Abstract: To overcome the disadvantages of the traditional nondestructive testing methods such as the high cost and localization， a singleinput singleoutput (SISO) experimental modal analysis method was used to analyze the steel bar with the diameter of 8mm in different damage. Strain modal difference curve was served as the evaluation index through the analysis of the corresponding dynamic parameter. The results show that the index can accurately determine the actual damage location and assess the degree of injury. The method can be used for the nondestructive testing and evaluation of the engineering structure defects in the dynamic test.

Key words: steel bar, experimental modal, damage identification, crack defect, singleinput singleoutput