Finite element modeling of HIC propagation in pipeline steel with regard to experimental observations

In this research, hydrogen induced cracking (HIC) phenomenon in pipeline steel has been investigated by finite element modeling (FEM) with the help of experimental observations. Abaqus software has been utilized to model the crack. To this, first an API 5L X70 pipeline steel was electrochemically charged by hydrogen for 8 h to create different types of HIC cracks. Then, SEM was used to observe different types of hydrogen cracks. Based on the observations, most of HIC cracks were observed at the center of cross section where center segregation of some elements occurred. The results showed that HIC cracks propagated in stepwise, sinusoidal, straight and disordered manner. Moreover, HIC crack nucleated from a point with high stress concentration factor which was between non-metallic inclusion or void and metal matrix. The initiated micro-cracks from two neighbor inclusions link together to form a long HIC crack. Based on the experimental observations and FEM modeling, it was concluded that the driving force for the HIC crack propagation is the presence of hydrogen at the crack tip after it is initiated. Crack tip usually acts as a very small void and the combination of hydrogen atoms makes a high pressure which propel the crack forward. Moreover, the HIC crack propagation path was predicted by fracture mechanics approach showing that the J-integral had its maximum amount when the HIC crack tended to propagate horizontally.     

ZKB型直线振动筛侧板裂纹研究及寿命分析

为了解直线振动筛侧板裂纹的综合性能,首先对侧板进行静力学分析得到侧板危险区域。其次对该区域进行裂纹布置,应用断裂力学理论对振动筛侧板进行应力强度因子的计算,分析侧板危险区域裂纹扩展特性,同时针对不同形状、大小的裂纹进行参数分析,得到振动筛侧板裂纹扩展规律。最后对侧板进行疲劳寿命计算,得到含初始裂纹处侧板的疲劳寿命及安全系数,为侧板的设计优化提供理论指导。     

列车车轮踏面滚动接触疲劳研究进展

随着高速与重载铁路的发展,车轮踏面滚动接触疲劳损伤问题变得更加显著,不仅影响乘车舒适度,增加维护成本,还会直接危害行车安全,目前尚无根本的解决办法。对国内外车轮踏面滚动接触疲劳损伤的形成机理、研究方法及影响因素进行了归纳总结。车轮滚动接触疲劳损伤形式有很多,根据疲劳裂纹在踏面下方萌生位置的不同,将踏面滚动接触疲劳损伤分为表面滚动接触疲劳、次表面滚动接触疲劳和较深层次滚动接触疲劳。随着冶金和车轮制造技术的提高,由低周疲劳或棘轮效应造成的表面滚动接触疲劳损伤成为主要的疲劳损伤类型。车轮踏面滚动接触疲劳损伤的研究方法主要包括现场调研、数值仿真和试验研究。结合已有研究成果,主要从车轮材料、车轮既有损伤、线路条件、列车运行参数、轮轨间第三介质等方面对踏面滚动接触疲劳损伤的影响因素进行了总结,并进一步提出了减缓踏面滚动接触疲劳损伤的具体措施。此外,探讨了车轮踏面滚动接触疲劳损伤未来的研究方向。     

一种射频抗电磁干扰的矿用红外温度传感器

设计了一种适用于复杂条件下实施井下温度探测的射频式红外温度传感器。借助于光学系统、光电探测器实时感应井下温度并提取温度信号,同时在DC-DC电源隔离模块中实施EMI滤波以抗电磁干扰,处理后的信号经过A/D转换、运算器放大后显示在LCD上,实施读取数据并记录在传感器的存储片上,实现了矿井复合灾害条件下的温度测试,测试精度控制在±2%。     

