11 Décembre – Thesis defense - Dorra Nouira
09 h Full videoconferencing
Non-linear interactions between US waves and contact interface.
The past decades have been marked by a significant increase in research interest in nonlinearities in cracked solids. As a result a number of different nonlinear methods have been developed for damage detection. However, there still limited understanding of physical mechanisms related to the various nonlinearities due to contacts. This thesis is addressed to study the nonlinear interaction between a wave and an interface while taking into account adhesion, in order to, eventually, propose an efficient NDT method for characterization of contact interfaces. The study of the second-harmonic evolution to characterize the damage will be the focus of this work. The nonlinear interaction between a longitudinal wave and a contact interface is considered in one-dimensional medium by using the Finite Elements method.
Numerically, the contact interface is modelled by combining two approaches. One is based on acoustic methods and used in traction, while the other one is based on vibration methods and used in compression. The first one, consists in modelling the contact with an RCCM law. The study propose a detailed analysis on the interface behaviour in traction while taking into account the adhesion. It allows identifying the key parameters that govern the nonlinear signature of the RCCM contact law and so better understanding the interaction between a compression wave and a contact interface that exhibits adhesion in traction. The second one, used in compression, is based on a nonlinear interface stiffness model where the stiffness property of the contact interface is described as a function of the nominal contact pressure. The study consists in a complementary numerical and experimental analysis of nonlinear vibrational response due to the contact interface. It shows that the stiffness-pressure trend at lower pressures has a major effect on the nonlinear response of systems with contact interfaces.
Finally, in order to exploit the proposed contact law defined in compression and traction, a strategy to identify the interface parameters during the interaction between a wave and an interface is proposed. The numerical results are promising in view of the characterization of contact interfaces.