Influence of thickness and initial groove angle in M–K model on limit strain of 7B04 by considering through-thickness stress

Marciniack–Kuczinski (M–K) model is widely used to predict material’s forming limit curve (FLC). The prediction of FLC traditionally neglected through-thickness normal stress. However, it cannot be neglected in some forming processes. Much work has been done to study the effect of through-thickness normal stress on FLC with constant through-thickness normal stress or constant ratio of through-thickness normal stress and maximum principal stress. In addition, based on Nakazima test process, the ratio of through-thickness normal stress and maximum principal stress has been derived, which was a function of instantaneous thickness and loading path. Here, initial groove angle in M–K model was not considered. In this paper, uniaxial tension tests and Nakazima tests were performed on 7B04 aluminum alloy. Based on Hill 48 yield criterion and M–K model, the prediction model of FLC was established. The increase of thickness can enhance FLC. Meanwhile, it is necessary to consider through-thickness normal stress and initial groove angle in prediction model. On the left side of FLC, the effect of initial groove angle on FLC is weakened by increasing sheet thickness. On the right side of FLC, the effect of initial groove angle on FLC is strengthened by increasing sheet thickness. On the right side of FLC, the relation between limit strain points with different thicknesses is linear under one certain loading path. Thickness has decisive effect on through-thickness normal stress level and the changing trendy of through-thickness normal stress during calculation is different under different stress condition.     

A new interpretation of the historical records of observing Venus in daytime with naked eye: Focusing on the meteorological factors in the astronomical observation records

Observing Venus during the daytime is challenging. However, observational data of Venus during the daytime can be found in history books from East Asian countries such as Korea, China and Japan. In this study, we are focused on data from Korean history book, and using records left in the Joseon wangjo sillok, one of the Korean history books from the Joseon dynasty (CE 1392–1910), tries to prove whether the reported observations were actual observation data. We collected these 4663 records from the Joseon wangjo sillok to determine whether they were actual observations, and to confirm the scientific validity of the records. When we looked at the distribution of observations on a yearly basis, we noticed that there were more observations in the fall and winter, while there were only limited numbers of observations in the spring. This difference in distribution suggests that observations were strongly affected by atmospheric conditions due to the weather. From the 4663 data collected, we found a cycle of about 1.6?years. The cycle of about 1.6?years is assumed to be related to the conjunction cycle of Venus. And, we found a cycle of about 1.0?years. The cycle of about 1.0?years is assumed to reflect the indirect effects of the Asian dust phenomenon. Our research result verified the record as actual observational data. In addition, this result verified that meteorological factors were involved in the recorded astronomical observation data. We think that our data can be helpful to climate studies on the natural sources of key climate-affecting aerosols.     

含有任意多个椭圆孔弹性板的应力场计算

本文应用弹性力学的复变函数理论,用多保角变换的方法,导出了含有任意多个椭圆孔的无限大弹性板多复变量应力函数的表达式。每个孔的大小、位置和孔边作用的载荷均为任意指定。板的无限远处作用有和坐标轴方向一致的均匀拉压载荷P_x,P_y和均匀剪切载荷P_(xy)。并在孔边进行复Fourier级数展开,用待定系数法确定应力函数的未知系数,从而计算弹性板的应力场。编制了相应的FORTRAN77标准化程序,进行了考题和算例分析,给出了级数的收敛状况和孔边周向应力的分布图。     

利用热源温度场迭加法诊断持续点热源的强度及位置

可重复使用运载器的防热瓦故障会使航天器的局部结构产牛热源，并在结构中形成温度场。应用热源温度场迭加法的解函数，解得结构温度历程，然后据此温度的变化率趋势判断出热源位置，在此基础上依据多点测最值构造出辨识参数用于热强度识别，通过对一薄壁结构模型算例的计算仿真，证明了本文所提方法的有效性。论文工作为进一步开展热源诊断技术研究，提供了可资工程实践应用的数值算法体系以及有益的数值计算结论。     

阻尼材料在飞机炮振减振上的应用

阻尼材料在飞机结构上的应用是一个新课题。在飞机炮舱区应用新型阻尼材料,组成一个全新的阻尼结构系统来吸收由航炮射击时产生的冲击能量,以实现减振的设计目的,进而改善其炮击的振动环境。通过理论计算和地面试验实测,证明了应用新型阻尼材料可使炮舱区的动应力下降近30％。     

超声马达工作性能影响因素的研究

系统阐述在超声马达的设计、制作过程中的机构设计、制作工艺、驱动电源等方面的关键问题。重点讨论超声振子的粘接技术,振子参数优化设计的方法,以及驱动电源的匹配和频率自动跟踪设计,最终设计出高性能的超声马达。     

CFG桩复合地基应力比数值分析

本文采用有限元ANSYS程序对CFG桩复合地基的单桩桩体荷载传递规律、应力比及影响因素进行了分析,得出了减小应力比的方法和措施,对工程可起借鉴的作用。     

悬筐式蒸发器的结构设计

本文从设计角度对悬筐式蒸发器的结构进行了介绍和总结,并提出了一些结构的改进意见。     

TC11钛合金的热态变形行为研究

采用等温恒应变速率压缩试验法,研究了TC11合金在780℃-1080℃和应变速率为0.001s-1~70s-1范围内的高温压缩变形行为。考察了变形温度、应变速率及变形程度对流动应力的影响关系。结果表明,流动应力对变形温度和应变速率敏感,随变形温度升高和应变速率降低流动应力减小,特别是在α β两相区变形温度对流动应力的影响显著。     

正—反激组合式变换器与单端式变换器的比较

以５０Ｗ变换器为例，分别从磁性元件的大小，功率管上的电应力、磁恢复问题，输出纹波及输出特性等方面，详细分析比较了组合式变换器与单端式变换器的优缺点，并给出了具体数据，提出了正－反激组合式变换器具有电压应力低，磁性元件小，体积小，重量轻，输出纹波小及可靠性高的结论。