ボルト締結体の振動特性評価と接触面剛性を考慮した有限要素解析

摘要

機械構造物を設計する場合，実用的な精度で固有振動数を求めておくことは，作動状態において繰り返し外力による共振現象を避けるために極めて重要である．固有振動数を求める手法は古くから種々提案されており，近年複雑な形状の構造物の固有振動解析には有限要素法が広く用いられている．一般に機械構造物は多くの部品から構成されており，それらはボルト・ナットを用いて締結される場合が多い．%Evaluation of the natural frequency and the natural mode of vibration of a bolted joint is particularly important to avoid the failure of the structure due to the resonance. The vibration characteristics of a bolted joint are largely influenced by such factors as the surface roughness of contact surfaces, the magnitude of axial bolt force, the arrangement of clamping bolts, etc. In this paper, natural frequencies of the bending vibration of a bolted joint with simple configuration are measured using strain gages mounted on the surface of test specimen, and the effects of surface roughness, axial bolt force and the bolt location are systematically investigated. Then, a numerical procedure is proposed to analyze the free vibration problem of a bolted joint, where the effects of interface stiffness due to surface roughness are incorporated into the finite element formulation. It is also presented that the computation efficiency for solving the eigen value problem concerned can be fairly-improved by introducing selective reduced integration (SRI) scheme. The effectiveness of the numerical procedure proposed here is validated by experimental measurements of the natural frequencies of the first mode.