Measuring Crack-type Damage Features in Thin-walled Composite Beams using De-noising and a 2D Continuous Wavelet Transform of Mode Shapes

A new method is described, allowing to locate and also measure the length and orientation of cracktype damage features in thinwalled composite beams (TWCB), a capability not previously reported. The method is based on a modalanalysis technique and is shown to work on a hollow composite beam, going beyond previous work limited to simple beams and plates. The method is shown to be capable to function down to signaltonoise ratios (SNR) of about 15, corresponding to far noisier conditions than in most previous work. This capability is achieved by a combination of wavelet denoising and the use of a 2D Continuous Wavelet Transform (CWT), applied to two modal analysis metrics, COMAC and Mode Shape Differences (MSD). The length and orientation of the crack can be determined accurately using a 2D curve fitting approach. Using either COMAC or MSD produces reliable results, but MSD is found to be somewhat more noisetolerant. The new method is believed to be useful for the measurement of damage features in a variety of thinwalled composite beams such as aircraft wings and wind turbine blades, among others.