New ‘ηpl'' and ‘γ'' functions to evaluate J–R curve from cracked pipes and elbows. Part II: experimental and numerical validation

Experimental evaluation of J–R curve in a crack growth situation requires ‘η_pl' and ‘γ' functions that are specific to a cracked geometry and loading condition. In Part I [Engng. Fract. Mech., in press] of this paper, new η_pl and γ functions, which are not available in the literature, for pipe and elbow geometry with various crack configurations under different loading conditions have been derived. In this paper, some of these newly proposed η_pl and γ functions have been validated experimentally through comparison of crack initiation load and J–R curve. In few cases, numerical validation has also been provided by comparing the J-integral values calculated through η factor approach and finite element method.     

Emission probability measurement of γ-ray of Rh

¹⁰⁵Rh becomes a stable ¹⁰⁵Pd after β⁻-decay with a half-life of 35.36 h. The energies of especially strong γ-rays emitted from ¹⁰⁵Rh are 306.1 and 318.9 keV, and the emission probabilities are evaluated to be 5.1±0.3% and 19.1±0.6% by de Frenne et al. To improve the certainty, the γ-ray emission probabilities were determined from the disintegration rate and absolute γ-ray intensities measured using a 4πβ(ppc)-γ(HPGe) coincidence apparatus with two-dimensional data-acquisition system. The results for the 306.1 and 318.9 keV γ-rays were 4.76±0.05% and 16.99±0.17%, respectively.     

γ-ray emission probabilities of Os

Precise measurements of disintegration rates by using a 4πβ-γ coincidence apparatus have resulted in improved certainties of the principal γ-ray emission probabilities of ¹⁹³Os. Most of the uncertainties are less than 1%, whereas the uncertainties of emission probabilities evaluated in the Nuclear Data Sheets (83 (1998) 921) are more than 6%. The precision is improved for the β-ray branching ratio for direct transition to the ground state and the value is larger than the evaluated value by about 6%.     

Dissolution of the γ′ phase in a nickel base superalloy at equilibrium and under rapid heating

Dissolution of the γ′ phase in a PM superalloy Astroloy was studied at equilibrium and under rapid heating. The ‘solvus’ temperature of primary and secondary γ′ precipitates was determined experimentally. The most prominent feature concerns the large departure from equilibrium for the dissolution of the γ′ precipitates during rapid heating and this departure depends on the initial size of the precipitates. A model for γ′ dissolution during fast thermal cycling is proposed.     

Practical use of the ‘equivalent’ measured stress intensity factor to control fatigue crack propagation rates in aircraft full-scale fatigue tests—First assessment of the method in testing of a pressurized aircraft fuselage

In the case of circumferential cracks in a cylindrical fuselage, the comparison of some analysis and test results shows that the theoretical stress intensity factor is a suitable correlation parameter of fatigue crack propagation rates, both in aircraft fuselages and in plane panels. Values of the ‘equivalent’ stress intensity factor, computed by applying the Barrois-Bhandari method to slot-opening measurements performed under decreasing loading levels, agree well with the values computed from two dimensional Theory of Elasticity, using the method of finite elements.

In the case of longitudinal cracks, the experimental values of the ‘equivalent’ stress intensity factor, i.e. the stress intensity factor of the infinite plane sheet containing a centre crack with the same elastic strain and stress distributions near the boundary of the plastically strained region around the crack tip, yield a good correlation of fatigue crack propagation rates of the cracked fuselage and of cracked plane structures. The values of the ‘equivalent’ stress intensity factor are lower than those of the theoretical stress intensity factor, the interest of which disappears, but are also far higher than the bidimensionally computed values, which are no longer to be considered.

Some meant of safety provided to limit crack openings will make it possible, in the near future, to investigate test conditions reaching the ultimate residual static strength of cracked structures, while avoiding, however, catastrophic failures.     

Interface structure at the large misfit, still common epitaxy β-FeSi2(101) or (110)//Si(111)

In this paper we compare the elastic energies obtained by tight-binding molecular dynamics simulations for several strained structures of β-FeSi₂, corresponding to the most frequent epitaxial relationships ‘on’ and ‘in’ silicon. Our results confirm that, for coherent interfaces, the very common β-FeSi₂(101) or (110)//Si(111) orientation generates a very large contribution to the elastic energy, due to the large misfit. Therefore, we suggest that the frequent nucleation of such epitaxial relationships in precipitates is provided by the correspondence of the two-dimensional crystal structure for the Si sites between Si(111) and β-FeSi₂(101) or (110). We show it to be maintained even after misfit relaxation in the silicon matrix, as simulated by a large-scale molecular dynamics run.     

