Investigations on welding residual stresses in penetration nozzles by means of 3D thermal elastic plastic FEM and experiment

Recent discoveries of stress corrosion cracking (SCC) in weldments including penetration nozzles at pressurized water reactors (PWRs) and boiling water reactors (BWRs) have raised concerns about safety and integrity of plant components. It is well known that welding residual stress is an important factor resulting in SCC in weldments. In the present work, both experimental method and numerical simulation technology are used to investigate the characteristics of welding residual stress distribution in penetration nozzles welded by multi-pass J-groove joint. An experimental mock-up is fabricated to measure welding residual stress at first. In the experiment, each weld pass is performed using a semi-circle balanced welding procedure. Then, a corresponding finite element models with considering moving heat source, deposition sequence, inter-pass temperature, temperature-dependent thermal and mechanical properties, strain hardening and annealing effect is developed to simulate welding temperature and residual stress fields. The simulation results predicted by the 3D model are generally in good agreement with the measurements. Meanwhile, to clarify the influence of deposition sequence on the welding residual stress, the welding residual stress field in the same geometrical model induced by a continuous welding procedure is also calculated. Finally, the influence of a joint oblique angle on welding residual stress is investigated numerically. The numerical results suggest that both deposition sequence and oblique angles have effect on welding residual stress distribution.     

High‐pressure short time behavior of traction fluids

The squeeze film formation ability of traction fluids is studied under impact load by dropping a steel ball‐bearing against a flat anvil made of mild steel. The effect of the pressure–viscosity coefficient and of the viscosity is investigated for plastic impact. The depth difference between the lubricated surface dent and the dry dent increases linearly with the product αη of the pressure–viscosity coefficient α and the viscosity η. The importance of the lubricant parameter αη is observed under the squeeze film formation ability from contact voltage or elastohydrodynamic lubrication central film thickness measurement at rolling condition. The intensity of each impact collision is measured by means of an acoustic emission (AE) sensor. The high‐pressure short‐time solidification of traction fluids was confirmed by dent analysis after the impact tests and AE analysis under impact loads. Copyright © 2006 John Wiley & Sons, Ltd.     

Clinical experience of Rotablator

26 patients (27 lesions) who had severe calcified and diffuse lesions underwent Rotablator treatment, lesion characteristics were type B2, Type C of AHA/ACC classification. There were no patients who had type A1, type B1 lesions. Procedural success rate is 96%, coronary perforation occurred in one patient but not necessary for surgical treatment. Non Q myocardial infarction occurred only in one patient. Follow up Angioplasty were performed 1 and 3 months later after procedures. There were no restenosis after 1 month, but after 3 months, 56% of patients had restenosis.     

Scaling-parameter-dependent model for subthreshold swing S indouble-gate SOI MOSFET's

We derived a simple formula for the subthreshold swing S in double-gate (DG) SOI MOSFET's. Our formula, which depends only on a scaling device parameter, matches the device simulation results. From these results, our equations are simple and give a scaling rule for DG-SOI MOSFET's     

Crystallographic Domain Structure of an Epitaxial (Pr0.7Ca0.3)MnO3 Thin Film Grown on a SrTiO3 Single Crystal Substrate

We characterized the structure of the crystallographic domain of a (Pr_0.7Ca_0.3)MnO₃ (PCMO ( x =0.3)) thin film epitaxially grown on a (001)SrTiO₃ (STO) single-crystal substrate. We found that the domain structure exhibited an atomically smooth coherent interface with the STO substrate with no misfit dislocations. The crystallographic relationships between the domains and the substrate in their planes were interpreted to be PCMO ( x =0.3)[110][001]//STO[100][010] and PCMO ( x =0.3)[001][1-10]//STO[100][010]. The domain structure of PCMO ( x =0.3)[110][1-10]//STO[100][010] has less possibility of having the larger anisotropic strain energy found in a monoclinically distorted pseudo-cubic perovskite unit cell of PCMO ( x =0.3). This epitaxial growth structure is totally different from the previously reported PCMO ( x =0.5) epitaxial thin-film structure on STO substrate. Our observations suggested that an x value change strongly influences the structure of epitaxial PCMO thin films.     

Automated synthesis of radiopharmaceuticals for positron emission tomography: an apparatus for [1-11C] labeled carboxylic acid

A fully automated apparatus for the synthesis and formulation of short-lived ¹¹C (t_1/2 = 20 min)-labeled carboxylic acids for positron emission tomograpy (PET) has been developed. Injectable solutions of [1-¹¹C]acetic acid, [1-¹¹C]octanoic acid and [1-¹¹C]palmitic acid wilh radioactivities of 6.36-8.29 GBq, 0.070-1.43 GBq and 0.42-0.89 GBq were obtained. The preparation time was under 40 min after the end of bombardment. An automatic washing function means that labeled compound of the same or different kinds can be produced several times a day without any maintenance of the system. The control system is sited away from the ‘hot laboratory’, so operator exposure to radiation is minimized.     

Mass spectroscopy for the anode gas layer in a semi-passive direct methanol fuel cell using porous carbon plate: Part II. Relationship between the reaction products and the methanol and water vapor pressures

Subsequent to Part I, in situ mass spectrometry using a capillary probe was conducted in order to evaluate the gas condition of the anode gas layer of a semi-passive direct methanol fuel cell (DMFC) employing a porous carbon plate (PCP). Different types of PCPs were used for the DMFC, and the production of intermediates besides CO₂, i.e., methylformate (HCOOCH₃), formaldehyde (HCHO) and formic acid (HCOOH), were investigated. The profiles of the vapor pressures of these products were related to the vapor pressure of methanol and water in the gas layer. The production rate of each intermediate was formulated as a power function of the methanol and water vapor pressure ratio, P_CH3OH/P_H2O, with the power factors of 2.07, 0.47 and −0.57 for methylformate, formaldehyde and formic acid, respectively. Based on these equations of the production rates, the product distribution could be quantitatively estimated.     

Relation between low temperature fluidity and sound velocity of lubricating oil

Low temperature fluidity is important for lubricating oil. Viscoelastic solid transition temperature at atmospheric pressure T_VE0 represents the low temperature fluidity of lubricating oil, which is estimated from the occurrence of photo elastic effect by lowering the temperature using liquid nitrogen. Sound velocity in lubricating oil is measured using Sing around technique. Then the adiabatic Bulk modulus K is calculated from the measured sound velocity. A relation is found between the adiabatic bulk modulus and the viscoelastic solid transition temperature of lubricating oil. The relation depends on the molecular structure of lubricating oil. The oils of a group belong to almost same molecular structure, follows the same relation. For same molecular structure T_VE0 decreases as decreasing the adiabatic bulk modulus of lubricating oil. It is also found that, the viscoelastic solid transition temperature of blend oils can be predicted from the base oils’ T_VE0 and K.     

Magnetic interactions between metal nanostructures within porous silicon

Electrochemically deposited magnetic nanostructures arranged in a three-dimensional system are investigated with respect to their cross-talk between each other. The nanostructures are embedded in porous silicon templates with different morphologies which means pores offering dendritic growth of different strengths. An increase of the uniformity of the pores is concomitant with an increase of the smoothness of the metal deposits which strongly influences the magnetic behavior of the system. Less dendritic structures lead to an increase of the coercivity of the nanocomposite which reveals less cross-talk between the metal deposits due to a modification of the stray fields. The system allows in a cheap and simple way to tune the magnetic interactions of magnetic nanostructures in a three-dimensional arrangement.

PACS

81.05.Rm; 81.07.Gf; 75.75.-c