Three dimensional virtual crack closure-integral method (VCCM) with skewed and non-symmetric mesh arrangement at the crack front

In this paper, an extension of virtual crack closure-integral method (VCCM) for three dimensional linear fracture mechanics analysis using hexahedron finite elements is presented. In conventional three dimensional VCCM, there are some inherent requirements on the finite element model. They are (i) the faces of finite elements across the crack front have the same areas and (ii) they must be arranged symmetrically across the crack front. In present study, we developed a three dimensional VCCM without such requirements by considering work required to open one element face area whose shape is arbitrary. Though we assume the use of an ordinary 20 node serendipity element, present approach can be applied to other types of hexahedron elements.     

Edge cracks in a transversely isotropic hollow cylinder

The analytical solution for the linear elastic, axisymmetric problem of inner and outer edge cracks in a transversely isotropic infinitely long hollow cylinder is considered. The z = 0 plane on which the crack lies is a plane of symmetry. The loading is uniform crack surface pressure. The mixed boundary value problem is reduced to a singular integral equation where the unknown is the derivative of the crack surface displacement. An asymptotic analysis is done to derive the generalized Cauchy kernel associated with edge cracks. It is shown that the stress intensity factor is a function of three material parameters. The singular integral equation is solved numerically. Stress intensity factors are presented for various values of material and geometric parameters.     

Structural shape optimization using equivalent static loads transformed from dynamic loads

In structural optimization, static loads are generally utilized although real external forces are dynamic. Dynamic loads have been considered only in small‐scale problems. Recently, an algorithm for dynamic response optimization using transformation of dynamic loads into equivalent static loads has been proposed. The transformation is conducted to match the displacement fields from dynamic and static analyses. This algorithm can be applied to large‐scale problems. However, the application has been limited to size optimization. The present study applies the algorithm to shape optimization. Because the number of degrees of freedom of finite element models is usually very large in shape optimization, it is difficult to conduct dynamic response optimization with conventional methods that directly treat dynamic response in the time domain. The optimization process is carried out by interfacing an optimization system and an analysis system for structural dynamics. Various examples are solved to verify the algorithm. The results are compared to the results from static loads. It is found that the algorithm using static loads transformed from dynamic loads based on displacement is valid for very large‐scale shape optimization problems. Copyright © 2005 John Wiley & Sons, Ltd.     

Long‐term Reliability Prediction of 935 nm LEDs Using Failure Laws and Low Acceleration Factor Ageing Tests

Numerous papers have already reported various results on electrical and optical performances of GaAs‐based materials for optoelectronic applications. Other papers have proposed some methodologies for a classical estimation of reliability of GaAs compounds using life testing methods on a few thousand samples over 10 000 hours of testing. In contrast, fewer papers have studied the complete relation between degradation laws in relation to failure mechanisms and the estimation of lifetime distribution using accelerated ageing tests considering a short test duration, low acceleration factor and analytical extrapolation. In this paper, we report the results for commercial InGaAs/GaAs 935 nm packaged light emitting diodes (LEDs) using electrical and optical measurements versus ageing time. Cumulative failure distributions are calculated using degradation laws and process distribution data of optical power. A complete methodology is described proposing an accurate reliability model from experimental determination of the failure mechanisms (defect diffusion) for this technology. Electrical and optical characterizations are used with temperature dependence, short‐duration accelerated tests (less than 1500 h) with an increase in bias current (up to 50%), a small number of samples (less than 20) and weak acceleration factors (up to 240). Copyright © 2005 John Wiley & Sons, Ltd.     

Cracked Brazilian disc specimen subjected to mode II deformation

The centrally cracked Brazilian disc specimen has been used by many researchers to study mode I and mode II brittle fracture in different materials. However, the experimental results obtained in the past from this specimen indicate that the fracture toughness ratio (K_IIc/K_Ic) is always significantly higher than the theoretical predictions. It is shown in this paper that the increase in the ratio K_IIc/K_Ic can be predicted if a modified maximum tangential stress (MTS) criterion is used. The modified criterion takes into account the effect of T-stress in addition to the conventional singular stresses. The fracture toughness ratio K_IIc/K_Ic is calculated for two brittle materials using the modified criterion and is compared with the relevant published experimental results obtained from fracture tests on the cracked Brazilian disc specimen. A very good agreement is shown to exist between the theoretical predictions and the experimental results.     

四氟硼酸二芳基碘鎓盐的合成及其表征

本文合成了四氟硼酸二芳基碘鎓盐阳离子紫外光引发剂，并且从红外、核磁、紫外光谱以及熔点测定进行了表征。结果表明，该合成方法的产率达58%，接近国外文献报道产率。     

高等院校师生道德失范的成因及对策

近几年来，由于社会环境因素和高等院校内部自身的原因，在部分教师和学生中存在着道德失范问题。要解决高等院校师生的道德失范问题，必须从内、外两个方面着手，紧紧抓住以德育人这一中心，加强法制建设和思想政治教育，从制度上规范广大师生的道德行为，使高等院校的道德建设取得令人满意的成果。     

城市污水生物除磷脱氮系统剩余污泥量的计算

剩余污泥量的计算是活性污泥法工艺设计的关键，而活性污泥法是同时生物除磷脱氮的主体工艺形式，因此，准确计算生物除磷脱氮系统的剩余污泥量十分必要。结合昆明市污水处理厂的运行实际。分析比较了传统计算法、污泥龄法和数学模型法在计算城市污水生物除磷脱氮系统剩余污泥量时的准确性，建议现阶段采用污泥龄法进行计算，提出修正系数K(0．75-1)与具体工艺形式有关，并给出K的几个建议值，同时指出数学模型法（ASM2）应是发展方向．     

并联型有源电力滤波器的控制

分析了并联型有源电力滤波器的常规控制方法，提出了并联型有源电力滤波器的新的控制策略及具体的控制方法，并对所提出的控制方法进行了计算机仿真，仿真结果证明了该方法的正确性。以80C196MC单片机为核心，设计了一套实验装置，实验结果证实了该方法在实际中的可行性以及并联型有源电力滤波器所具有的良好的补偿特性。     

焦化原料的表征与延迟焦化性能

研究了锦州石化分公司两种焦化原料样品及自制焦化循环油的基本性质及分子结构,采用实验室微型反应釜考察了这些试样的延迟焦化性能。结果表明,虽然两种焦化原料的性质相差较大,如残炭质量分数分别为17.3%和20.1%、沥青质分别为1.9%和5.6%,但是它们的平均结构参数比较接近,60%～80%的硫氮原子富集在胶质组分中。另一方面,锦州焦化原料的密度、残炭、灰分、金属质量分数都显著高于国内熟知的孤岛减压渣油,而硫质量分数较低,约为后者的10%;尽管循环油的性质总体优于焦化原料,但是其沥青质质量分数高于相应焦化原料的沥青质质量分数、残炭也占两种焦化原料残炭的20%以上。延迟焦化性能考察表明,温度和焦化原料都可影响产物分布,高温有利于增加液收、提高柴汽比、降低焦中硫质量分数,而焦化原料与焦化循环油的共焦化可抑制焦炭增加液收。