転造ねじ継手の二段多重疲労寿命の推定

抄録

In order to investigate applicability of the life prediction method for smooth specimens subjected to two-step loadings, axial load controlled fatigue tests under two-step loading were carried out using rolled bolt-nut joints. It was concluded that this life prediction method for smooth specimens was applicable to life prediction of rolled bolt-nut joints and the minimum accumulated life-fraction at failure, D_f, was 0.74 when the life-franction due to primary stress was about 0.5. Then, dividing the cycles corresponding to this condition of the minimum D_f into 2, 4 and 8 blocks, fatigue tests under two-level multi-step loading were carried out by repeating the divided cycles alternately. As a result, D_f became equal to about 1. Life prediction were tried and a modified linear damage rule taking into account the loading history and material properties was proposed. Fairly good agreement was obtained between predicted and experimental results. According to this prediction method, it was known there were cases of smaller D_f under two-level multi-step loading than the minimum D_f under two-step loading.