汽流激振机理分析及某330MW汽轮机故障处理

介绍了汽流激振故障发生的机理及特征。某330 MW汽轮机组在单阀带大负荷时,1瓦、2瓦出现较大的低频振动,结合阀门试验时的频谱图和汽流激振的机理进行分析,发现该机组故障为典型汽流激振,通过调整2瓦标高,解决了低频振动问题。     

对位芳纶纤维打浆及其对无石棉胶乳抄取板的影响

研究了芳纶纤维的打浆性能及其在无石棉胶乳抄取板中的应用。研究表明,芳纶纤维具有高的Zeta电位,呈现强负电性;随着磨浆转数提高,其打浆度逐渐增加,负电性逐渐下降;在磨浆转数为20000转时,纤维长度和粗度明显减小,细纤维化显著,打浆度为30oSR,此时用该芳纶纤维配抄的无石棉胶乳抄取板的抗张指数达到最大值。     

Extraction and Characterization of Novel Natural Cellulosic Fibers from Pigeon Pea Plant

ABSTRACT

This study is mainly focused on the extraction and characterization of the lingo-cellulosic fibers from the Pigeon Pea plant. The chemical components of the fibers such as cellulose content (55.03%), lignin (18.32%), wax content (2.38%), moisture content (8.13%), and density (1.7389 g cc^?1) were identified. Functional groups present in the fibers were obtained by infrared spectroscopy. By using X-ray diffraction analysis, Crystallinity Index is found to be 68% and thermogravimetric analysis showed that thermal degradation of the fiber begins at 225°C.The results suggest that the Pigeon pea fibers can be used as reinforcement in polymer-matrix composites.     

蒸汽发生器传热管流弹失稳计算

蒸汽发生器管束一旦出现流弹失稳现象,可以在很短的时间内破坏传热管的完整性,影响核电站安全。因此,在设计蒸汽发生器时要预测与防止传热管流弹失稳现象。通过有限元软件ANSYS的梁单元建立传热管模型,进行模态分析并提取相关结果;然后将模态分析的结果代入MATLAB计算传热管流弹不稳定率并和专用软件进行对比。该方法计算结果与专用软件吻合,且分析表明套筒开口区与弯管区流速对流弹不稳定率影响较大;管子高频时不易发生流弹失稳现象。     

Dynamic characteristics of multi-degrees of freedom system rotor-bearing system with coupling faults of rub-impact and crack

Extensive studies on rotor systems with single or coupled multiple faults have been carried out. However these studies are limited to single-span rotor systems. A finite element model for a complex rotor-bearing system with coupled faults is presented. The dynamic responses of the rotor-bearing system are obtained by using the rotor dynamics theory and the modern nonlinear dynamics theory in connection with the continuation-shooting algorithm（commonly used for obtaining a periodic solution for a nonlinear system） for a range of rub-impact clearances and crack depths. The stability and Hopf instability of the periodic motion of the rotor-bearing system with coupled faults are analyzed by using the procedure described. The results indicate that the finite element method is an effective way for determining the dynamic responses of such complex rotor-bearing systems. Further for a rotor system with rub-impact and crack faults, the influences of the clearances are significantly different for different rub-impact stiffness. On the contrary, the influence of crack depths is rather small. The instability speeds of the rotor-bearing system increase due to the presence of the crack fault. The results obtained using the new finite element model, presented for computation and analysis of dynamic responses of the rotor-bearing systems with coupled faults, are in accordance with measurements in experiment. The formulations given can be used for diagnosis of faults, vibration control, and safe and stable operations of real rotor-bearing systems.     

纳米石墨烯掺杂浓度对XLPE击穿性能的影响

制备了分散性良好的6种不同配比XLPE/纳米石墨烯聚合物,运用差式扫描量热法排除了结晶度对击穿性能的影响;对试样进行了工频击穿强度测量并通过拉伸强度测试评估了机械性能。实验表明,掺杂纳米石墨烯能使聚合物的工频击穿强度最大提高27. 66%,拉伸强度最大提高10. 64%,在工业实现上有积极意义。通过等温去极化电流计算聚合物陷阱密度及能级,并结合动态热机械分析从界面分子结合力探究不同含量石墨烯影响击穿性能的机理。研究表明掺杂少于0. 01 wt%的纳米石墨烯能增大陷阱能级,同时增大聚乙烯基体分子间作用力,进而提升聚合物击穿性能。     

粘土的拉裂试验及声发射检测

综述击实粘土拉裂试验的各种方法。三轴拉伸试验和周期拉压试验，用于研究静力拉裂和周期加荷拉裂的破坏，在土石坝有限元分析中判别防渗体土料拉裂和震裂的发生与发展。对试样拉裂时进行声发射检测，可研究试样拉裂破坏的过程，随着围压增大，试样由拉裂破坏而逐渐变为剪切破坏     

压边力对IF钢极限拉深比的影响

采用拉深试验方法对IF钢进行了不同压边力下的拉深试验,探讨了极限拉深比与压边力的关系,并得到了描述IF钢极限拉深比和压边力的数学关系式。研究认为,极限拉深比与压边力的关系可分为两个阶段,在第1阶段,随着极限拉深比的增大,压边力急剧下降;在第2阶段,随着极限拉深比的增大,压边力下降平缓,并逐渐趋于一定值。     

焊接速度对GTA焊接AZ31B镁合金接头组织和拉伸性能的影响

研究焊接速度对脉冲电流钨极惰性气体保护焊接（PCGTAW）AZ31B镁合金接头组织和拉伸性能的影响。实验中焊接速度为105-145 mm/min。结果表明,焊接速度为135 mm/min时,所得接头具有最好的拉伸性能。在熔合区生成的细小晶粒组织和均匀分布的析出相是导致较好的拉伸性能的主要原因。     

MgAl2O4颗粒增强型AC4C基复合材料的微观组织及力学性能

采用搅拌铸造方法制造MgAl2O4颗粒增强型AC4C基复合材料。考察MgAl2O4颗粒的尺寸及尺寸的分布对颗粒分散度的影响,并且测试复合材料的微观组织、强度与疲劳性能。5～25gm范围内的MgAl2O4颗粒可以提高复合材料的抗拉强度。疲劳性能测试表明,在250℃、10^7循环周期内,MgAl2O4颗粒使复合材料的疲劳性能提高27％。在MgAl2O4颗粒周围,观察到了大量位错,产生这种情况的主要原因是MgAl2O4与Al两者之间的热膨胀系数不匹配。在MgAl2O4颗粒周围产生裂纹,但在扩展过程中大量的裂纹发生了转向和弯曲,这有助于材料疲劳性能的提高。