A spatially reversible and programmable piezoelectric metamaterial concept is introduced for the manipulation of surface acoustic waves to achieve on-demand wave mode conversion and reflection. The concept uses an array of inductive-shunted piezoelectric elements (with gradually varying inductors in space) attached to the surface of an elastic propagation domain. The value of each inductor directly controls the phase velocity of the Rayleigh wave locally as quantified through unit cell band diagram analysis that guides the design process. By varying the spatial inductance distribution, the proposed piezoelectric metamaterial domain can be programed to convert incident surface waves into bulk shear waves or reflect them completely. The location of surface-to-bulk wave mode conversion or wave reflection can be tailored by means of the inductance distribution, and the directional behavior in space can be reversed. The proposed concept may enable novel surface acoustic wave devices and filters, via digital or analog programmable shunt circuits.
An analytical procedure is developed to predict workpiece dynamics in a complete machining cycle in order to obtain frequency response functions (FRF), which are needed in chatter stability analyses. For this purpose, a structural modification method that is an efficient tool for updating FRFs is used. The mass removed by machining is considered to be a structural modification in order to determine the FRFs at different stages of the process. The method is implemented in a computer code and demonstrated on different geometries. The predictions are compared and verified by FEA. Predicted FRFs are used in chatter stability analyses, and the effect of part dynamics on stability is studied. Different cutting strategies are compared for increased chatter-free material removal rates considering part dynamics.
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