The nature of direct current potential drop (DCPD) on carbon steel (SS400) having different surface conditions is investigated in this study. The spring-loaded macroscopic DC four-point-probe sensor was used for the measurements of potential drop. Three samples from the same type of carbon steel are prepared under three different conditions, namely, exposures for short and long periods in atmosphere and heat treatment at low temperature of the sample experienced short exposure. In an attempt to verify the repeatability nature of DCPD, the measurements are performed on different locations of the test surface under the same experimental conditions and used for analysis. The natures of potential drop on oxide scale free surface and oxidized surfaces were compared. The effect of oxidized surfaces on DCPD in all the three cases is observed markedly. From these observations, it is worth understanding that the DCPD technique through spring-loaded macroscopic four-point-probe is able to distinguish the oxidized surface from oxide scale free surface. Finally, electrical resistivities of oxide scale in all the three cases were successfully evaluated by using electrical image method with oxidized sample considering as a two-layer structure. The almost unique value of evaluated electrical resistivity of oxide scale in all the cases indicates that the oxide materials are similar in type in respect to electrical resistivity.

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We investigated the characteristics of amorphous Ni—Nb—Zr alloys for fabricating dies for molding high-precision optical glass lenses. Two amorphous Ni—Nb—Zr samples with similar compositions were prepared using carousel-type and parallel plate sputtering systems; we refer to these samples as the synthesized sample and the target sample, respectively. These two samples were evaluated and compared the desired characteristics for molding dies for optical glass lenses, namely a high mechanical strength, a high hardness, a thermally stability of amorphous state, a high oxidation resistance, a similar linear expansion coefficients to that of glass, and a high machinability. The thermal stability of amorphous state, oxidation resistance, and linear expansion coefficient did not depend on the fabrication method, whereas the mechanical properties, hardness, and machinability did. In particular, the target sample exhibited excellent mechanical strength and machinability. Finally, we fabricated a molding die made from amorphous Ni₃₅Nb₄₀Zr₂₅ alloy for optical glass lenses using diffraction gratings.

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This paper presents the experimental result on the response and collapse of sharp-notched circular tubes subjected to cyclic bending with different curvature-rates. The tube bending machine and curvature-ovalization measurement apparatus were used for conducting the cyclic curvature-controlled experiments on sharp-notched 304 stainless steel tubes. According to the capacity of the bending machine, three different curvature-rates, 0.0035, 0.035 and 0.35 m^-1s^-1, were controlled to highlight the characteristic of the response and collapse. It is observed that the higher the applied curvature-rate, the greater is the degree of hardening on metal tube. However, the ovlization of tube cross-section increases when the applied curvature-rate increases. In addition, due to the higher degree of the ovalization of tube cross-section under cyclic bending, the number of cycles to produce collapse is corresponding reduces.

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A one-sided fastening bolt using the plastic buckling of a pipe which is annealed along the length is studied in this paper. In fastening process the pipe is buckled to form a buckling head in the annealed area under an axial compressive load and the formed buckling head can be used as the backside head of the bolt. Since the pipe geometry is the single design variable for the strength of fastening bolt, estimations of effects of the geometry parameters of the pipe on the fastening process are very important. The whole fastening process is studied by the nonlinear finite element analysis consistently. Effects of the pipe length on the deformation and the load in the fastening process are investigated for two different diameter pipes. The buckling experiment and the fastening experiment are carried out to verify the simulation method proposed. Numerical results are compared with experimental results for the deformation and the load in the buckling step and the fastening step, showing fairly good coincidence. Three different types of deformation modes in the fastening process are found in the analyses and experiments. Under the mode which has a large area to contact the bolt head, the higher fastening strength is obtained.

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Elasticity solutions of plates have been widely researched and used in practice. However, elasticity solutions of plane problems are applicable to structures only under the premise that such structures are very thin. The precise values of thickness for which elasticity solutions are valid have not been studied in detail. It is necessary to clarify the range of appropriate thickness values in order to apply two-dimensional elasticity solutions properly. In this study, we use finite element analyses to study three flat-plate models each containing a U-shaped hole of the same radius, and compared the three-dimensional finite element solutions with two-dimensional elasticity solutions. From the results, the limits of application of two-dimensional elasticity solutions are discussed.

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The equivalent stiffness of clamped plates should be prescribed not only to evaluate the strength of bolted joints but also to evaluate deformation and vibration characteristics of practical structures with many bolted joints. The axial stiffness and bending stiffness of clamped plates were evaluated by using Finite Element (FE) analyses while taking the contact condition on bearing surfaces and between the plates into account. We constructed the FE models for bolted joints tightened with M8, 10, 12 and 16 bolts and plate thicknesses of 3.2, 4.5, 6.0 and 9.0 mm, and the axial and bending compliances were precisely evaluated. These compliances of clamped plates were compared with those from VDI 2230 codes (German Engineering Society), in which the equivalent cylindrical and conical compressive stress fields in the plate had been assumed. The compliances of the clamped plates for the preload states were estimated between the predictions as the cylindrical and the conical fields. Meanwhile, the axial and bending compliances of FE analysis can basically be expressed by the VDI 2230 (2003) with the conical field. However, the VDI 2230 (2003) gives the slightly large axial stiffness, and thus the internal force borne to the bolt is predicted in a little bit dangerous failure. Also, it cannot follow the case of clamped plates with different thickness due to assumption of its model.

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