Steel conveying rollers used in hot rolling mills must be changed very frequently at great cost because hot conveyed strips induce wear on the roller surface in short periods. In this study new roller structure is considered where a ceramics sleeve is connected with two short shafts at both ends by shrink fitting. Here, ceramics sleeve may provide longer life and reduce the cost for the maintenance. However, care should be taken for the maximum tensile stress between the sleeve and shafts because the fracture toughness of ceramics is extremely lower than the values of steel. In this study FEM analysis is applied to the structure, and the maximum tensile stress has been investigated with varying the dimensions of the structure. It is found that the maximum tensile stress appearing at the end of sleeve takes a minimum value at a certain amount of shrink fitting ratio.

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The objective of the present paper is to propose a new FEM analysis method which takes the phase transformation and the tempering effect into account. We developed an algorithm in which the tempering effect, that is shrinkage and mechanical properties change, is represented by the change of carbon concentration. The proposed FEM analysis method correctly estimates the volume shrinkage phenomenon during tempering. This method is applied to the evaluation of residual stress in a steel block subjected to locally heating and its variation due to tempering. The calculate results well explain the change of residual stress due to tempering than the conventional quenching simulation code, and the advantage of the proposed method is confirmed.

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In the nano-plastic deformation, material properties such as yield stress cannot be described by the average rate of whole dislocation behavior, and it becomes increasingly necessary to trace individual motion of dislocations. The relationship between indent load-displacement in nanoindentation test is the typical example of recognizable nano-plasticity. Molecular dynamics (MD) is one of the most effective methodologies to obtain dislocation motion directly. However, MD simulation depends on the computer power so strongly that it is difficult to treat mesoscopic behavior including collective dislocation motion. On the other hand, discrete dislocation mechanics (DD) based on dislocation theory has a unique ability to treat dislocation motion, although boundary value problem in the DD framework would pose considerable difficulties. In the present paper, we construct a combined approach including both DD and the boundary element method (BEM), and succeed in representing the stress field of dislocation in the vicinity of traction free surface. Finally, we apply this model to the nanoindentation problem and found the relationship between displacement burst and collective dislocation motion.

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In general, internal cells are required to solve thermo-elastoplastic problems using a conventional boundary element method (BEM). However, in this case, the merit of BEM, which is the easy preparation of data, is lost. The conventional multiple-reciprocity boundary element method (MRBEM) cannot be used to solve the elastoplasticity problems, because the distribution of initial strain or initial stress cannot be determined analytically. In this paper, it is shown that two-dimensional thermo elastoplasticity problems can be solved without the use of internal cells, by using the triple-reciprocity boundary element method and a thin plate spline. Initial strain and initial stress formulations are adopted and the initial strain distribution is interpolated using boundary integral equations and a thin plate spline. A new computer program was developed and applied to several problems.

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Developments of sea ice polycrystals from the sea surface are simulated in two-dimensional approximation by combining numerical methods for crystal growth, salinity diffusion and flux of heat. An anisotropic growth of ice crystals from a number of nuclei and their mutual impingements are numerically reproduced by a simple and novel technique, named Voronoi dynamics. Discharge of salt from solidified region and salinity condensation at the solid-liquid interface are also taken into consideration. Diffusion process of salinity and heat flux are evaluated by solving equations for diffusion and heat conduction, and growth of ice crystals is affected by these two factors. Results show that a layer of granular grains is formed near the sea surface and columnar shaped grains develop below it. Brine regions are mainly formed along grain boundaries in the layer of granular grains. In the region of columnar shaped grains, brine regions exist not only along grain boundaries but also inside grains. Columnar shaped crystal grains consist of ice platelets growing in the vertical direction and brine layers between them. These microstructural features are in accordance with experimental observations.

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The bolts and nuts are widely used in various fields as important joining elements with long history. However, screw loosening is easily induced by vibration and external loads, and sometimes causes very serious accident without notice. In this paper, a special stud bolt named “Super Stud Bolt (SSB)” is studied, which can prevent loosening effectively. Between the upper threads and the lower threads, there is a thin walled tube which can be deformed along the axial direction so that the phase difference is designed and SSB is developed. During fastening, this phase difference induces the contrary forces on the surfaces of the upper threads and the lower threads, which bring out the antiloosening performance. In this study, both courses of processing and fastening are simulated, and the relationship between axial force and displacement is illustrated with the finite element method. In this analysis, the large plastic strains and elastic-plastic large deformation theory are applied to 4 nodes axial symmetric FEM models. Through the comparison among the results, the desirable range of the phase difference of lower and upper threads is decided. Since the thin walled tube is the heart of anti-loosening mechanism, optimum original dimensions are discussed in this study.

