防振橡胶材料疲劳寿命研究方法综述

防振橡胶因其具有很大的弹性和良好的绝缘性、可塑性、隔水隔气等特点,广泛应用于汽车工业、国防、建筑等领域。防振橡胶材料的疲劳寿命理论与技术研究对于提高防振橡胶产品耐久性的设计和制造具有重要意义。针对防振橡胶产品的工作特点,指出防振橡胶材料疲劳特性分析的技术难点。从橡胶的疲劳裂纹萌生法、疲劳裂纹扩展法和疲劳损伤法三个角度综述目前橡胶材料疲劳特性的研究进展。针对国内外橡胶疲劳特性研究现状,提出在橡胶疲劳特性研究中应考虑橡胶材料在疲劳载荷作用下特有的Mullins效应、永久变形、循环应力软化等非线性特性,并指明基于连续损伤力学的疲劳损伤法更便于解决复杂疲劳载荷下橡胶材料和结构的疲劳损伤和寿命预测问题。     

球墨铸铁凝固过程的微观模拟

采用过冷形核与扩散控制生长模型,对凝固时球墨铸铁显微组织的形成过程进行了模拟。比较了瞬时形核和连续形核两种形核模型,并讨论了工艺参数对形核和石墨/奥氏体共晶生长的影响。     

Li_2O-Al_2O_3-SiO_2超细粉末的制备及其核化晶化过程的研究

以正硅酸乙脂、钛酸丁脂及Li、Al等的无机盐为原料,采用溶胶-凝胶工艺制备了Li_2O-Al_2O_3-SiO_2(LAS)玻璃陶瓷超细粉末。所得粉末的平均粒径为130 nm,比表面积为160 m~2/g。由差热分析、X射线衍射研究了LAS超细粉的核化与晶化过程。结果表明,超细粉的核化为表面核化,其核化温度与晶体析出温度,比类似组成的块状玻璃降低了100℃与100～200℃。由该超细粉制备的LAS陶瓷具有低的热膨胀系数α<10×10~(-7)℃~(-1)。     

球形非金属夹杂物与焊缝金属的断裂

对四种不同强度级别的焊缝金属的廷性断口和脆性断口上的夹杂物进行了系统的观察与分析,探讨了球形非金属夹杂物对焊缝金属断裂性能的影响。焊缝金属的延性断裂性能与所含夹杂物的数量存在直接的关系,而焊缝金属的解理断裂中有相当大的一部分由尺寸相对较大的,与基体结合强度较高的Ti型夹杂物所引发。     

稀土镁球铁中的非金属夹杂物

提供了非金属夹杂物作为球状石墨非自发形核心的视觉证实。球铁中的非金属夹杂物按其分布有:作为球状石墨核心的夹杂物;被石墨晶体包围的夹杂物;和石墨共生的夹杂物;孤立块状分布在基体中的夹杂物。对球铁性能影响最大的非金属夹杂物是孤立分布的夹杂物。     

针形超微粒α－Fe_2O_3还原过程成核生长动力学

基于成核生长动力学经验方程，导出了气固反应过程成核生长动力学方程，应用于针形超微粒ａ－Ｆｅ２Ｏ３在氢氮气氛中还原过程。利用ＴＰＲ技术得到还原过程成核生长动力学方程。针形超微粒ａ－Ｆｅ２Ｏ３表面氧还原速率随还原程度的增加而增加，体相氧还原速率随还原程度的增加而减小。以制备磁粉为目的的还原最佳温度为３６０～４００°Ｃ。     

Experimental study on crystallization kinetics of alkali feldspar under high T-P conditions

In the granite-NaF-H₂O system, there exists a nucleation lag in the course of alkali feldspar crystallization indicated by experiments on crystallization kinetics. The nucleation lag time is about 18 h at 700℃ and about 6 h at 650℃. Meanwhile, both nucleation rate and crystal-growth rate of alkali feldspar are not constant during the crystallization process, but vary with crystal- lization time. Here we suggest that the lag time should be taken into account in the calculation formula of nucleation rate and crystal-growth rate to obtain more reliable parameters.     

Preparation and characterization of SiO2 non-catalytic nucleation coating for the solidification of undercooled melt

SiO2 non-catalytic nucleation films were coated onto a ceramic substrate and the inner surface of a ceramic crucible by the Sol-Gel method. The surface morphology of the coatings was characterized with an atomic force microscope and a scanning electronic microscope. The non-catalytic effect of the coating on the heterogeneous nucleation of metal melts was tested through measuring the nucleation undercooling. Investigation results indicated that the prepared coating could act as a baffle-wall to prevent the metal melt from nucleating heterogeneously on the inner surface of the crystalline crucible. The tiny holes with a diameter below 2 μm and heaves on the coating surface have no evident effect on the undercooling of metal melts. For a poly-layer coating, the super-layer can cover the cracks in the sub-layers, which prevents the cracks in the coating from spreading in the direction vertical to the coating layers and thus eliminates the effect of cracks on the coating.     

碳含量对中碳含钒微合金钢晶内铁素体等温形成的影响规律

研究了碳质量分数分别为0.26%, 0.33%和0.42%的三种含钒微合金钢在600, 550, 500和450℃下等温处理时碳对晶内铁素体形成的影响,测量了不同等温温度处理后钢的维氏硬度、500℃下晶界和晶内铁素体的纳米硬度,并探讨了晶内铁素体的形核位置. 结果表明:在相同温度下等温处理时,随着钢中碳含量的增高,钢中非共析铁素体的含量降低,铁素体晶粒的尺寸减小,钢的硬度升高. 在500℃等温处理后,晶界铁素体的纳米硬度远高于晶内铁素体的纳米硬度;且随着碳含量的增高,晶界和晶内铁素体的纳米硬度都随之升高,但各实验钢中晶内铁素体的纳米硬度相差不大. 适当的夹杂物和先析出晶内铁素体都可以作为形核位置诱导晶内铁素体析出.     

Formation and transformation of volatile nanoparticles from a diesel engine during exhaust dilution

A classic H 2 SO 4-H 2 O binary homogeneous nucleation model coupled to an aerosol dynamics model,suitable for studying the formation and transformation of volatile nanoparticles (VNPs) during diesel engine exhaust dilution,has been developed.Using the H 2 SO 4-H 2 O binary homogeneous nucleation model,the nucleation ratio and molecular cluster size were calculated.The effect of aerosol dynamic processes on VNP number size distributions was studied.The effects of fuel sulfur content (FSC) and sampling conditions in the laboratory on VNP number size distributions were also calculated.Our simulations demonstrated that nucleation increased the cluster number concentration and that FSC,temperature and humidity significantly affected the nucleation ratio and molecular cluster size.Coagulation promoted the evolution of cluster-particle size distributions from monodisperse to polydisperse.Soot present in the exhaust can suppress the formation of VNPs.FSC and sampling conditions,like the primary dilution temperature,the primary dilution relative humidity,residence time and the primary dilution ratio have significant effects on VNP number size distributions.