BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI - Universitatea ...

Bul. Inst. Polit. Iaşi, t. LVI (LX), f. 2, 2010 93
of ultrasonic waves from transducer through the examined piece, the reflection
modalities of the waves and the way displaying on the screen of the device.
When the diameter of transducer is comparable to the width of the piece, due to
the divergence and partial reflection of the beam from the lateral surfaces of the
piece, along the back wall echo and additional signal is formed, more or less
distinct, named divergence marginal echo [2]. The necessary condition for
eliminated this effect is:
(1)
B−Dp ⎡ ⎛ λ ⎞⎤
≥ tg ⎢arcsin ⎜1, 22 ⎟⎥,
2l
⎣ ⎝ Dp⎠⎦
where: B – the diameter of the piece; Dp
– the diameter of the transducer; l –
the length of the piece; λ – the divergence beam of fascicle. Also the back wall
echo can be confused with a fault echo. These confusions occur due to the piece
geometry, to the transducer diameter which is comparable to the diameter of the
piece and to the differences in length. To eliminate these interpretation errors of
and disturbances we will present several different cases.
3. Experimental Results
The experimental studies were performed with the devices type
Krautkramer (USM 35 X and USLT 2000) in order to check possible errors in
measurement. The pieces subjected to ultrasonic testing are: an aluminum bar
with dimensions Ø 90 x 318 mm and one axle in OL47, forged and heat treated.
By conducting the experiments we achieved the following results.
3.1. First case. In this case the back wall echo can be confused with an
echo of a defect (See fig. 3). These echoes can be called divergent effects.
Fig. 3 – Ultrasonic testing display. Fig. 4 – The divergent effect.