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In the previous paper, a concept of “molecular chain slip system” was newly proposed for glassy polymer by analogy with the crystal plasticity theory for metals. An inelastic response law based on a probabilistic theory considering change of local free volume was adopted as a hardening law. An FE simulation was carried out for PMMA under plane strain tension. Macroscopic neck propagation with high strain rate shear band and directions of molecular chains in the oriented region were computationally visualized. Moreover, a nonlinear viscoelastic behavior was accurately predicted. However, amorphous state in which molecular chains were entangled at random was not expressed appropriately because same initial directions of molecular chains were given to each material point. In addition, elastic isotropy was assumed and change of elastic modulus due to orientation of molecular chains was not considered. In this paper, the extended Taylor model, in which many slip systems are given to a material point and their initial directions are random, is applied to the present theory in order to represent more realistic amorphous state of glassy polymer. Furthermore, anisotropy parameter is defined from dispersion of slip system directions and it is attempted to express an elastic anisotropy induced by molecular chain orientation with plastic deformation, introducing anisotropy parameter into the elastic constitutive equation.

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EPDM composites with carbon black (CB 50, CB 25), with silica (SC 60), and without fillers (NF) were exposed to 0.6 to 10 MPa hydrogen gases at 30°C, and the influence of fillers on hydrogen content and blister fracture of EPDM composites was investigated. The hydrogen contents of CB 50, CB 25, SC 60, and NF were proportional to hydrogen pressures up to 10 MPa. It is confirmed that the behavior of their hydrogen contents follows Henry's law. The addition of the carbon black raised the hydrogen content of EPDM composites, while the addition of the silica did not raise that of EPDM composites. With respect to diffusivity, the carbon black lowered the diffusivity of EPDM composites, while the silica hardly influences that of EPDM composites. According to the observation of blister damages of CB 50, CB 25, SC 60, and NF, the blister damage of SC 60 is the slightest. It is considered to be due to lower hydrogen content and relatively better tensile properties compared with the others.

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In this paper, the compression behavior of low-density porous materials is inspected to apply them to the various parts of machines like shock absorbing structures. The multiaxial behavior of the compression process should be observed for the application in addition to the fundamental uniaxial compression mechanics of the materials. Then equibiaxial pre-strained compression testing is adopted for the observation. Here, polyurethane form is targeted as testing material because of its simplicity in the mechanics of compression process. The results of uniaxial and pre-strained compression testings show that the pre-strain causes the hardening of the porous material, and the change of the hardness depends on the amount of total volume change. The parameter of cell disappearance rate, which is concerning with volume change, is used to formulate the multiaxial stress-strain relationship. The multiaxial behaviors of the experiments can be simulated by using the formulated equations, and these results also show the importance of volume change effect in the compression behavior.

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The hybrid process, Polymer Impregnation and Pyrolysis combined with Powder Space Holder (PSH-PIP) method, has been newly developed to improve the reliability in structure and mechanical properties of SiC/SiC composite. This process can yield an open micro-porous structure derived from a precursor polymer which is ready for being densified by a subsequent PIP processing. Systematic experimental study has been done for the effects of the size and the fraction of the space holding particles on the microstructure. Consequently, SiC porous bodies without any significant cracks were successfully obtained by achieving efficient gas purge and homogeneous thermal shrinkage.

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Rotating bending fatigue tests were carried out using partially notched specimens of Ni-base super alloy Inconel 718 at room temperature in order to investigate the effect of aging condition on fatigue properties. Aging conditions selected were the under-aged and the over-aged conditions with the same hardness and the peak-aged condition. The conventional double-aged condition was also selected for comparison. Fatigue strength of the double-aged condition was the highest among the alloys, especially at fatigue limit. The growth rate of a crack smaller than the length of a few grains was suppressed in the double-aged alloy, though the growth rates of a longer crack were nearly the same in all of the alloys.

