Full-field imaging of nonclassical acoustic nonlinearity

Abstract

The feasibility of full field shearographic detection of nonclassical acoustic nonlinearity is investigated. Traditional frequency analysis of the sinusoidally excited sample, as used in scanning techniques, turns out to be not practical due to the inherent optical detection nonlinearity of the shearography system itself. An alternative method, based on determining the asymmetry between shearographic images stroboscopically obtained for positive and negative displacements, is proposed. This approach allows us to easily and rapidly detect the tension-compression asymmetry which typically arises where nonbounded contact interface defects are present.

Investigation of contact acoustic nonlinearity in delaminations by shearographic imaging, laser doppler vibrometric scanning and finite difference modeling

“…fig. 15 depicts the experimental excitation amplitude dependence of the asymmetry-averaged image obtained on the test sample as was outlined in previous work [13]. the underlying resulting dynamic fringe pattern depends not only on the vibration pattern, but also on the shearing distance and on the nonlinear interferometric transfer function, making it quite hard to predict or interpret the obtained intensity-averaged images and their dependence on the vibration amplitude.…”

“…substantial work on nonlinearity in adhesive joints was performed by Hirsekorn [8], [9], Zaitsev and Gusev et al [10], and Van den abeele, johnson et al [11], [12] obtained very interesting experimental and theoretical results related to acoustical nonlinearity in bulk materials. recently, the authors have shown that a similar approach can be used in combination with dynamic shearographic imaging providing full-field visualization of the defect-selective acoustic nonlinearity [13]. the advantage of this approach is the combination of an increased detection speed with nonlinearly enhanced defect contrast.…”

“…However, it is very difficult to obtain fast and reliable results in practice, particularly when working with non-optimal industrial samples that exhibit complex displacement patterns and even more complex fringe patterns. therefore, a simpler and more straightforward technique was proposed by the authors (sarens et al [13]) to detect clapping behavior, eliminating the troublesome fringe demodulation and integration procedure. as mentioned previously, locations around defects presenting contact acoustic nonlinearity are essentially characterized by lower stiffness in tension [4].…”

“…for displacements of several hundreds of nanometers (known from calibrations by laser doppler vibrometry), the local stress is high enough to open the delamination and the sample shows a nonlinear elastic response at the location of the defect. using the algorithm described in sarens et al [13], the location of the defect can be revealed. a careful look at fig.…”

Imaging of transient surface acoustic waves by full-field photorefractive interferometry

“…They have attracted much attention, by virtue of their non-contact, non-destructive nature and high flexibility of implementation. [1][2][3][4][5][6] Moreover, possible bandwidth limitations of electronic detection can be circumvented by making use of an optical delay line. 7,8 Optical detection of SAW induced displacements at a single location can be done with high sensitivity, e.g., by interferometric detection, 9,10 laser beam deflection, 11,12 modulated optical reflection, 13 or heterodyne diffraction detection.…”