Numerical Analysis of Crack Propagation Path Using an Advanced Element Cracking Method

The determination of the crack path is important for predicting the unexpected failures or assessing fatigue life in engineering material. To simulate the crack path under mixed mode loading using a finite element model, a new local element cracking technique was proposed. The waiting cracking element was divided into two units along crack propagation direction based on the maximum circumference ( 0) KII criterion. Then, the information of element number and nodal number was also modified and singular elements were avoided by the transfixion method. With advantages of small remeshing only on a local region, this method also examined three classic problems of stationary crack growth, i.e., edge crack propagation in double cantilever beam, mode I cracking in an asphalt concrete beam, a crack in typical longitudinal connection of large natural gas carriers. The calculated stress intensity factors and the predicted crack trajectories using this method agree well with the theoretical solutions existing in literature. Optimal design of structure against failure by fast fracture is discussed.Определение траектории трещины является важным при прогнозировании непредвиденного разрушения или при оценке усталостной долговечности конструкционного материала. Предложен новый метод моделирования траектории локальной трещины при нагружении смешанного типа с помощью модели, основанной на методе конечных элементов. Элемент, моделирующий трещину, разбивают на два вдоль распространения трещины с использованием критерия максимальных касательных напряжений (KII 0). Затем изменяется информация о номерах элемента и узла, поскольку метод трансфикции исключает использование сингулярных элементов. Преимущества незначительного перестроения конечноэлементной сетки только в локальной зоне позволили исследовать с помощью предложенного метода три классические проблемы роста стационарной трещины, т.е. распространение краевой трещины в двухконсольной балке, моделирование трещинообразования в асфальтобетонных балках и трещина в стандартном продольном соединении в газопроводе. Расчетный коэффициент интенсивности напряжений и траектория трещины, спрогнозированная с помощью описанного метода, хорошо соответствуют теоретическим данным, представленным в литературных источниках. Рассмотрена оптимальная конструкция структуры, которой несвойственно быстрое разрушение.Визначення траєкторії тріщини є важливим при прогнозуванні непередбачуваного руйнування або при оцінці довговічності від утомленості конструкційного матеріалу. Запропоновано новий метод моделювання траєкторії локальної тріщини під час навантаження змішаного типу за допомогою моделі, що базується на методі скінченних елементів. Елемент, що моделює тріщину, розбивають на два вздовж поширення тріщини з використанням критерію максимальних дотичних напружень ( ). KII 0 Далі змінюється інформація щодо номерів елемента і вузла, оскільки метод трансфікції виключає використання сингулярних елементів. Переваги незначної перебудови скінченноелементної сітки тільки в локальній зоні дозволили за допомогою запропонованого методу дослідити три класичні проблеми росту стаціонарної тріщини: поширення краєвої тріщини в двоконсольній балці, моделювання тріщиноутворення в асфальтобетонних балках і тріщина в стандартному поздовжньому з’єднанні у газопроводі. Розрахунковий коефіцієнт інтенсивності напружень і траєкторія тріщини, спрогнозована за допомогою описаного методу, добре відповідають теоретичним даним, представленим у літературних джерелах. Розглянуто оптимальну конструкцію структури, якій невластиве швидке руйнування

Effects of metallic spacer in layered superconducting Sr2(Mgy_yTi1−y_{1-y})O3FeAs

The highly two-dimensional superconducting system Sr2(Mg$_y$Ti$_{1-y}$)O3FeAs, recently synthesized in the range of 0.2 < y < 0.5, shows an Mg concentration-dependent $T_c$. Reducing the Mg concentration from y=0.5 leads to a sudden increase in $T_c$, with a maximum $T_c$ ~40 K at y=0.2. Using first principles calculations, the unsynthesized stoichiometric y=0 and the substoichiometric y=0.5 compounds have been investigated. For the 50% Mg-doped phase (y=0.5), Sr2(Mg$_y$Ti$_{1-y}$)O3 layers are completely insulating spacers between FeAs layers, leading to the fermiology such as that found for other Fe pnictides. At y=0, representing a phase with metallic Sr2TiO3 layers, the $\Gamma$-centered Fe-derived Fermi surfaces (FSs) considerably shrink or disappear. Instead, three $\Gamma$-centered Ti FSs appear, and in particular two of them have similar size, like in MgB2. Interestingly, FSs have very low Fermi velocity in large fractions: the lowest being 0.6$\times10^6$ cm/s. Furthermore, our fixed spin moment calculations suggest the possibility of magnetic ordering, with magnetic Ti and nearly nonmagnetic Fe ions. These results indicate a crucial role of Sr2(Mg$_y$Ti$_{1-y}$)O3 layers in this superconductivity.Comment: 7 pages; Proceedings of ICSM-201

Measurements of the observed cross sections for exclusive light hadron production in e^+e^- annihilation at \sqrt{s}= 3.773 and 3.650 GeV

By analyzing the data sets of 17.3 pb$^{-1}$ taken at $\sqrt{s}=3.773$ GeV and 6.5 pb$^{-1}$ taken at $\sqrt{s}=3.650$ GeV with the BESII detector at the BEPC collider, we have measured the observed cross sections for 12 exclusive light hadron final states produced in $e^+e^-$ annihilation at the two energy points. We have also set the upper limits on the observed cross sections and the branching fractions for $\psi(3770)$ decay to these final states at 90% C.L.Comment: 8 pages, 5 figur

Experimental determination and thermodynamic calculation of the phase equilibria in the Cu-Cr-Nb and Cu-Cr-Co systems

