Bending of a Plate with Two Identical Collinear Rectilinear Cracks According to the Theory of Reissner

Within the framework of the theory of Reissner, we study the problem of bending of an isotropic plate of constant thickness with two identical cracks located on the same line under the assumption that a self-balanced load (bending moments) is applied to the crack lips. By using the methods of the theory of functions of complex variable, we reduce the solution of the problem to a system of singular integral equations and solve this system numerically (by the method of mechanical quadratures). We also perform the numerical analysis of the stress intensity factors whose values, for some special cases, coincide with the data available from the literature.     

压电介质夹杂功能梯度压电带界面双裂纹反平面问题

利用积分方程方法,本文研究了夹在两个均匀压电半空间的功能梯度压电带界面共线双裂纹的反平面问题。在电渗透型边界条件下,通过Fourier余弦变换将所考虑的问题化为一对偶积分方程,再用Copson方法将该对偶积分方程转化为Fredholm方程进行数值求解,从而给出了裂纹尖端的应力强度因子,电位移强度因子的表达式。分析了裂纹长度,功能梯度非均匀参数以及材料的几何尺寸等对应力强度因子的影响。     

Elastodynamic Problem for Two Penny-Shaped Cracks: The Effect of Cracks’ Closure

The paper is devoted to the solution of the three-dimensional elastodynamic problem for linearly elastic, homogeneous and isotropic solid with two penny-shaped in-plane cracks under normally incident harmonic tension-compression wave with allowance for the contact interaction of crack faces. The effect of the distance between cracks on the stress intensity factor (opening mode) is studied for different wave numbers. The results are compared with those obtained neglecting the cracks’ closure.     

Stabilizing Energy Consumption in Unequal Clusters of Wireless Sensor Networks

In the past few decades, Energy Efficiency (EE) has been a significant challenge in Wireless Sensor Networks (WSNs). WSN requires reduced transmission delay and higher throughput with high quality services, it further pays much attention in increased energy consumption to improve the network lifetime. To collect and transmit data Clustering based routing algorithm is considered as an effective way. Cluster Head (CH) acts as an essential role in network connectivity and perform data transmission and data aggregation, where the energy consumption is superior to non-CH nodes. Conventional clustering approaches attempts to cluster nodes of same size. Moreover, owing to randomly distributed node distribution, a cluster with equal nodes is not an obvious possibility to reduce the energy consumption. To resolve this issue, this paper provides a novel, Balanced-Imbalanced Cluster Algorithm (B-IBCA) with a Stabilized Boltzmann Approach (SBA) that attempts to balance the energy dissipation across uneven clusters in WSNs. BIBCA utilizes stabilizing logic to maintain the consistency of energy consumption among sensor nodes’. So as to handle the changing topological characteristics of sensor nodes, this stability based Boltzmann estimation algorithm allocates proper radius amongst the sensor nodes. The simulation shows that the proposed B-IBCA outperforms effectually over other approaches in terms of energy efficiency, lifetime, network stability, average residual energy and so on.     

一维六方压电准晶中带三条不对称裂纹的圆形孔口的反平面问题

本文利用复变函数方法和保角映射,研究一维六方压电准晶材料中带不对称三裂纹的圆形孔口的的断裂问题。根据准晶压电材料基本方程的基础上,利用点群的对称性和一维六方准晶的线性压电效应,导出了一维六方准晶压电材料反平面问题的控制方程,并结合Cauchy积分公式,得到电非渗透与电渗透边界条件下的裂纹尖端场强度因子的解析表达式。当改变裂纹长度和孔口半径时,所得结果可以模拟出一些新裂纹模型。在不考虑电载荷作用时,所得结果和原有结果是一致的。通过数值算例讨论了材料的几何参数对场强度因子的影响,得出水平裂纹长度和圆半径可以促进裂纹增长。本研究为工程中材料的制备与应用将提供可靠的理论价值。     

Energy Analysis for Permeable and Impermeable Cracks in Piezoelectric Materials

This letter deals with an energy analysis for both permeable and impermeable cracks in piezoelectric materials. Computed numerical results are plotted in figures, which support Park-Sun's conclusion (1995a,b) that the total energy release rate (TERR) involving both mechanical and electric parts is not suitable to describe piezoelectric fracture for a plane impermeable crack because the two parts have different signs: the former is positive and the latter is always negative under any kinds of combined mechanical-electric loading. This provides the major reason as why the mechanical part (the mechanical strain energy release rate, MSERR) must be used as a fracture criterion empirically. Whereas the electric part of the TERR for a permeable crack does always vanish whatever the poling direction is oriented with respect to the remote electric loading direction. This finding supports McMeeking's (1990, 1999) conclusion that the TERR could be used as a fracture criterion for permeable cracks.     

双裂纹转子振动特性的有限元和实验研究

转子裂纹是旋转机械常见故障,目前对转子复合裂纹的研究尚不够深入。本文运用有限元方法对具有两条横向裂纹的转子系统动力学特性进行仿真分析,研究了不同裂纹夹角的转子动力学行为,得到转动过程中两条裂纹开闭的关系。与实验结果对比,验证了模拟的有效性。     

Calculation of J 1 and J 2 using the L and M integrals

Path-independent integrals of linear plane elasticity are treated analytically and numerically. The application of the integrals and their physical significance in terms of energy-release rates are illustrated with a closed-form solution of the hole-dislocation-interaction problem. It is shown that the use of the L and M integrals, desides J ₁ and J ₂, is beneficial to the numerical investigation of cracks under mixed-mode conditions.

