B4C/(W,Ti)C陶瓷喷砂嘴冲蚀磨损机理研究

采用热压烧结工艺制备了B4C／(W，Ti)C陶瓷喷砂嘴；采用SiC、白刚玉和棕刚玉磨粒对所制备的喷砂嘴进行冲蚀试验，在应力分析基础上探讨了陶瓷喷砂嘴的冲蚀磨损机理，结果表明：B4C／(W，Ti)C陶瓷喷砂嘴的冲蚀率随着磨粒硬度和粒度的提高而增大；喷砂嘴入口磨损最严重，出口次之，而中间区域磨损相对较轻；相应的应力分析结果同试验结果相吻合；以棕刚玉作为冲蚀磨料时，B4C／(W，Ti)C陶瓷喷砂嘴主要呈现应力疲劳断裂冲蚀特征，而以白刚玉和SiC作为冲蚀磨料时，喷砂嘴入口处主要呈现脆性断裂冲蚀特征，中问区域则主要呈现应力疲劳断裂冲蚀特征。     

Al2O3基陶瓷刀具材料摩擦磨损特性及其有限元分析

以添加TiC、Ti（C，N）和SiCw 3种Al2O3基陶瓷刀具材料作为研究对象，在MRH-3型高速环-块摩擦磨损试验机上研究3种陶瓷刀具材料在相同试验条件下的摩擦磨损性能，通过扫描电子显微镜对陶瓷的磨损表面进行观察，并利用ANSYS有限元软件分析计算磨损时的应力分布．结果表明，Al2O3基陶瓷刀具材料的摩擦磨损特性与其添加剂的种类有关，其抗磨性能由大到小顺序依次为Al2O3／SiCw〉Al2O3／Ti（C，N）〉Al2O3／TiC．Al2O3基陶瓷刀具的摩擦磨损性能与其硬度（H）、弹性模量（E）和断裂韧性（KIC）有关，磨损率W随E／H增加而增大，随KIC增加而减小．Al2O3／TiC陶瓷刀具材料的磨损机理以粘着磨损为主，Al2O3／Ti（C，N）和Al2O3／SiCw陶瓷刀具材料的磨损机理主要为磨粒磨损．     

陶瓷水煤浆喷嘴的热冲击特性及有限元分析

采用热压烧结工艺制备出口无锥度(直口)和出口带锥度(锥口)2种Al2O3/TiC陶瓷水煤浆喷嘴,在工业锅炉上研究其热冲击行为,采用扫描电子显微镜分析喷嘴磨损表面形貌和微观组织结构,利用有限元法分析喷嘴的温度场和热应力.结果表明:陶瓷水煤浆喷嘴的出口结构对其热冲击行为影响很大,锥口喷嘴因所受热辐射面积小于直口喷嘴,内部的温度梯度和热应力较低,表现出较好的抗热冲击性能;Al2O3/TiC陶瓷喷嘴的温度梯度和热应力由入口到出口逐渐增大,出口部位的较高温度梯度和热应力是导致其磨损失效的主要原因;Al2O3/TiC陶瓷喷嘴的磨损形式表现为脆性断裂、研磨损伤、热裂纹和热崩等特征,其中热裂纹和热崩为主要磨损形式.     

SiC/(W,Ti)C梯度陶瓷喷嘴材料的制备及其冲蚀磨损机理研究

针对陶瓷喷嘴磨损特点,在喷嘴材料的设计和制造中提出运用梯度功能材料理论,通过控制陶瓷喷嘴材料的成分分布以实现其力学性能的合理梯度变化,将梯度陶瓷喷嘴材料制备过程中所产生的残余压应力引入喷嘴入口以提高喷嘴入口的力学性能,从而缓解喷嘴入口的高应力,提高其抗冲蚀磨损能力.采用热压烧结工艺制备SiC/(W,Ti)C梯度陶瓷喷嘴材料并分析其冲蚀磨损机理.结果表明,在相同冲蚀磨损条件下,梯度陶瓷喷嘴材料的抗冲蚀磨损性能较非梯度陶瓷喷嘴材料显著提高,这是由于梯度陶瓷喷嘴应力状态的改善及其力学性能提高的缘故.梯度陶瓷喷嘴材料的磨损机制为入口处呈现疲劳断裂、中间呈现微切削、出口处呈现疲劳断裂和脆性断裂特征.     

