FRP加固混凝土梁的有限元分析

碳纤维复合材料(CFRP)加固混凝土结构是一种新型结构加固方法。在大比例模型试验的基础上,应用有限元程序对 T 型梁进行了加固分析,以研究 CFRP 布加固对混凝土梁抗弯能力及刚度的提高程度。分析结果表明,CFRP 布加固可应用于大型钢筋混凝土桥梁。     

某工程地下室混凝土结构裂缝原因分析及加固方案

针对南昌市某商住楼工程,介绍了其地下室混凝土结构的施工方案,分析了其地下室上浮和底板、顶板及柱开裂的原因,并提出了加固处理方案,可供类似工程参考。     

3D random Voronoi grain-based models for simulation of brittle rock damage and fabric-guided micro-fracturing

A grain-based distinct element model featuring three-dimensional （3D） Voronoi tessellations （randompoly-crystals） is proposed for simulation of crack damage development in brittle rocks. The grainboundaries in poly-crystal structure produced by Voronoi tessellations can represent flaws in intact rockand allow for numerical replication of crack damage progression through initiation and propagation ofmicro-fractures along grain boundaries. The Voronoi modelling scheme has been used widely in the pastfor brittle fracture simulation of rock materials. However the difficulty of generating 3D Voronoi modelshas limited its application to two-dimensional （2D） codes. The proposed approach is implemented inNeper, an open-source engine for generation of 3D Voronoi grains, to generate block geometry files thatcan be read directly into 3DEC. A series of Unconfined Compressive Strength （UCS） tests are simulated in3DEC to verify the proposed methodology for 3D simulation of brittle fractures and to investigate therelationship between each micro-parameter and the model＇s macro-response. The possibility of numericalreplication of the classical U-shape strength curve for anisotropic rocks is also investigated innumerical UCS tests by using complex-shaped （elongated） grains that are cemented to one another alongtheir adjoining sides. A micro-parameter calibration procedure is established for 3D Voronoi models foraccurate replication of the mechanical behaviour of isotropic and anisotropic （containing a fabric） rocks.
2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.     

Characterization of the masonry lining of an underground structure by geoendoscopy

Maintenance and sustainability of underground structures are the major tasks for infrastructure owners. To carry out these tasks, managers need to qualify the actual state of these facilities. There are very few operational methods to describe separately each component of an underground structure (structure lining, contact interface and surrounding soil). Therefore, most usual diagnosis methods are qualitative and focus the surveying operations on the tunnel intrados. In consequence, they collect limited quality information for maintenance decision.This article focuses on a new methodology for diagnosis of the lining status of an underground structure in order to obtain a mechanical characterization of materials.The methodology is based on an analysis of low diameter drillings on tunnel lining using geoendoscopy and automatic image recording. Then an automatic image processing, is applied on the recorded images in order to locate discontinuities and evaluate the tunnel lining condition. A definition of lining layers were adopted thanks to discontinuities rate criteria. In parallel, a comparative study of the mechanical parameters of old masonry materials by laboratory test cores’ samples was carried out Finally, based on the result of the geoendoscopy analysis and on the laboratory study the methodology establishes a link between the local state of the lining and the mechanical parameters of materials.The application of this methodology to carry out an evaluation of masonry lining of the Paris Metro System shows that the proposed method and tools are particularly well adapted to obtain masonry lining characterization at the local scale. It has been possible to identify each discontinuity leading to a grade of masonry alteration. Using this information it was possible to define a simplified model of lining by sectioning the masonry thickness on three homogenized layers with different mechanical properties.     

Numerical modelling of the effects of joint spacing on rock fragmentation by TBM cutters

The influence of joint spacing on tunnel boring machine (TBM) penetration performance has been extensively observed at TBM site. However, the mechanism of rock mass fragmentation as function of the joint spacing has been scarcely studied. In this study, the rock indentation by a single TBM cutter is simulated by using the discrete element method (DEM), and the rock fragmentation process is highlighted. A series of two-dimensional numerical modelling with different joint spacing in a rock mass have been performed to explore the effect of joint spacing on rock fragmentation by a TBM cutter. Results show that the joint spacing can significantly influence the crack initiation and propagation, as well as the fragmentation pattern, and can hence affect the penetration rate of the TBM. Two crack initiation and propagation modes are found to fragment the rock mass due to the variation of joint spacing. The simulation results are analyzed and compared with in situ measurements.     

