Experimental Contact Acoustic Nonlinearity of Interfaces During Loading-Unloading Cycle: Combined Effects of Elastoplastic Nonlinear Spring, Crack-Clapping, and Adhesion

Experimental results are presented for the contact acoustic nonlinearity of interfaces between two solid surfaces in dry contact which experience a moderate level of plastic deformation. The current research aims at investigating the effects of the elastoplastic hysteresis, surface roughness, and possible adhesive force on the acoustic nonlinearity. The ultrasonic results are compared with results from the elastoplastic contact model of Kim and Lee (2007) and the clapping model of Blanloeuil et al. (2020), which reveals that the nonlinearities are dominated by clapping of lightly contacting cracks at the interface at low pressures and by the elastoplastic nonlinear spring at high pressures. On top of this major trends, there are consistent minor trends which are attributed to the effects of adhesive force. There is a critical pressure level at which the adhesive clapping of cracks starts being more pronounced. As predicted by the model, the nonlinearity increases with the surface roughness and thus is always lower during unloading in the high pressure regime. The effects of the adhesion are investigated by measuring the nonlinearity at two different relative humidity levels. Some systematic, physically reasonable trends in the experimental results illustrates possible effects of the adhesive force on the acoustic nonlinearity.