Ultrasonic velocity test

Ultrasonic velocity test This lab test is conducted on cores in the longitudinal direction. 

Solids usually have larger ultrasonic velocities and acoustic impedance, than liquids, which have larger values than gasses. Air has a very low acoustic impedance compared to liquids or solids which means that it is difficult to transmit ultrasound from air into a condensed material. This can be a problem when ultrasound is used to test dry materials, e.g., biscuits or egg shells. A small gap of air between an ultrasonic transducer and the sample to be tested can prevent ultrasound from being transmitted into the material. For this reason coupling materials (often aqueous or oil based) can be placed between the transducer and sample to eliminate the effects of the air gap, or alternatively soft-tip ultrasonic transducers can be used. 

The development of damage in the form of matrix cracks within 1-D CMCs subject to tensile loading has been traced by direct optical observations on specimens with carefully polished surfaces, and by acoustic emission detection,7 9 62,79-81 as well as by ultrasonic velocity measurements.82 Interrupted tests, in conjunction with sectioning and SEM observations, have also been used. Analysis of the matrix damage found in 1-D CMCs provides the... 

After initial tests with V-(4- -nonyloxy-benzylidene)-4-toluidine [241], it was demonstrated in a variety of work on azomethine compounds of the nO.m type [58, 98, 100, 103,104,116,137,140-142,148,242-244] and other compounds [119, 148, 160, 177] that, with the ultrasonic velocity v, temperature T, and molar weight M, parameters... 

In practice ultrasound is usually propagated through materials in the form of pulses rather than continuous sinusoidal waves. Pulses contain a spectrum of frequencies, and so if they are used to test materials that have frequency dependent properties the measured velocity and attenuation coefficient will be average values. This problem can be overcome by using Fourier Transform analysis of pulses to determine the frequency dependence of the ultrasonic properties. 

The transmitting frequency / of the UVP-DUO systems is 4 MHz in all tests. The ultrasound wavelength X is 370 pm and the sound velocity in water c is 1,480 m/s. 100 mm ion exchange (Diaion) particles are added to the flow as flow tracers their ability to follow the liquid flow has been assessed using Basset s analysis (Melling, 1997). Owing to theoretical considerations, the size of the flow tracers must be larger than one quarter of the emitted ultrasonic burst (Met-Flow, 2002). 

For composite samples the method discriminated separate Ti02 and CaC03 components and accurately determined their proportions. In addition, in combination with ultrasonic attenuation measurements, the size fractions of iron ore slurries below 10 and 30 pm were determined to within 1.3% and 1.0% respectively when compared with laser diffraction measurements [272]. According to Coghill et. al. velocity measurements are complementary to attenuation methods but better suited to the finer size fractions. A description of the analyzer and the results of plant feasibility tests and on-line installation has been presented [273]. 

Ultrasonic examination is currently the most commonly used NDT method for inspection of composites. It presents desirable features such as providing information about defects situated deeply inside a material, but equally this method has several limitations. Flaws modify ultrasonic parameters such as wave velocity, refraction, reflection, scattering, and intensity, thus affecting the efficiency of ultrasound in defect location. In order to fully understand the concept of ultrasonic testing, it is necessary to use some mathematics, which will be kept to a minimum. The principle, advantages, and limitations of ultrasonic NDT techniques for composite inspection are described next. 

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