A commercial as-cast ME21 magnesium alloy containing rare-earth (RE) element was processed by equalchannel angular pressing to obtain fine-grained micro structure. Stress corrosion cracking (SCC) behaviors of the fine...A commercial as-cast ME21 magnesium alloy containing rare-earth (RE) element was processed by equalchannel angular pressing to obtain fine-grained micro structure. Stress corrosion cracking (SCC) behaviors of the fine-grained samples were studied by slow-strain-rate testing in air, distilled water and Hanks’solution at the strain rate of 1×10^(-6) s^(-1). All samples show a relatively low SCC sensitivity in distilled water but a great SCC tendency in Hanks’ solution. The microscopic observations of the fracture surfaces and the side surfaces reveal obvious active anodic dissolution and hydrogen embrittlement cracks, which indicate the higher SCC susceptibility in Hanks'solution. The fine-grained microstructure with more crystal defects promotes the passivation process of the oxide film and restrains the hydrogen induced cracking of the ME21 magnesium alloy, leading to the higher general corrosion resistance as well as SCC resistance.展开更多
中密度纤维板(Medium Density Fiberboard,MDF)作为木材综合利用率高的一种人造板材,其厚度精度决定了板材的力学性能,从而影响其质量。本文将连续热压机电液位置伺服系统作为被控对象,针对MDF板坯厚度控制问题,提出一种带高增益观测器...中密度纤维板(Medium Density Fiberboard,MDF)作为木材综合利用率高的一种人造板材,其厚度精度决定了板材的力学性能,从而影响其质量。本文将连续热压机电液位置伺服系统作为被控对象,针对MDF板坯厚度控制问题,提出一种带高增益观测器的滑模控制策略。首先通过设计高增益观测器对系统输出的位置信号进行观测,将位置、速度及加速度信号的估计值返回滑模控制器,实现了无需速度、加速度测量的滑模控制,保证了观测误差一致最终有界。然后通过构造合适的Lyapunov函数,证明了所提出的控制策略不但能使系统指数渐近稳定,而且保证了跟踪误差的一致最终有界性。仿真实验结果表明,所提出的控制方法可以保证系统精准快速地跟踪位置信号,从而可以保证MDF获得良好的厚度精度。展开更多
基金supported by the Key Research and Development Project of Jiangsu Province of China(BE2017148)the Fundamental Research Funds for the Central Universities(HHU2016B10314)Six Major Talent Peaks Project of Jiangsu Province of China(2014-XCL-023)
文摘A commercial as-cast ME21 magnesium alloy containing rare-earth (RE) element was processed by equalchannel angular pressing to obtain fine-grained micro structure. Stress corrosion cracking (SCC) behaviors of the fine-grained samples were studied by slow-strain-rate testing in air, distilled water and Hanks’solution at the strain rate of 1×10^(-6) s^(-1). All samples show a relatively low SCC sensitivity in distilled water but a great SCC tendency in Hanks’ solution. The microscopic observations of the fracture surfaces and the side surfaces reveal obvious active anodic dissolution and hydrogen embrittlement cracks, which indicate the higher SCC susceptibility in Hanks'solution. The fine-grained microstructure with more crystal defects promotes the passivation process of the oxide film and restrains the hydrogen induced cracking of the ME21 magnesium alloy, leading to the higher general corrosion resistance as well as SCC resistance.
文摘中密度纤维板(Medium Density Fiberboard,MDF)作为木材综合利用率高的一种人造板材,其厚度精度决定了板材的力学性能,从而影响其质量。本文将连续热压机电液位置伺服系统作为被控对象,针对MDF板坯厚度控制问题,提出一种带高增益观测器的滑模控制策略。首先通过设计高增益观测器对系统输出的位置信号进行观测,将位置、速度及加速度信号的估计值返回滑模控制器,实现了无需速度、加速度测量的滑模控制,保证了观测误差一致最终有界。然后通过构造合适的Lyapunov函数,证明了所提出的控制策略不但能使系统指数渐近稳定,而且保证了跟踪误差的一致最终有界性。仿真实验结果表明,所提出的控制方法可以保证系统精准快速地跟踪位置信号,从而可以保证MDF获得良好的厚度精度。
