Fatigue Strength of Bolt Tightened in Plastic Region. Relation Between Fatigue Strength and Turning Angle at Tightening.
Fatigue Strength of Bolt Tightened in Plastic Region. Relation Between Fatigue Strength and Turning Angle at Tightening.
复制标题
塑性区域拧紧螺栓的疲劳强度。
DOI：
10.2472/jsms.44.122
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发表时间：
1995
期刊：
影响因子：
--
通讯作者：
T. Kanoh
中科院分区：
文献类型：
--
作者：
K. Saruki;S. Hotta;T. Kanoh
塑性区域的紧固螺栓能够产生稳定且高的紧固力，已被用于各种机器部件的连接。在这项研究中，研究了在塑性区域拧紧的螺栓的疲劳强度与螺栓或螺母的转角的关系。疲劳试验中使用的螺栓为（A）杆部直径（SD）为7.2mm的加长螺栓，（B）杆部加长螺栓（SD：7.5mm）和（C）螺纹加长螺栓（SD：8.3mm）。疲劳试验针对螺栓接头和单独的螺栓进行。前者通过改变螺栓或螺母的转动角度在弹性或塑性区域紧固。后者不仅在不车削的情况下进行夹紧，而且在轴向加载的情况下进行车削，直至达到初始平均载荷，以模拟实际拧紧情况。得到的结果如下：（1）杆部加长螺栓的螺栓接头塑性区域外载荷的持久极限高于螺纹加长螺栓，并且杆部直径较小的拉长螺栓的耐久性极限更高。原因认为，即使外载荷相同，低刚性螺栓产生的力也小于高刚性螺栓。(2)在弹性区域拧紧至90°转角(TA)的螺栓的持久极限载荷高于单独螺栓(不转转)的螺栓，并且在塑性区域拧紧(TA<180°)的螺栓也高于在弹性区域拧紧的螺栓。认为这是由于紧固时螺纹表面的刮擦接触更加均匀，导致螺纹牙脊圆周上的载荷均匀率增加所致。这些现象与单独螺栓的模拟试验结果类似。(3)但转角为270°和360°的螺栓连接在塑性区的持久极限载荷低于弹性区。单独对螺栓进行模拟试验时，当转角超过180°时，耐久极限载荷迅速降低，在180°~1080°之间几乎保持恒定。螺栓连接的结果与上述关系很好地吻合。这被认为是因为高负载引起的螺杆微螺距误差导致第一螺纹脊的负载分布增加。
Tightening bolts in plastic regions, which can generate stable and high tightening force, has come to be used for joints of various machine parts. In this study, the fatigue strength of bolts tightened in plastic regions was investigated in its relation to the turning angle of the bolt or nut. The bolts used in fatigue tests were (A) shank-elongation bolts with a shank diameter (SD) of 7.2mm, (B) shank-elongation bolts (SD: 7.5mm) and (C) thread-elongation bolts (SD: 8.3mm). The fatigue tests were carried out for bolted joints and bolts alone. The former was tightened in elastic or plastic regions by varying the turning angle of the bolt or nut. The latter was chucked not only under no-turning but also under turning while loading axially till the initial mean load for simulating the actual tightening.The results obtained are as follows:(1) The endurance limit of the external load of the bolted joints in plastic regions was higher for shank-elongation bolts than for thread-elongation bolts, and that of the shank-elongation bolts with smaller shank diameter was higher. The reason is considered that the force generated in lower-rigidity bolts is smaller than that in high-rigidity bolts even if the external load is equal.(2) The endurance limit load of the bolts was higher for the bolts tightened to the turning angle (TA) of 90° in elastic regions than for bolts alone (no turning), and also higher for the bolts tightened (TA<180°) in plastic regions than in elastic regions. It is considered that these are caused by the increase in the uniformity rate of the load on the circumference of the thread ridge because of more uniform contact with scrape of the thread surface during tightening. These phenomena were similar to the results of the simulation tests for bolts alone.(3) However, the endurance limit loads of the bolted joint tightened to the turning angles of 270° and 360° in plastic regions were lower than that in elastic regions. In the simulation tests of the bolts alone, the endurance limit load reduced rapidly when the turning angle was over 180°, and it was almost constant between 180° and 1080°. The results of the bolted joints corresponded well with the above relation. These are thought to be because the load distribution of the first thread ridge increases due to the screw micro-pitch-error induced by high load.