高碾压混凝土重力坝分区材料-结构界面特性与变形协调仿真分析

高碾压混凝土重力坝不同功能部位"结构特性"与"材料性能"的差异产生的变形协调问题直接关系到工程结构的安全运行,现阶段变形协调分析多是对结构变形和受力进行分析,对异种材料变形协调机理认识不足,缺乏理论基础研究。本文基于界面力学理论,考虑混凝土坝分区中常见的两种双材料界面形式与理想界面的连续边界条件,基于奇异性特征值的特征方程,提出了以应力奇异性特征值作为异种材料变形协调的评价指标,并通过有限元分析验证了理论计算的正确性与有效性;进而分析了界面结合角度和异种材料组合对单侧自由界面端与埋入界面折点处应力奇异性的影响,通过非均质有限元数值仿真分析了复合试件破坏模式,研究了抗压强度与应力奇异性特征值的关系;最后通过统计实际混凝土坝工程中不同坝段内的双材料界面的材料参数(弹性模量)与结构参数(界面形式与结合角度),计算奇异性特征值,评价了该工程中界面的变形协调特性,为高混凝土坝分区材料-结构设计与材料选取提供新的思路。     

采场围岩变形与破坏监测技术研究进展及展望

深部煤炭资源开发面临更多复杂、多变、高难的开采地质问题,采场围岩形态结构是矿井安全生产的重要评价指标之一,开展采场围岩变形与破坏测是判别矿井隐蔽致灾地质问题的重要技术保障。在煤炭工业快速发展的近20余年时间里,围岩体形变监测技术取得了长足的进步,基于矿山采场围岩体变形与破坏的影响因素,按照监测形式对监测技术进行了划分,归纳了当前用于矿山采场围岩变形与破坏监测的钻孔测试技术、地球物理探测技术、光纤监测技术及其他测量技术及其特点,结合煤层顶底板、巷道两帮空间监测的工程应用实例,介绍了不同监测技术的主要进展、优缺点以及适用性,讨论了探测技术的革新趋势和未来矿井安全生产中采场围岩变形与破坏监测技术的发展方向。同时,也认识到现有监测技术虽然已取得显著的监测效果,但是仍不能够满足矿井现代化、智能化生产需要。对于监测技术的进步而言,既需要技术装备的不断优化,更是要跨学科、跨专业科学技术理论的完善与更新。在当前地学大数据、云计算、人工智能新一轮科技创新基础上,今后采场围岩变形与破坏的监测技术必然向多元化、多参数、智慧化、全程监控的方向发展,监测方式也将不断地向可视化、动态化的监测预警模式过渡,融合监测技术发挥多参数的作用将越来越重要。     

深部软岩巷道围岩变形特征及数值模拟分析

针对深部煤矿开采条件下软岩巷道围岩出现持续流变时间长、变形大、地压高、巷道难以维护等特点，首先分析了深部软岩巷道变形特征，采用FLAC^3D数值模拟软件，分析了不同埋深条件下巷道围岩垂直应力分布、水平应力分布以及巷道围岩塑性区扩展规律。研究得出，深部软岩巷道的围岩岩块呈松散破碎形态，相互翻转和滑移，岩体的模量和强度低；随着巷道埋深的逐渐增加，巷道围岩应力集中系数逐渐减小，巷道垂直、水平应力峰值逐渐变大，塑性破坏范围扩展速率逐渐增加。研究为深部软岩巷道支护提供理论基础。     

Study on stress and deformation of keyhole gas tungsten arc-welded joints

Keyhole gas tungsten arc welding(K-TIG)of Q345 low alloy steel plates was simulated by using SYSWELD software.The temperature field of the K-TIG welding process was simulated with three different combined heat sources and was compared with the weld profile that was obtained experimentally.The temperature field that was obtained by a combination of a double ellipsoid heat source on the upper half and a three-dimensional Gauss heat source on the lower half was similar to the real situation.The effects of plate thickness,gap and welding speed on the deformation and stress of the K-TIG welded joints were investigated by K-TIG welding numerical simulation.A reduction in the thickness of the weld plates reduced the z-direction deformation and transverse residual stress;an appropriate gap reduced the residual stress and an increase in the welding speed reduced deformation after welding,but did not help to control the residual stress after welding.     

