Correlation between the distributions of nonradiative microdefects and dislocations in a Si-doped n-GaAs wafer has been investigated with a photothermal-radiation (PTR) microscope. We measured the PTR image with the wavelength of excitation light fixed at 895nm, and compared the PTR image with the dislocation-density distribution. The PTR image shows negative correlation with the dislocation-density profile. The PTR signal apparently originates from the nonradiative microdefects generated dominantly in the low-dislocation-density regions. The effect of annealing on the microdefects in the Si-doped n-GaAs wafers has been investigated with the PTR and photolurninescence(P1) microscope. We found that the PTR intensity decreases after annealing, while the PL intensity increases. Upon etching of the surface, the PL intensity decreases but the PTR intensity shows no appreciable change.
Conventional close stirrup has been widely used in RC beams to avoid shear failure behavior but the effect of internal vertical stirrup legs on the shear strength and the initiation of three-dimensional diagonal shear crack in RC beams is still debatable. In this study, three-dimensional crack evaluation was conducted to determine the shear failure mechanism of RC beams with different (two, three and four) vertical stirrup legs across beam width, with almost same stirrup contribution in design equation, using three-point loading test. The load displacement relationship, surface crack initiation and propagation, internal cracking patterns in cross section, vertical stirrup leg strain and concrete strain relationships, shear resistance components were discussed in detail. It was concluded that the presence of two equally spaced internal vertical stirrup legs with conventional close stirrup restricts the initiation and propagation of internal cracks to side surfaces of tested RC beams and influenced the shear strength.
RCはり部材に対する曲げひび割れ進展挙動について,クリープ,収縮,コンクリートの硬化過程に伴う材料特性の変化と,鉄筋の付着性状を考慮した3次元有限要素解析を用いて解析的に評価を行った.鉄筋の付着性状を考慮することにより,荷重増加によるRCはり,PRCはりのひび割れ性状およびひび割れ幅について評価できることが示された.また,時間依存挙動を考慮することにより,持続荷重による全体挙動およびひび割れ進展挙動を,強度による材料特性の違いに依らず,妥当に評価できることが示された.さらに,本解析手法を用いて,乾燥収縮量や自己収縮量,乾燥領域,クリープがひび割れ進展挙動に及ぼす影響を検討した.
Tensile fracture of fiber reinforced cement-based composites (FRCC) with rebar was investigated via a mesoscale analysis using discretized short fibers. Herein, the effects of fiber volume fraction, steel reinforcement ratio, FRCC–rebar bond characteristics, and fiber distribution on tensile fracture behavior were investigated. In some cases, localized crack was observed in the post-yield range of rebar. The localization mechanism was numerically explained and then inhibited by focusing on the bridging forces of the fibers and rebar. The effectiveness of steel reinforcement in enhancing the strain capacity of strain-hardening cement-based composites was confirmed. This paper is based on an original paper (Ogura et al. 2016) written in Japanese.
Large amount of radioactive erosion and corrosion products are produced in the IFMIF lithium loop in addition to the deuteron-lithium reaction remnant 7Be. An analysis was conducted to estimate the radioactive corrosion products with a design code ACT-4 developed in JAERI, the activation cross sections based on the FENDL library and the IEAF-2001 library, the latest version of nuclear activation data in the intermediate energy range up to 150 MeV. The result says the concentration of the corrosion in lithium is not very large compared with that of 7Be. However, the behavior of the nuclides such as accumulation and detachment on material has not been clarified yet. When the dose rate around the lithium loop was estimated under the condition of 100% plate-out, the value was beyond the acceptable level for the hands-on maintenance near the loop soon after the operation stop. It means that a very efficient cold trap is required so that the 90% activity in the lithium loop is removed.
