This paper presents experimental observations and a theoretical analysis of the operation of drop-on-demand piezoelectric ink jet devices. By studying experimentally the dependence of several operating characteristics on the length of the cavity in the nozzle of an ink jet device, we have gained insight into the physical phenomena underlying the operation of such a device. It is concluded that drop-on-demand ink jet phenomena are related to the propagation and reflection of acoustic waves within the ink jet cavity. A simple analysis is carried out on the basis of linear acoustics which is in good agreement with the experimental observations.
A model for the contact area and static friction of nominally flat rough surfaces and rough spherical surfaces is presented. The model extends previously published models, which are limited to plasticity index values below 8, to higher plasticity index values by accounting for fully plastically deformed asperities based on finite element results by Jackson and Green [2005, “A Finite Element Study of Elasto-Plastic Hemispherical Contact Against a Rigid Flat,” Trans. ASME, J. Tribol., 127, pp. 343–354]. The present model also corrects some deficiencies of the earlier models at very small plasticity index values below 0.5.
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