Experimental and Numerical Analysis of the Viscous Fingering Instability of Shear‐Thinning Fluids

Miscible flow displacements in a rectilinear Hele‐Shaw cell of Newtonian as well as rheologically well‐characterized shear‐thinning fluids are examined through experimental measurements and numerical modelling. Water is used as a displacing fluid while the displaced fluid consists of either a reference Newtonian glycerol solution or shear‐thinning solutions of Alcoflood? polymers of different molecular weights. The experimental measurements revealed that the shear‐thinning behaviour of the non‐Newtonian solutions resulted in more complex instability patterns and new finger structures not previously observed in the case of Newtonian displacements are identified and characterized. An analysis of the effects of the rheological behaviour of the shear‐thinning fluids on instability characteristics such as the finger width and finger tip velocity is presented. Numerical simulations using a pseudo‐spectral method are conducted and allowed to compare the predictions of the mathematical model based on an effective Darcy's law with the experimental measurements.     

A Thermo-Mechanical Study of Some Epoxy Adhesives Subjected to Combined Dynamic and Static Stresses

The object of the present study was to investigate the effect of superimposed dynamic and static stresses on mechanical and thermal properties of some epoxy adhesives. It was found that combinations of shear creep and torsional oscillations, applied simultaneously to adhesive joints at temperatures within the glassy range of the adhesive, led to strengthening of the joints in shear and to an increase in the glass transition temperature of the adhesive. Similar loading stresses applied at temperatures close to the T_g of the adhesive, led to opposite effects on the above mentioned properties of the joints. The width of the glassy-rubbery transition of the adhesives increased, in the whole range of temperatures used in this study and for all epoxy compositions, as a result of subjecting the joints to superimposed dynamic and static stresses. The broadening of the glass transition was interpreted as a result of the stiffening of polymer network during the combined stressing experiments. A linear relationship was found between the area of endothermal peaks in the first DSC scan of specimens subjected prior to test to superimposed dynamic and static stresses at temperatures below T_g, and the shear strength of the joints. In agreement with this observation and with literature data, a linear relationship was revealed also between the glass transition temperature of the resins (measured in the first DSC scan) and the shear strength of the joints. Based on experimental observations and on some literature information, it was suggested that the strengthening of the joint, as well as the changes in thermal properties of the adhesives, are mainly due to physical processes, such as short-range orientation of network chains and an increase in intermolecular interaction between highly polar sites of the network. The possibility that superimposed stressing led to changes in chemical crosslinking was discussed but it seems that no such reactions occurred.     

钢框架-钢板剪力墙结构修复后的使用性能指标

为便于钢框架-钢板剪力墙结构震后快速修复,统计既有实验结果,提出修复后使用的三级性能指标,基于等效拉杆理论,研究结构在侧向载荷作用下塑性铰的出现顺序、层间位移角和结构应力发展等情况,并建立有限元模型对指标进行验证.结果 表明:在一级修复性能指标(位移角1/220)下,结构板墙轻微受损,对应的修复方法为对板墙进行轻微修复;在二级修复性能指标(位移角1/110)下,结构板墙几乎全面进入塑性状态,需要考虑换板或增加加劲肋修复;在三级修复性能指标(位移角1/85)下,结构板墙已经全部进入屈服状态,而且框架梁端也出现塑性铰,此时不仅需要对板墙进行修复,还要考虑对框架进行修复.     

边界约束对弯曲-伸展元三轴波速试验的影响

利用弯曲-伸展元开展干砂小应变剪切波试验和除气水压缩波试验,研究了三轴试样的不同约束边界对弯曲-伸展元量测剪切波速和压缩波速的影响,并对波速试验结果进行分析。研究结果表明:以干砂为试验对象的剪切波速试验结果介于砂土中剪切波速与边界材料的剪切波速之间,受到约束边界的材质、长度和壁厚的显著影响;而以除气水为试验对象的压缩波速试验结果受样品约束边界的影响较小。在不同约束材质下,剪切波在干砂中的传播速度与约束材料的刚度有关,材料的刚度越小对干砂剪切波速测试结果影响越小。弯曲-伸展元激发频率的相关性与边界约束无关,只与测试材料有关。研究成果有助于获取准确的弯曲-伸展元波速试验结果。     