γ-CuI晶体的发光衰减时间和对X射线的能量响应

采用溶剂蒸发法生长出透明的带隙宽度为2.96 eV的γ-CuI晶体。在紫外光激发下, 该晶体在410、430 nm处分别呈现有近带边发射峰, 另在720 nm附近还出现一个与样品碘缺陷有关的宽发射带。经碘退火后, 样品720 nm发射带被基本抑制, 而在420 nm处出现了一个更强的近带边发射峰。使用扫描相机分别测量了γ-CuI晶体各发射峰(带)的衰减时间谱, 其中近带边发射峰的发光衰减时间常数均在数十皮秒量级, 表明γ-CuI晶体具有极快的时间响应特性; 而720 nm发射带的发光衰减时间常数主要在数十纳秒量级。X射线激发下, γ-CuI晶体具有435 nm近带边发射峰和680 nm发射带, 其近带边发射对X射线能量响应的测量结果表明, 当E_X<49.1 keV时, γ-CuI晶体闪烁光快分量对X射线的探测效率相对较高。     

Effects of palladium on the thermal behavior of the γ1-phase of the Ag-Sn-Cu dental amalgam

Effects of the addition of 1 weight percent (w/o) palladium on the thermal behavior of a lathe-cut type of high copper amalgam (13 w/o copper) were studied. Two identical alloys, with and without 1 w/o palladium were fabricated. X-ray diffraction studies of these amalgams have revealed the elimination of the γ₂-phase by palladium addition. DSC thermograms of non-palladium-containing alloy indicated the existence of two γ₁-phases, one with the transition temperature at 88 °C and the other at 109 °C. Aging for 18 months at 37 °C cannot eliminate the presence of the γ₁-phase which has a low transition temperature. The addition of 1 w/o palladium into amalgam produced a more thermally stable amalgam.     

Evidence for η6 Coordination to a Fullerene

Evidence for the first η⁶ derivative of a fullerene, [MoC₆₀F₁₈(CO)₃] has been obtained from reaction between [Mo(CH₃CN)₃(CO)₃] and C₆₀F₁₈.     

Color centers and charge state recharge in γ-irradiated Yb:YAP

Gamma-ray irradiation induced color centers and charge state recharge of impurity and doped ion in 10 at.% Yb:YAP have been studied. The change in the additional absorption (AA) spectra is mainly related to the charge exchange of the impurity Fe²⁺, Fe³⁺ and Yb³⁺ ions. Two impurity color center bands at 255 and 313 nm were attributed to Fe³⁺ and Fe²⁺ ions, respectively. The broad AA band centered at 385 nm may be associated with the cation vacancies and F-type center. The transition Yb³⁺ → Yb²⁺ takes place in the process of γ-irradiation. Oxygen annealing and γ-ray irradiation lead to an opposite effect on the absorption properties of the Yb:YAP crystal. In the air annealing process, the transition Fe²⁺ → Fe³⁺ and Yb²⁺ → Yb³⁺ take place and the color centers responsible for the 385 nm band was destroyed.     

Investigation of CdTex and Cd1-xZnxTe Schottky Barrier Diode Structure Based γ-Ray Detectors

Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CdZnTe) based detectors have been developed for hard X-ray and γ -ray detection. These semiconducting materials have high resistivity because of the wide bandgap and also have high photon absorption efficiency because of the large atomic number (Z_Cd = 48, Z_Te = 52). CdTe and CdZnTe substrates (7 mm × 9 mm × 0.5 mm) with different stoichiometry were taken for the fabrication of γ-ray detectors. The substrate was prepared by polishing the bulk crystals grown by the rotational Bridgman method. Crystals with maximum electrical resistivity were grown in this way. For fabrication of Schottky barrier diode structures, the Schottky contacts were made by electroless deposition for gold (Au) and thermal evaporation for Indium (In). The Au/CdTe/In and Au/CdZnTe/In Schottky barrier diodes were linked to the charge sensitive preamplifier by gold wires. Then, I-V measurement and detector efficiency like charge collection performance with energy resolutions were analyzed at room temperature by using ⁵⁷Co and ¹³⁷Cs gamma sources. The good energy resolutions of ⁵⁷Co (122 KeV) and ¹³⁷Cs (662 KeV) sources are obtained for both CdTe and CdZnTe diode detectors.     