热处理对NiTi形状记忆合金冲蚀磨损性能的影响

采用自制浆罐式砂水冲蚀磨损试验装置研究了4种经不同条件热处理的NiTi合金与1Cr18Ni9Ti不锈钢的冲蚀磨损性能;采用XL-30型扫描电子显微镜观察试样的冲蚀磨损表面形貌;采用MH-6型显微硬度计测量NiTi合金硬度;采用自制拉伸装置测量NiTi合金的力学性能.结果表明:5种试样的冲蚀磨损量随着冲蚀时间、冲蚀速度、砂水比及砂粒度的增加而增大,4种NiTi合金的耐冲蚀性能相近,均明显优于1Cr18Ni9Ti不锈钢,其中试样NiTi-3和NiTi-1表现出较好的耐冲蚀性能;硬度并非NiTi合金冲蚀磨损性能的决定因素,超弹性和超塑性是NiTi合金具有较好耐冲蚀性的主要原因,热处理使得NiTi合金的超弹性变形量减小,但增加了NiTi合金的塑性变形量;合金丝磨损表面不同部位的磨损机理不同,中部为典型的变形磨损,侧面为微切削磨损,5种试样均表现为典型的韧性材料冲蚀磨损特征.     

陶瓷刀具干切削等温淬火球铁(ADI)的磨损机理研究

采用陶瓷刀具(CC650)和YG6硬质合金刀具对等温淬火球墨铸铁(以下简称ADI)材料进行干式精车切削试验, 采用带有X射线能谱分析的扫描电子显微镜观察刀具磨损表面形貌, 用能谱仪对刀具磨损微区和工件表面成分进行分析, 用X射线衍射仪对刀具、 ADI材料和切屑等试样进行物相分析, 研究陶瓷刀具磨损形态及其磨损机理. 结果表明: 刀具磨损的主要形式为磨粒磨损、粘着磨损、 扩散磨损及微崩和脱落; ADI材料中含有微量Al和Ti元素, 在较高速度下切削ADI材料时, 刀具与工件之间的亲和性增加而导致粘着磨损; 在刀具前刀面平均切削温度大于800 ℃以上时,ADI材料中的元素Fe和Si扩散到刀面,刀具中的元素Al和Ti扩散到ADI材料表面,从而加剧刀具的磨损;切削后ADI材料表面出现的Al2O3相及切屑中的FeCr相等高硬度化合物颗粒是造成CC650刀具磨粒磨损的主要原因.     

钝化处理1Cr18Ni9Ti不锈钢在H2O2 水溶液中的摩擦学性能初探

为研究1Cr18Ni9Ti不锈钢钝化膜在H2O2水溶液中的摩擦学性能,对1Cr18Ni9Ti不锈钢表面进行了酸洗钝化处理,利用CS300电化学测试系统和XPS对不锈钢表面钝化膜的电化学行为、元素组成和化学状态进行了分析;用SST销-盘式摩擦磨损试验机研究了1Cr18Ni9Ti不锈钢盘与GCr15钢球摩擦副在不同浓度H2O2水溶液中配副时的摩擦学性能;用TR240形貌轮廓仪和扫描电子显微镜(SEM)观察分析了盘试样磨损处的轮廓形貌、磨痕面积和微区结构.结果表明,1Cr18Ni9Ti不锈钢经钝化工艺处理后,耐腐蚀性能显著提高,且表面形成一层富氧、富铬、贫铁的钝化膜,其主要成分是Cr2O3;钝化后的1Cr18Ni9Ti不锈钢在过氧化氢溶液中的摩擦系数较钝化前均出现不同程度的降低,耐磨性提高;钝化或未钝化的1Cr18Ni9Ti不锈钢在过氧化氢溶液中的磨损机理均表现为黏着磨损、磨粒磨损和腐蚀磨损,但在90%H2O2水溶液中,盘磨损表面的黏着作用明显减轻.     