Finite Element Analysis of Localized Plasticity in Al 2024-T3 Subjected to Fretting Fatigue

Fretting fatigue is a combination of two complex mechanical phenomena, namely, fretting and fatigue. Fretting appears between components that are subjected to small relative oscillatory motion. Once these components undergo cyclic fatigue load at the same time, fretting fatigue occurs. Fretting fatigue is an important issue in aerospace structural design. Many studies have investigated fretting fatigue behavior; however, the majority have assumed elastic deformation and very few have considered the effect of plasticity. The main goal of this study is to monitor the effect of different fretting fatigue primary variables on localized plasticity in an aluminum alloy (Al 2024-T3) test specimen. In order to extract the stress distribution at the contact interface under elasto-plastic conditions, a modified finite element contact model was used. The contact model was verified through comparison with an elastic analytical solution. Then, a bilinear elasto-plastic isotropic hardening model with a von Mises yield surface was implemented to simulate the material behavior of the aluminum alloy. The effect of different fretting fatigue primary variables, such as axial stress, contact geometry, and coefficient of friction, on localized plasticity was investigated. Finally, the relationship between the location of maximum localized plasticity and Ruiz fretting damage parameter with the crack initiation site is discussed.     

阳离子聚丙烯酰胺水处理剂

本文采用由氧化还原体系、偶氮化合物和辅助引发剂组成的复合引发体系,通过水溶液自由基共聚合,引发丙烯酰胺与阳离子单体反应得到阳离子聚丙烯酰胺,该产品可用于水处理絮凝剂。阳离子聚丙烯酰胺相对分子质量最高可达2.276×107,阳离子单体质量分数可在1%～100%范围内任意调控。考察了pH值,引发剂浓度、单体质量分数、引发温度和辅助引发剂等添加剂用量对聚合反应的影响。通过正交实验,确定了优化工艺参数;引发剂浓度,6×10-3%(对单体);单体质量分数,20%;pH值,8;引发温度,10℃;四甲基乙二胺浓度,6×10-2%;偶氮二异丁腈浓度,8×10-3%。     

加载波形对X65钢腐蚀疲劳裂纹萌生及扩展的影响

采用疲劳实验研究了不同加载波形下X65钢在空气和海水中的疲劳行为。结合SEM结果,对疲劳断口和次生裂纹进行了观察。结果表明,在空气和海水中,正锯齿波加载下X65钢的疲劳寿命最大,三角波次之,正弦波最短。与在空气中相比,X65钢在海水中的疲劳寿命显著降低。正弦波与三角波加载时应力上升时间较短,有利于位错开动,加快裂纹萌生。其中正弦波在σ_max的保载时间最长,有利于位错滑移形成,疲劳裂纹扩展速度最快。在海水环境中,Cl^-促进了X65钢表面点蚀萌生,成为腐蚀疲劳裂纹源。当裂纹形成后,电解质进入裂纹间隙,在交变应力作用下裂纹反复张开与闭合,导致裂纹快速扩展。在海水中,当加载波形为正锯齿波时,X65钢的腐蚀疲劳裂纹的扩展机制为阳极溶解,而当加载波形为正弦波和三角波时,X65钢的腐蚀疲劳的扩展机制均为氢脆+阳极溶解混合机制,其中加载正弦波时腐蚀疲劳开裂敏感性最大。     

模具零件线切割加工中的开裂原因分析

裂纹和开裂是电火花线切割加工模具零件时常会发生的一种现象,文章从模具加工设计、材质、热处理工艺、电火花线切割工艺和磨削裂纹等方面来分析线切割加工中模具零件产生开裂的原因．并提出了控制措施和改进建议。