Lamb Wave Propagation and Low Velocity Impact Damage Identification in Carbon Fiber Reinforced Plastic (CFRP) Laminates

Abstract

In the present work, A <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> Lamb wave mode is used to identify the impact damages in the composite plate structures. Different bi-directional carbon fiber reinforced plastic (CFRP) laminated plates are considered with surface mounted PZT sensors. The Lamb waves are generated using the PZT patches, mounted at the center of the plate and the propagating Lamb waves are subsequently captured by the PZT sensors, arranged in a circular array configuration. The damages are introduced in the plates using a low velocity impact test facility with different intensity and the impact damages are then identified through Lamb wave technique. Different CFRP plates are scanned using Laser vibrometer in order to examine the Lamb wave propagation. A 3.5 cycle windowed signal of 35 KHz frequency is used to generate Lamb wave in the plate structure. It is noticed that, the wave dynamics and moving patterns are distinctly different in various CFRP plates. The wave propagation pattern is elliptical in case of cross ply and angle ply laminated plates, whereas in multi directional composite plate the wave propagates in nearly circular form. Further, Lamb waves propagate faster in fiber direction compared to non-fiber direction in all the three plates. This is evident because CFRP plates are made of bi-directional pre-preg where fibers are oriented in 0 and 90 degrees (cross ply) and ± 45 degrees (angle ply). In case of multi directional plate, the fibers are oriented in 0, 90 and ± 45 degrees which lead the waves to propagate in circular form. The travelling speed of the waves along the fiber direction and matrix is different which is clearly seen from the experimental evidence captured through Laser Doppler Vibrometer (LDV). With these identified, distinguishable patterns, one can reasonably assess fiber dominated failures or matrix-based failures. Further, in the CFRP laminated plate, BVID’s are identified with damage identifying parameters using Lamb wave technique but C-Scan, a non-destructive evaluation technique could not able to detect the BVID. The damaged CFRP plates are subsequently scanned using LDV, in order to examine the Lamb wave propagation in damaged area. It is evident that, on-line data capturing is the right approach to monitor the impact event; however, the presence of damage, if any due to impact event may be diagnosed by the sensors, placed close to that particular event. The proposed Lamb wave-based methodology using PZT sensor network can be applied for impact related damage detection in real time applications.