J resistance behavior in functionally graded materials using cohesive zone and modified boundary layer models

This paper describes elastic–plastic crack growth resistance simulation in a ceramic/metal functionally graded material (FGM) under mode I loading conditions using cohesive zone and modified boundary layer (MBL) models. For this purpose, we first explore the applicability of two existing, phenomenological cohesive zone models for FGMs. Based on these investigations, we propose a new cohesive zone model. Then, we perform crack growth simulations for TiB/Ti FGM SE(B) and SE(T) specimens using the three cohesive zone models mentioned above. The crack growth resistance of the FGM is characterized by the J-integral. These results show that the two existing cohesive zone models overestimate the actual J value, whereas the model proposed in the present study closely captures the actual fracture and crack growth behaviors of the FGM. Finally, the cohesive zone models are employed in conjunction with the MBL model. The two existing cohesive zone models fail to produce the desired K–T stress field for the MBL model. On the other hand, the proposed cohesive zone model yields the desired K–T stress field for the MBL model, and thus yields J _R curves that match the ones obtained from the SE(B) and SE(T) specimens. These results verify the application of the MBL model to simulate crack growth resistance in FGMs.     

Sliding wear resistance of Fe-, Ni- and Co-based alloys for plasma deposition

Performance of Fe-, Ni- and Co-based alloys was evaluated in sliding wear and in the impact wear tests to simulate wear of valves and valve inserts in internal combustion engines. From the SEM investigations adhesive wear was confirmed by metal transfer between rubbing surfaces while surface deformation testify to abrasive wear. It was found that oxides formed on the surface prevented direct metal-to-metal contact and reduced the coefficient of friction thereby reducing wear. A comparison of wear resistances of Fe, Ni- and Co-based alloys used as hardfacings were given. It is also shown that Ni–Co alloys with Ni-alloy content between 40.4 and 64.3 have a considerable potential, they reveal above 2 times higher wear resistance than plasma-deposited cobalt alloy.     

Phase formation and modification of corrosion property of nitrogen implanted Ti-Al-V alloy

In the present investigation, polished samples were implanted with nitrogen ion at an energy of 60 keV and implantation doses were 1×10¹⁶, 5×10¹⁶, 1×10¹⁷ and 6×10¹⁷ ions/cm². Glancing incidence X-ray diffraction was employed on the implanted specimens to understand the phases formed with increasing dose. The valence states of nitrogen, titanium and carbon on the sample surfaces were analyzed by X-ray photoemission spectroscopy. The corrosion resistance was examined by the electrochemical methods in a solution with pH=10 at room temperature in order to determine the optimum dose that can give good corrosion resistance in a simulated nuclear reactor condition. Scanning electron microscopy was used to observe the topographies of nitrogen-implanted Ti-Al-Zr after potentiodynamic measurement. It was found that implanted nitrogen dissolved in titanium matrix with increasing dose and the resultant nitrides such as TiN and Ti₂N precipitated. Implantation of nitrogen ions into the surface of Ti-Al-V alloy improves its corrosion resistance, and the increase of the corrosion resistance depends on the nitrogen dose employed; the maximum improvement of the corrosion resistance was observed at a dose of 1×10¹⁷ N⁺/cm².     

Wear behavior of low-pressure plasma-sprayed AlCuFe quasicrystalline coating on titanium alloy

The wear-resistant AlCuFe quasicrystalline coating was fabricated on substrate of titanium alloy by low-pressure plasma-spraying (LPPS) method. The LPPS AlCuFe quasicrystalline coating has a rapidly solidified lamellar microstructure consisting of mainly icosahedral phase and small amount of cubic phase peaks. The results showed that AlCuFe quasicrystalline coating improved the wear resistance of titanium-based alloys under dry sliding wear test conditions. The excellent wear resistance may be attributed to the high hardness of AlCuFe quasicrystal and the formation of the tribofilm.     

电机换向器片间介电强度自动检测仪设计

介绍了一种交流串励电机换向器片间介电灶度自动偷测仪，采用步进电功饥驱动换向器转动，实现了检测停留时间的精确调节，同时还采用特殊的检测电路和机械结构，实现了检测电压的可调并充分考虑检测仪的可靠性和稳定性，以及对不同规格换向器适应性和操作的简易性。     

文丘里浓淡煤粉燃烧器的分离特性和阻力特性研究

通过对不同结构尺寸的文丘里管内气固两相流动的数值模拟,研究文丘里浓淡煤粉燃烧器的分离特性和阻力特性与文丘里管结构尺寸的关系,为设计和应用新型的浓淡煤粉燃烧器提供理论依据。该浓淡煤粉燃烧器将在防止燃烧器区域结渣,降低氮氧化物(NOx)排放和改善劣质煤着火特性方面发挥作用。     

WHDF增强密实(抗裂)剂对改进面板砼抗裂性能的影响

WHDF增强密实(抗裂)剂,是一种应用于面板堆石坝面板混凝土抗裂的高性能外加剂。笔者运用化学热力学和动力学等研究方法,从砼的微观结构着手,研究水泥水化机理,把水泥水化程度和水化产物与外加剂的抗裂作用机理结合起来研究,使得WHDF抗裂剂能促进水泥水化程度,优化水化产物和协同激发砼中活性混合材料与Ca(OH)2进行二次水化,从而提高砼中凝胶量,降低孔隙率,改善水泥石及其与骨料界面的结构,增强凝胶的粘结力,使砼具有良好的抗裂性能。湖北小溪口电站等近十个水电工程的面板混凝土掺用WHDF后,混凝土表面平滑光泽,均无收缩裂缝产生。     

水库大坝地基地震液化特性及动力有限元分析

为了考虑尔王庄水库大坝地基地碰液化及动力特性，首先通过室内动三轴试验研究粉土、粉砂在动荷载作用下的孔压累积特性。提出了选择双幅应变达到5％作为土样液化的标准；然后采用现场标贯试验和室内动三轴试验对水库坝基中的粉土、粉砂层进行了液化判别，并对判别结果进行了对比分析；同时在液化判别的基础上利用有效应力动力分析方法对坝基土体进行了考虑渗流和不考虑渗流的地震液化的非线性动力有限元分析，并将液化的判别结果与现场标贯试验、室内动三轴试验的判别结果进行对比，从中得出一些有益的结论可供类似工程参考。