A critical assessment of the Jastrzebski interface condition for the capillary flow of pastes, foams and polymers

This paper presents a review of unusual apparent slip effects in capillary flow rheometry. Many cases of paste, foam and polymer capillary flow have been reported where the classic analysis of Mooney has yielded unviable flow curves and apparent slip velocities; often the analysis of Jastrzebski has been used as an alternative and sometimes as the analysis of first choice. It is shown that the recently developed Tikhonov regularization method of Mooney analysis can be used to yield viable results for some of the cases where the classic Mooney analysis could not. All of the problematic foam and polymer results found in the literature were resolved, as well as some of the problematic paste results. It is shown that the use of the Jastrzebski interface condition, relating apparent slip to capillary radius, yields incorrect flow curves and apparent slip velocities. It is proposed that further research is required to understand the capillary flow of paste which does not conform to the classic Mooney analysis. In the absence of any physical grounding for the Jastrzebski interface condition, it is recommended that it should no longer be used.     

Microfluidic modeling and simulation of flow in membrane microreactors

We study the development of a mathematical model that describes isothermal microfluidic steady flow in a membrane microreactor, i.e., a silicon microreactor that houses a permeable membrane in one wall. The model employs the Navier-Stokes equation with appropriate boundary conditions for fluid permeation through the membrane and velocity slip at the walls to account for high Knudsen number. The model equations are solved analytically using finite Fourier transforms. The model solution is used to evaluate the effect of fluid permeation through the membrane and the Knudsen number on the velocity profile and pressure drop. For the simplified cases of no permeation and/or no slip, the derived solution is in excellent agreement with published experimental and theoretical results available in the literature. The utility of the model is illustrated by applying the results to a membrane microseparator used to separate hydrogen from the other effluents in a microreformer.     

Aqueous Slip Casting of Transparent Aluminum Oxynitride

Highly transparent Aluminum oxynitride (AlON) body has been produced using aqueous slip casting technique. High‐purity alumina and AlN were used as raw materials for the synthesis of single‐phase AlON powder. As‐synthesized AlON powder was surface modified to enable the AlON powders resistant to hydrolysis in water during aqueous slip casting. High solid loaded aqueous AlON slip was prepared for casting followed by drying and sintering to produce transparent AlON. Phase formation and stability was characterized by XRD, pH, and viscosity measurements. AlON powders before and after surface treatments were characterized. Sintered transparent AlON samples were characterized for their mechanical, microstructural, and optical properties. Sintered and polished AlON produced in this study has shown inline transparency up to 80% between 0.22 and 6 μm wavelength region.     

上胶机微机控制系统的研制

描述了用8031单片机对国产上胶机控制系统进行改造的硬件和软件设计以及采取的控制方法。信号的采集、滑差电动机的控制、干扰的抑制、防抖动与防溢出的处理、数字滤波和快速动态调节等措施、保证了系统能够安全可靠地工作。上胶机微机控制系统已投入现场运行。     

二维湍流近壁涡量产生的研究

从不可压Navier—stokes方程出发,分析二维湍流运动固体表面“搓”出涡量的过程,并求得其涡量源强度和拟涡能扩散强度。     

考虑滑移效应的体外预应力波形钢腹板梁桥的应力增量

体外预应力筋的应力增量在波形钢腹板梁桥理论中至关重要。在已有的应力增量计算方法中,适用于波形钢腹板梁桥的方法相对较少,考虑预应力筋滑移效应的更少。为研究适用于波形钢腹板组合梁体外预应力筋应力增量的计算公式,考虑在转向块处体外预应力筋与混凝土之间滑移效应的影响,通过分析预应力筋的变形和结构整体变形的几何关系,推导出对称荷载作用下的应力增量计算公式。结合现有试验数据,利用Ansys建立了实体模型,使用非线性弹簧单元Combin39来实现预应力筋的滑移效应;并将求得的计算值与试验值和模型值进行比对分析。结果表明：推导的应力增量公式计算值与波形钢腹板组合梁试验值吻合较好,验证了该方法的适用性;考虑滑移效应影响时,结构的整体挠度和应力增量增大,承载能力降低。     

