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Nonlinear Interaction Between Ultrasonic Waves and Cracks and Interfaces
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The subject of this thesis is the development of new ultrasound inspection techniques for detection of cracks that are smaller than the wavelength of the inspecting wave and the characterization of cracks in fluid-filled pipes as either surface-breaking or subsurface.

The spectrum of the scattered field of a partially closed crack comprises harmonic components not expected to be found in the case of linear scatterers such as pores or inclusions. Paper A presents an experimental investigation into the linear reflection and generation of the 2nd harmonic component following the incidence of an ultrasonic wave onto a dry or water-confining interface formed by elasto-plastic steel-steel surfaces in contact. The results indicate that water has an unexpected effect on the reflection, at low interfacial pressures, suggesting that fluid mediated forces play a role not accounted for in current models. The level of the generation of the 2nd harmonic measured provides support for further development of the technique for detection of dry, partially closed cracks or fluid-filled, nearly open cracks.

A theoretical model describing the nonlinear scattering of acoustic waves by surface-breaking cracks with faces in partial contact is presented in Paper B. Both linear and nonlinear response of the crack are shown to be the largest for a SV wave incident on the surface containing the crack at an angle just above the critical angle for longitudinal waves.

A method which provides information on whether a fracture is surface-breaking or subsurface has been modelled and its optimal experimental set-up examined in Paper C. The main assumption of the model is that water carried by pressurized pipes infiltrates and fills a surface-breaking crack, while a subsurface crack is dry. The model simulates an inspection in which the modulation technique is employed and the surface hosting the crack is not accessible. A parameter, constructed with signals recorded in backscattering configuration during a modulation cycle, is examined and shown to provide a clear criterion to distinguish subsurface from surface-breaking cracks when a SV wave at 45 degree incidence is employed as a probe.

Finally, in Paper D the modulation technique is experimentally tested on steel beams that host surface-breaking fatigue cracks. The method is shown to be a successful tool to distinguish a dry from a fluid-filled crack. Furthermore, it is revealed that the dynamics of the fluid needs to be accounted for in a more accurate simulation tool.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , xiii, 32 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2008:01
Keyword [en]
ultrasonic waves, crack, modulation, rough interface, partially closed, surface-breaking, fluid-filled
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-4604OAI: oai:DiVA.org:kth-4604DiVA: diva2:13055
Public defence
2008-01-31, Sal F3, F, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100906Available from: 2008-01-14 Created: 2008-01-14 Last updated: 2010-09-06Bibliographically approved
List of papers
1. On the linear and nonlinear acoustic properties of dry and water-confining elasto-plastic interfaces
Open this publication in new window or tab >>On the linear and nonlinear acoustic properties of dry and water-confining elasto-plastic interfaces
2006 (English)In: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences, ISSN 1364-5021, E-ISSN 1471-2946, Vol. 462, no 2067, 769-788 p.Article in journal (Refereed) Published
Abstract [en]

An experimental investigation into the linear reflection and generation of the second harmonic component following the incidence of an ultrasonic wave onto a dry or water-confining interface between elasto-plastic steel-steel surfaces in contact is presented. The results on dry interfaces show that, although the theoretical models currently used to estimate the stiffness of such interfaces constitute a valid framework, the statistics of asperities in contact requires further development to account for the effects of the elasto-plastic deformation. Similarly, the results with water-confining interfaces indicate that current models not accounting for the liquid-mediated forces between the solid surfaces cannot explain the results presented here. In fact, the experimental evidence is interpreted as suggesting that structural repulsive forces may be responsible for the observed phenomena. Finally. the level of second harmonic generation for these interfaces offers support by the development of inspection techniques which exploit such wave phenomena for the detection of partially closed and dry, or nearly open and water-trapping stress-corrosion surface-breaking cracks.

