Lei Qiu

Impact imaging of aircraft composite structure based on a model-independent spatial-wavenumber filter

The spatial-wavenumber filtering technique is an effective approach to distinguish the propagating direction and wave mode of Lamb wave in spatial-wavenumber domain. Therefore, it has been gradually studied for damage evaluation in recent years. But for on-line impact monitoring in practical application, the main problem is how to realize the spatial-wavenumber filtering of impact signal when the wavenumber of high spatial resolution cannot be measured or the accurate wavenumber curve cannot be modeled. In this paper, a new model-independent spatial-wavenumber filter based impact imaging method is proposed. In this method, a 2D cross-shaped array constructed by two linear piezoelectric (PZT) sensor arrays is used to acquire impact signal on-line. The continuous complex Shannon wavelet transform is adopted to extract the frequency narrowband signals from the frequency wideband impact response signals of the PZT sensors. A model-independent spatial-wavenumber filter is designed based on the spatial-wavenumber filtering technique. Based on the designed filter, a wavenumber searching and best match mechanism is proposed to implement the spatial-wavenumber filtering of the frequency narrowband signals without modeling, which can be used to obtain a wavenumber-time image of the impact relative to a linear PZT sensor array. By using the two wavenumber-time images of the 2D cross-shaped array, the impact direction can be estimated without blind angle. The impact distance relative to the 2D cross-shaped array can be calculated by using the difference of time-of-flight between the frequency narrowband signals of two different central frequencies and the corresponding group velocities. The validations performed on a carbon fiber composite laminate plate and an aircraft composite oil tank show a good impact localization accuracy of the model-independent spatial-wavenumber filter based impact imaging method.

Damage Imaging of Aircraft Composite Structure Based on 2-D Cruciform PZT Array and Spatial-Wavenumber Filters

This paper presents a new model-independent spatial-wavenumber filtering and imaging method based on a 2-D cruciform array for damage monitoring. In this method, a wavenumber searching and best match mechanism, which is not relied on any Lamb wave propagating models, is proposed to implement spatial-wavenumber filtering based on a linear piezoelectric transducers (PZT) array to obtain a wavenumber-time image of damage-scattering signal relative to the array. And the damage localization of 360 degree with no blind angle can be achieved based on the two wavenumber-time images of the 2-D cruciform array. The validation experiment performed on a carbon fiber composite laminate plate shows that the damage localization errors of this method are less than 1 cm. doi: 10.12783/SHM2015/73

An Energy-weighted Factor Based Localization Method for On-line Wireless Impact Networking Monitoring

Due to the widely use of composite materials in aerospace vehicles, the poor impact resistance of such materials may cause serious degradation of aircraft structures. Aiming at monitoring impact online for large scale aircraft composite structures, a wireless impact monitoring network based on digital wireless impact monitors has been developed. However, the digital localization method adopted in the network only works in single monitor, resulting in the localization confliction among multiple monitors and the false impact localization result of mid-region. In order to meet the needs of wireless impact networking monitoring, this research puts forward an energy-weighted factor based localization method with the ability of solving localization confliction and locating mid-regions. To verify the performance of the method, a wireless impact monitoring network based on a number of monitors are built and conducted on a composite unmanned aerial vehicle structure. Experimental results show that the method performs well. doi: 10.12783/SHM2015/4