Visualization of defects using nonlinear acoustics

摘要

The present paper deals with the development of an inverse method for identification of unknown defects embedded in a thick elastic anisotropic plate by inversing the vibration amplitudes detected by ultrasound Doppler devices. For thick platesthe contribution of transverse shear stress waves is important and the kirchoft-Love assumption implies infinite transverse shear stiffnesses. For this reason these kind of materials exhibit much larger transverse shear effect and the limitation of thethin plate theory is no longer practicable. The basis of this work is a higher-order shear wave theory (HSWT) proposed by REDDY [1] and FREDERIKSEN [2]. The displacement field allows for distortion of third order of normals to the midplane of theundeformed plate, while the transverse deflection is assumed to be constant through the thickness. Thus, the theory is an advanced two-dimensional theory which accurately describes the global behaviour of the plate. We have chosen to concentrate on shear waves, since low-frequency londitudinal waves have wavelengths that are too large compared to samples of interest at the frequencies used in sonoelasticity imaging.