Significance of residual stress on fatigue properties of welded pipes

The mean stress effect on the fatigue properties of two kinds of welded pipes was investigated in cantilever bending. The fatigue strength changed with the mean stress on fillet welded pipes, but did not change on butt welded pipes. The fatigue crack initiated from the toe of weld on the outer surface of fillet welded pipes and from the undercut on the inner surface of butt welded pipes. The measurement of the fatigue crack propagation rate and the residual stress distribution through the thickness of pipe revealed that the difference in the fatigue properties between fillet and butt welded pipes arose from the weld-induced residual stress, tension on the inner surface and compression on the outer surface. It is suggested that the production of compressive residual stress along the inner surface would be an effective means for improving the fatigue strength of butt welded pipes.     

Oxidation of Fe (II) in sulfuric acid solutions with dissolved molecular oxygen

The oxidation of Fe(II) with dissolved molecular oxygen was studied in sulfuric acid solutions containing 0.2 mol · dm⁻³ FeSO₄ at temperatures ranging from 343 to 363 K. In solutions of sulfuric acid above 0.4 mol · dm⁻³, the oxidation of Fe (II) was found to proceed through two parallel paths. In one path the reaction rate was proportional to both [Fe⁻²⁺]² andp _{o 2} exhibiting an activation energy of 51.6 · kJ mol⁻¹. In another path the reaction rate was proportional to [Fe²⁺]², [SO ₄ ^{2 −}], andp _{o 2} with an activation energy of 144.6 kJ · mol⁻¹. A reaction mechanism in which the SO ₄ ^{2 −} ions play an important role was proposed for the oxidation of Fe(II). In dilute solutions of sulfuric acid below 0.4 mol · dm⁻³, the rate of the oxidation reaction was found to be proportional to both [Fe(II)]² andp _{o 2}, and was also affected by [H⁺] and [SO ₄ ^{2 −}]. The decrease in [H⁺] resulted in the increase of reaction rate. The discussion was further extended to the effect of Fe (III) on the oxidation reaction of Fe (II).     

Sub-Pixel Estimation Error Cancellation on Area-Based Matching

Area-based image matching and sub-pixel displacement estimation using similarity measures are common methods that are used in various fields. Sub-pixel estimation using parabola fitting over three points with their similarity measures is also a common method to increase the matching resolution. However, few investigations or studies have explored the characteristics of this estimation.This study analyzed sub-pixel estimation error using two different types of matching model. Our analysis demonstrates that the estimation contains a systematic error depending on image characteristics, the similarity function, and the fitting function. This error causes some inherently problematic phenomena such as the so-called pixel-locking effect, by which the estimated positions tend to be biased toward integer values. We also show that there are good combinations of the similarity functions and fitting functions.In addition, we propose a new algorithm to greatly reduce sub-pixel estimation error. This method is independent of the similarity measure and the fitting function. Moreover, it is quite simple to implement. The advantage of our novel method is confirmed through experiments using different types of images.     

Radiation-induced graft copolymerization of butadiene to polyethylene and polypropylene

Polyethylene and polypropylene films were irradiated by γ-irradiation from a Co⁶⁰ source in butadiene gas flow and in liquid butaidne. Irradiating in the butadiene gas flow is particularly convenient because the gas state monomer is available directly and little homopolymer is produced. In this case, there is a retardative effect on the grafting near the surface of the film and the grafting rate shows the maximum values at 50–60°C. for high-density PE (PEH) and PP. Irradiating in the liquid butadiene decreases the retardative effect near the surface. The effect of dose rate I on the grafting rate Rp is represented by R_p ∞ I^1/4 in this case. The grafting rate is always higher in PEH than in low-density PE (PEL). Results of x-ray diffractometry and electron microscopy indicate that the grafting reaction occurs predominantly near the surface of the crystallite (lamella) of PE and the grafting rate is not affected by the overall crystallinity of the trunk polymer but by the configurational structure, such as the degree of branching or side-chain length.     

Permeation, diffusion and dissolution of hydrogen isotopes, methane and inert gases through/in a tetrafluoroethylene film

Tetrafluoroethylene (TFE) is widely used for conventional tritium handling systems such as vacuum seals, tubing and so on. We measured the permeation of the three hydrogen isotopes, methane and the inert gases through a TFE film at room temperature by means of the time-lag method in order to establish the physicochemical properties which determine the solubility and diffusivity of those gases. It was found that the diffusion constant of the inert gases changed exponentially with the heat of vaporization and the solubility was an exponential function of the Lennard-Jones force constant of the gases. On the other hand, hydrogen isotopes and methane deviated from these relations. It is concluded that chemical interactions between the solute and the solvent play an important role for the dissolution and the diffusion of these gases in TFE.     

Anion-induced conformational transition of poly(l-arginine) and its two homologues

The interaction of various anions with poly(l-arginine) and its two homologues, poly(l-homoarginine) and poly(l-α-amino-γ-guanidinobutyric acid), has been studied in the neutral pH region. These polypeptides were found to change their conformations from coil to helix due to I^?, ClO^?₄ and SCN^?, and among them poly(l-homoarginine) and poly(l-arginine) were found to change conformation at smaller concentrations of the anions than poly(l-lysine). The helix of poly(l-homoarginine) was induced in the lyotropic series of the counteranions. Using the van't Hoff enthalpies for the transition of the polypeptides and the transition enthalpies obtained from calorimetry, the various thermodynamic parameters of the transitions were calculated by use of a theory based on the non-specific and the specific binding interactions of the anions with the charged sites on the polypeptides. The binding constants of ClO^?₄ and SCN^? with poly(l-homoarginine) and poly(l-arginine) were found to be four times as large as those with poly(l-lysine). The free energy changes of the transitions from coil to helix of poly(l-homoarginine) and poly(l-arginine) were found to be more negative than that of poly(l-lysine). From these results, the guanidinium ion can be concluded to form easily the ion pair with the anions on the polymer surface, thus allowing poly(l-homoarginine) and poly(l-arginine) to change their conformations at smaller concentrations of the anions than poly(l-lysine).     

Silicon carbide coating on molybdenum by chemical vapor deposition and its stability under thermal cycle conditions

Silicon carbide film (as thick as 25 μm) was chemically vapor deposited on molybdenum in the temperature range of 1050–1300°C by reaction of hydrogen and ethyltrichlorosilane as an application of a low-Z material to fusion reactor protective plates. The films were characterized by using scanning electron microscopy, X-ray diffraction, electron microprobe analysis, and infrared absorption spectroscopy. The deposits consisted of α and β-SiC and a small amount of SiO₂. Underlayer coatings were also attempted to improve the thermal cycling behavior. The coating with a boron underlayer was successfully cycled 2100 times between 800 and 1000°C, and then 560 times between 600 and 1200°C in air under thermal cycling conditions with a heating rate of 20°C/min. Problems in applying SiC-coated molybdenum to the first wall protective plates in a fusion reactor are discussed.