Applications of nonlinear ultrasonics to the NDE of materialdegradation

摘要

Nonlinear ultrasonics is suggested as a new approach for theneffective evaluation of material degradation. As its quantification, thenparameter Β is introduced on the basis of nonlinear elasticity, andna new method to measure the parameter Β using bispectral analysisnis proposed. Then, the correlation between Β and materialndegradation is investigated. From the results for several mild steeln(SS41, SS45) specimens that were degraded by stretching and cyclicnloads, it was confirmed that the parameter Β has a strongncorrelation with material degradation. As another practical application,nthe evaluation of the aging degradation in a high temperature materialnis tried. For this, Cr-Mo-V specimens that are generally used in turbinenrotors in power plants were prepared, and the variation of Β causednby aging time was investigated. For comparison, the fracture appearancentransition temperature (FATT) of the specimen was measured, and itsnbehavior showed good agreement with Β. In addition, for all of thenexperiments, no noticeable change in attenuation and sound velocity innthe same specimens with change of degradation were observed. From thesenresults, it may be concluded that nonlinear ultrasonics could be appliednto the quantitative evaluation of material degradation