光学材料的磨削损伤控制试验研究

基于K9玻璃不同的磨削工艺参数确定其磨削损伤层深度随工艺参数变化的规律，并通过工件磨削损伤层深度的动态检测研究其裂纹扩展规律。结果表明:工件磨削过程中的裂纹损伤是动态扩展过程。固定工艺参数下，裂纹稳态扩展，损伤层深度不变；采用损伤更小的工艺参数磨削，裂纹的扩展速度小于材料的去除速度，其损伤层深度逐渐减小，损伤的去除速度逐渐减慢直至二者间达到稳态平衡。同时，为了去除前道工序的损伤层，后道工序的材料去除量需达到前道工序损伤层深度的2～3倍。      

Experimental investigation on the self-acceleration of 10%H2/90%CO/air turbulent expanding premixed flame

The self-acceleration characteristics of a syngas/air mixture turbulent premixed flame were experimentally evaluated using a 10% H₂/90% CO/air mixture turbulent premixed flame by varying the turbulence intensity and equivalence ratio at atmospheric pressure and temperature. The propagation characteristics of the turbulent premixed flame including the variation in the flame propagation speed and turbulent burning velocity of the syngas/air mixture turbulent premixed flame were evaluated. In addition, the effect of the self-acceleration characteristics of the turbulent premixed flame was also evaluated. The results show that turbulence gradually changes the radius of the premixed flame from linear growth to nonlinear growth. With the increase of turbulence intensity, the formation of a cellular structure of the flame front accelerated, increasing the flame propagation speed and burning speed. In the transition stage, the acceleration exponent and fractal excess of the turbulent premixed flame decreased with increasing equivalence ratio and increased with increasing turbulence intensity at an equivalence ratio of 0.6. The acceleration exponent was always greater than 1.5.     

基于特征建模的TDD系统大气波导干扰控制体系研究

大气波导干扰是特定气象条件下发生的时分双工（time-division duplex，TDD）系统内干扰，是TDD移动通信系统大规模组网面临的顽疾。在总结分析大气波导干扰成因和分类等的基础上，对大气波导干扰进行建模和表征，验证了海量干扰源在时域和频域的功率集总特征，并结合大量4G/5G现网实测数据给出了典型条件下内陆波导和海面波导的量化干扰信号传播模型，对于干扰的预测和预防具有重要意义。基于干扰特征，给出了TDD系统预防大气波导干扰的帧结构与组网的4项设计原则，5G现网数据表明干扰控制方案有效，上行干扰下降10 dB以上，相关原则对于6G系统的设计也具有指导意义。     

Recovery of Collided RFID Tags With Frequency Drift on Physical Layer

In a passive ultra-high frequency (UHF) radio frequency identification (RFID) system, the recovery of collided tag signals on a physical layer can enhance identification efficiency. However, frequency drift is very common in UHF RFID systems, and will have an influence on the recovery on the physical layer. To address the problem of recovery with the frequency drift, this paper adopts a radial basis function (RBF) network to separate the collision signals, and decode the signals via FM0 to recovery collided RFID tags. Numerical results show that the method in this paper has better performance of symbol error rate (SER) and separation efficiency compared to conventional methods when frequency drift occurs.      

Study on flame propagation of premixed N2O–NH3/N2O–NH3–C3H8 in cylindrical vessels

The flame propagation behavior of premixed N₂O–NH₃/N₂O–NH₃–C₃H₈ was experimentally investigated in elongated vented cylindrical vessels with central ignition. The effect of vessel diameter and propane concentration ([C₃H₈] = 1.96–7.41 wt.%) on the process of flame acceleration was studied and discussed. The results revealed that the maximum value of flame acceleration rate was found in the cylindrical vessel with an inner diameter of 7 mm, followed by 5 mm, 10 mm, and 15 mm. At a constant vessel diameter, the rate of flame acceleration was noticeably improved by adding propane ([C₃H₈] = 1.96–3.85 wt.%) to the premixed N₂O–NH₃. However, a further increase in the propane fraction up to 5.66%, caused a decline in the flame acceleration rate, probably as a consequence of a combined effect between the reduction of oxygen and greater dilution of the ammonia in the total concentration.