Modeling of Preload Bolted Flange Connection Structure for Loosening Analysis and Detection

The specified finite element model is proposed for preload bolted flange connection structure widely used in aerospace and rocket design. A fine hexahedral mesh model of the bolt is used to predict the dynamic response of the structure accurately. The tightening process, which is ignored in the traditional I-shaped simplified model of bolted flange connection structure, can be simulated well based on the proposed model. After the vibration analysis and stress analysis of the bolted flange connection structure under impact load, it is found that the change of contact state of the flange surface results in a larger sticking contact area. And the reduction of the contact area at the thread causes slippage when the bolt is loose. As bolt loosening leads to changes in the time and frequency domain of response, a new loosening detection method for the preload bolted flange connection is provided. The index for identifying the loosening is designed using empirical mode decomposition and discrete integral in the high-frequency domain. The experiment of the preload bolted flange connection structure under impact load shows the efficiency of the proposed method which can identify loosening based on acceleration signal quickly and nondestructively.