Longitudinal ultrasonic absorption and velocity measurements were made in molten zinc chloride in the frequency range 5–95 Mc/sec. Shear relaxation measurements were obtained in the frequency range 43–118 Mc/sec. A single relaxation time was observed for the absorption of longitudinal waves at each temperature investigated. The absorption data demonstrated the existence of a volume viscosity which was found attributable to a structural single-relaxation mechanism. Shear and structural relaxations were both present with the same single relaxation time. The activation energies for the shear and compressional flows are approximately equal. The variation of the relaxation time with temperature is in accordance with the rate theory. The shear modulus and the relaxational part of the compressional modulus increase exponentially with decreasing temperature. The temperature dependence of the former is predicted by the two-state model of the hole theory. From numerous physical properties of molten zinc chloride and from the known crystalline state, a structural model is proposed for the melt. Two points are emphasized: (1) that there exist large ion complexes and (2) that there is a lack of network character in liquid ZnCl2. Based on this model, an explanation of the existence of distribution of relaxation times, observed in the glass-forming network liquids, is offered which attributes the presence of a whole spectrum of relaxation times in these liquids to the cooperative nature of their flow process. The measured single relaxation time of molten zinc chloride owes its origin to its nonnetwork character.
Type and size are the most important defect characteristics that need to be determined for reliable prediction of the remaining service lifetime of a defective structure or part. The analytical and supporting experimental results presented in this paper concern a universal ultrasonic defect-identificationand-subsequent-sizing method. The conceived satellite-pulse technique (SPT) is based on the interpretation, in terms of defect types and dimensions, of the separation in time-of-arrival between the specularly-reflected pulse and its tipdiffracted or tangentially-scattered "satellite" contained in the composite defect signal. Several alternate calibration procedures were also developed, any one of which enables the ultrasonic examiner to make the time scale of the oscilloscope read directly in terms of equivalent crack depth or void diameter as appropriate.
Ultrasonic waves returning from an internal bulk flaw to a wideband transducer contain information on several characteristics of this flaw. Measurements made with waves of different mode, dominant frequency, incidence angle, beamwidth, etc. are, therefore, necessary to solve the inverse problem for flaw composition, size, and orientation in an unambiguous manner.The plan for the development of a reliable and accurate volumetric-flaw characterization module encompasses three basic elements: a transducer selection protocol, a deconvolution algorithm, and the Born as well as the Franz-Gruber (satellite pulse) models for the interaction of weakly and strongly scattering internal bulk flaws, respectively. The flaw-diameter estimates obtained by applying the Born Inversion Technique (BIT) and the Satellite-Pulse Observation Technique (SPOT), based on the above models, to the results of ultrasonic backscattering experiments are compared in this paper with the nominal effective diameters of five spherical voids in a titanium-alloy specimen tested under blind conditions.
High-frequency ambient-noise measurements were made in five North American ports. At a given frequency, the total span of noise levels for the five harbors was about 25 dB. At 30 kHz, levels 30 dB higher than the extrapolated deep-water Knudsen value for sea state 2 were observed. Comparison is made with some 20- to 50-kHz data for other harbors.
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