چكيده به لاتين
Application of guided waves in structural health monitoring and damage detection especially in sheet structures (known as Lamb waves), is steadily increasing. The reason for this is the low attenuation and applicability at high frequencies, resulting in high detection power of these waves. In recent years, damage detection methods based on the material characterization has been increasingly investigated by many researchers.
The purpose of this study was to simulate a non-destructive evaluation method based on the propagation of Lamb waves for the characterization of elastic properties and the detection of delamination in fiber-metal laminates (FMLs). Delamination is known as the most important damage in FMLs among other damages. In this study, the computational characterization of FMLs using the Lamb wave propagation mathod through finite element method (FEM) simulations was conducted first. The developed FEM model consisted of an FML sample with [Al/90/Al/90/Al] layup, an actuator and several sensors. Antisymmetric Lamb waves with different frequencies ranging from 50 to 400 kHz were propagated on the sample using the actuator. The sensors were then used to obtain the induced wave characteristics, including the displacement phase and amplitude at different locations along the propagation direction. The Lamb wave velocity was obtained using the measured wave characteristics. Then the corresponding inverse Lamb wave propagation problem was solved and the elastic modulus of the FML sample was estimated. The measured elastic modulus values were compared with the results reported in an experimental prior research work and obtained using the classical lamination theory (CLT). It was observed that the estimated elastic modulus was more accurate at low frequencies with an error smaller than 7%, whearas the error increased at high frequencies. Afterwards, the computational study for the detection of delamination was conducted in the FML sample using the first symmetric and antisymmetric Lamb wave modes with different excitation frequencies (S_0 and A_0). The variation of Lamb wave velocity in the delamination region was more signifacnt for the S_0 mode compared with the A_0 mode. It was concluded that the S_0 mode is more sensitive to delamination than the A_0 mode in FMLs and is more efficient for delamination detection purposes.
Keywords: Fiber-metal laminates (FMLs), Non-destructive evaluation, Lamb wave velocity, Material characterization, Delamination defect detection.