Keyword
confined water, elasto-plastic interface, ultrasonic waves
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-7888 (URN)10.1098/rspa.2005.1595 (DOI)000235237800004 ()2-s2.0-33845543443 (Scopus ID)
Note
QC 20100906Available from: 2008-01-14 Created: 2008-01-14 Last updated: 2010-12-17Bibliographically approved
2. Nonlinear acoustic scattering by a partially closed surface-breaking crack
Open this publication in new window or tab >>Nonlinear acoustic scattering by a partially closed surface-breaking crack
2005 (English)In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 117, no 2, 592-600 p.Article in journal (Refereed) Published
Abstract [en]

A theoretical model describing the nonlinear scattering of acoustic waves by surface-breaking cracks with faces in partial contact is presented. The nonlinear properties of the crack are accounted for by suitable boundary conditions that are derived from micromechanical models of the dynamics of elastic rough surfaces in contact. Both linear and nonlinear responses of the crack are shown to be largest for a shear vertical wave incident on the surface containing the crack at an angle just above the critical angle for longitudinal waves. These findings question the fitness for the purpose of a conventional inspection method, which utilizes shear vertical waves at 45degrees of incidence to search for surface-breaking cracks in many engineering components. For angles of incidence proximal to the critical angle of longitudinal waves, the efficiency of the second harmonic's generation appears to be the highest. Thanks to the increased sensitivity to surface-breaking cracks, this configuration seems to offer a solution to the localization problem, a task that has eluded nonlinear techniques operating under other circumstances. Finally, this model suggests a simple interpretation of the highly localized nonlinear response of delaminations in composite materials.

Keyword
Composite materials, Composite micromechanics, Cracks, Elasticity, Mathematical models, Second harmonic generation, Localisation, Longitudnal waves, Surface-breaking cracks
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-7889 (URN)10.1121/1.1850052 (DOI)000226986900013 ()2-s2.0-13544262435 (Scopus ID)
Note
QC 20100906Available from: 2008-01-14 Created: 2008-01-14 Last updated: 2010-12-17Bibliographically approved
3. So… is this a surface-breaking crack?
Open this publication in new window or tab >>So… is this a surface-breaking crack?
2006 (English)In: Journal of Mechanics of Materials and Structures, ISSN 1559-3959, Vol. 1, no 4, 743-762 p.Article in journal (Refereed) Published
Abstract [en]

An inspection technique used to assess the structural integrity of critical components in a nuclear power plant must be able to discern surface-breaking cracks from subsurface cracks. This work proposes an ultrasonic method to provide that information and presents a theoretical investigation into it. The main assumption of the model is that water carried by pressurized pipes infiltrates and fills a surface-breaking crack, while a subsurface crack is dry. The model simulates an inspection in which the modulation technique is employed and the surface hosting the crack is not accessible. A ratio, R, constructed with signals recorded in backscattering configuration during a modulation cycle, is examined and shown to provide a clear criterion allowing subsurface cracks to be distinguished from surface-breaking cracks when a shear vertical wave at 45 degree incidence is employed as a probe.

Keyword
partially closed cracks, modulation, wave scattering stress-corrosion
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-7890 (URN)000207728400008 ()
Note
QC 20100906Available from: 2008-01-14 Created: 2008-01-14 Last updated: 2010-12-17Bibliographically approved
4. Discriminating surface-breaking from subsurface cracks in pressurized water pipes by means of a parametric modulation technique
Open this publication in new window or tab >>Discriminating surface-breaking from subsurface cracks in pressurized water pipes by means of a parametric modulation technique
2008 (English)In: NDT & E international, ISSN 0963-8695, Vol. 41, no 3, 208-216 p.Article in journal (Refereed) Published
Abstract [en]

The discrimination of surface-breaking cracks from cracks that are entirely embedded within the material is paramount to the assessment of the integrity of pressurized water pipes. This work addresses this issue investigating the use of a parametric modulation technique towards this end. Tests are conducted on 1D surface-breaking cracks that are either dry or contain water. The response of these defects is investigated as a function of crack depth and closure, as well as of amplitude and frequency of the modulation. The ensuing results suggest that fluid-filled and dry cracks can be discriminated from each other. The origin of the different response of these defects is discussed in terms of both crack's stiffness and modulation-induced dynamics.

Keyword
modulation, surface-breaking, crack, ultrasonic waves
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-7891 (URN)10.1016/j.ndteint.2007.09.005 (DOI)000253385400008 ()2-s2.0-37849042450 (Scopus ID)
Note
QC 20100906Available from: 2008-01-14 Created: 2008-01-14 Last updated: 2010-09-06Bibliographically approved

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