Abstract
When material is subjected to an intense load, its stiffness changes due to elastic nonlinearity. This effect is especially pronounced in damaged materials, so that nonlinearity can be used as an indication of incipient damage. Under dynamic load, mechanical constraint between the fragments of planar defects provides gigantic nonlinearity in finite-amplitude contact vibrations. The local vibration spectra acquire a number of new frequency components which are used as signatures of damage. The experimental implementation of nonlinear NDT relies on the use of laser interferometers (Nonlinear Laser Vibrometry, NLV) to detect the nonlinear waves that are generated selectively by defects. In addition, the planar defects as localized sources of nonlinear vibrations efficiently radiate nonlinear airborne ultrasound (Nonlinear Air-Coupled Emission, NACE). The frequency conversion mechanism concerned with contact nonlinearity of the defect vibrations provides an efficient generation of air-coupled higher-order ultra-harmonics, ultrasubharmonics, and combination frequencies. Both the NLV and NACE are proposed for remote scanning and high contrast defect-selective imaging in nonlinear NDT.
Highlights
Conventional ultrasonic Non-Destructive Testing (NDT) is normally based on the scattering of acoustic waves by defects leading to the amplitude and phase variations of the input signal due to the wave-defect interaction
At low amplitudes of the driving excitation, the nonlinear spectrum follows the non-resonant scenario of the previous section and comprises the higher harmonic (HH) and the wave modulation (WM) frequency components
Our experiments show that nonlinear air-coupled emission (NACE) operates well in various constructional materials with raw surfaces and rugged defects in components, like bolted joints, arc welds, etc
Summary
Conventional ultrasonic Non-Destructive Testing (NDT) is normally based on the scattering of acoustic waves by defects leading to the amplitude and phase variations of the input signal due to the wave-defect interaction. The dynamic nonhookean behaviour of the material is concerned with non-linear response of defects, which is related to the frequency changes of the input signal These spectral changes are caused by anomalously nonlinear local dynamics of defects of various scale and nature. The nonlinear response is provided by the Contact Acoustic Nonlinearity (CAN) [1]: strongly nonlinear local vibrations of defects due to mechanical constraint of their fragments, which efficiently generate multiple ultra-harmonics and support multi-wave interactions. Another contribution to the nonlinear spectrum comes from resonance properties of planar defects [2]. NNDT are demonstrated for a series of hi-tech materials and industrial components
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Strojniški vestnik – Journal of Mechanical Engineering
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
