A nanotwin-based analytical model to predict dynamics in cryogenic orthogonal machining copper

Cryogenic cooling helps to improve the machining performance and reduce the tool wear. Cryogenic condition could activate these substructures such as deformation twins and dislocation cells. The effects of the substructures are not taken into consideration in the conventional machining models. The conventional models cannot characterize the dynamics in cryogenic machining, i.e., the evolutions of cutting force and temperature with time. Here, considering the effect of the substructures, a new analytical model for metal cutting was proposed to predict the dynamics in cryogenic orthogonal machining. To validate the applicability of the proposed model, the experiments of orthogonal cutting copper at liquid nitrogen temperature and room temperature were conducted. Transmission electron microscope observations show that nanotwins formed in cryogenic cutting copper. The comparisons between experimental cutting forces and the proposed model or the conventional models validate the rationality of the nanotwin-based analytical model. Numerical calculations were further carried out to reveal the underlying mechanism. The periodic oscillation of cutting force in liquid nitrogen condition is a phenomenon of Hopf bifurcation resulting from the formation of nanotwins

Microstructural Evolution of Shear Localization in High-Speed Cutting of CoCrFeMnNi High-Entropy Alloy

Shear localization is one of the most important failure mechanisms subjected to high-strain-rate deformation and has significant effects on the process, plastic deformation, and catastrophic failure of a material. Shear localization was observed in serrated chips produced during the high-speed cutting of the CoCrFeMnNi high-entropy alloy. Electron backscatter diffraction was performed to systematically investigate microstructural evolution during shear banding. The elongation and subdivision of the narrow grains were observed in the areas adjacent to the shear band. The microstructure inside the shear band was found to be composed of equiaxed ultrafine grains. The results reveal that grain subdivision and dynamic recrystallization might have significant roles in the microstructural evolution of shear bands. These results offer key insights into our understanding of shear localization and high-speed machining behavior for high entropy alloys

一种飞机拦阻综合模拟试验系统

本发明公开了一种飞机拦阻综合模拟试验系统,包括滑车机构、驱动机构、阻尼机构和测量机构等。滑车机构利用第一滑块沿着轨道滑动来模拟各种机型的重量、着陆速度等飞机相关参数；驱动机构利用压缩空气驱动第二滑块沿管道以预定速度运动,撞击第一滑块,实现对第一滑块的快速加速；阻尼机构利用永磁铁块和阻尼轨道提供阻力在预定的拦阻距离上实现第一滑块减速；测量机构用于测量拦阻钢索在拦阻过程中的张力大小。本发明可模拟不同机型及不同着陆速度的飞机拦阻过程,具有便捷实用、安全可靠、试验周期短、节约试验成本等优点,同时也为研究拦阻钢索的损伤累积诱致破坏机理和寿命预测打下坚实实验基础

中空夹层玻璃及其支承系统的爆炸冲击响应研究

玻璃幕墙已被广泛应用于建筑结构中，但目前的设计主要针对静力荷载，对可能发生的爆炸等意外事件所产生的冲击荷载作用尚缺乏可靠研究。对爆炸冲击下的玻璃进行数值分析时，多数研究模型将边界条件过度简化，使玻璃面板直接承受爆炸冲击，忽略了支承体系中诸如框架、垫片、结构胶、滑移块等元件的缓冲作用。这种差异在中空夹层玻璃系统上更为明显，导致数值分析难以精确地模拟结构系统在冲击荷载作用下的响应。为此，对一玻璃幕墙系统进行足尺爆炸冲击试验研究，并采用LS-DYNA软件进行了精细化建模，考虑支承体系内的各元件作用及元件之间的接触行为，以及各元件对玻璃的夹紧力作用等因素。分析结果表明，相比于简化边界条件的模型，考虑多要素的框架模型得出的玻璃面板挠度及速度时程曲线、能量传递等更加合理，且裂纹模态和裂纹动态扩展与试验结果更加吻合。爆炸冲击下中空夹层玻璃的两种常用简化分析模型均不能获得准确的结果：简化的夹板支承模型缺少必要的约束条件，导致玻璃系统整体位移过大而发生破坏；简支模型则约束过强，会导致玻璃应力增大，尤其会在边界区域发生更多的强度破坏。因此，设计抗爆玻璃时应重视缓冲体系的设计，在数值分析时则应充分考虑支承系统各元件的影响

无机热化学数据库中复氧化物高温熵的预报

标准熵的估算方法以W.M.Latimer法最为著名。本文对此作了若干修正,并成功地将它推广应用到高温情况。作为试验,本文预报了二十个复氧化物在不同温度下的熵值,其中十八个化合物的均方根偏差小于5cal/mol·K,即与若干复氧化物标准熵的实验误差相当。因此本方法可以装入“无机热化学数据库”。使它增加预报复氧化物高温熵的功能

Primary Study on Multiporpers Liallid Fertilizer in Dry Land

试验针对旱地深施化肥利用率不高的问题，从改进肥料类型与施肥技术入手，通过研究适于旱地应用的液肥品种与适期叶面喷施试验，表明新型多功能液肥具有提高叶水势、增强作物抗旱力、提高作物光合速率与水肥利用效率等多种功能，并在大旱之年，经在多种作物与大面积示范，可使单产提高２１３～５４７５ｋｇ／ｈｍ２（平均７０５ｋｇ／ｈｍ２），增产率达１０％～３０％（平均２１．６％）