Modal Strain Flexibility-based Damage Identification Technique Research In Mechanical Structures

Damages such as cracks or corrosion in structures would affect the global safety, reliability and operational life. Especially for the complicated structures under the fatigue load, with the damage continuously expanding, it may have a huge potential safety hazard and even lead to economic losses and causalities. Therefore, to locate—the damage efficiently is very important for repairing the structure and using safely.This paper introduced and studied the damage identification theory and methods based on the variation of the dynamic features of the structure. The numerical simulation about the truss and plate structure and experimental research were carried out. The followings are the detailed content:(1) Firstly, the strain flexibility matrix was derived from the structure dynamic motion equation; the physical meaning about the element in the matrix was clarified. Combining with the Fiber Bragg Sensors, a novel damage identification index was constructed by using the Strain Field under Uniform Unit Load (SFUL).(2) A study on truncation effect was performed both for the beam and plate structure to select appropriate strain modes. And only the first four strain modes are needed to obtain the SFUL, which is very important in practice while high modes are difficult to be acquired from experimental test.(3) The numerical simulation about the truss and plate structure was investigated by using the math software MATLAB. The parameters SFUL were constructed both for the undamaged and damaged structure. The damage location could be identified from the variation of SFUL between undamaged and damaged structure. A Gapped Smoothing Technique (GST) has been introduced while the information of the undamaged structure was lacked.(4) The effect of the noise on the damage identification was studied in numerical analysis, due to the noise was inevitable in practice.(5) The reliability of this method was verified by the strain modal analysis of the plate using Fiber Bragg Grating sensors.