安心读书，踏实做事儿，你必有用，

人大太犬

大侠，我读交流控制，觉的比直流难多了，先期不理解的东西好多，只好死记硬背了。磁的部分懂的太少了，学交流机就是硬伤啊。

爱猫人士薛定谔

如果没有8爷以及必威体育网址各位大侠的指点，我可能早就被周围的“差不多就行了”，“随便搞一下”，“凑活”，“百度一下”给带阴沟里了。接触的人多了，越发觉得只有有基础有数学才是真正的硬道理，还在继续努力，总会有所收获

天水蓝

村子里有些人，就是早上出来，蹲在南墙根晒太阳，天南海北啥都懂闲扯， 顺便抱怨一下老天如何不公，老板如可刻薄，隔壁那个sb那么卖力气挣不了几个钱，有啥用， 等等。 然后回家喝粥吃咸菜， 下午接着出来晒着太阳，择虱子。
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一路一路

大侠的意思是北京是英雄不问出处，你行你就上，而上海就是要先看学历看业绩再论其他吗？
* S C' N1 g/ J' U像我这种本科在上海是不是得事倍而功半。

feibiaoshebei

努力，共勉

walyem

昨天翻了下笔记，居然看了那么多书，而笔记上基本都不记得了。碰到急的就抓耳挠腮的，发现很多东西好理解，用起来就难.

爱猫人士薛定谔

http://www.astm.org/DIGITAL_LIBRARY/JOURNALS/JAI/PAGES/JAI13069.htm
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Influence of Cold Rolling Threads Before or After Heat Treatment on the Fatigue Resistance of High Strength Fine Thread Bolts for Multiple Preload Conditions

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b8 }1 s- h! FSI class 12.9 high strength steel bolts were used to investigate the fatigue behavior of bolt threads rolled before/after heat treatment at five different preload values. Bolts used were 3/8 UNRF-24 (fine) and preloads were taken as 1, 50, 75, 90, and 100 % of roll before heat treatment proof stress. Since proof stress was lowered 10 % for roll after heat treatment, these preloads for roll after heat treatment bolts were then actually 1.1, 55, 83, 100, and 110 % of proof stress (to keep load the same). The tests produced a range of R ratios (R=Smin/Smax) between 0.03 and 0.92. Maximum near surface residual compressive stresses, obtained via x-ray diffraction, ranged from ?500 to ?1000 MPa. Axial loads were applied through the nut and all fatigue failures occurred at the first thread of the nut/bolt interface with crescent shaped cracks dominating in most tests. Multiple ratchet marks (separate crack nucleation sites) occurred for roll before heat treatment bolts, while fewer or no ratchet marks, were evident for the roll after heat treatment. Scanning electron microscopy evaluation indicated all fatigue crack growth regions contained multiple fatigue facets, while final fracture regions contained ductile dimpling. Cyclic creep/ratcheting was monitored and little, or none, was observed for preload tests equal to or less than 75 %. Replication data indicated a log-normal distribution on life was very reasonable. The fatigue resistance for fine threads rolled after heat treatment with preload stresses of 1 % (R ratio less than 0.05) caused very large increases (158 %) in 107 cycles fatigue strength compared to roll before heat treatment. This is in agreement with other roll before/after low R-ratio results. The roll after heat treatment bolts when tested at the higher proof loads had 107 fatigue strengths of 69 to 30 % increase. These increases are much less than the 158 % at 1 % preload, but still significant. Constant life Haigh diagrams at 105 and 107 cycles were in qualitative agreement with VDI 2230 bolt preload guidelines.

因为没法下载，也不清楚这种12.9级高强螺栓用的什么材料，
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如果我要描述我手上现有的某种材料（线材）的这方面性能，但又没有将其制成成品的条件，是否可以做某种试样，在上面进行您说的冷作，做两组对比上试验机

初涉池中

很好的文章

活得精神

默默的给个赞

hai9053

受教了，好好干事