Dynamic anti-plane interaction between an impermeable crack and a circular cavity in an infinite piezoelectric medium

Wave propagation in an infinite elastic piezoelectric medium with a circular cavity and an impermeable crack subjected to steady-state anti-plane shearing was studied based on Green＇s function and the crack-division technique. Theoretical solutions were derived for the whole elastic displacement and electric potential field in the interaction between the circular cavity and the impermeable crack. Expressions were obtained on the dynamic stress concentration factor （DSCF） at the cavity＇s edge, the dynamic stress intensity factor （DSIF） and the dynamic electric displacement intensity factor （DEDIF） at the crack tip. Numerical solutions were performed and plotted with different incident wave numbers, parameters of piezoelectric materials and geometries of the structure. Finally, some of the calculation results were compared with the case of dynamic anti-plane interaction of a permeable crack and a circular cavity in an infinite piezoelectric medium. This paper can provide a valuable reference for the design of piezoelectric actuators and sensors widely used in marine structures.     

沉管结构预制阶段裂缝控制参数影响分析

混凝土沉管隧道在越江和跨海工程中得到了较广的应用,预制方法从传统的干坞法预制发展为工厂法预制。沉管隧道的混凝土管节在工厂化预制阶段容易因温度梯度、收缩以及约束等原因出现危害性裂缝,影响沉管结构的正常使用和长期耐久性。采用数值仿真和试验研究相结合的方法,基于水化度方法建立了混凝土材料模型,综合考虑混凝土温度变形、自收缩和徐变等时变体积变形以及热-力学边界条件;针对沉管工厂化预制的各个阶段,对配合比、入模温度、养护环境温度、模板、拆模时间、养护时间以及保温养护措施等参数进行了对比分析;在温度场和应力场计算结果基础上,以开裂风险指数为主要判断依据,得到了沉管在预制过程中裂缝控制的关键影响因素。研究结果表明:工厂化预制沉管隧道混凝土管节的入模温度和养护温度是沉管结构预制各阶段的关键裂缝控制影响因素,两者之间的关系对沉管结构的裂缝控制有直接影响,入模温度较高时,可以通过提高养护温度来保证沉管开裂风险指数大于1.4。在冬季时,养护温度的提高使沉管有较好的保温效果,进而降低内外温差和开裂风险;但在夏季还需注意控制其内部最高温度。最后开展足尺节段温控试验,提出入模温度和养护温度的控制措施,并通过温度监测得到较高环境温度下的温度控制指标,以指导工厂化混凝土沉管预制阶段裂缝控制。     

浅谈水泥混凝土路面早期裂缝危害及分类防治

以本地区近年来新建的水泥混凝土路面为例,就其早期出现裂缝的原因、特点、分类及其危害进行了阐述,对如何防止和减少水泥混凝土路面早期裂缝提出了有效的对策.     

关于海工混凝土耐久性问题的探讨

海洋环境下的混凝土结构腐蚀现象十分严重,采用高性能混凝土是解决混凝土腐蚀问题的有效措施,控制高性能混凝土的开裂问题是推广应用高性能混凝土的关键.介绍了海工混凝土应用中存在的几个问题及对策措施.     

On vehicle/track impact at connection between a floating slab and ballasted track and floating slab track's effectiveness of force isolation

When a vehicle runs over the connection between a floating slab track (FST) and ballasted track, wheel/rail impact may occur because of the stiffness difference in the two kinds of track, and thus a transition sector is usually included at the connection to smoothen the stiffness change. This phenomenon is studied by numerical simulation using a time-domain model for an idealised case without such a transition to determine whether it is actually necessary. Calculation results show that the wheel/rail impact load is moderate for a light FST and increases with the vehicle speed or decreasing the natural frequency of the FST. From simulation the wheel/rail parametric excitation is observed, as a result of variation in the stiffness of the FST with the period of the single slab length. The wheel/rail load due to the parametric excitation also increases with the vehicle speed. In addition, good performance of vibration isolation can be seen for the FST in terms of the force transmitted to the infrastructure.     

某型船用主机汽缸镶台肩套强度分析研究

某船柴油机由于汽缸体缸套装配凸肩出现严重裂纹,在修理时采用镶套的方法进行了修补,文章根据标准对镶套进行常规强度校核和变形的有限元计算,分析表明整个修理方法完全符合要求。     

沥青路面裂缝的条带补缝工艺及补缝机研究开发

针对沥青路面裂缝的修补，通过研究传统灌缝修补工艺存在的不足，开发了条带补缝新工艺，并配套设计了可实现裂缝条带补缝工艺机械化施工的补缝机，为沥青路面裂缝的修补提供了一种修补外观质量和可使平整度更好的新工艺。实践证明：条带补缝工艺对沥青路面的修补效果优于传统灌缝工艺，使用配套的补缝机可实现对沥青路面裂缝的快速一次性修补，具有很好的推广应用价值。     

昆山市震川西路水泥混凝土路面改建设计关键技术

随着交通量的增加和路面状况的恶化，大量的水泥混凝土路面都面临着翻修改建的任务，加铺沥青混凝土罩面是其中最常用的方法之一。为确定经济合理的加铺结构层，保证路面结构强度，延长道路使用寿命，防治反射裂缝是其关键技术。通过介绍震川西路改建的设计及施工方案，为类似工程提供参考。     

高速铁路CRTSⅢ型先张轨道板质量控制关键技术探讨

通过对高速铁路CRTSⅢ型双向先张预应力轨道板初张拉和终张拉过程完成后单根预应力筋张拉力的测试分析,提出"初张拉控制均匀性、终张拉控制总张拉力"的控制理念,并提出初张拉力值偏差应控制在3 k N以内。针对轨道板早期脱模特点,提出胶凝材料粒度匹配和活性激发技术;为减少板底浮浆、实现骨料适量自然外露,提出减小混凝土坍落度、多层连续浇筑的技术措施。     

轨道车辆座椅裂纹分析及改善措施仿真研究

文章介绍了轨道车辆常见座椅分类及其布置,针对某型轨道车辆统计了运行中座椅裂纹分布情况及位置信息,分析了座椅裂纹产生原因,提出了改善座椅裂纹的措施,并通过相应计算及仿真分析验证了座椅裂纹改善措施的可行性。