Coulomb Damping of Aluminum Structures Via Ultrasonically Welded Foil Layers

An ultrasonic welding process based on a rotating sonotrode has been used to join aluminum alloy foil layers to a solid substrate representative of an aluminum structure in order to significantly damp the structure via a Coulomb damping mechanism.  Foil layers were added with the intent to produce damping through either “implicitly” or “explicitly” defined areas.  In all cases the damping features consist of discrete areas of opposing unbonded surfaces which are in frictional engagement with one another.  In production of “implicitly” damped samples, the ultrasonic welding parameters were de-tuned via reductions in load or welding amplitude, or increases in welding speed in order to produce incompletely bonded interfaces.  “Explicitly” damped structures were produced by welding foil layers with a patterned sonotrode that has a series of lands and grooves on the surface.  This process produced layers with strongly bonded and unbonded areas corresponding to the male and female features on the sonotrode.  Experimental samples took the form of 120mm diameter by 6mm thickness discs that exhibit natural harmonic vibrations over the frequency range of ~2-18kHz.  Disks were excited with an instrumented hammer while the surfaces were sequentially scanned with a laser vibrometer in order to determine frequency response functions for the discs.  Damping extents were correlated with specimen processing variations.