塑性締めボルトの疲労強度 : 再使用時の疲労強度保証

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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 test 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 7 μm 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 (ΔK_<th>) 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 ΔK_<th> and ΔK agreed approximately with the fatigue limit of a cracked bolt. This prediction clarified that the microrcacks of about 7 μm length had little influence on the fatigue limit of bolts but that the fatigue limit decreased with increasing the crack length beyond 7 μm.
社団法人日本材料学会の論文
1995-03-15

塑性締めボルトの疲労強度 : 再使用時の疲労強度保証

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