Erosion-corrosion investigation of high chromium cast irons using newly designed jet type tester

A jet type erosion-corrosion tester was developed for the erosion-corrosion investigation of high-chromium cast irons. During tests the size and the shape of particles in the slurry can be maintained stable. The jet velocity and attack angle can be accurately controlled. The repeatability and ranking consistency of the test results are satisfactory. The test parameters can be adjusted in a wide range, so that the tester can simulate various practical working conditions. Electrochemical test data can be automatically collected and processed. Dynamic polarization curves can be obtained during erosion-corrosion test, which can be used to study the dynamic corrosion characteristics.Two high chromium cast irons were studied in hot concentrated alkaline slurry. The results show that the erosioncorrosion mass loss rate and dynamic corrosion rate of 295Cr26 iron is lower than that of 185Cr13 under the conditions similar to alumyte processing. The mechanism of erosion-corrosion of 295Cr26 and 185Cr13 was studied by using the tester. The interaction between erosion and corrosion was also quantitatively evaluated.     

不同应力状态下铝合金变形及损伤机理的研究

利用改装的Arcan夹具对铝合金（6063）的蝶形试样进行0°，30°，45°，60°，90°的拉伸及拉伸卸载试验，研究了铝合金在不同应力状态下变形及损伤机理。结果表明：铝合金在不同应力状态下的工程应力一应变曲线明显不同。0°加载时，在蝶形中心产生微孔洞，微孔洞之间剪切，从而产生了微裂纹。随着微裂纹的扩展、连接导致试样断裂。随着试样中三轴应力度的减小，在蝶形试样中心的剪切应力不断增大，同时在蝶形试样中的剪切变形带越来越集中。显微裂纹首先在剪切带中产生，随着微裂纹的扩展导致试样的断裂。90°拉伸时，在蝶形中心形成明显的剪切变形带。90°加载时，在试样中产生的剪切带是形变剪切带而非相变剪切带。利用有限元软件ABAQUS对不同角度拉伸试验进行模拟，从而得出了不同应力状态下的塑性区的形状和大小。     

采用锥型砧座测定微小钢球的硬度及其方差分析

在WELSON－A653T洛氏硬度计上,采用自制凹锥形砧座测试微小钢球的硬度,解决了微小钢球在常用平面砧座和V形砧座上易打滑,不易固定,致使压头打在砧座上,损坏压头和砧座的难题,并采用方差分析的方法,将该法与传统试验方法相比较,验证其检测结果与传统法所获得检验结果无显著性差异。     

国外先进的用于生产过程控制的硬度计及其新技术简介

提出了过程控制硬度计这一全新的概念,指出了作为过程控制硬度计应该具有的性能特点;全面地分析了国产硬度计同国际上先进的用于过程硬度控制的硬度计在性能和功能上的差距;介绍了作为国际上专门生产过程控制硬度计的瑞士ERNST公司的产品及其产品的特点,为国内硬度计的使用单位采购硬度计的选型,以及为硬度计的制造企业今后产品的研制方向提供了一个很好的参考.     

非晶Pd—Cu—Si合金的流变行为

在连续温条件下，测量了非晶Ｐｄ－Ｃｕ－Ｓｉ合金的应变速率和粘度随温度的变化曲线，在玻璃转变和晶化温区分别观测到伴随玻璃转变和晶化过程的粘度极小值，研究了升温速率对粘度极小值的影响，用结构转变的界晶模型解释了非晶Ｐｄ－Ｃｕ－Ｓｉ合金的粘滞行为。     

30MnCrNiMoB低合金钢绝热剪切带的形成机制与微结构

研究了３０ＭｎＣｒＮｉＭｏＢ低合金钢在穿甲弹冲击下绝热剪切带（ＡＳＢ）的形成机制。指出在高速变形（冲击）条件下ＡＳＢ的形成是应变硬化、热软化和位错动态发时导致的应变软化等因素相互耦合产生的塑性失稳现象。进一步确认ＡＳＢ内具有周期性微观结构，并说明ＡＳＢ中周期性开裂与微结构的关系。