The Research On Damage Monitoring In Smart FRP Sandwich Beam And Plate By Wavelet Analysis

Since an ocean-going ship is under expectable environment during its service life, it is vulnerable to fatigue damage. Fiber reinforced plastic (FRP) sandwich composite materials are widely used in the construction of marine structures. However, internal defects can occur, which if not identified on time, can lead to rapid structural degradation, and even cause catastrophe. In order to ensure marine safety and life-span, a simple fast and non-destructive damage evaluation method is required to assess and locate the internal defects in the FRP sandwich composite materials.Based upon intelligent structure technology and wavelet analysis, a method of damage monitoring was preliminary explored in the thesis, which was used to identify the damage on smart FRP sandwich beam and plate separately.For the smart FRP sandwich beam, a debond damage was monitored by numerically simulated calculation and experimental research separately, so was crack damage. Intelligent sensors could be used to monitor the strain response signals of sandwich beam, and then the first order complex Guassian wavelet transformation was applied to the strain response signals. By analyzing the singularity characteristics of wavelet transformation coefficients, the damage could be identified effectively. Damages with various sizes and in different positions were researched by the wavelet analysis. And the experimental data from sandwich beams was investigated also in order to demonstrate the validity of the numerically simulated calculation.For the smart FRP sandwich plate, just the debond damage was researched by numerically simulated calculation. Finite element method was used to simulate the strain response signals of FRP sandwich plate, and then the first order complex Guassian wavelet transformation was applied to the strain response signals. By analyzing the singularity characteristics of the wavelet transformation coefficients, the debond damage could be identified effectively. The study in this paper showed the validity of using wavelet analysis to identify whether there was any damage, where the damage was and the degree of damage.