Application of system reliability‐based assessment for collapse fragility of braced moment‐resisting frames

This paper presents a system reliability‐based framework for collapse fragility assessment of steel braced moment‐resisting frames (BMRFs). The conditional failure of intermediate events is calculated, considering two important features in the design of BMRFs: (i) different failure scenarios (FSs) with multiple sequences of components failure formation and (ii) structural reliability analysis based on the failure propagation from components to system. The system collapse reliability‐based assessment of BMRFs is developed with an efficient algorithm using the Monte Carlo simulation procedure incorporated into a nonlinear finite element (FE) analysis program. An appropriate nonlinear FE model of such systems is demonstrated, and the probability of various predefined components' failure over the most likely FSs in the presence of both epistemic and inherent uncertainties is calculated. Then, a system‐simulated reliability index (SSRI) is computed by lower and upper bounds in the probability of BMRF system collapse. Finally, fragility curves based on the SSRI is compared with the ones from incremental dynamic analysis, and later, the outcomes from multiple FSs are compared with the codified main collapse criterion. For the BMRFs analyzed herein, it is shown that the existing allowable story drift for the collapse limit state is conservative, and a new criterion is appraised. Copyright © 2015 John Wiley & Sons, Ltd.     

宜兴抽水蓄能电站高重力挡墙稳定性综合评价

 受地形地质条件所限，宜兴抽水蓄能电站上库主坝为一修建在斜坡上的土石坝与高重力挡墙联合作用构成的混合坝型，这种坝型为国内外较少见，高45.9 m的重力挡墙在国内外也十分少有。高挡墙在土石坝堆石的强大推力作用下，如何在斜坡上保持稳定，一直为各方所关注。根据监测资料和三维有限元数值分析结果，得到作用在高重力挡墙后的土压力大小及其分布规律，确定典型剖面上土压力的作用位置和作用方向，验证太沙基关于挡墙后土压力不是作用在传统认为的下三分点，而是作用在0.4倍左右墙高位置的论断。在此基础上，根据设计和有关规范要求分析了高重力挡墙在水库运行条件下的抗滑、抗倾稳定安全度，同时，结合挡墙及其地基的内、外部变形和受力监测资料，对高重力挡墙的稳定性做出综合评价。     

基于数值模拟技术的轿车零件成形工艺优化设计

采用有限元数值模拟技术,对轿车结构零件的拉延成形过程进行了模拟分析.对影响拉延成形质量的工艺参数进行了优化,着重优化了板料的形状和零件形面.通过对FLD图和成形结果的分析,得到了板料的形状和零件形面.最终将优化后的模拟结果与实际生产出来的拉延件结果进行了对比.验证了数值模拟的有效性.     

Experiment and FEA of impact resistance of CFST columns with circular cross-section

为研究钢管混凝土柱在侧向冲击荷载作用下的受力性能,通过对圆钢管混凝土柱进行横向落锤冲击试验,获得柱在冲击荷载作用下的破坏形态、整体变形和应变分布规律,分析了冲击力和试件跨中挠度时程曲线的特征;并通过有限元分析,研究了钢材和混凝土强度等参数对圆钢管混凝土柱力学性能的影响。研究结果表明：在试验参数范围内,随着冲击能量的增加,试件冲击力峰值、跨中挠度峰值、冲击持续时间增加;含钢率较大试件的冲击力峰值和冲击力平台值较大,跨中挠度峰值较小、冲击持续时间较短;钢材屈服强度对试件抗冲击性能的影响较大,而混凝土抗压强度对试件抗冲击性能的影响则相对较小。     

Structure characterization of switched Ag – metal oxide contact materials

The structural changes of several Ag ‐ metal oxide composites during switching operations were investigated. During the switching operation the contact material is melting and for a short moment (ca.10 ms) the metal oxide particles will be floating in the liquid silver resulting in structural changes. These processes affect the switching performance of contact materials and shall be described in this work. The low hardness of the Ag‐matrix requires careful sample preparation in order to avoid preparation artifacts and to reveal the actual structural features. This was achieved by a final step, in which the polished surface was ion beam etched. The samples will be analyzed by stereography, light microscopy, field emission scanning electron microscopy (FE‐SEM) and electron back scatter diffraction (EBSD). It was found that the structure of a switched material can be divided into four category regions: Firstly, the bulk material, secondly, a very small heat affected zone, thirdly, a broad fusion zone and finally, the surface layer. The fusion zone is characterized by large columnar grains, increasing porosity and oxide agglomeration towards the surface. These structural phenomena can only be revealed by ion beam etching, as will be illustrated by examples of selected contact material.     

Applicability of the crack tip element analysis for damage prediction of composite T-joints

The expanding application of polymeric composite materials in the Aerospace industry has led to the extension of its application to other industries such as the marine industry. A typical joint between the hull and bulkhead used in a monocoque structure is known as a T-joint. It consists of composite overlaminates over a shaped fillet to allow the transmission of direct and membrane shear stresses. The CTE (crack tip element) method offers the capability to provide accurate results with minimum computational resources. It is also an excellent damage prediction tool for composite laminates where oscillatory singularity exists at the crack tip. This paper describes the application of the CTE method for damage prediction of the T-joint. Issues involved in the current modeling approach and recommended solutions are discussed.     

高温拉压环境下DZ125高温合金的热障涂层失效

采用电子束物理气相沉积法（EB-PVD）在定向凝固Ni基高温合金DZ125基体上制备了NiCoCrAlY粘结层和YSZ陶瓷层，研究了高温拉压环境下热障涂层的失效模式，并对其进行了有限元分析。实验结果表明，热障涂层的失效与仅受热载荷作用下的有很大不同，仅有热载荷作用下的热障涂层裂纹多萌生于热氧化层（TGO）内部，进而扩展引起热障涂层的失效。而高温拉压试验后热障涂层体系存在两种裂纹，分别萌生于TGO／粘结层界面和粘结层／扩散层界面附近。有限元模拟结果显示TGO／陶瓷层和TGO／粘结层处存在应力状态的转变和应力值的突变，径向应力的突变导致了界面分离现象的产生，而轴向应力的突变加速了垂直于界面裂纹的扩展，并导致了试样的最终断裂。