被締結物のクリープによるねじ締結体のボルト軸力低下

抄録

In developing automobiles, the weight reduction has become important more and more as one of solutions for the environmental issue. One of countermeasures is to adopt lightweight materials such as Magnesium and resin. However, some of those materials have the characteristic of creep deformation, especially in high temperature atmosphere. In case of the bolted joints, if clamped parts are made of the material such as Magnesium, there is possibility that the contact surface of the clamped part with a bolt or a nut deforms compressively due to the creep characteristic. It causes decreases of the bolt axial tension. Thus, it is important to predict the amount of the bolt axial tension reduction at the initial designing of the bolted joint. In this paper, the prediction method of the bolt axial tension reduction due to compressive creep characteristic is investigated using the hollow disc specimen made of Magnesium AZ80-F. At first, bolt axial tension reductions are shown by a physical test in a thermostatic chamber. Then elasto-plastic FEM analyses are conducted based on both of the compressive stress-strain and creep characteristics. Influences on the reduction of contact stress, temperature and dimension of specimen are shown. Further, the simple prediction method using the mean permanent set are proposed.