FRACTURE MECHANISMS AND LIFE ASSESSMENT UNDER HIGH-STRAIN BIAXIAL CYCLIC LOADING OF TYPE 304 STAINLESS STEEL

Abstract— In order to investigate the elevated-temperature low-cycle fatigue characteristics of Type 304 stainless steel under biaxial loading, strain-controlled push-pull and torsional fatigue tests were conducted at 550°C under proportional and nonproportional loading conditions with phase differences of 0, α/6, α/4, α/3 and α/2 between the applied sinusoidal axial and torsional strains. Based on the experimental results, this study presents a discussion on fracture mechanisms and failure criteria. In the case of proportional loading, the fracture mode was found, from fractographic observations, to be classified into either Mode I or Mode II, while the fractures were of mixed mode under nonproportional loading. However, failure lives under both the loading conditions could be correlated well in this study with the equivalent shear strain range, Δy, defined by extending the β -plane theory of Brown and Miller. The failure life under nonproportional loading could also be predicted by applying a strain-energy-based approach.     

On Reflectionless Nature of Self-Consistent Multi-Soliton Solutions in Bogoliubov–de Gennes and Chiral Gross–Neveu Models

Recently the most general static self-consistent multi-soliton solutions in Bogoliubov–de Gennes and chiral Gross–Neveu systems were derived by the present authors (Takahashi and Nitta, Phys. Rev. Lett. 110:131601, 2013). Here we show a few complementary results, which were absent in our previous work. We prove directly from the gap equation that the self-consistent solutions need to have reflectionless potentials. We also give the self-consistent condition for the system consisting of only right-movers, which is more used in high-energy physics.     

First-principles molecular dynamics simulation on interatomic interaction of Fe crystal with Pb and Bi atoms

The interaction mechanism between Fe crystals and Pb and Bi atoms was investigated using the first-principles molecular dynamics theory based on the density functional theory, which was the first step of an analytical approach to the simulation of steel corrosion in high temperature lead–bismuth (Pb–Bi) cooled fast breeder reactors and accelerator driven systems. The Vanderbilt ultrasoft pseudopotentials for Fe, Pb and Bi elements were calculated with the exchange and correlation corrections by the local density approximation. Crystal lattice constants calculated using the potentials agreed well with experimental ones. Using the calculated pseudopotentials, the first-principles molecular dynamics simulations were performed to investigate the interatomic interaction between Fe crystal and Pb, Bi atoms. The result shows the reasonable motions of Pb and Bi atoms near the surface of the Fe crystal and those of Fe atoms in the crystal.     

Rashba Spin–Orbit Interaction and Its Applications to Spin-Interference Effect and Spin-Filter Device

The Rashba spin–orbit interaction in InGaAs quantum wells (QW) is studied using the weak antilocalization analysis as a function of the structural inversion asymmetry (SIA). We have observed a clear cross-over from positive to negative magnetoresistance near zero-magnetic field by controlling the degree of the SIA in the QWs. This is a strong evidence of a zero-field spin splitting that is induced by the Rashba effect. The spin-interference effect in a gate-controlled mesoscopic Aharonov–Bohm ring structure is investigated in the presence of Rashba spin–orbit interaction. The oscillatory behavior appearing in ensemble averaged Fourier spectrum of h/2e oscillations as a function of gate voltage is possibly because of the Aharonov–Casher type interference. We propose a spin-filter device based on the Rashba effect using a nonmagnetic resonant tunneling diode structure. Detailed calculation using InAIAs/InGaAs heterostructures shows that the spin-filtering efficiency exceeds 99.9%.     

Volume and dislocation diffusion of iron,chromium and cobalt in CVD ß-SiC

Impurity tracer diffusion of ⁵⁹Fe, ⁵¹Cr and ⁵⁷Co in CVD b-SiC has been studied in the temperature range between 973 and 1873 K. The temperature dependence of the volume diffusion coefficients of iron and chromium can be expressed by linear Arrhenius equations. The preexponential factor and the activation energy are estimated to be 8.7 × 10¹⁵ m² s^-1 and 111 kJ mol^-1 for iron, respectively, and 9.5 × 10¹⁵ m² s^-1 and 81 kJ mol¹ for chromium, respectively. The diffusion coefficients of iron and chromium are much higher than those of the self-diffusion in ß-SiC. Furthermore, the activation energies for the diffusion of iron and chromium are about one-tenth of those for carbon and silicon in b-SiC. Therefore, it seems that an interstitial mechanism is predominant for the diffusion of iron and chromium in b-SiC. On the other hand, the diffusion coefficient of cobalt above 1673 K is higher than that of iron, while at lower temperatures it is much lower than that of iron. The difference in the diffusion coefficients at 1173 K is more than three orders of magnitude. Thus, the temperature dependence of the diffusion coefficients of cobalt shows a strongly curved Arrhenius relation. This suggests that cobalt atoms diffuse by an interstitial mechanism at higher temperatures and by a substitutional mechanism at lower temperatures. From the deeper regions of the penetration profiles of iron, chromium and cobalt the dislocation diffusion coefficients of them have been estimated.     

Anti-reflection Coating for Cryogenic Silicon and Alumina Lenses in Millimeter-Wave Bands

A dielectric lens with high refractive index is suitable for focusing cryogenic devices in millimeter-wave bands when an appropriate anti-reflection (AR) coating is applied. Two types of AR coatings for silicon and alumina were studied at the millimeter-wave (220 GHz) band: one is by direct machining of mixed epoxy for a silicon lens array, while the other is by laser machining of an antireflective subwavelength structure for a large alumina lens used in a re-imaging optics system. The millimeter-wave optical properties of silicon, alumina, aluminum nitride, and Stycast epoxies were measured with a Fourier Transform Spectrometer (FTS) at cryogenic temperatures. The measured refractive index of the AR coating with a mixture of Stycast 1266 (n = 1.68) and Stycast 2850FTJ (n = 2.2) for silicon at 30 K was 1.84. The thickness of the epoxy AR coating was precisely controlled with direct machining. Transmittance of the AR-coated silicon substrate, measured with FTS, was approximately 95 % at the center frequency of the 220 GHz band with a bandwidth of 25 % at 27 K. An antireflective subwavelength structure was designed for an alumina sample with periodic cylindrical holes. The measured 220-GHz-band transmittance was above 90 % with a bandwidth of 25 % at 25 K.