弾塑性を考慮したボルト-ナット締結体の3次元有限要素モデリング

摘要

様々な機械や構造物において，ボルト-ナツトを用いた締結は広く利用されている.その理由としては，容易かつ安価に締結を行うことができる上，締結管理も可能であることが挙げられる.締め付けの際のトルク-軸力関係式や，ボルトのねじ山の荷重分担，応力集中などは，実験結果が既に報告されている.また，これらを3次元の有限要素解析(FEM)で評価した結果も報告されている.有限要素解析は，実験では評価の難しいボルト-ナツト面における微小なすベり等の接触状態を考慮に入れることを可能とする.また，経験式と比較することで，その従来の締結理論を見直していくこともできる.先に述べたねじ山の荷重分担，応力集中は軸対称ねじモデルで解析が可能であるが，トルク-軸力関係，ゆるみ挙動等の評価には3次元らせんねじモデルでの解析が必要である.%In various machines and structures, threaded fastener using a bolt-nut is widely used. The reason is not only that it is easy and inexpensive to tighten, but also that it is possible to maintain a tightening state. Experimental results have already been reported for the relation between the tightening torque and pre-load, the load distribution and stress concentration of thread. In addition, the results of tightening and loosening mechanism by three-dimensional finite element method (FEM) have also been reported. The FEM analysis makes it possible to consider the contact state such as minute slip on the bolt-nut surface which is difficult to evaluate in the experiment. It also allows to review classical theories concerning threaded fastener by comparing it with empirical equations. The load distribution and stress concentration can be analyzed with the axial-symmetry model, but it is necessary to analyze with a three-dimensional model in order to evaluate the loosening mechanism and the relation between tightening torque and pre-load. In this study, modeling three-dimensional threaded fastener, we simulate the tightening process of the bolt-nut taking into account the elastic and plastic deformation and analyze the stress and the contact state on the thread by comparing it with empirical equations.