职业学校课程项目化教学改革

项目化教学是一种面向就业市场的新型教学模式,正逐步走进职业学校的课堂。在获得师生认可的同时,该教学方式在教学改革中体现出的矛盾也十分突出。本文对当前职业学校课程项目化教学改革中的诸多问题进行系统分析,提出比较现实的解决对策及具体的实施过程。     

微波动态雨衰减时间序列模型的修正

In ordor to investigate the dynamic rain attenuation forecast in countermeasure rain fade techniques on the microwave link, in typical temperate and subtropical rain areas in China, the power spectra for the rain attenuation time series simulated by the EMB (Enhanced Maseng and Bakken) model are in agreement with the measured results at 12.5GHz, but there are differences between the fade slopes statistics based on simulated series and measured data. The rain attenuation time series by the EMB model are improved by using a circular inserting data method. By the improved method, the statistical probabilities of the fade slopes are very close approximation to the measured results. The probabilities of the fade duration based on the simulated time series by the improved processes are compared with the results by unimproved processes, the results based on the measured data and by the ITU-R predicted results. It is shown that the statistical results for the fade slopes are improved, and that the differences between the fade duration probabilities by the improved series and measured data are smaller than that between the results by unimproved and measured. The results show that the improved process to the EMB model is feasible in typical rain areas in China.     

E玻璃纤维增强环氧树脂基复合材料轴向拉伸力学性能的应变率效应

采用MTS-810材料试验机、Zwick-HTM5020高速拉伸试验机及分离式Hopkinson拉杆（SHTB）实验装置,并结合数字图像相关性（Digital image correlation,DIC）分析方法,对E玻璃纤维增强环氧树脂基复合材料棒材在10^-3~2 400 s^-1应变率范围内的轴向拉伸力学性能进行了较系统的实验研究,获得了不同应变率下材料的应力-应变曲线,揭示了应变率对材料的拉伸强度和断裂应变的影响规律。通过显微分析拉伸试样的断口形貌,揭示了试样的断裂机制及对应变率的依赖性。实验结果表明：E玻璃纤维增强环氧树脂基复合材料的力学性能具有强烈的应变率效应,归一化拉伸强度随着应变率对数线性增加,而归一化断裂应变则随着对数应变率线性减小;断口显微分析显示：E玻璃纤维增强环氧树脂基复合材料的轴向拉伸断裂模式依赖于应变率,低应变率加载下试样发生沿45°方向的剪切断裂,随着应变率增大,试样断裂模式逐渐过渡到沿轴向的拉伸断裂,特别是在高应变加载下,观察到大量的玻璃纤维丝被拉断,同时环氧树脂基体也发生严重的碎裂现象,这反映了基体材料与玻璃纤维之间相互约束作用在增强。     

Tensile Mechanical Behavior and Spall Response of a Selective Laser Melted 17-4 PH Stainless Steel

The tensile mechanical behavior and spall response of a selective laser melted (SLM) 17-4 precipitation-hardening (PH) stainless steel were studied comprehensively through tensile test, plate impact experiment and microstructure characterization in the present study. The results reveal a steel with significant strain rate dependence on the tensile mechanical behavior and spall response. As the strain rate increases, the tensile yield stress increases, but there is no monotonic variation trend for the peak stress; grain structure remains unchanged first and then becomes fine; high-angle grain boundaries (HAGBs) increase; the martensite phase decreases at first and then increases. There is a close correlation among impact velocity, strain rate, peak stress, Hugoniot elastic limit (HEL) and spall strength. Strain rate, peak stress and HEL increase, while spall strength remains almost constant with the increase of impact velocity. As impact velocity increases, grain structure becomes fine, HAGBs increase and the martensite phase increases. The significant phase transformation is responsible for the tensile mechanical behavior and spall response, and the temperature rise was calculated to analyze its effect on phase transformation. Whether the preferred orientations are along the building direction or tensile direction is dependent on strain rate. Tensile and spallation specimens exhibit the ductile fracture mode and the damage originates from voids. It is interesting that the voids always tend to nucleate at melt pool boundaries. A spall damage evolution model is illustrated to describe the damage process.

     

电镀耐蚀性锌镍合金工艺研究

介绍了一种新的锌镍合金电沉积工艺和镀液配方,采用了新的钝化液配方及相应的工艺对锌镍合金进行钝化处理,描述了锌镍合金镀液及镀层中锌、镍含量的测定、镀液的维护方法以及对该镀层进行了性能测试。该配方具备工艺简单、操作方便、镀层易钝化等优点。