石墨烯/环氧树脂复合涂层的γ射线辐照损伤及其腐蚀防护性能

用硅烷偶联剂对石墨烯表面进行修饰, 制备石墨烯/环氧树脂复合涂层。通过交流阻抗(EIS)和塔菲尔极化曲线(Tafel slope)等电化学方法分析复合涂层经伽马射线辐照后的腐蚀防护性能。采用电子自旋共振(ESR)和傅里叶红外光谱分析仪(FTIR)等测试复合涂层的γ射线辐照损伤, 探索了石墨烯在环氧树脂中抗辐照损伤的作用机理。Tafel结果显示复合涂层经280 kGy辐照后, 腐蚀电流为6.140×10^-9 A/cm², 而纯环氧树脂涂层的腐蚀电流则为1.340×10^-8 A/cm², 说明石墨烯可以使复合涂层保持较好的腐蚀防护性能。ESR分析表明, 复合涂层中的石墨烯可以降低环氧树脂基体在γ射线辐照过程中产生的过氧自由基, 表明石墨烯可有效吸收辐照过程中的自由基。辐照前后复合涂层的FT-IR图谱没有发生明显变化, 说明石墨烯有效降低了伽马射线对环氧树脂的结构损伤。因此, 可以认为石墨烯能够减缓环氧树脂在高能辐照环境中的老化, 从而延长其使用寿命。     

γ-NaxCoO2粉体的聚丙烯酸钠凝胶法制备及其表征

本研究发展了一种用于制备氧化物热电材料γ-Na_xCoO₂粉体的化学合成方法——聚丙烯酸钠(PAAS)凝胶法。主要研究了PAAS/Co²⁺摩尔比、原料浓度和煅烧温度对产物相组成及微观形态的影响规律, 探讨了物相形成机制, 同时用该方法结合SPS制备了不同Na离子浓度的Na_xCoO₂多晶样品, 并对其热电性能进行了表征。结果表明, PAAS/Co²⁺摩尔比对产物相组成产生了显著影响, 随着PAAS/Co²⁺摩尔比的增加, 样品的相组成由Co₃O₄相向单相γ-Na_xCoO₂转变, 合适的PAAS/Co²⁺摩尔比为0.8~1.1。而反应原料浓度对产物相组成的影响存在一个临界值(0.025 mol/L), 大于临界值抑制单相形成, 小于临界值促进单相形成。煅烧温度的升高有助于γ-Na_xCoO₂单相的形成, 800℃煅烧得到γ-Na_xCoO₂单相, 晶粒形态呈片状, 平均厚度约200 nm, 片状方向的尺寸在1~4 μm之间。随着Na含量的增加, 样品的Seebeck系数增大, 电导率增加, 热导率降低, 最终导致ZT值大幅增加。     

Analysis of ISE in dynamic hardness measurements of β-Sn single crystals using a depth-sensing indentation technique

The dynamic indentation tests on (001) plane β-Sn single crystals having different growth directions under different peak indentation test load (10, 20, 30, 40, and 50 mN) has been investigated. The experimental results reveal that the measured hardness values exhibit a peak-load dependence, i.e., indentation size effect (ISE). Such peak-load dependence is then analyzed using the Meyer's law, the Hays–Kendall's approach, the Elastic/Plastic Deformation model, the Proportional Specimen Resistance (PSR) model, and the Modified PSR (MPSR) model. As a result, Modified PSR model is found to be the most effective for dynamic hardness determination of β-Sn single crystals.     

Photoreflectance study of δ-doped semiconductor layers by a fast Fourier transformation

Photoreflectance (PR) spectroscopy has been applied to the investigation of Si δ-doped GaAs, Al_0.35Ga_0.65As and AlAs layers grown by metal–organic vapor phase epitaxy (MOVPE) on GaAs substrates. The observation of Franz–Keldysh oscillations (FKO) and the application of fast Fourier transform (FFT) has allowed us to determine the internal electric field and, hence, the potential barrier between surface and δ-doped region of the layer. The FFT of the photoreflectance spectra has exhibited two separate heavy and light hole frequencies showing that the FKO in the PR signal are always the superposition of these two components.     

