Author
K. Pfleiderer
Bio: K. Pfleiderer is an academic researcher from University of Stuttgart. The author has contributed to research in topics: Flexural strength & Nondestructive testing. The author has an hindex of 8, co-authored 13 publications receiving 264 citations.
Papers
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TL;DR: It was shown for the first time that nonlinear vibrations of cracks resulted in radiation of a very high-order harmonics of the driving excitation in air that enabled imaging of cracks remotely by registration their highly nonlinear "acoustic emission" with air-coupled transducers.
63 citations
TL;DR: Air-coupled ultrasound testing is now feasible because of low impedance focused narrow band transducers and sensitive electronics, both of which improve the signal-to-noise ratio.
57 citations
01 Apr 2006
TL;DR: In this article, a focused slanted transmission mode (FSTM) was proposed for NDE applications of air-coupled ultrasound, which combines the benefits of plate wave excitation with a high spatial resolution and enables to characterise local elastic properties of a material.
Abstract: The area of NDE-applications of air-coupled ultrasound is expanded substantially for a weakly focused acoustic wave incident obliquely on a plate-like sample at an angle of ‘resonance’ transmission. Such a focused slanted transmission mode (FSTM) combines the benefits of plate wave excitation with a high spatial resolution and enables to characterise local elastic properties of a material. It was shown that the in-plain elastic anisotropy could be obtained by measurement of the ‘resonance’ transmission angle of the FSTM-output signal as a function of the azimuth angle. A striking contrast enhancement was demonstrated for the FSTM-C-scan imaging of cracked defects and delaminations. Non-contact FSTM-measurements of local variations of flexural wave velocity were used to detect fine structural changes and damage induced in polymer and composite materials during tensile tests.
40 citations
TL;DR: In this article, the authors show the possibility of fatigue damage characterization in GFRP-tube-like components by using circumferential plate waves and show that the results indicate that the technique is applicable to fatigue damage assessment in complex-shaped components of composite materials.
33 citations
TL;DR: In this article, the Focused Slanted Transmission of air-coupled ultrasound is used to generate and detect locally the flexural waves in wood as well as to measure their velocities.
Abstract: The results of non-contact measurements of local inplane elastic anisotropy in wood by monitoring the flexural plate wave velocity as a function of azimuth angle of propagation are reported. The Focused Slanted Transmission of air-coupled ultrasound is used to generate and detect locally the flexural waves in wood as well as to measure their velocities. The analysis presented shows that for thin plates the flexural wave velocity can be readily used to evaluate the anisotropy of Young's modulus. This conclusion is confirmed by measurements of the plate wave anisotropy factors for veneer laminae and cross-ply laminates of spruce and beech. The technique is sensitive enough to detect the anisotropy variation of earlywood caused by the incorporation of latewood areas in growth rings. A new approach based on dynamic nonlinearity of wood is developed and applied to acoustic imaging of wood structure and detecting of defects in wood. The hysteresis mechanism of the dynamic nonlinearity is shown to dominate in clear wood and to manifest in a primary generation of odd acoustic harmonics. Local maxima of the odd higher harmonic amplitudes in the LR- and LT-planes of softwood are observed in the earlywood area close to latewood/earlywood transition interface that indicates the lower stiffness and strength of wood in those areas. The higher-order even harmonics and subharmonics in the nonlinear vibration spectra of wood are mostly produced by clapping in defect areas. Measurements of local amplitudes of these modes are applied to nonlinear acoustic imaging of cracks, delaminations and knots in wood and wood composites.
29 citations
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TL;DR: In this paper, the authors reviewed the overall progress in nonlinear ultrasonic technique with the brief introduction of basic principle in the application of each nonlinear Ultrasonic phenomenon, including higher harmonic generation, subharmonic generation, nonlinear resonance, or mixed frequency response.
Abstract: The nondestructive assessment of the damage that occurs in components during service plays a key role for condition monitoring and residual life estimation of in-service components/structures. Ultrasound has been widely utilized for this; however most of these conventional methods using ultrasonic characteristics in the linear elastic region are only sensitive to gross defects but much less sensitive to micro-damage. Recently, the nonlinear ultrasonic technique, which uses nonlinear ultrasonic behavior such as higher-harmonic generation, subharmonic generation, nonlinear resonance, or mixed frequency response, has been studied as a positive method for overcoming this limitation. In this paper, overall progress in this technique is reviewed with the brief introduction of basic principle in the application of each nonlinear ultrasonic phenomenon.
581 citations
TL;DR: In this article, the authors present a comprehensive review of the current state of knowledge of second harmonic generation (SHG) measurements, a subset of nonlinear ultrasonic non-destructive evaluation techniques.
Abstract: This paper presents a comprehensive review of the current state of knowledge of second harmonic generation (SHG) measurements, a subset of nonlinear ultrasonic nondestructive evaluation techniques. These SHG techniques exploit the material nonlinearity of metals in order to measure the acoustic nonlinearity parameter, $$\beta $$
. In these measurements, a second harmonic wave is generated from a propagating monochromatic elastic wave, due to the anharmonicity of the crystal lattice, as well as the presence of microstructural features such as dislocations and precipitates. This article provides a summary of models that relate the different microstructural contributions to $$\beta $$
, and provides details of the different SHG measurement and analysis techniques available, focusing on longitudinal and Rayleigh wave methods. The main focus of this paper is a critical review of the literature that utilizes these SHG methods for the nondestructive evaluation of plasticity, fatigue, thermal aging, creep, and radiation damage in metals.
271 citations
TL;DR: In this paper, a review of modeling approaches used for nonlinear crack-wave interactions is presented, including models of crack-induced elastic, thermo-elastic and dissipative nonlinearities.
248 citations
TL;DR: Developments in air-coupled transduction and electronics are briefly treated, although the emphasis here is on methods of characterization and inspection, and in overcoming limitations inherent in the use of such a tenuous sound coupling medium as air.
206 citations