Cell distributions in and sound absorption characteristics of flexible polyurethane foams

In this article, the two-dimensional distributions of cells from the cross section of some flexible polyurethane foams were cleared, and the three-dimensional distributions of cells based on Saltykov's theory were estimated further. As a result, it was found that a mean of the two-dimensional distributions of cells was a good linear relation with a mean of the three-dimensional distributions of cells, and it was confirmed that cell structure of the foams which should have been analyzed in the three-dimensional distributions was evaluated by analysis of the two-dimensional distributions fully. It was also found that not only cell number but also cell distribution was necessary in the evaluation of flexible polyurethane foams, and cell diameter was closely related to the sound absorption coefficient in polyester-based flexible polyurethane foams. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1395–1402, 1997     

In Situ Synthesis and Microstructures of Tungsten Carbide-Nanoparticle-Reinforced Silicon Nitride-Matrix Composites

A W₂C-nanoparticle-reinforced Si₃N₄-matrix composite was fabricated by sintering porous Si₃N₄ that had been infiltrated with a tungsten solution. During the sintering procedure, nanometer-sized W₂C particles grew in situ from the reaction between the tungsten and carbon sources considered to originate mainly from residual binder. The W₂C particles resided in the grain-boundary junctions of the Si₃N₄, had an average diameter of ∼60 nm, and were polyhedral in shape. Because the residual carbon, which normally would obstruct sintering, reacted with the tungsten to form W₂C particles in the composite, the sinterability of the Si₃N₄ was improved, and a W₂C–Si₃N₄ composite with almost full density was obtained. The flexural strength of the W₂C–Si₃N₄ composite was 1212 MPa, ∼34% higher than that of standard sintered Si₃N₄.     

Experimental measurement on tangential momentum accommodation coefficient in a single microtube

The tangential momentum accommodation coefficient (TMAC) was investigated experimentally from the mass flow rate through a single microtube under the slip flow and the early part of the transition regime. The measurements were carried out by the constant-volume method under the mean Knudsen number smaller than 0.3, which is based on the mean pressure of the inlet and the outlet of the microtube, to apply the second-order slip boundary condition. To measure TMACs on various materials, quite large microtube was employed, which require the reduction in leakage. TMAC was obtained from the slip coefficient determined by the relation of the mass flow rate to the mean Knudsen number. The obtained mass flow rate was well explained by the theoretical equation. TMACs of deactivated-fused silica with argon, nitrogen, and oxygen were measured, showing the tangential momentum was not accommodated completely to the surface, and the values showed good agreement with previous studies. From the comparison between microtubes with different inner diameter, it is showed that TMAC is determined mainly by gas species and surface material.     

Visual appearance and its fidelity evaluation of digital images displayed by means of orthogonal transform and adaptive spatial filter

The comparison between modified and/or compressed digital images and original digital images, i.e. reconstructed digital images, may be simply demonstrated by means of two-dimensional orthogonal transform techniques and adaptive spatial filters in the domain of the spatial frequency. The main purpose of this study is to examine how much the visual appearance of the reconstructed images is essentially affected by two types of parameters: the number of the threshold value and the value of the weighting coefficients necessary to the concept of an adaptive spatial filter, which is generally used in a small divided block domain in connection with simplified digital image compression techniques. Moreover, the suitability of 3D visualization and/or quasi-colour representation techniques is verified as a means for intuitively understanding the discriminating features of reconstructed images. To sum up, this study is executed to examine the contrast between the visual appearance of difference images and fidelity evaluation of image quality.     

Effects of high-temperature ageing on the creep-rupture properties of cobalt-base L-605 alloys

Effects of high-temperature ageing on the creep-rupture properties of cobalt-base L-605 alloys were investigated at 1089 and 1311 K in air. The specimens with serrated grain boundaries and those with normal straight grain boundaries were aged for 1080ksec at 1273 or 1323 K to cause the matrix precipitates of tungsten-rich b c c phase and M₆C carbide. The creep-rupture strength of both specimens were improved by the high-temperature ageing. The rupture strength at 1311 K was the highest in the specimens with serrated grain boundaries aged at 1273 K, while the specimens with straight grain boundaries aged at 1273 K of the highest matrix hardness had the highest rupture strength at 1089 K. The high-temperature ageing did not decrease the rupture ductility of specimens. The ruptured specimens with serrated grain boundaries exhibited a ductile grain-boundary fracture surface which consisted of dimple patterns and steps, regardless of whether high-temperature ageing was carried out. The fracture mode of the specimens with straight grain boundaries was changed from the brittle grainboundary fracture to the ductile one similar to that of the specimens with serrated grain boundaries by high-temperature ageing, since large grain-boundary precipitates which gave nucleation sites of dimples were formed during the ageing. The grain-boundary cracks initiated in the early stage of creep (transient creep regime) in both non-aged and aged specimens of L-605 alloys in creep at 1089 and 1311 K, although the time to crack initiation is shorter in the specimens with straight grain boundaries than in those with serrated grain boundaries. Thus, the period of crack growth and linkage occupied most of the rupture life. The strengthening mechanisms of the aged specimens were also discussed.     

Improvement of fatigue-crack growth resistance by grain-boundary reaction precipitates at high temperature

Effects of grain-boundary reaction precipitates on fatigue-crack growth rate were investigated using austenitic 21 wt% Cr-4 wt% Ni-9wt% Mn heat-resisting steel at 973 K in air. Grain boundaries were serrated by-the grain-boundary reaction precipitates. The crack growth rate was considerably decreased by these precipitates, especially at low crack growth rates. Fatigue cracks extended to the serrated grain boundaries or to the interface between the grain-boundary reaction nodule and the grain. Therefore, the cracks grew along zigzag paths, and brittle intergranular fracture was inhibited. The decrease in the fatigue-crack growth rate was explained by these changes in fracture mode.     

Further discussion on magnetic vector potential finite-elementformulation for three-dimensional magnetostatic field analysis

A linear soft-iron and current model called the IEE Japan model using a novel vector potential finite-element formulation is examined. Calculated and measured results are in close agreement. For comparison, the same model was calculated by the conventional variational formulation. The divergence of magnetic vector potential equals zero at the boundary of different materials and the values themselves are small enough at the Gaussian quadratural points, which means that uniqueness of the solution is guaranteed. The gauge condition is determined by the formulation, not by the boundary conditions. The new formulation requires less computing time and memory than the conventional variational formulation     

Effect of heat treatment on precipitation behaviour and high temperature strength in a wrought Co-base superalloy

The effects of solution and ageing temperatures on the grain boundary reaction as well as on matrix precipitation in the interior of the grains were investigated using wrought Co-base superalloy HS-21. The grain boundary reaction occurred during furnace-cooling after solution-heating. The phase that precipitated in the grain boundary reactions nodule was M₂₃C₆ carbide. It also occurred during ageing after solution treatment, but the extent of it was considerably influenced by cooling procedure after solution heating. The activation energy of the grain boundary reaction was 244 kJ mol^–1 for the early stage of the grain boundary reaction in HS-21 alloy, and was considered to be the activation energy of grain boundary diffusion of chromium. The extent of the matrix precipitation that occurred during ageing was also influenced by the cooling procedure. Creep rupture tests were carried out at 1088 K in air. An excellent combination of long rupture life and large ductility was attained on a specimen, which involved both the grain boundary reaction nodules (about 7% in area fraction) and the matrix precipitates. The improvement of creep rupture properties results from the retardation of brittle intergranular fracture, which is achieved by grain boundary serration owing to the grain boundary reaction and by the increase of strength in the interior of grain due to the matrix precipitation.