蠕动进给超声磨削ZrO_2陶瓷实验研究

建立了超声磨削在小直径磨轮、大切深、蠕动进给条件下单颗磨粒最大切深模型; 对ZrO2陶瓷进行蠕动进给机械磨削和蠕动进给超声磨削对比试验, 考察了磨削参数对磨削力的影响.实验结果表明: 超声振动可减小磨削力.     

Steady regimes of conversion in a viscoelastic medium

The problem of propagation of a steady conversion front in a viscoelastic medium is solved by the method of matched asymptotic expansions in the approximation of low strains. The heat flux is assumed to satisfy the Fourier law, and the components of the stress and strain tensors are related by the Maxwell relations including the shear coefficient of viscosity. The temperature of the products and the velocity of propagation of the steady reaction front are found. The solution of the problem is obtained for the limiting cases of the small and large times of relaxation of viscous stresses. It is demonstrated that the model contains different regimes of reaction-front propagation, like the coupled models of solid-phase combustion for a thermoelastic body, and viscous stresses insert additional features. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 5, pp. 63–73, September–October, 2006.     

Shear creep resistance of styrene–isoprene–styrene (SIS)‐based hot‐melt pressure‐sensitive adhesives

The effects of the properties of substrates and tackifier on the shear creep of SIS‐based HMPSAs were investigated. The holding power (t_b) and shear adhesion failure temperature (SAFT) were measured. The relationship between the complex viscosity and the holding power was examined. The holding power and SAFT values of the triblock SIS blends were higher than those of the diblock‐containing SIS blends, perhaps because blends using triblock SIS have higher crossover temperature and complex viscosity than those using diblock‐containing SIS. Higher levels of aromatic resin‐modified aliphatic tackifier and rosin ester were found to decrease the holding power of the HMPSAs. This maybe due to the fact that rosin ester and aromatic‐modified aliphatic resin are compatible with both the ends and midblocks of SIS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 825–831, 2006     

轮胎稳态侧倾力学特性理论建模

研究了轮胎侧倾建模机理,并在此基础上导出了轮稳仿而倾的侧向力、回正力矩、纵向阻力和翻转力矩特性表达式。讨论了车轮定位时侧倾角与前束角的关系,引入了有效侧倾角概念,并基于此给出了子午线轮胎比斜交轮胎侧倾侧向力小的理解解释。     

基于最小熵增法编程确定非共沸混合工质的最佳组分比

以非共沸混合工质在蒸发器中沿程温度分布变化所导致传热不可逆熵增为目标函数,建立混合工质与冷媒水在蒸发器中的稳态换热模型,以换热温差最小值为基准,编程分析计算得出二元混合工质R290／R600在不同组分比下的相对熵增,选取其中最小值对应组分比为最佳组分比。     

Recent progress in the modeling of high-temperature creep and its application to alloy development

Recent progress in the understanding of high-temperature creep of alloys is discussed in the context of theoretical modeling and its application to alloy development. Emphasis is placed upon those engineering alloys specifically designed for high-temperature applications, such as precipitation and dispersion-strengthened (DS) alloys and metal-matrix composites (MMCs). Currently, these theoretical models use one of two different approaches, (a) a phenomenological approach, which is used in such models as those based on the internal stress concept, and those based on empirical creep equations; and (b) micromechanical models that are based on dislocation mechanisms and the interactions of dislocations with solute atoms, second-phase particles, and other reinforcements such as fibers. All these theoretical models have a common goal, namely, the understanding of high-temperature strengthening mechanisms and the relationship between high-temperature strength and the micromechanical mechanisms during high-temperature plastic deformation of the alloys. These theoretical studies can provide information that is useful in alloy design and processing, such as the selection of alloy chemistry, and the optimization of phase microstructural features (e.g., reinforcement amount, shape, size, and distribution; matrix grain size; and matrix and reinforcement interfaces) by optimization of processing methods. L. Shi, Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22901, USA     

THE CREEP─DAMAGE BEHAVIOUR FOR SINGLE CRYSTAL NICKEL-BASE SUPERALLOY

基于镍基单晶合金蠕变过程中的细、微观组织结构变化及损伤特点，本文建立了考虑材质劣化和空洞损伤的双参数蠕变损伤本构方程及寿命预测模型。利用ＤＤ３单晶材料〈００１〉晶体取向的７６０，８５０和１０００℃实验结果考核表明，所建模型可以比较准确地预测蠕变第二、第三阶段变形状态及破坏特征。第二阶段持续时间、第三阶段开始时间可以表示成蠕变应力的指数函数；随着温度的升高，材料劣化加剧，空洞损伤也增加。     

CREEP DEFORMATION OF INTERMETALLIC ALLOYS

ＣＲＥＥＰＤＥＦＯＲＭＡＴＩＯＮＯＦＩＮＴＥＲＭＥＴＡＬＬＩＣＡＬＬＯＹＳＧｅｒｈａｒｄＳａｕｔｈｏｆｆ（Ｍａｘ－Ｐｌａｎｃｋ－ＩｎｓｔｉｔｕｔｆｕｒＥｉｓｅｎｆｏｒｓｃｈｕｎｇＧｍｂＨ．，Ｄ－４００７４Ｄｕｓｓｅｌｄｏｒｆ，Ｇｅｒｍａｎｙ）Ａｂｓｔ...     

蠕变局部损伤理论在裂纹扩展研究中的应用

根据局部损伤理论和相似原理,给出了蠕变裂纹启裂前的孕育上下限时间并了蠕变裂纹扩展率方程。在常载荷下用2．25Cr-1Mo钢作了蠕变裂纹扩展试验,高拘束使早期局部损失发展迅速,试验结果与孕育结果下限接近。稳诚预测值由于忽略未开裂部分材质劣化而略低于试验结果值。