بررسی اثر شل‌شدگی اتصالات غیر دائمی پیچی در سازه‌ی فلنج نبشی بر روی ویژگی‌های ارتعاشی آن

In this research, the simulation of non-permanent screw joints in a sheet structure with corner flange connections was first conducted. The bolt and nut simulation method, incorporating an interface layer, was investigated to enhance the accuracy of the vibration behavior analysis. To validate and update the finite element model, modal testing was performed under free-free boundary conditions. The simulation results were then compared with laboratory data to assess the accuracy of the bolt and nut connection simulation method. Finally, through experimental modal testing, the effect of screw joint loosening on the natural frequencies of the structure was examined and compared. The findings reveal that after updating the finite element model, the approximation of the interface layer for the bolt connection proved accurate. Additionally, the screw-tightening torque did not have a uniformly direct effect on all-natural frequencies; some frequencies exhibited opposite trends. However, the loosening of the bolts and nuts showed a more pronounced negative effect at higher natural frequencies.