Testing Procedure
28 www.ndtjames.com
In order to obtain the spectrum of the signal and the resonance
frequency, the Enter key should be pressed. On the screen will
appear
the message “calculating spectrum please wait”. It will take
approximately 45 seconds.
The system will show the fundamental frequency from the FFT,
frequency value of the maximum amplitude on the FFT.
The system will obtain the fundamental frequency from the FFT.
The fundamental frequency will appear on the first screen with the
corresponding value. In order to view the complete frequency
spectrum, you can use the left and right arrow key to change from
different screens. The frequency spectrum is presented in 2 to 4
different screens.
For concrete specimens the resonance frequency will generally be
in the range 1 kHz to 10 kHz depending on the dimensions of the
specimen (see Figure 22).
Figure 22: Range of longitudinal fundamental resonant frequencies of concrete prism
and cylinder specimens
The system will calculate the dynamic Poisson’s ratio according to
eq. (ii), using the obtained value of (E) from the Longitudinal test
and assuming a value of (G) that shall be input before to run the
Longitudinal test.
In order to obtain a meaningful result of µ, it is recommended to run
a Torsional test beforehand to obtain a value of (G) and then input
this value as a parameter to compute the Poisson’s ratio.
Specimen dimensions (inches)
Approximate range
of Frequency (Hz.)
6” x 6” x 30”
1700
– 3000
6” x 6” x 28”
2000
– 3200
4” x 4” x 30”
1700
– 3000
4” x 4” x 20”
3000
– 4500
4” x 4” x 12”
5000
– 7000
6” x 12” cylinder
5000
– 7000
