UVM Theses and Dissertations
Format:
Print
Author:
Frost, Harold M.
Dept./Program:
Physics
Year:
1974
Degree:
Ph. D.
Abstract:
A literature review of selected publications concerning the 'mechanical' effects of ultrasound on bulk solids reveals that diverse media--such as metals and biological tissue--have received considerable attention, while materials intermediate in elastic or viscous properties--such as plastics--have not. Investigation of viscoelastic solids such as plastics would help serve i) to fill a gap in our present knowledge and ii) to encourage a more unified approach in our attempts to understand the action of ultrasound on solid-like media in general.
An ultrasonic composite vibrator with appropriately shaped metal tip was vibrated continuously at 80 to 90 kHz and at tip displacement amplitudes uo of 0 to 8 æm while pressed by a static force Fs against the edge surface of a thin plate of a transparent, strain birefringent, cross-linked and flexibilized epoxy which demonstrated fast creep loading due to its markedly viscoelastic nature as a soft solid. The sample was mounted on the stage of a circularly polarizing microscope operating in transmission mode. Consequently, ultrasonically time-averaged deformation in the epoxy plate was characterized by chronological series of photographs of photoelastic fringes (chiefly isochromatics). The vibrator was driven within a negative feedback loop responsive to just the motional current through a resonant piezoelectric transducer bonded to a tuned stepped Mason horn, with time-dependent shifts in resonant frequency determined by action of a self-excited oscillator sensitive to the acoustic loading effects of the flexibilized epoxy sample pressed normally against the horn tip.
Other theory is developed for interpreting i) resonant-frequency changes in the composite, mechanically-loaded electroacoustics system in terms of the material properties of the epoxy and the dynamics of Hertzian contact for the special test geometry involved of two, parallel, right-circular cylinders of different radii pressed together laterally, ii) photoelastic data in terms of both the field and localized aspects of sonically induced deformation, and iii) the intensity of light emerging from the analyzer of a polarizing microscope, via a matrix multiplication method.
Some possible applications of this work include i) biomedical uses such as a new glaucoma test and a novel ultrasonic scalpel, ii) measurement of the elastic properties of plastics, iii) a new technique for "locking in" strain in three-dimensional photoelasticity for experimental stress analysis, and iv) determination of static contact force in Mason horn studies of biological tissue such as single plant cells.
An ultrasonic composite vibrator with appropriately shaped metal tip was vibrated continuously at 80 to 90 kHz and at tip displacement amplitudes uo of 0 to 8 æm while pressed by a static force Fs against the edge surface of a thin plate of a transparent, strain birefringent, cross-linked and flexibilized epoxy which demonstrated fast creep loading due to its markedly viscoelastic nature as a soft solid. The sample was mounted on the stage of a circularly polarizing microscope operating in transmission mode. Consequently, ultrasonically time-averaged deformation in the epoxy plate was characterized by chronological series of photographs of photoelastic fringes (chiefly isochromatics). The vibrator was driven within a negative feedback loop responsive to just the motional current through a resonant piezoelectric transducer bonded to a tuned stepped Mason horn, with time-dependent shifts in resonant frequency determined by action of a self-excited oscillator sensitive to the acoustic loading effects of the flexibilized epoxy sample pressed normally against the horn tip.
Other theory is developed for interpreting i) resonant-frequency changes in the composite, mechanically-loaded electroacoustics system in terms of the material properties of the epoxy and the dynamics of Hertzian contact for the special test geometry involved of two, parallel, right-circular cylinders of different radii pressed together laterally, ii) photoelastic data in terms of both the field and localized aspects of sonically induced deformation, and iii) the intensity of light emerging from the analyzer of a polarizing microscope, via a matrix multiplication method.
Some possible applications of this work include i) biomedical uses such as a new glaucoma test and a novel ultrasonic scalpel, ii) measurement of the elastic properties of plastics, iii) a new technique for "locking in" strain in three-dimensional photoelasticity for experimental stress analysis, and iv) determination of static contact force in Mason horn studies of biological tissue such as single plant cells.