2017. Vol.20. No. 1, pp. 50-55
Nonlinear NDT: A Route to Conventional Ultrasonic Testing
The “conventional” nonlinear effects, like higher harmonic generation and wave mixing are not the only dynamic scenario of nonlinear phenomena for resonant defects. At higher level of excitation, a combined effect of LDR and nonlinearity results in qualitatively new features characteristic of nonlinear and parametric resonances. Under resonance conditions nearly total input energy at fundamental frequency can be converted into higher harmonic or subharmonic vibrations of the defects. Both super- and subharmonic LDR are strongly localized in the defect area that provides a background for highly-sensitive defect-selective imaging. LDR mode of nonlinear NDT requires much lower acoustic power to activate nonlinearity of defects that makes it possible to avoid high-power ultrasonic instrumentation and switch to conventional ultrasonic equipment instead.
Keywords: local defect resonance, nonlinear non-destructive testing of composites.