评估法兰结构螺栓松动的改进损伤指标研究

基于压电阻抗法的采用统计学参数作为损伤指标评估螺栓松动的方法有着广泛的应用，然而采用该方法的试验对象多数为实验室条件下的板等结构，并非真实结构。因此，针对真实的法兰结构，这些损伤指标是否适用、是否需要改进仍需进一步研究。通过实验，得出不同损伤指标与法兰结构螺栓松动之间的规律:螺栓松动的程度越大位置越近，均方根偏差（RMSD）、平均绝对百分比偏差（MAPD）、相关系数差（CCD）的值越大，而指标R_y/R_x因无显著规律不适合作为评估法兰结构螺栓松动的损伤指标。通过对比结果发现:结构差异对前3个损伤指标均有不同程度的影响，改进后的损伤指标均方根变化率（RMSCR）只与法兰结构螺栓松动的位置和程度有关，受结构差异影响小。因此，RMSCR具有重要实践意义:当任一压电片损坏时只需更换为同型号的压电片即可，无需更新损伤指标库。通过实验验证了上述结果的正确性与基于RMSCR的法兰结构螺栓松动检测方法的适用性。 

Research on Improved damage index for evaluating bolt looseness of flange structures

The method based on the piezoelectric impedance method using statistical parameters as the damage index to evaluate loose bolt has a wide range of applications. However, most of the test objects adopting this method are structures such as plates under laboratory conditions, which are not real structures. Therefore, for real flange structures, whether these damage indexes are still applicable and whether these damage indexes need to be improved need further study. The rules between different damage indexes and loose bolt of flange structure are obtained through experiments:the larger the degree of bolt looseness is and the closer the position is, the larger the values of the Root Mean Square Deviation (RMSD), the Mean Absolute Percent Deviation (MAPD), and the Correlation Coefficient Difference (CCD) are, and R_y/R_x is not suitable to be used as a damage index for evaluating the loose bolt of flange structures because it has not a significant rule. The comparison of results shows that the structural difference affects the first three damage indicators to different degrees, and the improved damage index Root Mean Square of Change Rate (RMSCR) is only related to the position and degree of the loose bolt of flange structures, which is barely affected by the structural difference. Hence, the RMSCR has a crucial practical significance:when any piezoelectric sheet is damaged, it only needs to be replaced with a piezoelectric sheet of the same type without updating the damage index library. Finally, verification experiments verify the correctness of the above results and the applicability of the detection method for loose bolt of flange structure based on RMSCR.