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41.
Recently, it has been reported by our group and others1.2 that loss of curing agent is encountered during the curing of small droplets or thin films of amine cured epoxies. In our earlier study3 results were reported on loss of curing agent in small droplets used in conducting the rnicrobond, single fiber test for determination of interfacial shear strength (ISS). It was reported that use of a volatile curing agent (meta-phenylene diamine (m-PDA) with DGEBA resin) resulted in increasing amounts of curing agent being lost (as measured by T8 of the cured droplets) with decreasing droplet size during the processing procedure. Droplets smaller than 150 micrometers were seen to lose up to 40% of the curing agent leading to alteration of the mechanical properties of the droplet and, therefore, causing measured values of ISS to be exceedingly low. Use of a less volatile curing agent (Jeffamine 700, a polyether diamine, Texaco Specialty Chemicals) in combination with DGEBA resin produced results which indicated that loss of curing agent was not occuring. This study was undertaken to show the relationships between film (or droplet) size and the amount of curing agent lost (during the processing) for three different aminecured epoxy systems. 相似文献
42.
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 Tg 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 Tg, 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. 相似文献
43.
主要介绍了粘接技术在高功率铁氧体移相器上的应用。通过对其工艺途径及关键工序的控制,提出了采用粘接技术完成高功率移相器铁氧体的连接,不仅可以大量地缩短工作时间,而且可以使制造成本大幅度降低。 相似文献
44.
轧机机架强度和刚度的研究 总被引:3,自引:0,他引:3
本文对轧机机架的强度和刚度进行了研究。研究结果表明,增加机架横梁的高度是改善轧机机架刚度最有效也是最经济合理的方法。 相似文献
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46.
对调质状态800MPa低合金高强度钢及其焊接接头进行了系列温度的断裂韧性测试,讨论不同焊接方法对焊接接头断裂韧性的影响。发现板材的轧制方向对断裂韧性影响显著,LT方向试件的断裂韧性远超过TL方向试件的断裂韧性。在-60℃以上,母材处于上平台延性断裂范畴。在-80℃,裂纹扩展过程中有延脆断裂模式的转变。焊条电弧焊焊缝的断裂韧性与气体保护焊焊缝的断裂韧性相当。尽管常温下焊缝金属的断裂韧性甚至优于母材,但随着试验温度的降低,焊缝金属的断裂韧性迅速下降。在-20℃已发生断裂模式转变,这在结构服役时要引起重视。本研究为大型工程机械的断裂安全评定奠定了基础。 相似文献
47.
48.
为优化线路的整体投资,需在线路设计各个环节进行控制,包括路径的优化、铁塔及基础的选型等,其中基础型式的选择对工程投资影响极大,文章对斜插式基础受力问题做简要分析. 相似文献
49.
50.
Ravi Shanker Vidyarthy Dheerendra Kumar Dwivedi Vasudevan Muthukumaran 《Materials and Manufacturing Processes》2018,33(7):709-717
In the present work, the influence of process parameters such as welding current (I), welding speed (S), and flux coating density (F) on different aspects of weld bead geometry for example depth of penetration (DOP), bead width (BW), depth to width ratio (D/W), and weld fusion zone area (WA) were investigated by using the central composite design (CCD). 9–12% Cr ferritic stainless steel (FSS) plates were welded using A-TIG welding. It was observed that all input variables have a direct influence on the DOP, BW, and D/W. However, flux coating density has no significant effect on WA. Mathematical models were generated from the obtained responses to predict the weld bead geometry. An optimized DOP, BW, D/W, and WA of 6.95?mm, 8.76?mm, 0.80, and 41.99?mm2, respectively, were predicted at the welding current of 213.78 A, the welding speed of 96.22?mm/min, and the flux coating density of 1.99?mg/cm2. Conformity test was done to check the practicability of the developed models. The conformity test results were in good agreement with the predicted values. Arc constriction and reversal in Marangoni convection were considered as major mechanisms for the deep and narrow weld bead during A-TIG welding. 相似文献