03:50 Jan-29-2004 Ed Ginzel R & D, - Materials Research Institute, Canada, Joined Nov 1998 1191
Re: about creeping wave and mode conversion Mr. Park: The best work on the description of the so-called creeping wave is a paper entitled "On the nature of the so-called subsurface Longitudinal wave and/or the surface Longitudinal Creeping wave" by K.J Langenberg, P. Fellinger, and R. Marklein, Research in Nondestructive Evaluation, Springer - Verlag, 1990 pp 61-81. Regards Ed
----------- Start Original Message ----------- : hi there, : Can anybody inform me about the theoretical background of creeping wave and mode conversion? please help me... T.T ------------ End Original Message ------------
Re: about creeping wave and mode conversion ----------- Start Original Message ----------- : hi there, : Can anybody inform me about the theoretical background of creeping wave and mode conversion? please help me... T.T ------------ End Original Message ------------ The name „creeping waves“ has been introduced around 1975 (if I am correctly informed at first in Germany) for a phenomenon observed at angle beam probes with a wedge angle close to the angle of total reflection of the longitudinal wave in steel (e.g. with a perspex wedge angle around 27°). The waves then generated in steel do have a complex structure. They do propagate into the halfspace as shear waves with a refraction angle around 33,2° and are linked to a remaining long-wave trace at the surface – a kind of longitudinal headwave, also known as lateral wave in the TOFD applications or as “creeping waves”, which is strongly attenuated with increasing distance from the probe due to the energy loss by the 33,2°-shear waves constantly irradiated from the surface into the half space. The term “creeping wave” is somehow misleading. It has been applied a lot earlier than 1975 for waves surrounding cylindrical reflectors hit by shear waves and producing small indications in A-scans of such reflectors which may be used for the determination of the reflector diameter. But once introduced into practical application, it has been impossible to correct this ambiguity. Nowadays, the term “creeping wave” is linked to some important applications e.g. on stainless steel welds. The fast distance decay forces to use transmitter receiver probes. The family of transmitter-receiver probes for inclined longitudinal waves (TRL or SEL probes) is among others used with refraction angles around 70° (for the L-wave in steel!) eg. for the detection of sub-cladding cracks or with a wedge angle around 27° (producing more or less pure “creeping waves” ) for surface and near surface cracks. Since the always excited 33,2°-shear-wave may convert back into a longitudinal wave when hitting the opposite surface of a plate, one may use also this L-wave (which propagates nearly in parallel to the opposite surface) to detect cracks or other defects close to the opposite surface. The use of different interactions using different waves modes at one single probe is a typical multimode application producing quite complex patterns of A-scans which can only be evaluated with some success based on the context information of images like TD-, B-, or C-scans, that means it requires an automatic inspection.