چكيده به لاتين
The purpose of the present study is to use a non-destructive method by propagation of Lamb waves to diagnose and classify the cracking damage in polymer based composites to identy the elastic and viscoelastic properties. The matrix cracking is known as a primary damage to the onset of other damage modes and consequently, the failure and fracture of multi-layer composites under static and dynamic loadings. In this study, glass/epoxy composites with a layup of [02/906]s were fabricated and the matrix cracking with several densities werfe induced in 90o layers using a tensile testing machine. Then, the induced cracks in specimens were optically investigated using a digital microscope and the crack density for each specimen was obtained. The stiffness reduction associated with each specific crack density was extracted. Then, the Lamb waves a non-destructive test was performed on the samples with different crack densities. By using the inverse solution of the Lamb wave equations and processing of received signals from the samples, variations in the elastic and viscoelastic properties of the samples with an appropriate precision were obtained. The elastic properties of specimens and viscoelastic properties of them, including the shear storage modulus, the shear loss modulus, and the loss factor were obtained by the measurement of the Lamb wave velocity and loss of the amplitude. The results obtained for the loss of elastic properties were in a very good agreement with the results of the Hashin stiffness reduction theory. The viscoelastic properties of samples also showed a good sensitivity to the matrix cracking damage. Using this sensitivity, a proper classification was made for this damage was performed. In general, the results of these experiments showed that, along with the changes in elastic properties as an indicator of the severity of the matrix cracking damage, an important property of the material, known as the loss factor (results from the viscoelastic properties of the material) can also be charaterized with a proper sensitivity. The loss factor can be considered as another important parameter to determine the severity of the matrix cracking damage in polymer composites. Thus, in this research for the first time, with the help of non-destructive measurements of elastic and viscoelastic properties of composite by using Lamb waves, the identification and classification of matrix cracking damage was done with a proper accuracy.
