Pulse-Echo Elastic Measurements

Data from ref [31] the elastic constants were measured by the pulse-echo technique j3 was determined from low-temperature specific heat data. 

A unique set of interfaciai stiffness constants suffices to characterize the macroscopic elastic response of an interface between two rough contact surfaces regardless of the direction of incidence of the ultrasonic wave [35], In addition, the stiffness constants of a double interface can be successfully recovered by combining ultrasonic spectroscopy and pulse-echo measurements with the theoretical procedures available for a single imperfect interface. 

The microstructures of the consolidated and deformed samples were characterized by X-ray diffraction, optical and electron microscopy (SEM and TEM). The samples for mechanical testing have been prepared by spark erosion. The linear thermal expansion was determined by using a thermomechanical system (TMA). The temperature-dependent elastic moduli have been measured by the resonance frequency and the pulse-echo method. The bulk moduli were determined by synchrotron radiation diffraction using a high-pressure diamond-die cell at HASYLAB. The compression and creep tests were performed with computer-controlled tensile testing and creep machines. 

Fig. 16. Schematic geometries of four pulse-echo specimens of a NbTi/Cu composite. Filaments are indicated by striping. Eighteen wave velocities were measured (three modes in (100) and (110) directions shown as dashed lines) to determine nine elastic constants.

The elastic modulus, measured using the pulse echo method, was about 180 GPa, and the fracture strength determined by the three-point flexure test was about 800 MPa in the grain-alignment direction. This strength, which is relatively high for the large porosity of 25%, is almost equivalent to that of commercially available... 

Greiner et al. (1976) also have determined the single crystal elastic constants from 6 to 300 K using the ultrasonic pulse-echo-overlap (10 MHz) method. No thermal expansion corrections for density and acoustic path length were made because no thermal expansion data were available in the experimental temperature range. In addition to the four constants measured by Lenkkeri and Palmer (1977), Greiner et al. measured C13 consequently, polycrystalline elastic... 

The density of the hot pressed samples was measured using Archimedes method, elastic modulus was measured using an acoustic pulse-echo apparatus. 

Stark pulse on, but radiates when it is off, the emission is Stark shifted from the laser and four heterodyne beat frequencies are produced at the detector, each beat being due to two transitions M M. The four lines are 170 KHz wide and are spaced at 0.83 MHz [11.50]. The exponential decay of the echo signal with increasing delay time t, which is plotted in Fig.11.31, samples the homogeneous dipole dephasing rate due to elastic and inelastic collisions (see Sect.11.4.1). This technique therefore allows measurement of collision rates separately for different M levels. Since different velocity groups of molecules can be sampled, depending on the Stark shift, information on the velocity dependence of the collision rates can also be obtained (see Chap.12). 

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