Measurement of Elastic Constants Using Ultrasound:Procedure

Equipment

Ultrasonic/Receiver (Panametrics Model 5072 PR)

Transducer cable

5 MHz longitudinal wave transducer (Panametrics Model V110)

5 MHz shear wave transducer (Panametrics Model V156)

Oscilloscope

Micrometer Caliper

Specimen Blocks:303 Steel, 6061-T6 aluminum, brass, quartz disk, red blocks

Glycerin coupling

Shear wave coupling and pipette

2 BNC-BNC cables

Paper towels

Figure 1: Ultrasonic Testing Apparatus

Procedure

  1. Put a few paper towels down on the lab station workbench to keep it clean.
Measuring Elastic Constants
  1. Measure all the dimensions of the metallic and quartz specimen blocks, being sure to note any uncertainty.
  2. With the power to the Pulser/Receiver (P/R) turned off, connect the longitudinal wave transducer (lightly marked V110 on the top of the transducer) and the oscilloscope to the P/R as shown in Figure 1.Turn on the oscilloscope and the P/R.
  3. Set the oscilloscope to: 500 mV/Div, 4µs/Div, and Auto-level Triggering (Found by selecting the Trigger Menu ModeAuto buttons on the oscilloscope). Note that it may be necessary to adjust these values for different specimens and transducers.
  4. Set the settings on the Pulser/Receiver as follows:
  5. PRF (Hz): Regulates the frequency at which pluses are applied to the transducer. Because our samples are relatively thick, we can set this to the maximum value of 5kHz without experiencing excessive noise.
  6. Energy: Regulates the pulse width and amplitude. Setting should be kept at the minimum that will give good results, in our case 1.
  7. Damping: Used to match the impedance of the P/R to the impedance of the transducer to ensure good energy transfer and prevent excessive oscillation. For the longitudinal transducer (V110) setting 3 (50Ω) should work. For the shear transducer (V156) use 8.
  8. Gain: Amplifies the received signal to ensure appropriate signal amplitude. A gain of +30dB should allow for a clear signal with adequate sensitivity, but the gain needed may differ depending on the transducer used. For the shear transducer (V156) use +20dB.
  9. HPF: The high pass filter will filter out all frequencies below 1MHz and should be set toOUT.
  10. LPF: The low pass filter will filter out all frequencies above 10MHz and should be left to allow the Full BW (35MHz Bandwidth).
  11. Mode:this allows you to toggle between pulse-echo and through transmission modes. For this lab you need mode 1, meaning the transmitter will be both sending the pulse and receiving the echo pluses back.
  12. Hold the dark side of the transducer against the quartz specimen using a small amount of the glycerin couplant (squeeze bottle).Adjust the oscilloscope settings (including Gain on the P/R) until you see a train of echoes, similar to that shown in Figure 2 below.

Figure 2: Echoes Received

  1. Make a coarse measurement of the time between the first echo and the second echo using the Cursors(only press Cursors one time, and use Multipurpose a and Multipurpose b to adjust the location of the cursors).Make sure you are using the actual echoes and not the noise. An easy way to tell is to make sure there isn’t a bigger peak after the one you are measuring. You do not have to record it.
  2. Now you will make a more accurate measurement using the horizontal magnification feature on the oscilloscope.
  3. Use the Zoom knob and the Pan knob to zoom in on the first echo(not the first pulse). The full waveform is shown at the top of the screen, and the magnified portion of the waveform is displayed below the full waveform. Only if necessary, adjust the time/Div (horizontal Scale), V/Div (vertical Scale)until only the first echoisclearly displayed. Be aware that these adjustments will likely change the magnified area and the cursor locations.
  4. Set the “a”cursor at the very start of the first echo. Note: Be sure that both the vertical and horizontal cursors are NOT displayed. If both cursors are displayed, press Cursors twice to enable only the horizontal cursors.
  5. Use the Zoom knob and the Pan knob to zoom in on the second echo. Only if necessary, adjust the time/Div (horizontal Scale), V/Div (vertical Scale) until only the first echo is clearly displayed. Be aware that these adjustments will likely change the magnified area and the cursor locations.
  6. Set the “b” cursor at the very start of the second echo.
  7. Record the difference in time between the two cursors (displayed next to the ∆ symbol).
  8. Repeat Step #8 for each dimension of the piece (i.e., width, length, and height).
  9. Repeat Steps #8 and #9 for the other specimen materials:steel, aluminum, and brass.
  10. TurnOFFthe P/R.Clean the longitudinal wave transducer and replace it with the red shear wave transducer (marked V156).
  11. Change the damping setting to 8.
  12. Lower the Gain switch to (+20); lower further until clear echo is visible.
  13. Turn ON the P/R.
  14. Put a small dab of the shear wave couplant (brown gel) on the quartz specimen using the pipette. Hold the shear wave transducer (black side down) against it. Since it is difficult to transmit shear forces across an interface, it is necessary to use firm pressure between the transducer and the specimen.But do not exceed the pressure that you can apply by hand - DO NOT clamp the transducer as this will result in damage to the device.
  15. Adjust the gain until the echoes are once again clearly visible. Again measure the time between the first echo and the second echo as accurately aspossible using the horizontal magnification explained above. Make sure you have the correct echo because the shear waves will produce a lot of noise.
  16. Repeat the shear wave transit time for the other specimen materials in each direction.
Finding the Embedded Coins
  1. A coin is embedded in each red block specimen, so take measurements across all dimensions that you feel are useful in determining the size of the hidden coin.
  2. When finished, clean off the transducers, lab station, and specimen blocks using a damp paper towel.Return all equipment to your TA.

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