波纹钢板-混凝土界面黏结滑移性能试验

为研究波纹钢板-混凝土界面黏结滑移性能,综合考虑混凝土强度、保护层厚度及钢板埋置长度,设计了10个波纹钢板混凝土试件进行推出试验,研究其破坏形态、受力机理、应变分布、黏结强度与黏结滑移本构关系等关键问题。结果表明：波纹钢板混凝土组合构件主要发生黏结劈裂破坏和黏结锚固破坏,试件荷载-滑移曲线可分为微滑移段、滑移段、陡降段、缓降段及残余段;在荷载上升段,波纹钢板应变沿埋置长度呈指数分布形式,钢板自由端应变可能出现过零点现象;通过分析混凝土强度、保护层厚度及钢板埋置长度对波纹钢板-混凝土界面黏结强度的影响,线性拟合得出特征黏结强度计算式,理论值与试验值误差较小;基于波纹钢板-混凝土界面黏结滑移本构模型,通过ABAQUS软件对典型试件进行数值模拟,有限元模型曲线与试验曲线吻合度较高。     

Failure mechanism and stability control of a large section of very soft roadway surrounding rock shear slip

The measured data and simulation test phenomenon of surrounding rock deformation and failure at the project site indicate that shear failure which firstly occurs in surrounding rock, block slip and second shear failure are the root cause of deformation and damage of supporting structure of the surrounding rock at a large scale. We derived limit load of surrounding rock shear slip failure and reasonable support resistance of given load by means of shear slip line field theory, discussed the main factors which influence the limit load of surrounding rock. Shear slip line field and limit load of circular tunnel surrounding rock were obtained by means of physical simulation test, which agreed well with the theoretical analysis results. Based on the theoretical analysis and physical simulation test, the cause deformation and failure at large scale of Xinshanghai No. 1 coal mine big section ingate was analyzed, and the shear failure resistance and block slip in surrounding rock were proposed as the core technical supporting ideas. Proper range of supporting resistance which came from calculation was suggested. The support scheme which is mainly composed of large grouting anchor, sprayed anchor net support technique and full-face grille concrete finally ended the dilemma of repeated failure and mending of ingate and created critical conditions for smooth production in the coal mine.     

软土超深基坑失稳破坏的离心模型试验研究

通过土工离心机对三组挖深24 m软土超深基坑的开挖施工过程及失稳破坏进行模拟,研究了软土超深基坑稳定影响因素、破坏特征与征兆等.结果显示,墙趾进入硬土层后的嵌固作用对"踢脚"变形控制非常有利,也显著提高了基坑稳定性.嵌固作用在墙趾插入到硬土层中一定深度以后不再随插入深度增加而增强.挡墙位于上海典型软黏土中且不进入硬土层时,其临界插入深度比为0.78.软土深基坑失稳破坏征兆:(1)挡墙"踢脚"明显,量值约为墙体最大水平位移1/3;(2)坑外地表沉降达到1.38%H(开挖深度),地面出现大量横裂缝;(3)坑底靠近挡墙的土体隆起大于基坑中部,最大量值达到3.1%～3.8%H;(4)坑内土体处于被动土压力极限状态.可用于综合评判基坑的稳定性,指导类似超深基坑的设计、施工和安全监控.     

高温高应变率下AM60B镁合金力学性能及失效行为

为了研究镁合金在高温、高应变速率下的变形行为及失效机制,采用分离式Hopkinson压杆在应变速率为1 600~4 500 s^-1、温度为27~150 ℃范围内,对真空压铸AM60B镁合金进行了动态压缩实验,并采用金相显微镜和扫描电子显微镜对压缩后的组织进行了观察.结果表明:在所测试的应变范围内,随着应变率的提高,应力-应变曲线均呈现上升趋势,且最大应变也随之增加,表现出正应变率强化效应.在150 ℃时真空压铸AM60B镁合金变形能力最好; 50 ℃时断裂强度最高.真空压铸AM60B镁合金在高温及高应变率下的断裂方式为以解理断裂为主并伴有韧性断裂的混合断裂方式.当变形温度低于150 ℃时,真空压铸AM60B镁合金在高应变率压缩下的变形机制主要是滑移.