Structural Damage Detection Based On Local Vibration Model

Due to the effects of natural disasters,fatigue and corrosion,different degrees of damage may exist in the aerospace and civil engineering systems.After a long period of accumulation,it will inevitably lead to structural destruction or performance degradation.In order to improve the safety and integrity of the system,more attention has been paid to the non-destructive testing technology.Based on the vibration technology and the non-contact laser measurement technology,the “pseudo-excitation” method has been developed recently for structural damage detection,which requires neither benchmark structures nor baseline signals.This thesis is divided into the following contents.Firstly,an in-depth insight about the original “pseudo-excitation” method is made.However,the method requires the rigorous differential equations of vibration and the mechanical parameters of the structures.On the basis of various plate and beam theories,a new method based on the general vibration model identification(GVMI)is proposed in this paper.The response of structural vibration is described in the form of a multi-order differential equation.The least squares method is used to fit the coefficients in the equation,and the generalized local oscillation differential equation is established.Then,taking an aluminum honeycomb sandwich cantilever beam as an example,the finite element model is established.Considering the damage in the skin and core layers,the damage identification abilities of the GVMI method are quantitatively evaluated under a flexural harmonic excitation.According to the damage detection results,the appropriate sampling interval is selected to improve the anti-noise ability of the GVMI method.Changing the distance between damage and the fixed end of the beam,the detection blind areas are appeared.To solve this problem,the relationships between the damage detection results and the vibration displacement wavelength are analyzed,the reason is also surmised for the difference of the insensitive regions.In order to eliminate the detection blind area,the GVMI method is enhanced using excitation frequency extension.The effective frequency range is determined,and the values of the damage index are merged for a better observation after normalization.Finally,the experimental platform is built,and the vibration displacements of the structure are measured using a scanning laser vibrometer.The single and multiple damages are discussed respectively.The feasibility of the GVMI method is verified by both of the two kinds of damages.