Estimation of viscoelastic material parameters of polymers using Lamb waves (vor Ort)

* Presenting author
Day / Time: 22.03.2022, 15:40-16:20
Room: 57-04
Typ: Poster
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Abstract: For a realistic simulation of ultrasonic waves in components, the material parameters of its constituents need to be known. Especially in polymers, viscoelastic behaviour must be considered to account for the material’s absorption. A possible method for material characterisation is based on Lamb waves using broadband thermoelastic excitation. Signal acquisition of ultrasonic waves at different distances from the excitation yields a matrix of signals depending on time and space. A 2D-Fourier transform yields a matrix in the temporal and spatial frequency domain similar to a dispersion diagram from which the propagating modes are extracted. Subdividing the propagation distance in N subdomains and applying a 2D-Fourier transform to each matrix results in N sub-matrices depending on frequency and real wavenumber. These are used to fit an exponential function in the spatial domain for each frequency and real wavenumber pair yielding the acoustic absorption, i.e. the imaginary part of the wavenumber. In an inverse procedure, the detected frequencies and complex wavenumbers are inserted into the analytic, complex Rayleigh-Lamb-equation, which is balanced by varying the complex, viscoelastic material parameters using a global optimisation algorithm. The resulting values for the material parameters serve as estimates for a quantitative description of the viscoelastic material behaviour.


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