Propagation of surface cracks on beam blank in the mould during continuous casting

ABSTRACT

We focus on crack propagation to investigate surface cracks in the mould during continuous casting, based on the crack initiation mechanism proposed in previous studies. The temperature and stress data of a solidified shell were extracted, and an extended finite element model based on the continuous damage theory of elastic–plastic materials was developed to simulate surface crack propagation. The results showed that, in the cracked area, stress concentration occurred at the crack tip, and the element split open and the crack propagated when the maximum principal stress in the stress concentration area reached the critical value. Prefabricated cracks in the fillet and web mainly developed into longitudinal cracks in the mould. The theoretical mechanism of this study was found to be the same as the crack propagation mechanism observed during the actual production of beam blanks. Thus, this study reveals the theoretical principle of crack initiation and propagation and can provide theoretical guidance for controlling surface cracks during beam blank continuous casting.     

真空玻璃支撑压痕控制准则

为避免过大的支撑物支撑应力导致真空玻璃基片赫兹裂纹的产生,首先建立了力学模型,分析了支撑物接触部位玻璃的应力分布特征.应用Griffith断裂理论和均强度理论,分别得到了玻璃基片在不产生压痕下支撑物的最大临界支撑力计算公式.通过与试验结果进行比较,发现两种理论计算结果均与试验结果相吻合,,但断裂力学理论得到的支撑物临界支撑力比试验结果偏小,而均强度准则结果偏大.对真空玻璃结构设计,在已知的真空玻璃材料参数下,根据上述理论,计算出玻璃基片不产生压痕下支撑物的最大临界支撑力,从而确定支撑物最佳排列间距,使真空玻璃达到"热学与力学"最佳配制.     

扫描电镜中颗粒能谱定量分析的质量效应

利用扫描电镜和能谱仪对精密合金中第二相颗粒的表面形貌和化学成分进行了分析,研究了颗粒能谱定量分析的质量效应。结果表明:颗粒能谱定量分析时有明显的质量效应;颗粒与基体的成分差异越大,质量效应越明显,加速电压对质量效应也有影响;颗粒能谱定量分析中存在一个临界尺寸,当颗粒尺寸大于临界尺寸时,质量效应消失;由于样品抛光表面上颗粒的二维表观尺寸与实际的三维尺寸不尽相同,使得质量效应的表观临界尺寸有别于理论临界尺寸,但颗粒能谱定量分析质量效应的变化趋势和统计规律是十分明显的。     

Transport and Magnetic AC Losses in Ag/Tl-1223 Tape and the Effect of Mechanical Damage

In this paper we present the results of AC loss measurements on silver clad monocore tapes of Tl-1223 prepared by the powder-in-tube method. Losses arising from an external AC magnetic field are compared with those generated by AC transport currents (self-field losses). Critical current densities are derived from magnetic loss data and compared with those measured by the four point transport method. It was found that mechanically induced stresses (introduced by bending) only have a significant effect on the transport losses, via the critical current degradation. Such changes are not seen in measured magnetic losses, which are independent of mechanical stress, and remain unchanged, at least in the stress range used in our experiment.     

TiC增强颗粒进入钢液的条件判据

通过泡沫载体的引载作用实现TiC增强颗粒混入钢液,在液态模锻工艺条件下成型20%TiC/铸钢（ZG270-500）制件。计算分析了泡沫载体消失气化时TiC增强颗粒在气隙中的运动行为及其进入钢液的条件。实验结果表明,TiC增强颗粒的运动速度随浇注温度、充型速度和排气孔口与型腔横截面积比的增大而递增。当钢液前沿TiC颗粒的运动速度大于临界速度时才能进入钢液,且TiC增强颗粒运动速度越大,越容易进入钢液,分布越均匀。     

The influence of piston shape on air‐spring fatigue life

This paper presents how the piston shape of an air‐spring can influence both its load‐deflection characteristic and the fatigue life. Two piston shapes are considered in this study for which load‐deflection characteristics and fatigue lives are compared. A method for the estimation of air‐spring fatigue life is upgraded by adding the influence of the mean stress level and afterwards used together with finite element analysis to predict the fatigue life and, ultimately, the timing and global location of failure within the air‐spring. These predictions are then compared with measured results and show good agreement thus proving the validity of the method used here for calculating fatigue life. Both experimental and predicted results show that the highest fatigue life can be expected if a noncylindrical, back tapered piston is used. This is only the case if the air‐spring is mounted at its optimal design height as the study also shows that moving away from optimal design height does have a detrimental effect on the fatigue life of back tapered air‐springs. This is due to the appearance of higher stress amplitudes in the flex member during operation. Such stress amplitudes and consequently fatigue damage can be reduced by avoiding sharp transitions in the piston design that cause additional bending of the flex member in a direction opposite to the deflection in the flex member fold.     

弹性力学Hamilton体系下的稳定问题

通过在Hellinger-Reissner广义势能中引入应变的非线性项,推导出了弹性力学Hamilton体系下的屈曲基本方程。并运用弹性力学方程组一般解的统一理论给出其一般解。最后作为例子,给出了两端简支的梁、组合梁和四边简支板、组合板的临界载荷,并与经典解做了比较。结果是严格弹性力学意义(没有引入任何几何变形假设)下的精确解。为衡量各种计入剪切变形的薄板、中厚板理论的准确性提供了一个标准。     

BDCP:一个有效的相关任务调度算法

表调度算法ＢＤＣＰ采用动态关键路径技术并均衡考虑关键路径结点和非关键路径结点,使得对相关任务图调度长度影响最大的就绪得结点能够被优先调度,从而极大地缩短了调度长度。分析和实验结果表明,该算法要明显优于ＭＣＰ和ＥＴＦ算法。     

Transport properties of 1,1,1,2-tetrafluoroethane (R134a)

New equations for the thermal conductivity and the viscosity of R134a that are valid in a wide range of pressures and temperatures are presented. They were obtained through a theoretically based, critical evaluation of the available experimental data, which showed considerable inconsistencies between data sets, in particular in the vapor phase. In the critical region the observed enhancement in the thermal conductivity is well represented by a crossover model for the transport properties of fluids. Since thermodynamic properties enter into the calculation of the critical enhancement of the transport properties, a new fundamental equation for the critical region was developed also.Paper dedicated to Professor Joseph Kestin.     

基于塑性应变能的多轴低周疲劳寿命预测模型

在分析多轴疲劳损伤机理的基础上,提出一个新的多轴低周疲劳寿命预测模型。此模型以临界平面上的塑性应变能作为疲劳损伤参量,分析了临界平面的特点并给出了损伤参量的计算过程。利用该模型预测了不同加载路径下的304不锈钢试件的疲劳寿命,并与试验值进行比较。结果表明,该损伤参量具有明确的物理意义,能够适用于多轴比例与非比例等各种复杂的加载情况。