Analytical modeling, finite-difference simulation and experimental validation of air-coupled ultrasound beam refraction and damping through timber laminates, with application to non-destructive testing

Sanabria, Sergio J.; Furrer, Roman; Neuenschwander, Jürg; Niemz, Peter; Schütz, Philipp (2015). Analytical modeling, finite-difference simulation and experimental validation of air-coupled ultrasound beam refraction and damping through timber laminates, with application to non-destructive testing Ultrasonics, 63, pp. 65-85. Elsevier B.V. 10.1016/j.ultras.2015.06.013

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Reliable non-destructive testing (NDT) ultrasound systems for timber composite structures require quan- titative understanding of the propagation of ultrasound beams in wood. A finite-difference time-domain (FDTD) model is described, which incorporates local anisotropy variations of stiffness, damping and den- sity in timber elements. The propagation of pulsed air-coupled ultrasound (ACU) beams in normal and slanted incidence configurations is reproduced by direct definition of material properties (gas, solid) at each model pixel. First, the model was quantitatively validated against analytical derivations. Time-varying wavefronts in unbounded timber with curved growth rings were accurately reproduced, as well as the acoustic properties (velocity, attenuation, beam skewing) of ACU beams transmitted through timber lamellas. An experimental sound field imaging (SFI) setup was implemented at NDT fre- quencies (120 kHz), which for specific beam incidence positions allows spatially resolved ACU field char- acterization at the receiver side. The good agreement of experimental and modeled beam shifts across timber laminates allowed extrapolation of the inner propagation paths. The modeling base is an ortho- tropic stiffness dataset for the desired wood species. In cross-grain planes, beam skewing leads to position-dependent wave paths. They are well-described in terms of the growth ring curvature, which is obtained by visual observation of the laminate. Extraordinary refraction phenomena were observed, which lead to well-collimated quasi-shear wave coupling at grazing beam incidence angles. The aniso- tropic damping in cross-grain planes is satisfactorily explained in terms of the known anisotropic stiffness dataset and a constant loss tangent. The incorporation of high-resolution density maps (X-ray computed tomography) provided insight into ultrasound scattering effects in the layered growth ring structure. Finally, the combined potential of the FDTD model and the SFI setup for material property and defect inversion in anisotropic materials was demonstrated. A portable SFI demonstrator was implemented with a multi-sensor MEMs receiver array that captures and compensates for variable wave propagation paths in glued laminated timber, and improves the imaging of lamination defects.

Item Type:

Journal Article (Original Article)

Division/Institute:

Architecture, Wood and Civil Engineering
Architecture, Wood and Civil Engineering > Institute for Materials and Wood Technology
BFH Centres > BFH Centre for Wood - Resource and Material

Name:

Sanabria, Sergio J.;
Furrer, Roman;
Neuenschwander, Jürg;
Niemz, Peter and
Schütz, Philipp

Subjects:

Q Science > Q Science (General)
Q Science > QA Mathematics
Q Science > QA Mathematics > QA75 Electronic computers. Computer science
Q Science > QC Physics
T Technology > T Technology (General)
T Technology > TA Engineering (General). Civil engineering (General)
T Technology > TH Building construction
T Technology > TJ Mechanical engineering and machinery

ISSN:

0041-624X

Publisher:

Elsevier B.V.

Submitter:

Christelle Ganne-Chédeville

Date Deposited:

21 Apr 2020 11:18

Last Modified:

21 Apr 2020 11:18

Publisher DOI:

10.1016/j.ultras.2015.06.013

Uncontrolled Keywords:

Finite-difference time-domain simulation Air-coupled ultrasound Wood bonding assessment Anisotropic wave propagation Inverse problem

URI:

https://arbor.bfh.ch/id/eprint/11293

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