Comparison of LVI and QSI damage induced anisotropy in GFRP composites by ultrasonic immersion tests

Low-velocity impacts (LVI) are very common sources of damage for structural components made of polymer composites. For the experimental analysis of LVI damage, LVI tests are relatively difficult and expensive to perform, and their results are often largely disperse and of complex interpretation. This justify an increasing number of researches on the equivalence between LVI tests and quasi-static indentation (QSI) tests for the characterization of LVI damage behavior of polymer composites, being QSI tests much more simple and easy to perform and interpret. Here we adopt an innovative ultrasonic approach for the characterization of damage in composites in order to perform a comparison between LVI tests and QSI tests induced damage for glass fiber–reinforced polymer composites (GFRP). The key concept of our ultrasonic approach is that of experimentally identifying the damage induced anisotropy superimposed to the constitutive anisotropy of the composite: thus, we ultrasonically study the change in the anisotropy of the acoustic response of the material. To this aim, we use an innovative goniometric ultrasonic immersion device designed and built at our laboratory, and we study the change in the slowness curves of the composite before and after the damage