is also found that the tensile strength and the elongation at high strain rates are drastically lowers in over 3% of defect area ratio.

View full abstract

In order to investigate the tensile characteristics of lead-free solder at high strain rates, impact tensile test equipment for solder materials was developed, on the basis of the direct tension split Hopkinson bar technique. By using this equipment, tensile stress-strain characteristics data of the Sn-3.0 Ag-0.5 Cu lead-free solder and the Sn-Pb conventional solder up to fracture were measured with a high accuracy at strain rate of 1.66 x 10³ and compared with those at quasi-static strain rates of 1.2 and 1.2 x 10^-2. The results show that the proof stress and tensile strength of the Sn-3.0 Ag0.5 Cu lead-free solder increase significantly with increasing strain rate comparing with the Sn-Pb conventional solder. It is also shown that the fracture morphology of Sn-3.0 Ag-0.5 Cu solder changes from ductile fracture to brittle fracture with increase in the strain rates.

View full abstract

Elastic-plastic fracture toughness tests were conducted at 77K and 4K to examine an influence of thermal aging on fracture properties of an austenitic stainless steel JN 1 at cryogenic temperature, which is a candidate material for superconducting magnet structures of fusion reactors. The tests were applied to solution-treated material and materials aged at 923-1073 K for 5 h. The experimental results showed that the fracture toughness J_IC measured on the thermally aged materials were smaller than that on the solution-treated material and decreased with increasing aging temperature. This decrease in fracture toughness due to thermal aging was caused by precipitation and coarsening of grain boundary M₂₃C₆ carbides. Additionally, small punch (SP) tests were conducted at cryogenic temperatures to investigate the relationship between the obtained J_IC and SP properties. It was found that the equivalent fracture strain ε_qf in SP specimens was linearly correlated with J_IC irrespective of testing temperature. This correlation suggests that the SP testing technique provides a useful tool for evaluating J_IC at cryogenic temperature.

View full abstract

All structures have the potential to contain inclusion. Tensile load was given to inclusion. High stress appeared on the matrix in the circumference of the inclusion, which exfoliates from the matrix due to the high stress. Cracks them appeared on the matrix, gradually spread and destroyed the structure. This study researched elliptic inclusion in the tensile load. The direction of the tensile load is defined in the zero. Elliptic inclusion has some angle value. Studies on inclination elliptic inclusion did not exist until today. This study used the photoelastic method, method of caustics and finite element method. There are a few studies on inclusion by the experimental analysis but experimental analysis is difficult. However, this study identified a method for the experimental analysis of inclusion. If this method is used, results can easily be obtained by the experimental analysis of inclusion. As a result of this study, an elliptic inclusion equation was obtained. Elliptic inclusion can approximate all inclusions, and the result of this study can be applied to all inclusions.

View full abstract

The adhesion contact analysis using the theory of elasticity is presented in the paper. The boundary condition considering the surface stresses, which are originated from surface energy, was employed for the surfaces of indenter and substrate. Furthermore, it was supposed the surface stresses in an adhesion region are different from that in non-adhesion region and are reduced from the original surface stresses. In the present analysis, a paraboloidal indenter is pressed into the substrate and adhesion occurs between two surfaces of the indenter and the substrate. The surfaces at the adhesion regions of the indenter and the substrate deformed inward due to the variation of the surface stresses. This means that the attractive force between the adhesion region occurs for maintaining the contact of the regions and the pall-off force of the indenter from the substrate is needed. The distribution of contact pressure, the surface profile of adhesion region and adhesive force between the indenter and the substrate were precisely examined. The results in the analysis were compared with those in the Hertz theory. The total force between the indenter and the substrate was about the value of 0.04 to 0.06 reduced from the dimensionless contact load based on Hertz theory.

View full abstract

A theoretical study of stress wave propagation has not yet been done in which three properties of solid materials, that is, elasticity, plasticity and viscoplasticity are took into account in uni-axial strain state. In this paper, a theoretical analysis of a dynamic behavior of solid materials is done in uniaxial strain state using an elastic-plastic-viscoplastic constitutive equation. And, numerical calculations are also shown. Moreover, a theoretical analysis and numerical calculations are also done for the case in which an elastic-plastic constitutive equation is used. And both cases are also compared and discussed.

View full abstract

The present paper provides a quantitative analysis on the variant change of ferromagnetic martensite driven by the magnetization energy under magnetic field. The feasiblity study of the actuator mechanism using the magnetic-field induced strain is given. The model predicts an upper limit of output power of the actuator : the maximum output force of NiMnGa shape memory alloy is estimated as less than 1 MPa : the output energy is 2 000 times smaller than that of conventional NiTi shape memory alloys driven by heat.

View full abstract

For the improvement of car safety in collision, the development of high-speed processing technology, the refinement of practical constitutive equations for numerical simulation, and so forth, it is important to obtain accurate stress-strain relation of various materials in wide ranges of strain and strain rate. Through a series of numerical simulations of the specimen model of practical geometry by using the computer code LS-DYNA, some useful results in the determination of the geometry and dimensions of specimen suitable for dynamic tension test under the specified strain rate in the range 10²-10³ s^-1, such as the effects of the rising time of input velocity and the lengths of grip and fillet on transient vibration, the relationship between the limits of gauge length and strain rate to give an adequate accuracy of dynamic stress-strain curves, and so forth, are obtained.

View full abstract

The influences of the sintering additive content of rare-earth oxide (Y₂O₃, Gd₂O₃, Sm₂O₃) on microstructure and mechanical properties of ceria ceramics were investigated by scanning electron microscopy and small specimen technique. A small punch testing method was employed to detemine the elastic modulus and biaxial fracture stress of the ceria-based ceramics, and the fracture toughness was estimated by vickers indentation method. Rare-earth oxides doped ceria powders with a composition of (CeO₂) _1-x (RO_1.5) _x (R=Y, Gd, Sm and x=0, 0.10, 0.15, 0.20, 0.30, 0.40, 1.00) were prepared by a coprecipitation method. The powders were compacted by die pressing (50 MPa) followed by cold isostatic pressing (120 MPa), and sintered at 1 500°C in air for 5h. Grain growth in the rare-earth oxides doped ceria ceramics were significantly suppressed, compared to the pure ceria ceramics. However, the elastic modulus, fracture stress and fracture toughness were decreased significantly with increasing additive content of the rare-earth oxides, possibly due to the oxygen vacancies induced by the rare-earth oxides doping. The experimental results suggest that the change in the mechanical properties should be taken into account in the use of ceria-based ceramics for solid oxide fuel cells, in addition to the improvement of oxygen ion conductivity.

View full abstract