Nondestructive testing of defects in adhesive joints

esults were compared. Measurements were repeated in two different methods, to confirm the
results.
3. Results and discussion
The compressive modulus obtained was 1 GPa. The epoxy resin employed largely controls the
modulus of the composite. Hence it is proposed to use resin having larger modulus. Upto a certain
level of loading, magnetostriction of the composite increases as shown in Fig.5 with the volume
fraction of the Terfenol-D powder added . The present composite having 60 % loading shows a
magnetostriction of 450 ppm at a DC magnetic field of 2000 Oe. The remnant magnetic field
present in the composite influences utilization of the devices for high frequency applications . As it
is evident from the Fig. 6, the remnant magnetic field present in the composite is negligible. The
composite exhibits saturation tendency above 4000 Oe. Fig. 3 shows a photograph of the realized
drive as per the scheme in Fig.2 (a). The drive module was inserted into an elliptical Aluminum
shell of a flex-tensional transducer (FT). Fig.4 shows a photograph of the assembled
magnetostrictive transducer. End plates with O-rings were fastened to make the device waterworthy.
As magnetostrictive transducers are current-driven devices, Transmitting Current
Responses (TCRs) are used to characterize them, in place of the usual Transmitting Voltage
Responses (TVRs) used in the case of transducers with piezoceramic drive.Fig. 7 shows the measured
TCRs of the above FTs with monolithic Terfenol-D rods and composite rods respectively .The
advantage of the composite is a slight lowering of the frequency at which the device shows peak
performance. The peak performance is about 10 dB less for the FT with composite rods, compared
FT with Terfenol-D rods.
5. Conclusion and suggestion for future work
Composite of Terfenol-D / epoxy resin exhibits magnetostriction. The magnetostiction values are
largely depend on the percentage of Terfenol-D powder added. The magnetostrictive composite
transduction material developed can drive elliptical aluminum shell. Magnetic circuit design play
important role in the performance of the transducer. For improving the performance of the transducer,
magneto-mechanical properties such as Young’s modulus, magneto-mecahnical coupling factor etc
has to be optimized.
Acknowledgement:
Authors would like to thank Prof. Markeyandalu, Dept. of physics, IIT-Madras, Chennai for the
materials properties measurement. The encouragement and support of ASD(ME&MEMS) and the
permission of the Director, NPOL to publish this work is greatly acknowledged.
6. Reference
[1] Moffett, M B, Porzio, R., Bernier, G L, “High Power Terfenol-D Flextensional Transducer –
Revision A”, NUWC Technical Document No. 10883A, 12 May 1995.
[2] M.B. Moffett, J.M. Powers, J.Acoust. Soc. Am. 90 (1991) 1184.
[3] J.H. Goldie, M.J. Gerver, J. Olesky, .P. Carman, T.A.Duenas, Proc. SPIE 3675 (1999),243.
[4] T.A. Duenas, G.P. Carman, Proc. ASME 291 (1998) 63.