钢纤维轻骨料混凝土单轴受压应力-应变曲线研究

采用100%烧结膨胀页岩陶粒作为粗细骨料,以占胶凝材料总质量20%的粉煤灰等质量替代水泥作为胶凝材料,按绝对体积直接计算法设计并制备了钢纤维全轻混凝土。以水泥强度等级（42.5和52.5）、钢纤维体积率（0%、0.4%、0.8%、1.2%、1.6%）为参数,进行了钢纤维全轻混凝土轴心抗压试验研究,分析了钢纤维全轻混凝土单轴受压破坏形态及其应力-应变曲线特征。结果表明：钢纤维全轻混凝土单轴受压应力-应变曲线的峰值应力及其对应应变随钢纤维体积率和水泥强度等级的提高呈现增大趋势;钢纤维体积率的增加使试件的破坏形态由脆性向塑性转变。结合相关文献研究成果,对轻骨料混凝土（砂轻混凝土、全轻混凝土）和钢纤维轻骨料混凝土（钢纤维砂轻混凝土、钢纤维全轻混凝土）单轴受压应力-应变曲线进行了综合分析,提出了两类混凝土单轴受压应力-应变曲线统一计算模型及其特征点计算公式。     

汽车稳定杆用 55Cr3弹簧钢室温旋转弯曲疲劳性能

从汽车稳定杆用钢的实际应用需求出发,采用横向轴向应变控制方法,在应变循环比 R为－1,频率 83Hz和室温环境下,测试了 55Cr3弹簧钢旋转弯曲疲劳性能,得到了试样的 S-N曲线。并通过扫描电镜观察疲劳断口,研究了 55Cr3弹簧钢旋转弯曲疲劳特性。结果显示：生产的汽车稳定杆用 55Cr3弹簧钢具有高纯净度和良好的强度与塑韧性配合,其旋转弯曲疲劳试样的疲劳极限可达 730MPa;在较高应力下,裂纹起源于试样表面因加工刀痕和擦伤等引起的缺陷,且存在多处裂纹源。     

一种碳锰曲轴钢的奥氏体连续冷却转变规律

使用DIL805L型膨胀仪分析了曲轴钢的相变规律,得到了其奥氏体连续冷却转变曲线（CCT）。结果表明,试验钢的临界点为：Ac1＝682 ℃,Ac3＝765 ℃;当冷速为0.2～5 ℃/s时,转变产物为铁素体＋珠光体;当冷速大于5 ℃/s时,转变产物为铁素体、珠光体、贝氏体与马氏体的混合组织;当冷速增大到15 ℃/s时,转变产物为贝氏体和马氏体组织;冷速越大冷却后马氏体含量越多,硬度逐渐增加。     

65Mn弹簧钢盘条相变组织分析

为合理制定65Mn盘条控冷工艺和球化退火工艺,使用热模拟相变膨胀法,结合金相组织分析及硬度试验方法,研究65Mn弹簧钢的组织相变规律。试验测定了65Mn动态连续转变CCT曲线,同时测定了该钢种的Ac1、Ac3、Ar1、Ar3等临界相变点温度,结果表明,当冷却速度低于7 ℃/s时,仅发生铁素体和珠光体组织相变,此时钢中组织为索氏体＋珠光体＋铁素体,索氏体含量随冷却速度的增加而增加。冷却速度大于7 ℃/s时,开始发生马氏体相变。冷却速度大于30 ℃/s时仅发生马氏体相变。采用本试验研究成果,制定了合理的65Mn盘条控冷工艺,生产出了力学性能合格的65Mn盘条。同时制定了合适的盘条球化退火工艺,供下游用户参考,用户使用该工艺对盘条进行球化退火处理,可获得均匀的球化组织。     

Horizontal bracing to enhance progressive collapse resistance of steel moment frames

In this paper, the effect of horizontal bracing on enhancing the resistance of steel moment frames against progressive collapse is investigated. Previously designed 6 bay by 3 bay 18‐story steel frame prototype building with 6 m bay span (namely, unbraced frame), which was susceptible to progressive collapse, is retrofitted by four types of horizontal bracing systems on the perimeter of the topmost story and analyzed using 3D nonlinear dynamic method. Six different cross‐sections for each bracing system type are considered, and the capacity curves for each model are obtained. Three column removal circumstances, namely, Edge Short Column, First Edge Long Column, and Edge Long Column are considered in this paper. The results imply that horizontal bracing would increase the resistance of moment frames against progressive collapse. However, one of the bracing types in which axial compressive force is created in braces is not appropriate for retrofitting.     

Seismic performance of corrugated steel plate concrete composite shear walls

In this paper, composite shear walls with different encased steel plates (flat, horizontal corrugated, and vertical corrugated) were tested and simulated by Abaqus to investigate the seismic behavior of corrugated steel plate concrete composite shear walls (SPCSWs). The failure characteristics, deformation and energy dissipation capacity, and stiffness and bearing capacity of the structures under low‐frequency cyclic load were analyzed, and indexes of the seismic performance were obtained. The formulas of the shear‐bearing capacity of steel plate concrete composite shear walls are suggested, and the shear‐sharing ratio of each member is obtained. According to the obtained results, corrugated steel plates can bond with concrete well, and the bearing capacity of the vertical corrugated SPCSW are higher than that of the horizontal corrugated SPCSW. Compared with flat SPCSW, corrugated SPCSW has higher initial stiffness and lateral stiffness, better ductility and energy dissipation ability, and the degradation of bearing capacity and stiffness is slower. The shear‐sharing ratio of a steel plate is larger than that of reinforced concrete in the flat SPCSW and the vertical corrugated SPCSW, the shear force shared by steel plate and reinforced concrete in horizontal corrugated SPCSW is basically the same.     

