چكيده به لاتين
Among structural health monitoring (SHM) techniques, which can identify, locate and quantify structural damage before failure, high frequency Lamb waves have become widely used since they can cover large areas and also identify micro damages. In this research, finite element (FE) simulations are used to assess the matrix cracking in composite materials using the guided Lamb wave propagation. The developed FE model consists of a plate composite sample, an actuator and several sensors. Antisymmetric Lamb waves with different frequencies ranging from 100 to 500 kHz were propagated on the sample using the actuator, which was modeled as two excitation rectangular areas located on the top and bottom surfaces of the sample at one end. The sensors were then used to obtain the induced wave characteristics including displacement phase and amplitude at different locations along the propagation direction. These characteristics vary with the crack density of the matrix. In composites, the fiber distribution generates structural damping. The matrix cracking may also lead to structural damping, especially in the case of high frequency excitations (short wavelengths). The wave speed and damping properties of the sample were obtained using the measured wave characteristics. Then, the corresponding inverse Lamb wave propagation problem was solved and the equivalent viscoelastic properties (complex modulus) of the sample were obtained. A two-step approach was used in this study to model and assess a glass/epoxy plate sample with different crack densities. In the first step, the RVE of a unidirectional ply consisting of fiber and resin with no crack was modeled and its elastic properties were characterized using the proposed Lamb wave propagation method. Then, in the second step, these equivalent properties were applied to a global model consisting of units with transversely isotropic material separated by micro-cracks, which can properly model cross ply composites with matrix cracking. The viscoelastic properties of such global model were obtained using the Lamb wave propagation method, similar to that performed for the unidirectional ply RVE. Finally, the changes in viscoelastic properties were used to identify the matrix cracking density in the modeled composite samples
