A BOUNDARY-ELEMENT SOLUTION FOR A MODE CONVERSION STUDY OIL THE EDGE REFLECTION OF LAMB WAVES

The boundary element method, well known for bulk wave scattering, is e xtended to study the mode conversion phenomena of Lamb waves from a fr ee edge. The elastodynamic interior boundary value problem is formulat ed as a hybrid boundary integral equation in conjunction with, the nor mal mode expansion technique based on the Lamb wave dispersion equatio n. The present approach has the potential of easily handling the geome trical complexity of general guided wave scattering with improved comp utational efficiency due to the advantage of the boundary-type integra l method. To check the accuracy of the boundary element program, verti cal shear wave diffraction, due tea circular hole, is solved and compa red with previous analytical solutions. Edge reflection factors for th e multibackscattered modes in a steel plate are satisfied quite well w ith the principle of energy conservation. In the cases of A0, A1, and S0 incidence, the variations of the multireflection factors show simil ar tendencies to the existing results for glass. It is observed that t he reflection of an incident wave becomes close to zero over a certain frequency range seen through energy interaction with other reflected modes, and increases again beyond this minimum point due to reverse mo de conversion. The reflections of the higher symmetric incident modes, S1 and S2, are also investigated. It turns out that S1 mode is an unu sual mode which is nearly unaffected by the mode conversion in the Lam b wave edge reflection. (C) 1996 Acoustical Society of America.