通讯作者地址: Wang, CP (通讯作者), Xiamen Univ, Coll Mat, Dept Mat Sci & Engn, 422 Siming S Rd, Xiamen 361005, Peoples R China 地址: 1. Xiamen Univ, Coll Mat, Dept Mat Sci & Engn, Xiamen 361005, Peoples R China 2. Xiamen Univ, Res Ctr Mat Design & Applicat, Xiamen 361005, Peoples R China 3. Tohoku Univ, Grad Sch Engn, Dept Mat Sci, Sendai, Miyagi 9808579 Japan 电子邮件地址: [email protected] equilibria in the Cu-Cr-Nb and Cu-Cr-Co systems were, respectively, determined by metallography, X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray (SEM-EDX) techniques. The thermodynamic assessments of the Cu-Cr-Nb and Cu-Cr-Co systems were carried out by using CALPHAD (CALculation of PHAse Diagrams) method on the basis of the experimental data measured by the present and previous works. The Gibbs free energies of the liquid and solid solution phases were described by the subregular solution model, and those of intermetallic compounds were described by the sublattice model. A consistent set of the thermodynamic parameters has been obtained, and the evaluated thermodynamic parameters lead to a better fit between calculated results and experimental data in both the Cu-Cr-Nb and Cu-Cr-Co systems. (C) 2008 Elsevier B.V. All rights reserved.National Natural Science Foundation of China 50425101 50771088 Ministry of Education, PR China 20050384003 707037 Core Research for Evolutional Science, and Technology (CREST) Japan Science and Technology Agency (JST

Search for the Rare Decays J/Psi --> Ds- e+ nu_e, J/Psi --> D- e+ nu_e, and J/Psi --> D0bar e+ e-

We report on a search for the decays J/Psi --> Ds- e+ nu_e + c.c., J/Psi --> D- e+ nu_e + c.c., and J/Psi --> D0bar e+ e- + c.c. in a sample of 5.8 * 10^7 J/Psi events collected with the BESII detector at the BEPC. No excess of signal above background is observed, and 90% confidence level upper limits on the branching fractions are set: B(J/Psi --> Ds- e+ nu_e + c.c.)<4.8*10^-5, B(J/Psi --> D- e+ nu_e + c.c.) D0bar e+ e- + c.c.)<1.1*10^-5Comment: 10 pages, 4 figure

Measurements of psi(2S) decays to octet baryon-antibaryon pairs

With a sample of 14 million psi(2S) events collected by the BESII detector at the Beijing Electron Positron Collider (BEPC), the decay channels psi(2S)->p p-bar, Lambda Lambda-bar, Sigma0 Sigma0-bar, Xi Xi-bar are measured, and their branching ratios are determined to be (3.36+-0.09+-0.24)*10E-4, (3.39+-0.20+-0.32)*10E-4, (2.35+-0.36+-0.32)*10E-4, (3.03+-0.40+-0.32)*10E-4, respectively. In the decay psi(2S)->p p-bar, the angular distribution parameter alpha is determined to be 0.82+-0.17+-0.04.Comment: 8 pages, 8 figure

Partial wave analysis of J/\psi \to \gamma \phi \phi

Using $5.8 \times 10^7 J/\psi$ events collected in the BESII detector, the radiative decay $J/\psi \to \gamma \phi \phi \to \gamma K^+ K^- K^0_S K^0_L$ is studied. The $\phi\phi$ invariant mass distribution exhibits a near-threshold enhancement that peaks around 2.24 GeV/$c^{2}$. A partial wave analysis shows that the structure is dominated by a $0^{-+}$ state ($\eta(2225)$) with a mass of $2.24^{+0.03}_{-0.02}{}^{+0.03}_{-0.02}$ GeV/$c^{2}$ and a width of $0.19 \pm 0.03^{+0.06}_{-0.04}$ GeV/$c^{2}$. The product branching fraction is: $Br(J/\psi \to \gamma \eta(2225))\cdot Br(\eta(2225)\to \phi\phi) = (4.4 \pm 0.4 \pm 0.8)\times 10^{-4}$.Comment: 11 pages, 4 figures. corrected proof for journa

Measurements of the observed cross sections for e+e−→e^+e^-\to exclusive light hadrons containing π0π0\pi^0\pi^0 at s=3.773\sqrt s= 3.773, 3.650 and 3.6648 GeV

By analyzing the data sets of 17.3, 6.5 and 1.0 pb$^{-1}$ taken, respectively, at $\sqrt s= 3.773$, 3.650 and 3.6648 GeV with the BES-II detector at the BEPC collider, we measure the observed cross sections for $e^+e^-\to \pi^+\pi^-\pi^0\pi^0$, $K^+K^-\pi^0\pi^0$, $2(\pi^+\pi^-\pi^0)$, $K^+K^-\pi^+\pi^-\pi^0\pi^0$ and $3(\pi^+\pi^-)\pi^0\pi^0$ at the three energy points. Based on these cross sections we set the upper limits on the observed cross sections and the branching fractions for $\psi(3770)$ decay into these final states at 90% C.L..Comment: 7 pages, 2 figure

Direct Measurements of Absolute Branching Fractions for D0 and D+ Inclusive Semimuonic Decays

By analyzing about 33 $\rm pb^{-1}$ data sample collected at and around 3.773 GeV with the BES-II detector at the BEPC collider, we directly measure the branching fractions for the neutral and charged $D$ inclusive semimuonic decays to be $BF(D^0 \to \mu^+ X) =(6.8\pm 1.5\pm 0.7)$ and $BF(D^+ \to \mu^+ X) =(17.6 \pm 2.7 \pm 1.8)$, and determine the ratio of the two branching fractions to be $\frac{BF(D^+ \to \mu^+ X)}{BF(D^0 \to \mu^+ X)}=2.59\pm 0.70 \pm 0.25$