No abstract

The techniques of acoustic positioning without the use of resonant cavities have been explored and developed over a number of years and the currently available capabilities are reviewed. The performance and characteristics of these nonresonant acoustic systems are described in regard to containerless processing with emphasis on the low-g environment. This includes manipulation and mixing of liquid drops, super-cooling phenomena, heating to temperatures of 1600°C or higher, rapid cooling solidification, and surface shape control. Some possible applications are measurements of physical properties of substances at high temperatures or of highly reactive specimens, and the formation of unique glasses and alloys of new compositions.

Low-frequency reciprocatory-rotary motion is imparted to a conventional axially vibrated ultrasonic cutter (18 kHz) that is impregnated with diamond grit of average size 0.003 in. The rotary motion is in a plane normal to the cutter axis. Cutting rates in rock materials of 10 ft/h are exceeded for 1-in. diam circular holes drilled to depths greater than 1 ft. Peak axial amplitude was 1.6 mil and the rotary motion was less than three to-and-fro oscillations per minute. Specific energy of the cutting process was measured to be less than 100 J/cm3 or less than that involved in the rotary cutters used for oil well drilling. Pulsed excitation at a 50% duty cycle leads to an 8%–10% increase in drilling rate for the same power input. Self pumping of the abraded material is obtained through subharmonic vibration of the cutter on pulse excitation. Static pressure, peak amplitudes, and rotary motion are optimized.

The process of inducing plastic flow in metals under the combined action of static and large vibratory stresses using a high-powered horn driver is discussed. In particular, where the metal is ferromagnetic, one has the situation that many properties of the material, including magnetic properties, change under the combined stress action. This necessarily affects the end uses of the material as, for example, in magnetostrictive transducers. Experiments are described in which the properties of nickel are investigated, for example, and the plastic flow threshold curve under combined stress action is determined. It is found that vibratory stress is much more effective in producing flow than static stress. In addition, it is found that, subsequent to the occurrence of plastic flow, the mechanical Q of a sample is altered but partially recovers over a period of hours at room temperature, and the material is hardened against further flow. The separation of the total energy loss into macroeddy, elastic, and microeddy loss is discussed. The alteration of the magnetic properties of plastically flowed samples is quite marked at points near the flow maxima in the samples containing standing intense acoustic waves, and the change in internal friction provides a possible means for predicting impending fatigue in metals without destruction of the materials. [This work was supported by the Office of Naval Research.]

Relative resonant displacement of bar magnetostrictors as a function of polarization at atmospheric stress and at a compressional, axial stress of 230 atm is measured. Laminated bars of nickel and 2V-permendur are driven at frequencies both at and well below the resonant frequency of the bars, about 23 kc. Measurements of the Q and the reversible permeability enable one to compare the magnetostrictive constants and the coupling at the two stress levels for both materials. The resonant displacement was found to change only slightly upon application of the compressive stress, for polarizing fields up to 100 oe. The compressive stress increased the maximum coupling for permendur by about 10%, the stress decreased the maximum coupling for nickel by about 10%.