Shape coefficient of impact-echo for small-size short cylinder/circular tube structures

The results tested by the impact-echo method of the small-size short cylinder/circular tube structure were fundamentally different from that of the large-size long one. This phenomenon cannot be described by the existing calculation formulas. To modify the classical calculation formula, finite element models of various sizes of small-size short cylinder/circular tube structures, including 80 cylinders and 125 circular tubes, were established. Modal analysis frequency was compared with numerical simulation of impact-echo frequency under partial working conditions. In addition, the impact-echo frequency of whole working conditions was counted for later analysis. The impact-echo frequency correction formulas of the small-size short cylinder/circular tube considering the model length and the cross-sectional size of the cylinder/circular tube were proposed. Moreover, their reliabilities were verified through tests. The results showed that the impact-echo frequency of the small-size short cylinder structure increased linearly with the increase in diameter, decreased with the increase in length, whereas the relationship among frequency, outer diameter, and wall thickness of the circular tube component was complicated. Moreover, the modal of the whole member was excited rather than the free modal of the cross section of the large-size cylinder/circular tube when the small-size short one was impacted.