Initial evaluation of novel polyamide-imides and their copolymers as adhesives

—An adhesive screening study was performed at NASA Langley Research Center on two linear aromatic polyamide-imide (PAI) homopolymers and two linear aromatic PAI copolymers. The homopolymers were made with either of two amide diamines, 3,3'- or 4,4'-diaminobenzanilide (DABA), and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA). The two copolymers studied were prepared with a combination of 3,3'-DABP and amide diamines. These aromatic PAIs possess high thermal stability because of intermolecular hydrogen bonding and chain stiffness. Lap shear strength (LSS) tests, conducted at room temperature, 177, 204 and 232°C, were the primary criterion for evaluation of the polymers as adhesives. Included in the study were measurements of the glass transition temperature made on fractured specimens for each bonding condition and a visual determination of the type of bond failure for specimens at each test temperature. Of the four adhesive candidates investigated, the best LSS values were obtained with the PAI copolymer identified as LARC-TPI(25% 3,3'-DABA). However, the LSS values were higher for the LARC-TPI polyimide with which the adhesive strengths were compared. The combination of a high molecular weight and the increased interchain electronic interaction associated with the amide group appears to contribute to the poor flow properties observed.     

Sliding-induced adhesion of stiff polymer microfibre arrays. I. Macroscale behaviour.

Gecko-inspired microfibre arrays with 42 million polypropylene fibres cm(-2) (each fibre with elastic modulus 1 GPa, length 20 microm and diameter 0.6 microm) were fabricated and tested under pure shear loading conditions, after removing a preload of less than 0.1 N cm(-2). After sliding to engage fibres, 2 cm2 patches developed up to 4N of shear force with an estimated contact region of 0.44 cm2. The control unfibrillated surface had no measurable shear force. For comparison, a natural setal patch tested under the same conditions on smooth glass showed approximately seven times greater shear per unit estimated contact region. Similar to gecko fibre arrays, the synthetic patch maintains contact and increases shear force with sliding. The high shear force observed (approx. 210 nN per fibre) suggests that fibres are in side contact, providing a larger true contact area than would be obtained by tip contact. Shear force increased over the course of repeated tests for synthetic patches, suggesting deformation of fibres into more favourable conformations.     

Investigation of thixotropy behavior of crude oil—Polyacrylamide emulsions

This investigation focuses on the study of the thixotropy behavior of crude oil–polyacrylamide emulsions. A wide range of crude oil and polymer concentrations were covered. Crude oil concentrations of 0–75% by volume and polymer concentrations of 0–10⁴ ppm were used. Two polyacrylamides of Alcoflood polymers, AF1235 and AF1285, were examined. RheoStress RS100 rheometer from Haake was employed to study the thixotropy behavior of crude oil–polymer emulsions. Measurements of thixotropy were conducted under the controlled rate mode. The aqueous solutions of Alcoflood polymers show thixotropy behavior. AF1235 aqueous solutions show lower hysteresis rheograms and thixotropy area than the aqueous solutions of AF1285. Polymer concentration shows strong influence on the ramp‐up and ramp‐down curves. The crude oil–polymer emulsions behave in an antithixotropy response instead of thixotropy behavior experience for the polymer aqueous solutions. The yield stress values of the crude oil–polymer emulsions increase strongly with polymer concentration for ascending and descending cycles. However, for polymer concentration of less than 1000 ppm, crude oil shows strong effects on the emulsion yield stress values for the ramp‐down cycles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

离合式高速飞剪机的动态研究与精度控制

分析了离合式高速棒材飞剪机的响应特性，以及影响和制约其剪切精度的主要因素，提出了提高剪切定尺精度的方法。     

剪力墙非线性分析中多垂直杆元模型的分析与改进

多垂直杆元模型是目前最为常用的一种用于剪力墙结构非线性分析的宏观模型。本文主要对该模型中轴力杆的恢复力特性进行了讨论，文中列举了已有的几种对轴力杆的处理方法，并分别对其适用性进行了分析，然后在已有试验和理论分析基础上，对其中的一种处理方法进行了改进，提出了一个更为符合实际的轴力杆恢复力模型。用这一改进模型对一单片实体墙模型的试算证明它可以用于剪力墙的非线性分析。     

华威商住大厦厚板转换结构设计

介绍四川华威商住大厦工程概况、结构选型、计算及主要技术措施。着重介绍合理调整转换结构竖向刚度满足底部大空间使用要求以及上部短肢剪力墙设计措施。     

京城大厦超高层钢结构设计初探

正在兴建的京城大厦是我国目前最引人注目的一座超高层钢结构建筑。本文对其基础、结构体系、抗风抗震系统、楼盖、构件连接及防锈防火等几个方面进行探讨,并对设计上值得商榷之处提出了自己的见解。     

Wettability of Surface Oxyfluorinated Polypropylene Fibres and Its Effect on Interfacial Bonding with Cementitious Matrix

The surface of high molecular weight polypropylene monofilament fibre was modified using a oxyfluorination method. The oxyfluorination treatment level was varied and a hydrolysis post-treatment was also applied. Contact angles of oxyfluorinated, hydro-lyzed oxyfluorinated and unmodified polypropylene fibres were obtained by dynamic contact angle (DCA) measurement using three liquids of known dispersion, acid and base surface free energy components. The surface free energies were then calculated according to the acid-base theory developed by Good, van Oss and Chaudhury. Surface oxyfluorination largely increased the acid and base components of the fibres' surface free energy compared with unmodified polypropylene fibres. The oxyfluorinated and unmodified polypropylene fibre surfaces were observed by Scanning Electronic Microscopy and Photoacoustic Infrared Spectroscopy. It was found that the surface oxyfluorination largely increases the roughness of the polypropylene surfaces and the carbonyl group content increases as the treatment level increases. The interfacial shear bond strengths between the cementitious matrix and the polypropylene fibres treated under various conditions were determined by embedded fibre pull-out tests. Results showed that the fibre surface oxyfluorination treatments increase the interfacial bond strengths. The correlations between the shear bond strengths and surface free energy components were established. Results showed that fibre/concrete interfacial bonding was best correlated with the acid component of surface free energy of polypropylene fibres.     

三维最大剪应力迹线上的正应力变化规律

利用坐标变换法证明了一般三维塑性流动问题任意点应力状态 ,可以完全由三维最大剪应力迹线上的信息确定 ,进而利用共斜面法给出了三维塑性流动问题沿最大剪应力迹线正应力的变化规律。该规律为求解三维问题的应力应变分布 ,提供了重要的基本方程     

Geometrical imperfection and adiabatic shear banding

This work addresses the effect of small geometrical imperfections on adiabatic shear band (ASB) formation. The separate effect of the length and radius of short notches is systematically investigated in AM50 and Ti6Al4V alloys, using shear compression specimens. It is observed that the length of the imperfection does not influence ASB formation in these experiments. By contrast, the notch-root radius appears to be the dominant parameter for the two materials, in perfect agreement with the analytical predictions of Dinzart et al. [The catastrophic development of shear localization in thermoviscoplastic materials. J Phys 1994; IV(C8): 435–40]. The distribution of deformation energy over the gauge length is modeled numerically. The calculated average dynamic deformation energy levels are quite similar to those that are measured for the two investigated alloys. It is concluded that the global measure of the dynamic deformation energy provides valuable information about ASB failure from geometrical imperfections.