Fatigue Strength of Bolts Tightened in Plastic Region. Fatigue Strength Assurance in Reusing.
Fatigue Strength of Bolts Tightened in Plastic Region. Fatigue Strength Assurance in Reusing.
复制标题
塑性区域拧紧螺栓的疲劳强度。
DOI：
10.2472/jsms.44.338
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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：
Haruhiko Yamada;K. Saruki;S. Hotta;T. Kanoh
在重复使用时，螺栓被反复拧紧和松开。本研究从疲劳强度的角度，研究了塑性区紧固的杆拉伸螺栓和螺纹拉伸螺栓的重复使用性能。对两种螺栓在塑性区进行了10次循环紧固的疲劳试验。结果表明，10次拧紧对螺栓的疲劳极限影响不大。而螺纹延长螺栓在塑性区反复拧紧后，在螺纹根部出现了长约7μm的微裂纹。然后利用断裂力学方法对裂纹螺栓的疲劳极限进行了预测。通过预应变光滑试件在高应力比下的疲劳裂纹扩展试验，确定了螺栓材料的门槛应力强度因子范围(Δkth)。在不考虑应力集中的情况下，利用单边裂纹的应力强度因子范围(ΔK)方程计算了螺纹根部的应力强度因子范围。在该方程中，用实际裂纹长度和潜在裂纹长度组成的裂纹长度作为有效裂纹长度。由上述ΔKth和ΔK预测的疲劳极限与裂纹螺栓的疲劳极限基本一致。这一预测表明，长度约为7μm的微裂纹对螺栓的疲劳极限影响不大，但超过7μm后，随着裂纹长度的增加，疲劳极限降低。
In reusing, a bolt is repeatedly tightened and loosened. In this study, the reusing properties of a shank-elongation bolt and a thread-elongation bolt tightened in plastic region were investigated from a viewpoint of fatigue strength. The fatigue tests were carried out on both types of bolts which were subjected to 10-cycle tightening in plastic region. As a result, the 10-cycle tightening had little influence on the fatigue limit of the bolts. However, on the thread-elongation bolt, the microcracks (about 7μm length) appeared at the thread root after repeated tightening in plastic region. Then, the fatigue limit of a cracked bolt was predicted by using the fracture mechanics method. The threshold stress intensity factor range (ΔKth) of the bolt material was determined from the fatigue crack propagation tests with pre-strained smooth specimens under a high stress ratio. The stress intensity factor range (ΔK) of the thread root was calculated by using the equation for a single edged crack without considering a stress concentration. In this equation, the crack length made of the actual and latent crack length was used as the effective crack length. The fatigue limit predicted from the above mentioned ΔKth and ΔK agreed approximately with the fatigue limit of a cracked bolt. This prediction clarified that the microcracks of about 7μm length had little influence on the fatigue limit of bolts but that the fatigue limit decreased with increasing the crack length beyond 7μm.