Lamb Wave Interaction with Adhesively Bonded Stiffeners and Disbonds Using 3D Vibrometry

Abstract

There are many advantages to adhesively bonding stiffeners onto aircraft structures rather than using traditional mechanical fastening methods. However there is a lack of confidence of the structural integrity of adhesively bonded joints over time. Acousto-ultrasonic Lamb waves have shown great potential in structural health monitoring applications in both metallic and composite structures. This paper presents an experimental investigation of the use of acousto-ultrasonic Lamb waves for the monitoring of adhesively bonded joints in metallic structures using 3D scanning laser vibrometry. Two stiffened panels were manufactured, one with an intentional disbonded region. Lamb wave interaction with the healthy and disbonded stiffeners was investigated at three excitation frequencies. A windowed root-mean-squared technique was applied to quantify where Lamb wave energy was reflected, attenuated and transmitted across the structure enabling the size and shape of the defect to be visualised which was verified by traditional ultrasonic inspection techniques.

Detection of debonding in adhesive joints using Lamb wave propagation

“…The vibration energy distribution is the basis for a simple but very efficient technique that utilizes the calculation of a root mean square (RMS). Recently, the RMS has been successfully used to detect defects in aluminium plates [14][15][16], delamination in a composite T-joint [17], disbonds in a stiffened panel [18], notches and corrosion areas in aluminium plates [19], disbond inserts in composite elements [20] and voids in adhesive joints [7]. The root mean square for a continuous signal s(t) is calculated with respect to the formula:…”

Damage Imaging in Lamb Wave-Based Inspection of Adhesive Joints

“…This method was improved to be more applicable for damage detection by defining the weighted root mean square (WRMS) method [30]. Recently, the RMS has been successfully used in various damage detection applications [25,26,[31][32][33][34][35][36].Żak et al [30] investigated aluminum and composite plates as well as composite elements of a helicopter, all with the damage being simulated by an additional mass. They concluded that better resolution in WRMS maps corresponded to higher values of the weighting factor (linear or square).…”

“…Detection of delamination in a composite T-joint using RMS images was studied by Geetha et al [34]. Marks et al [35] presented experimental investigations on the detection of disbonds in a stiffened panel based on the RMS plots. Wave packets with three different frequencies, namely 100 kHz, 250 kHz, and 300 kHz, were applied.…”

Lamb Wave Local Wavenumber Approach for Characterizing Flat Bottom Defects in an Isotropic Thin Plate

“…Lamb waves are dispersive and multimodal [9]. Moreover, the propagating Lamb waves may include incident, reflected, and converted waves when they encounter a sudden thickness variation [10,11], such as circular flat bottom holes and rectangular grooves. Obviously, various wave modes make the interpretation of Lamb waves very difficult [12].…”