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131.
利用冷热疲劳试验机模拟分析了冷热循环对不锈钢复合板热疲劳性能的影响,并采用扫描电镜、电子探针和电子背散射衍射仪对热疲劳试样V形缺口及裂纹区域的形貌和成分进行了深入分析。结果表明,不锈钢复合板热疲劳试样经 20~550 ℃ 7 500次冷热循环后,结合界面处V形缺口区出现微裂纹,且微裂纹起裂于V形缺口尖端基层侧。随着冷热循环的继续进行,微裂纹向基层内扩展,但并非沿着结合界面处扩展,而是沿着基层侧扩展。此外,热疲劳裂纹的起裂和扩展与氧化和应力作用有关,微裂纹起裂于热疲劳试样 V 形缺口区域基层侧表层局部氧化孔洞,并在冷热循环的应力作用下向基层内扩展,同时加剧氧化。随着冷热循环的继续进行,晶界氧化逐渐加剧,导致微裂纹扩展成更为明显的裂纹。 相似文献
132.
针对大型薄壁铝铸件内腔表面出现的沟槽缺陷,从差压铸造、树脂砂、铸件结构等工艺条件方面探讨了产生的机理,并通过试验和对比研究,确定排气不畅是该缺陷的首要引发因素,找到了消除该缺陷的工艺方法,提出了相关预防措施,避免了因此产生的废品损失. 相似文献
133.
134.
Maltose long-chain fatty acid esters (MFAE), esterified at the 6 and 6′ position, were synthesized with stearic, palmitic,
myristic, and oleic groups. Synthesis yields were 15–20% based on initial maltose present, and structural confirmation was
obtained using plasma desorption mass spectrometry and nuclear magnetic resonance spectroscopy. These surfactants have surface
tensions in the range of 34–36 dyn/cm at their critical micelle concentrations (CMC) of approximately 10−5–10−6 mol/L. The increased chain lengths have a marked effect, reducing CMC values for MFAE by approximately three orders of magnitude
over similar carbohydrate-based dodecyl chain sources. Within chain lengths between 14 and 18 carbons, the rate of change
in CMC is significant and decreases with increasing chain length for MFAE. The melting points of MFAE are approximately 40°C,
and the heat capacities range from 1.6 to 1.9 J/g·K. These numbers are comparable to those of sucrose esters, indicating their
applicability in similar uses. However, because MFAE, unlike sucrose, possess an anomeric carbohydrate carbon position, these
surfactants maintain their reducing nature and are susceptible to further derivatization. They are also synthesized from renewable,
economical carbohydrates and lipids and may provide an excellent alternative to pertrochemical-derived products. 相似文献
135.
The modern society is fuelled by very comprehensive grids of gas and liquid pipelines. In recent years, various in-pipe robots have been developed for inspection and maintenance tasks inside such pipes. In this paper, a novel in-pipe robot is proposed and developed for gas/oil well interventions at thousands of meters downhole. Due to the nature of such intervention, in-pipe robot design must be capable of carrying a very large payload, as large as 2500?N inside a pipe with diameter as small as 54?mm. The proposed design concept is based on a compound planetary gearing system. One of the major novelties of this design is the use of pipe wall as a ring gear for one stage of the compound planetary gear system; the other novelty is the generation of helical angle when the planetary gears are expanded to press on the pipe wall. The proposed concept is compact, efficient, and has never been reported before. In this paper, the helical angle, the velocity, and load capability of the proposed system will be analyzed. The load transportation capability of the proposed robot is also measured based on an experiment. Initial data have shown great potential in carrying large payloads. 相似文献
136.
In this paper, nonlinear mapping (NM)-based backstepping control design is presented for a class of strict-feedback nonlinear systems with output constraint. By mapping output value set onto the set of all real numbers, the constrained system is transformed into a new strict-feedback unconstrained system to employ the traditional backstepping control while simultaneously preventing the constraint from being violated. It is proved that the original system has the similar convergence and bounded properties with the new one. Besides the nominal case where full knowledge of the plant is available, we also tackle scenarios wherein parametric uncertainties are present. Furthermore, the comparison with barrier Lyapunov function-based algorithm reveals the advantages of NM algorithm. The closed-loop system is guaranteed to be stable in the sense that all signals involved remain bounded, and the tracking error converges to zero asymptotically. Simulation studies illustrate the performance of the proposed control. 相似文献
137.
138.
In this paper, hyperbranched polyesters (HPs) were synthesized in the molten state from 2,2-bis(hydroxymethyl) propionic acid (bis-MPA) and 2-ethyl-2-hydroxymethyl-1,3-propanediol (TMP) using acid catalysis. The modified hyperbranched polyesters were obtained through the chemical modification of the hyperbranched polyester cores by substituting a controlled fraction of the terminal hydroxyl groups with touluene-4-sulfonyl chloride using triethylamine (TEA) as an acceptor of HCl. The resultant polyesters were characterized by 1H NMR, 13C NMR, FT-IR, UV and GPC and their self-assembly behaviors were investigated. The results revealed that self-assembled structures could be formed in selected solvents (trichloromethane/acetone or trichloromethane/n-hexane). 相似文献
139.
140.
针对远程开关控制技术的需求,提出一种基于GSM的远程开关控制装置设计.该装置的主要特点为使用公众GSM网络进行数据的传递,用户通过手机发送短信即可实现对设备开关的远程异地控制.详细介绍了该装置的硬件设计方案和单片机程序的设计方法,并对设计的装置进行了测试.测试与分析结果表明,设计的装置能实现远程开关控制和返回状态等各种功能,运行效果良好. 相似文献