# Comparing Bol Implementation Methods in Vibration Testing for Accurate Dynamic Behavior Analysis
## 4 Discussion
joint method provides higher contact stiffness than other bolt implementation methods, significantly impacting structural stiffness and vibration behavior. This study successfully identified a reliable bolt connection method for vibration test jigs through computational modal analysis and experimental validation, providing an approach for accurate dynamic behavior prediction. The modal analysis evaluated the dynamic behavior of the structure based on natural frequencies and mode shapes. Among the methods, the joint method indicated the most similar results, with approximately a 1.5% difference from the experimental values. These results are consistent with bolt connections for the dynamic analyses of an automotive engine [22], where a similar joint method showed a high correlation between the natural frequency of the computational analysis results and experimental results, further validating the reliability of this study. Furthermore, incorporating dynamic stress into this study's methodology could lead to a more refined design of structural dynamic behavior. A study on FE refinement for accurate dynamic stress [40] showed that considering dynamic stress in the evaluation process not only improved the structure's fatigue performance but also enhanced the reliability of the design under dynamic conditions. Thus, this approach could provide dynamic characteristic-based designs with greater practical applicability and improved overall performance. In terms of analysis efficiency, notable differences between the connection methods were observed. The adaptive bonded method required the longest analysis time at 598 s, followed by the beam method at 345 s, while the joint method required a relatively short analysis time of 97 s. The screw and fixed bolt methods had analysis times ranging from approximately 200 to 300 s. The bonded method required the shortest analysis time at 91.65 s, but exhibited significant discrepancies from the test results, limiting its ability to reproduce the dynamic characteristics of actual structures. During preprocessing, the joint and adaptive bonded methods required approximately 2 min per bolt to generate line bodies and assign contact conditions, and the beam method also required significant time for assigning contact conditions, resulting in low preprocessing efficiency. By contrast, the screw and fixed bolt methods significantly reduced preprocessing time by utilizing Inspire's Fastener functionality, which automates preprocessing. As a result, while the joint method provided high analysis accuracy, it required substantial time for preprocessing, making it the second most time-consuming method overall. The adaptive bonded and beam methods also required significant time for both preprocessing and analysis, whereas the screw and fixed bolt methods demonstrated their potential as efficient alternatives in the early stages of design owing to their simplified preprocessing and short analysis times. This study has some limitations. First, the analysis did not explicitly consider bolt preload and contact friction coefficients, indicating that the subtle effects that may occur under actual bolt fastening conditions were not fully captured. Second, the experiment was limited to excitation in the \(x\)-axis direction only, restricting a comprehensive evaluation of the dynamic behavior of the structure under various vibration directions. Third, the study was based on a single jig design case, limiting the generalizability of the findings to other structural designs. Nevertheless, this study demonstrated the utility of quantitatively comparing natural frequencies and mode shapes for various bolt implementation methods, providing valuable insights for the design and analysis of vibration test jigs.