聚氨酯-Si3N4陶瓷复合材料浆体冲蚀磨损性能研究

利用聚四氢呋哺醚二醇和甲苯二异氰酸酯反应得到预聚体，将预聚体同经过表面处理的Si3N4陶瓷粉末共混，利用模压硫化和常温硫化制得聚氨酯-Si3N4陶瓷复合材料；采用LJ-500型拉力试验机测定了所制备的聚氨酯-Si3N4复合材料的抗拉强度和断裂伸长率；采用MSH型冲蚀磨损试验机对比考察了聚氨酯、2Crl3钢、45^#钢及聚氨酯-Si3N4复合材料的抗冲蚀磨损性能；采用扫描电子显微镜观察了冲蚀磨损表面形貌，探讨了Si3N4陶瓷粉末增强聚氨酯弹性体的冲蚀磨损机理．结果表明：聚氨酯-Si3N4复合材料的抗冲蚀磨损性能显著优于2Crl3钢和45^#钢；当Si3N4粉末质量分数为5％～10％时，相应的聚氨酯-Si3N4复合材料的抗冲蚀磨损能力同聚氨酯弹性体相比提高80％以上；聚氨酯／Si3N4陶瓷粉末复合材料主要冲蚀磨损机制为Si3N4聚集体或附聚体的溃裂脱落．     

Al2O3—40%TiO2和Cr2O3等离子喷涂层的摩擦磨损特性

研究了AC4C铸铝合金表面等离子喷涂Al2O3-40%TiO2和Cr2O3陶瓷粉末涂层的滑动摩擦磨损特性;采用划痕试验方法测定了涂层与基体之间的结合强度;用扫描电子显微镜观察分析了磨痕形貌和涂层显微组织特征.研究结果表明:Cr2O3涂层的摩擦学性能优于Al2O3-40%TiO2涂层;涂层的结合强度、硬度和表面空隙对磨损影响较大;Al2O3-40%TiO2涂层的磨损机理主要表现为塑性变形和层状剥离;而Cr2O3涂层则主要为磨粒磨损     

稀土对6063Al镍基激光熔覆层组织及摩擦磨损性能的影响

利用激光熔覆技术,在6063Al表面制备了添加有La2O3、Y2O3、Ce O2的Ni60合金熔覆层,并通过SEM、XRD、显微硬度计和摩擦磨损试验机等设备的测试分析,研究稀土氧化物对6063Al表面Ni基激光熔覆层组织结构、硬度及摩擦磨损性能的影响.结果表明:不同成分熔覆层的主要相结构均为β-Ni Al(Cr)和少量的Al3Ni、Al Ni3和Al等,但La2O3+Ni60熔覆层中含稀土化合物Al4La,Y2O3+Ni60熔覆层中出现了YAl3、Al Ni Y和Ni17Y2,Ce O2+Ni60熔覆层中检测到了Ce Ni5和Ce3Ni6Si2;添加不同稀土氧化物的Ni60熔覆层呈现细密的、均匀分布的枝晶,无明显气孔,其晶粒较不含稀土的Ni60熔覆层明显细化;加入稀土氧化物的Ni60熔覆层硬度提高HV100~300,且随着深度的增加,硬度值比未加稀土的Ni60熔覆层过渡较平缓;和Ni60熔覆层相比,添加稀土氧化物La2O3、Y2O3和Ce O2的Ni60熔覆层磨损面崩损程度减小了,具有较平整的表面磨痕形貌,磨痕深度和宽度均大幅减小,磨损量减少了一个数量级,摩擦系数也较低,其中加入La2O3和Ce O2的熔覆层磨损量最低,耐磨性最好.     

Preface: Current research progress on mechanics of high speed rail

The construction and operation of high-speed rail（HSR）grid within the past two decades in China,in terms of the scale,may be possibly comparable to any national-wide construction in the history of China,even the Great Wall.By counting railways with commercial train service at the speed of200 km/h,China has the world’s longest HSR network with over 19 369.8 km of track in service today and this number     

ACTA MECHANICA SINICA 2014 ANNUAL SUBJECT INDEX

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人造地震动合成中的位移误差分析

三角函数级数法是合成人工地震动常用算法之一,但是通过对加速度积分求取位移时,却存在与零线漂移相类似的位移漂移现象。     

Rainwater rivulets on a cable subject to windFilets d'eau de pluie sur un câble soumis au vent