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Ultrasonic fatigue tests of plain specimens with different grain sizes were carried out for Ni-base super alloy, Inconel 718, in ambient air in order to investigate the effect of grain size on fatigue properties. Fatigue strength was increased with decrease in grain size. The increase in fatigue strength by refining grain size was mainly caused by the suppression of crack initiation. That is, the effect of grain size on crack growth rate was hardly recognized, though crack morphology was rougher in the specimen of larger grain, meaning that the crack growth in the large-grained specimens was suppressed by roughness induced crack closure. On the other hand, however, more flat facets caused by twin boundary cracking were observed in the large-grained specimens, which inversely led to crack growth acceleration.

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Ultrafine grained (UFG) copper was processed by equal channel angular pressing. After the processing, some samples were annealed at 160°C (3 min). Materials with and without annealing are referred to UFG-A and UFG, respectively. Although the tensile strength of UFG-A was about 20% less than that of UFG, fatigue strength in the long-life field in excess of 107 cycles was higher in UFG-A than in UFG. The change in surface damage was monitored successively, showing the difference in formation behavior of surface damage between UFG and UFG-A. The surface hardness of both materials was severely decreased with stressing. The decreasing trend of hardness was closely related with the formation process of surface damage. The higher fatigue strength of UFG-A in the long-life field was discussed based on the morphological feature of surface damage and its formation behavior. Moreover, the growth behavior of a small crack was studied. The crack growth rate, dl/dN, of UFG was determined by a term σⁿ_al for all stress amplitudes examined (σ_a/σ_u≥0.24, σ_u : tensile strength). For UFG-A, however, dl/dNwas determined byΔK and σnal according to the magnitude of stress amplitudes.

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The effects of hydrogen and pre-strain on tensile properties of JIS-STPG 370 carbon steel pipe for hydrogen pipelines were investigated. In order to pre-charge hydrogen, the specimens were immersed in a 20 mass% aqueous solution of ammonium thiocyanate at 313 K for 48 h. The hydrogen content increased with increasing the pre-strain. The reduction of area of hydrogen-charged specimens decreased with pre-strain. Although pearlite cracks were formed both in the uncharged and hydrogen-charged specimens, the initiation of pearlite cracks occurred at the lower true strain in the hydrogen-charged specimen. Furthermore, the pearlite cracks grew in the direction perpendicular to the loading axis in the hydrogen-charged specimen. The experimental evidences are shown to explain the mechanism of the initiation and growth of pearlite cracks in the hydrogen-charged specimen by the hydrogen enhanced localized plasticity model rather than the lattice decohesion model.

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This paper is the first in a series of studies on the effects of magnetic field on fretting wear damage of ferromagnetic materials. The effect of frequency of fretting vibration was tested in ranging 10 to 150 Hz under the basic Hertz-type contact between a steel ball and a steel plate. Two levels of magnetic fields of 0.08 and 0.22 T were applied with DC electronic magnets. The effects of worn volume and worn depth were examined through factors of frequency and number of cycles of fretting vibration, and morphology of appearance of worn surface. As a result, the following conclusions were derived : magnetic field increases fretting wear damage at lower frequencies, and decreases it at higher frequencies. The deference in the amounts of fretting wear debris formation is examined.

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Response surfaces generated by using an artificial neural network or a Kriging model can approximate multimodal responses and the responses of multi-variable functions, even if the prior information used in creating the surfaces contains noises. To prevent the response surfaces from fitting to the noises in the prior information, regularization methods are applied. The Bayesian regularization method works well with an artificial neural network, and the improved nugget effect method can be effectively applied to the regularization of an ordinary Kriging model. Which response surface model to select depends on the amount of prior information and the number of variables in the response function. The Kriging model generates a more accurate response surface with a smaller amount of prior information than the artificial neural network does. On the other hand, the artificial neural network is more effective for approximating the response of a multi-variable function than the Kriging model. As a result, we can apply the response surface method to find the variables that ensure the optimum response of a function. This may increase the opportunities for using optimization techniques in the practical design process

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Formation of porosity in the die casting process is unavoidable. The porosity has harmful influences on the mechanical properties, such as tensile strength and fracture toughness, of the products. We have introduced PRPC (Porosity Reducing Post Compression) process of ADC 12 aluminum alloy die castings to reduce inside porosity. In this study, influencing factor to reduction efficiency of porosity when applying PRPC process was investigated by quality engineering method. As a result, control factors of the PRPC process had a larger influence on reduction efficiency of porosity comparing to the influence of scatter due to each product.

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