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Résumé On traite par voie analytique et par voie numérique les intégrales indépendantes du parcours relatives à Relasticité plane et linéaire.L'application des intégrales et leur signification physique par rapport aux vitesses de relaxation de l'énergie, sont allistrées par une solution sous forme fermée du problème de l'interaction entre une lacune et une dislocation.On montre que l'emploi des intégrales L et M en plus de J ₁ et J ₂ est propice à l'étude numérique des fissures allistrées sous des conditions de mode mixte de sollicitation.

     

The Two Energy Scales of Tunneling Spectra of Cuprate Superconductors

The atomically resolved energy gap Δ(r) measured by Scanning Tunneling Microscopy has become a major challenge connecting to the nature of electronic states in cuprates superconductors. More recently, a two-energy-gap structure has been observed by many different experiments. We show that it is possible that the charge inhomogeneity gives rise to a potential barrier between the microscopic regions or grains that are the origin of these gaps. A larger Δ(r) is due to the single-particle bound states and the same potential gives rise to a smaller superconducting gap Δ _d (r). These results support the two-gap scenario and give a clear interpretation to the pseudogap phase.     

心脏除颤器释放能量100J以上量值不确定度评定

文章讲述心脏除颤器释放能量100J以上量值不确定度评定,给出结果。     

S355J2钢板表面裂纹分析

针对南钢中厚板卷厂生产的S355J2钢板表面出现裂纹缺陷,采用光学显微镜、扫描电镜和能谱仪进行了分析。结果表明,裂纹具有沿钢板纵向延伸且深度很小的规律性,裂纹产生的原因主要是Nb元素的碳氮化物表面偏聚所致,通过进行微钛处理成分设计并结合优化连铸工艺,可有效改善S355J2钢板表面裂纹问题。     

低周疲劳表面裂纹演化进程分析

低周疲劳表面裂纹演化可能具有非线性动力学特征。对 1Cr18Ni9Ti光滑试样进行了低周疲劳实验 ,在对裂纹进行分类的基础上 ,将裂纹演化划分为多裂纹相互作用和局域主裂纹控制两个阶段。从非线性动力学角度给出了短裂纹的新的定义。指出裂纹演化两个阶段对材料疲劳损伤破坏过程的贡献。     

论洁净空调空气处理过程中的两种节能措施

介绍了洁净空调空气处理过程中两种节能措施,同时联系实际工程和研究数据对传统的空气调节模式和采取节能措施后进行了比较,节能效果比较明显,对这些办法和成果在实际中的运用给予了讨论和展望。     

The Interaction between Microcapsules with Different Sizes and Propagating Cracks

The microcapsule-contained self-healing materials are appealing since they can heal the cracks automatically and be effective for a long time. Although many experiments have been carried out, the influence of the size of microcapsules on the self-healing effect is still not well investigated. This study uses the two-dimensional discrete element method (DEM) to investigate the interaction between one microcapsule and one microcrack. The influence of the size of microcapsules is considered. The potential healing time and the influence of the initial damage are studied. The results indicate that the coalescence crack is affected by the size of holes. The elastic modulus, the compressive strength and the coalescence stress decrease with the rising radius of holes. The initial damage in experiments should be greater than 95% of the compressive strength to enhance the self-healing effect. The large microcapsules require slight initial damage. Both a new type of displacement field near the crack and a new category of coalescence crack are observed. The influence of sizes of holes on the cracking behavior of concrete with a circular hole and a pre-existing crack is clarified.     

Failure Analysis of Cracks Formed at Extrados of Bend Pipe of API 5L X65M Grade

A metallurgical and root cause analysis was performed on hot induction bent pipes that exhibited cracking at the extrados. The bent pipe of 1016 mm (40 in.) diameter by 18.5 mm wall thickness was API 5L X65 PSL2 line pipe containing a longitudinal submerged arc weld. A metallurgical cross section was removed at a crack on the bent pipe extrados to document the crack morphology using optical microscopy. In addition to the cracking, golden-yellow streaks were visible at the extrados of the bent pipe. The composition of the streaks was examined using scanning electron microscopy with energy dispersive spectroscopy.     

On the Elastic Compliance of a Circular Hole with Two Symmetric Radial Cracks Initiated at its Boundary

A circular hole with two symmetric rectilinear radial cracks initiated at its boundary is analyzed from the point of view of its elastic compliance (contribution to the overall elastic properties of a representative volume). Results are obtained using Rice’s connection between stress intensity factor and effect of a crack on the elastic properties of a material. We compare our result with that for a combine contribution of noninteracting circular pore and a rectilinear crack to show when this combination can be used for approximation of the elastic compliance contribution.     

Three Improvements in Reduction and Computation of Elliptic Integrals

Three improvements in reduction and computation of elliptic integrals are made. 1. Reduction formulas, used to express many elliptic integrals in terms of a few standard integrals, are simplified by modifying the definition of intermediate “basic integrals.” 2. A faster than quadratically convergent series is given for numerical computation of the complete symmetric elliptic integral of the third kind. 3. A series expansion of an elliptic or hyperelliptic integral in elementary symmetric functions is given, illustrated with numerical coefficients for terms through degree seven for the symmetric elliptic integral of the first kind. Its usefulness for elliptic integrals, in particular, is important.     

Theory of Passive Mode Locking of a Laser Having Two Laser Amplifiers of Unequal Relaxation Time with a Slow Saturable Absorber

This paper presents a closed-form solution for the pulses of a laser having two homogeneously broadened laser amplifiers of unequal relaxation time mode locked by a ‘slow’ saturable absorber. The pulse shape is found to be secant-hyperbolic. It is found that the gains of both amplifiers participate in time-modulating the pulse and that the pulses are bandwidth-limited by the amplifier with a relaxation time longer than the cavity round-trip time. We have also shown that the model of a ‘slow’ saturable absorber and an amplifier of relaxation time longer than the cavity round-trip time does not give self-starting, mode-locking solutions.