International Symposium on Nonlinear Acoustics edition:19 location:Tokyo date:21-24 May 2012
Kissing bonds and clapping contacts, such as delaminations and surface breaking cracks, inherently demand a nonlinear diagnostic method. In order to detect such defects, it is ecessary to apply a finite excitation amplitude that is large enough to overcome the activation threshold to separate the two faces of the contact. To obtain a better understanding and analysis of the macroscopic nonlinear behavior, we developed and investigated the results of a finite element model that makes use of local node splitting and implements the nonlinear constitutive behavior by means of springdamper elements with local activation thresholds at the defect interface. Numerical experiments show that subharmonics and harmonics of the excitation frequency are generated by the clapping defect if the excitation amplitude is large enough to overcome the local activation threshold. As experimentally observed in NACE experiments (Nonlinear Air-coupled Emission), these nonlinear
vibrations cause emission of radiation patterns of harmonic energy in the surrounding air, which is also confirmed by the developed model.