Seismic risk analysis for reinforced concrete structures with both random and parallelepiped convex variables

This article develops an improved seismic risk assessment formulation exhibiting both random and bounded uncertainties using a probability and parallelepiped convex set mixed model. Limit thresholds for different types of components are described via a probabilistic model. The distribution parameters of limit thresholds are originally treated by employing a multidimensional parallelepiped convex model, in which marginal intervals are utilised to represent scattering levels for the distribution parameters, while relevant angle are employed to express the correlation between uncertain distribution parameters. The structural responses, i.e., engineering demand parameters (EDPs), are considered as correlated random variables and are assumed to follow a multidimensional lognormal distribution. A performance limit state function, which allows considering the relationship between the EDPs and the corresponding limit thresholds, is employed to reflect the coexistence of both random and parallelepiped convex variables. The limit state function is mapped into the standard parameter space via a transformation technique. Then, the improved seismic risk formulation, characterised through a probability and parallelepiped convex mixed variables, can be derived with the combination of the seismic fragility function and the ground motion hazard curve. The main purpose is to illustrate that the performance limit states should be properly modeled as random and parallelepiped convex mixed variables rather than only random or deterministic quantities. A six-story reinforced concrete building designed according to Chinese codes are used to illustrate the proposed approach for constructing hazard curves. The interstory drift and the peak floor acceleration are the selected EDPs, calculated through incremental dynamic analysis. The results demonstrate that the calculated failure probabilities for different limit states in 50?years are found capable of meeting the requirements of Chinese seismic norms after the proposed seismic risk formulation is adopted.     

水热溶液pH值对AZ91D镁合金表面珍珠质涂层性能的影响

目的研究水热溶液pH值对AZ91D合金基体上珍珠质涂层的成分、形貌、抗腐蚀能力以及细胞相容性的影响。方法使用不同pH条件下(5.8、7、8.8、11.8)的水热反应溶液,在AZ91D基体上水热合成珍珠质涂层。利用XRD、XPS和SEM分析涂层的化学成分以及微观形貌。用电化学测量系统评估材料在模拟体液(Simulated Body Fluid,SBF)中的开路电位和极化曲线。通过细胞计数试剂盒(CCK-8法)和拍摄细胞荧光照片,来检测珍珠质涂层的细胞相容性。结果珍珠质涂层的成分和形貌会随着水热反应溶液pH值的不同而发生明显的变化。电化学腐蚀试验证实,与空白对照试样相比,沉积有珍珠质涂层的样品的OCP值较高,其Jcorr值也减少了近10倍,Ecorr值向正电位方向移动。此外,弱碱性条件下所沉积涂层的耐蚀性最优,其Ecorr(vs.SCE)值提高了0.16V,Jcorr值降低了8.16?10–5A/cm2。细胞相容性测试结果表明,珍珠质涂层不具有毒性,珍珠粉原材料为涂层提供的大量骨生长因子,能够促进成骨细胞的增殖。结论采用水热反应法,成功地在AZ91D合金基体上制得珍珠质涂层,该涂层可以有效地改善镁合金在人体中的耐蚀性和生物相容性。     

基于NURBS算法的工业机器人轨迹规划研究

轨迹规划是工业机器人研究领域的重要内容之一。为解决使用直线与圆弧逼近不规则曲线方法带来较大误差的问题,提出使用NURBS拟合自由曲线,并使用S形速度曲线来控制机器人末端的运动速度和加速度,使各个插补点的位置、速度和加速度能够连续,将之反推到关节空间可以得到各个关节的角度、角速度和角加速度。最后以IRB2600工业机器人为仿真本体,通过MATLAB仿真证明:NURBS和S形速度曲线相结合的方法可以得到在关节空间连续、平稳的运行轨迹、速度曲线、加速度曲线,减弱了因各关节角度、角速度、角加速度突变带来的冲击影响,优化了机器人运行轨迹。     

铸件多功能作业机器人多臂协调轨迹规划与仿真

以铸件多功能作业机器人的工作臂为研究对象,采用笛卡尔空间变量法对机器人铸件搬运过程进行轨迹规划。结合多臂协调的运动约束条件以及伪逆法,对机器人的4个工作臂关节运动进行优化,得到多机械臂协调运动的关节位置和速度变化曲线。由MATLAB软件仿真得到的运动参数曲线可知,算法优化后得到的运动轨迹均能保持连续、平滑,有利于实现对机器人的精准控制。利用机械臂正运动学方程得到了机械臂末端执行器的轨迹曲线,曲线满足铸件搬运的要求,验证了算法的正确性。