Ca对Mg-Gd-Y-Zn-Zr合金热变形行为及热加工性能的影响

利用Gleeble3500热模拟试验机研究了Ca对Mg-Gd-Y-Zn-Zr合金在变形温度573～723 K,应变速率0.001～1 s-1的热变形行为及热加工性能的影响。结果表明:Ca增大了合金的流变应力及变形激活能,扩宽了加工安全区及最佳加工区范围,但降低了最大功率耗散因子及动态再结晶程度。结合激光共聚焦显微镜分析了合金热压缩后组织,验证了热加工图的准确性,并制定了合理的热加工工艺,Mg-Gd-Y-Zn-Zr合金的最佳加工区域为:应变速率0.001～0.01 s~(-1),温度623～723 K。根据最佳加工工艺参数获得了表面质量良好,无变形缺陷的等温锻造合金。     

等通道转角挤压制备超细晶材料的最新研究进展

等通道转角挤压(Equal channel angular pressing,ECAP)方法是制备性能优异超细晶材料最常见的大塑性变形方法之一。模角、挤压路径、挤压道次、挤压温度和挤压速度等因素都会影响等通道转角挤压制备超细晶材料的性能;等通道转角挤压的模具也在不断地优化,如背压-等通道转角挤压(Back pressure ECAP,BP-ECAP)模具、可加热的模具以及在等通道转角挤压基础上形成的板材连续剪切技术等,这些新的模具可以改变ECAP变形过程中的组织均匀性。本文综述了等通道转角挤压制备超细晶材料的最新研究进展,并指出了几个需要深入研究的问题及方向。     

Experimental and numerical assessment of energy absorption capacity of thin-walled Al 5083 tube produced by PTCAP process

The energy absorption capacity of the Al5083 thin-walled tube produced by parallel tubular angular pressing (PTCAP) process was evaluated. Also, microstructure, mechanical properties, and anisotropy coefficients were studied in the peripheral and axial directions. Results showed that values of energy absorption decreased with processing pass increasing and the values for the unprocessed, first and second passes were obtained to be 167, 161.4 and 160.7 J, respectively. The differences between the simulation results for the energy absorption values and their experimental values for the unprocessed, the first and the second PTCAP passes samples are about 5%, 10%, and 13%, respectively. The energy absorption capacity was related to the anisotropy coefficient and microstructure. The results demonstrated that grain refinement occurred and ultimate tensile strength (UTS) and microhardness after the first and second PTCAP passes were enhanced, while the increase rate in the first pass was much severer. Also, by applying PTCAP, the deformation modes were altered, such that the deformation mode of the annealed tube was quite symmetrical and circular while for the first and second passes there have been triple and double lobes diamond. The results of the numerical simulation for the deformation mode of the annealed and PTCAPed tubes were consistent with the experimental results. The deformation mode of tubes is dependent on their mechanical properties and variation of the mechanical properties during PTCAP process.     

Microstructure and mechanical properties of fine grained uranium prepared by ECAP and subsequent intermediate heat treatment

The microstructure and mechanical properties of fine grained uranium prepared by equal channel angular pressing (ECAP) and subsequent intermediate heat treatment were investigated systematically by the confocal laser scanning microscope (CLSM), electron backscatter diffraction (EBSD) and split Hopkinson pressure bar (SHPB). The results show that the initial coarse grained uranium was refined from about 1000 to 6.5 μm prepared by ECAP at 3 passes and subsequent heat treatment, and the corresponding dynamic yield strength increased from 135 to 390 MPa. For the ECAPed uranium samples, the relationship between grain size and yield strength could be described by classical Hall–Petch relationship, and the fitting Hall–Petch relationship for the fine grained uranium samples prepared by ECAP was drawn.     

免充气塑料轮胎支撑结构对性能的影响

免充气塑料轮胎的支撑结构对轮胎性能有直接影响。本研究提出了一种具有连续支撑结构的免充气轮胎,利用ABAQUS软件,与两种现有免充气轮胎进行应力大小、接地性能以及刚度性能的对比。结果表明:连续支撑结构可改善免充气轮胎的应力,接地压力的分布均匀性;同时,连续支撑结构轮胎的纵向刚度、横向刚度均远好于同规格现有免充气轮胎和子午线轮胎;扭转刚度性能接近同规格子午线轮胎。通过分析可知,连续支撑结构轮胎在复杂工况路面有显著的优势,具有良好的发展前景。