Experimental study of nonlinear waves in phononic materials with rough contacts

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Incorporating contacting interfaces in periodic media enables enriched wave dynamics from the combined effects of periodicity and nonlinearity. While Hertzian contacts have been extensively studied in the framework of engineered media, rough contacts have received relatively less attention. Recently, our numerical work showed that continuum phononic material with periodic rough contacts supports strongly nonlinear waves belonging to the family of solitary waves. In this talk, we experimentally study nonlinear waves in phononic material based on rough contacts, realized through an array of aluminum disks. The disks act as elastic layers and have roughness on either side, which is generated through surface treatment. First, we characterize a rough contact through optical imaging and ultrasonic measurements. We obtain the nonlinear contact stiffness–precompression relationship that informs the power exponent of the contact law. Then, we study nonlinear wave propagation through periodic rough contacts of the same roughness topography. We measure propagating waves through a laser vibrometer and investigate their frequency content, speed, and amplitude. This study develops a fundamental understanding of the role of rough contacts in the form of local nonlinearity on wave responses. Such understanding is useful in designing these phononic materials for wave propagation control.