Rainwater rivulets appear on inclined cables of cable-stayed bridges when wind and rain occur simultaneously. In a restricted range of parameters this is known to cause vibrations of high amplitudes on the cable. The mechanism underlying this effect is still under debate but the role of rainwater rivulets is certain. We use a standard lubrication model to analyse the dynamics of a water film on a cylinder under the effect of gravity and wind load. A simple criterion is then proposed for the appearance and position of rivulets, where the Froude number is the control parameter. Experiments with several geometries of cylinder covered with water in a wind tunnel show the evolution of the rivulets with the Froude number. Comparison of the prediction by the model with these experimental data shows that the main mechanism of rivulet formation and positioning is captured. To cite this article: C. Lemaitre et al., C. R. Mecanique 334 (2006).     

Hermitian space-time finite elements for estuarine mass transport

Space-time finite element solutions of the convection–dispersion equation using higher-order nodal continuity and Hermitian polynomial shape functions are described. Five separate elements ranging from a complete linear element with C^0,0 nodal continuity to a complete first-order Hermitian element with C^1,1 nodal continuity are subjected to detailed analysis. Wave deformation analyses identify the source of leading or trailing edge oscillations, trailing edge oscillations being the major source of difficulty. These observations are confirmed by numerical experiments which further demonstrate the potential of higher-order nodal continuity. The performance of the complete first-order Hermitian element is quite satisfactory and measurably superior to the linear element.     

Cristallisation par onde acoustique : le cas de l'héliumCrystallization by acoustic waves: the case of helium

We establish a theoretical model to explain the nucleation of a crystal of helium by an acoustic over-pressure. We explain the interfacial laws for this ultra-fast cristallization, close to the sound speed. Assuming spherical symmetry and taking into account the experimental data, we recover the dynamics of the growth and melting during an over-pressure impulse. To cite this article: M. Ben Amar et al., C. R. Mecanique 331 (2003).     

Structure initiale et propriétés de liquéfaction statique d'un sableInitial structure and static liquefaction properties of sand.

Based on the use of two different preparation procedures for reconstituting triaxial samples of sand, i.e. wet tamping and dry pluviation, significant differences in associated mechanical behaviour are observed on a reference sand with respect to the phenomenon of ‘static’ liquefaction. Wet tamping favours the initiation of liquefaction instability, whereas dry pluviation favours a more stable behaviour, less susceptible to liquefaction. Microscopic observation of corresponding sand specimens allows us to identify two well differentiated structures, i.e., for wet tamping, an irregular structure with predominance of aggregates (aggregated grains) and macropores, very contractant and unstable and, for dry pluviation, a more regular structure, without macropores, more dilatant and more stable. These observations show the importance of further characterization, based on the introduction of appropriate parameters, of the initial structure of sandy materials, strongly dependant upon their mode of formation (natural or artificial). To cite this article: N. Benahmed et al., C. R. Mecanique 332 (2004).     

Sources of Complexity in Human Systems

Complex is a special attribute we can give to many kinds of systems. Although it is used often as a synonym of difficult, it has a specific epistemological meaning, which is going to be shared by the incoming science of complexity. Difficult is an object which, by means of an adequate computational power, can be deterministically or stochastically predictable. On the contrary complex is an object which can not be predictable because of logical impossibility or because its predictability would require a computational power far beyond any physical feasibility, now and forever. For complexity refers to some observing system, it is always subjective, and thus it is defined as observed irreducible complexity. Human systems are affected by several sources of complexity, belonging to three classes, in order of descending restrictivity. Systems belonging to the first class are not predictable at all, those belonging to the second class are predictable only through an infinite computational capacity, and those belonging to the third class are predictable only through a trans-computational capacity. The first class has two sources of complexity: logical complexity, directly deriving from self-reference and Gödel's incompleteness theorems, and relational complexity, resulting in a sort of indeterminacy principle occurring in social systems. The second class has three sources of complexity: gnosiological complexity, which consists of the variety of possible perceptions; semiotic complexity, which represents the infinite possible interpretations of signs and facts; and chaotic complexity, which characterizes phenomena of nonlinear dynamic systems. The third class coincides with computational complexity, which basically coincides with the mathematical concept of intractability. Artificial, natural, biological and human systems are characterized by the influence of different sources of complexity, and the latter appear to be the most complex.