TY - JOUR A1 - Bause, F. A1 - Gravenkamp, Hauke A1 - Rautenberg, J. A1 - Henning, B. T1 - Transient modeling of ultrasonic guided waves in circular viscoelastic waveguides for inverse material characterization JF - Measurement science and technology N2 - In this contribution, we present an efficient approach for the transient and time-causal modeling of guided waves in viscoelastic cylindrical waveguides in the context of ultrasonic material characterization. We use the scaled boundary finite element method (SBFEM) for efficient computation of the phase velocity dispersion. Regarding the viscoelastic behavior of the materials under consideration, we propose a decomposition approach that considers the real-valued frequency dependence of the (visco-)elastic moduli and, separately, of their attenuation. The modal expansion approach is utilized to take the transmitting and receiving transducers into account and to propagate the excited waveguide modes through a waveguide of finite length. The effectiveness of the proposed simulation model is shown by comparison with a standard transient FEM simulation as well as simulation results based on the exact solution of the complex-valued viscoelastic guided wave problem. Two material models are discussed, namely the fractional Zener model and the anti-Zener model; we re-interpret the latter in terms of the Rayleigh damping model. Measurements are taken on a polypropylene sample and the proposed transient simulation model is used for inverse material characterization. The extracted material properties may then be used in computer-aided design of ultrasonic systems. KW - Viscoelasticity KW - Ultrasonics KW - Guided waves KW - Inverse problem KW - Scaled boundary finite KW - Element method PY - 2015 DO - https://doi.org/10.1088/0957-0233/26/9/095602 SN - 0957-0233 SN - 1361-6501 VL - 26 IS - 9 SP - 095602-1 EP - 095602-17 PB - IOP Publ. Ltd. CY - Bristol AN - OPUS4-33830 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Karabeliov, Krassimire A1 - Cuéllar, Pablo A1 - Baeßler, Matthias A1 - Rücker, Werner T1 - System identification of inverse, multimodal and nonlinear problems using evolutionary computing - Application to a pile structure supported on nonlinear springs JF - Engineering Structures N2 - This paper deals with the system identification of a mechanical structure supported by nonlinear springs subjected to an external load. If all mechanical parameters of the system were known, the displacement of the system subjected to this load could be easily calculated. However, the monitoring applications often deal with the inverse problem. The loads and displacements of the system are known and certain mechanical Parameters of the system are sought. The solution of such inverse problems can be difficult, especially when they have a nonlinear and multimodal character, which often makes them appear intractable at first sight. However, evolutionary computing can be applied to solve this inverse, nonlinear and multimodal problem. Sometimes a prior knowledge exists on certain system properties, which is difficult to implement into analytical or numerical solvers. This knowledge can play a decisive role in identifying the System properties and it can be easily included as a boundary condition when applying evolutionary algorithms. This article discusses how and under what conditions the unknown spring resistances can be identified. The practical application of this procedure is exemplified here with the mechanical system of a pile foundation. KW - Evolutionary computing KW - Inverse problem KW - Multimodal solution KW - System identification KW - Pile monitoring PY - 2015 DO - https://doi.org/10.1016/j.engstruct.2015.07.034 SN - 0141-0296 SN - 1873-7323 VL - 101 SP - 609 EP - 620 AN - OPUS4-39310 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Reimund, Verena A1 - Pelkner, Matthias A1 - Kreutzbruck, Marc A1 - Haueisen, J. T1 - Sensitivity analysis of the non-destructive evaluation of micro-cracks using GMR sensors JF - NDT & E international N2 - Micro-cracks in a magnetized ferromagnetic material cause stray fields that can be observed using giant magnetoresistive (GMR) sensors. This work investigates the applicability of GMR sensors to the non-destructive evaluation of micro-cracks via the observation of stray fields. For this purpose, our measurement setup is assessed using a fast new sensitivity analysis based on adjoint states, employing the finite-element method. A model for the GMR sensor is developed and verified. We are able to resolve micro-cracks with an opening of 3 µm and a depth of 30 µm. GMR positioning inaccuracies are analyzed. KW - Adjoint sensitivity analysis KW - Inverse problem KW - Magnetic stray field KW - Magneto-statics PY - 2014 DO - https://doi.org/10.1016/j.ndteint.2014.02.003 SN - 0963-8695 VL - 64 SP - 21 EP - 29 PB - Butterworth-Heinemann CY - Oxford AN - OPUS4-32236 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wu, Cheng-Chieh A1 - Weisbrich, S. A1 - Neitzel, F. ED - Nicoletto, G. ED - Pastrama, S. D. ED - Emri, I. T1 - Inverse finite element adjustment of material parameters from integrated analysis of displacement field measurement JF - Materials Today: Proceedings N2 - The determination of material parameters from displacement field measurement is being examined for linear elastic solid. A frequently used approach to compute material constants can be found in many studies. Even though they presented the approach in many different variations, but in the end they are essentially based on the same algorithm: Parameters are iteratively tuned until the computed results are in accordance with the measurements. The main drawback of this approach is that mainly commercial software is used that hinders us to investigate its inner evaluation process. This leads to the question, how the results from this commercial software can be trusted. On the contrary to these debatable approaches, we present a method that inverts the procedure of finite element method by using the most general model for a least-squares adjustment – the GAUSS-HELMERT Model. T2 - 32nd DANUBIA ADRIA SYMPOSIUM on Advances in Experimental Mechanics CY - Starý Smokovec, Slovakia DA - 22.09.2015 KW - Integrated analysis KW - Inverse problem KW - Finite element method KW - Least-squares adjustment KW - Model and measurement based analysis PY - 2016 UR - http://www.sciencedirect.com/science/article/pii/S2214785316002091 DO - https://doi.org/10.1016/j.matpr.2016.03.004 SN - 2214-7853 VL - 3 IS - 4 SP - 1211 EP - 1215 PB - Elsevier Ltd. AN - OPUS4-35629 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -