Tomasz Katkowski

Quantification of material nonlinearity in relation to microdamage density using nonlinear reverberation spectroscopy: Experimental and theoretical study

High amplitude vibrations induce amplitude dependence of the characteristic resonance parameters (i.e., resonance frequency and damping factor) in materials with microscopic damage features as a result of the nonlinear constitutive relation at the damage location. This paper displays and quantifies results of the nonlinear resonance technique, both in time (signal reverberation) and in frequency (sweep) domains, as a function of sample crack density. The reverberation spectroscopy technique is applied to carbon fiber reinforced plastic (CFRP) composites exposed to increasing thermal loading. Considerable gain in sensitivity and consistent interpretation of the results for nonlinear signatures in comparison with the linear characteristics are obtained. The amount of induced damage is quantified by analyzing light optical microscopy images of several cross-sections of the CFRP samples using histogram equalization and grayscale thresholding. The obtained measure of crack density is compared to the global macroscopic nonlinearity of the sample and explicitly confirms that the increase in nonlinearity is linked to an increased network of cracks. A change from 1% to 3% in crack density corresponds to a tenfold increase in the signature of nonlinearity. Numerical simulations based on a uniform distribution of a hysteretic nonlinear constitutive relation within the sample support the results.

Nonlinear Acoustic and Ultrasonic NDT of Aeronautical Components

In response to the demand for innovative microdamage inspection systems, with high sensitivity and undoubted accuracy, we are currently investigating the use and robustness of several acoustic and ultrasonic NDT techniques based on Nonlinear Elastic Wave Spectroscopy (NEWS) for the characterization of microdamage in aeronautical components. In this report, we illustrate the results of an amplitude dependent analysis of the resonance behaviour, both in time (signal reverberation) and in frequency (sweep) domain. The technique is applied to intact and damaged samples of Carbon Fiber Reinforced Plastics (CFRP) composites after thermal loading or mechanical fatigue. The method shows a considerable gain in sensitivity and an incontestable interpretation of the results for nonlinear signatures in comparison with the linear characteristics. For highly fatigued samples, slow dynamical effects are observed.

On the polarization of light diffracted by ultrasound

If light is diffracted by ultrasound in an isotropic medium with acoustically induced birefringence, the state of polarization is modified in each order of diffraction with respect to the initial state of polarization of the incident light wave. In the present paper, some polarization effects are discussed in the case of normal light incidence. In general a rotation of the main polarization plane occurs, together with a change of the ellipticity. However, while the former effect always takes place, the latter only occurs in the case of ultrasonic light diffraction of the intermediate type. Some experimental measurements are included in case of argon laser light being diffracted by an ultrasonic wave propagating in fused silica (SiO2).

Near field of light diffracted by an ultrasonic wave, beyond the Raman-Nath diffraction regime

The near field of ultrasonically diffracted light is examined for a wide range of Raman-Nath (v) and Klein-Cook (Q) parameter values up to the region of total light rediffraction phenomenon occurrence to the zeroeth diffraction order. The behavior of the secondary interference plane position is studied, both theoretically and experimentally, for vari- ous Q and v values. In addition, the relationship is shown between dif- fracted light intensity modulation minima localization shift and rediffrac- tion phenomenon. A comparison is made of the results of the general Fresnel region theory, including the influence of complex light amplitudes over the diffracted light intensity distribution, with those obtained from Cooks simplified near-field description. The same, limited validity range of the latter theory is revealed. For all the experimental conditions con- sidered, quite good agreement is observed between experimental data obtained and the appropriate theoretical predictions.

Polarization effects at acousto-optic interaction in anisotropic medium

Polarization effects that arise during diffraction of an arbitrarily polarized light by an acoustic wave in an anisotropic medium are studies both theoretically and experimentally. Peculiarities of these effects in the cases of isotropic and anisotropic scattering of the light are considered in detail. Results of polarization state measurements performed with a paratellurite acousto-optic cell in the zeroth order of diffraction are presented as well.

Diffraction of light by two ultrasonic beams of frequency ratio 1 :2, beyond the Raman-Nath diffraction regime

Light diffraction by two ultrasonic waves of frequency ratio 1:2 is examined beyond the Raman-Nath diffraction regime. Measurements were taken of +/- 1 order diffracted light intensities for some Raman-Nath parameter values, as a function of the phase shift between the sound beams. The experimental results obtained are discussed and compared with relevant theoretical predictions. Within the experimental conditions, a quite good quantitative agreement between the experimental data and the appropriate theoretical expectations is observed.

Near field of light diffracted by ultrasound in an isotropic medium with acoustically induced anisotropy

A theoretical model is presented for the study of the near field of light diffracted by ultrasound in an isotropic medium which becomes birefringent in the presence of an acoustic wave. Due to the interference with the sound wave, the diffracted light wave in its near field is seen to act as a quasi-monochromatic light wave which is partially polarized. The degree of coherence ins sen to coincide with the degree of polarization and can be controlled acoustically. Hence coherent laser light can be transformed into incoherent light by sending it through an isotropic material with acoustically induced birefringence. In the experimental part of the work, the non-diagonal elements of the diffracted light beam coherency matrix were measured and a good agreement with the theoretical model was obtained.

Light diffraction by ultrasound: near field investigation

Light diffraction by ultrasonic waves has been studied for many years, however we still can not say that the phenomenon has been examined completely. During the last decade the near field investigations received a particular attention. The new results obtained, both in the near field and in the far field of ultrasonically difracted light, forced us not only to change our point of view concerning this phenomenon but also to modify the formulas describing it. A brief review is given of some of the results which have been obtained up until now, both theoretical and experimental ones. Some new theoretical suggestions, based on the N-th order approximation (NOA) method are presented.

Diffraction of light by two parallel adjacent ultrasonic beams of the frequency ratio 1:1, beyond the Raman–Nath diffraction regime

Light diffraction by two adjacent ultrasonic waves having the same frequencies is examined experimentally beyond the Raman-Nath diffraction regime. Measurements were taken of the 0 and 61 order diffracted light intensities for a few (settled) Raman-Nath parameter val- ues, as a function of the phase shift between the sound beams. The experimental results obtained are discussed and compared with rel- evant, generalized, theoretically numerical predictions, as well as with the ones obtained by means of the 0 and 61 order approximation only. In both cases, however, within all the experimental conditions consid- ered, a quite good quantitative agreement between the experimental data and the appropriate theoretical predictions is observed.

Near field of light diffraction by two ultrasonic beams of frequency ratio 1:1 beyond the Raman-Nath diffraction regime

The amplitude of near field modulation of light diffraction by two ultrasound beams, simply depends on phase between two sound beams. This paper presents suggestion for measurement of this phase.