Calculation of efficiency functions in 4π β-γ counting

An attempt is made to calculate an efficiency function applicable to 4πβ-γ coincidence measurements as the first stage of evaluating the order of the polynomial of the fitting function. For this purpose, the β-ray energy spectra and self-absorptions of spherical particle sources are calculated by the Monte Carlo simulation under the continuous slowing down approximation. On the other hand, it is shown that three sets of absorption coefficients and partial intensity ratios corresponding to a β-ray group give analytically the self-absorption for the same particle sources. Finally, we show that the efficiency functions applicable to ⁵⁹Fe and ¹³⁴Cs are easily obtained by using the energy spectra or self-absorptions.     

The Dislocation Structure of a Single-Crystal γ + γ′ Two-Phase Alloy After Tensile Deformation

The dislocation structures of an industrial single-crystal γ + γ′ two-phase alloy DD3 after tensile deformation from room temperature to 1273K were studied by transmission electron microscopy. The strength of this alloy decreased with an increase in the temperature, and showed a strength peak at 1033K. At room temperature, the dislocations shearing the γ′ particles were found to be 1/3<112> partial dislocations on the dodecahedral slip system <112>{111}. Some dislocation pairs on the cubic <110>{100} system that blocked the glide of dislocations were found at a medium temperature of 873K. As a result, dislocation bands were formed. Shearing of γ′ particles by 1/3<112> partial dislocations on the dodecahedral slip system <112>{111} was also found at this temperature. At the peak temperature of 1033K, because of the strong interaction between dislocations on the {111} and {100} planes, the extent of dislocation bands with high dislocation densities was extensive. The 1/3<112> partial dislocations on the dodecahedral slip system <112>{111} also existed. When the temperature reached the high temperature of 1133K, the range of dislocation bands was limited. The γ′ particles were sheared by <110> dislocation pairs on the octagonal <110>{111} system and the cubic <110>{100} system. At 1273K, the regular hexagonal dislocation networks were formed in the γ matrix and at the γ/γ′ interface. The Burgers vectors of the network were found to be b₁ = 1/2[110], b₂ = 1/2[1–10], b₃ = [100], and the last one was formed by the reaction of b₁ + b₂ → b₃. Dislocations shearing the γ′ particles were found to be <110> dislocation pairs on the octagonal system <110>{111} and cubic slip system <110>{100} at 1273K.     

CaO-B2O3玻璃助烧的零膨胀系数β-锂霞石陶瓷的制备及性能研究

采用固相反应法制备CaO-B₂O₃玻璃（简称“CB”玻璃）助烧的零膨胀系数β-锂霞石陶瓷。通过差示扫描量热(DSC)、X射线衍射(XRD)、扫描电子显微镜(SEM)手段分别对CB玻璃的热学特性和助烧后的β-锂霞石陶瓷样品的物相与显微形貌进行表征。结果表明, CB玻璃具有良好的助烧效果, 可以显著降低β-锂霞石陶瓷的烧结温度(从1300℃降至1150℃), 并大幅提高陶瓷的相对密度(从93.3%提高到97.4%)。加入CB玻璃助烧剂, β-锂霞石陶瓷致密性显著提高, 内部无微裂纹存在。加入4wt%和6wt% CB玻璃的β-锂霞石陶瓷在室温~200℃范围内具有零膨胀系数, 分别为0.02×10^-6/K和0.4×10^-6/K。然而, 加入8wt% CB玻璃的β-锂霞石陶瓷样品中产生了具有高正膨胀系数的新物相LiAlO₂, 使样品的热膨胀系数提高至3.46×10^-6/K。     

Characteristics of a γ-radiation monitor utilizing solar cells

We have examined the characteristics of solar cells from the standpoint of developing a γ-radiation monitor. This study was performed using a test monitor (TM) manufactured from two monocrystalline-type silicon solar cells coupled to a CsI(Tl) scintillation crystal. The angular and temperature characteristics of current generation were examined using a high-intensity ⁶⁰Co γ-source. Subsequently, the test monitor was used for checking of transfer operations of spent nuclear fuels. The results obtained by the test monitor utilizing solar cells were better than expected: (a) It is very simple in construction, and (b) it exhibits a good response to high-intensity γ-radiation, and (c) it works without an electric power supply.