High-speed stereo imaging for the characterization of anisotropic viscoelastic media

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Time: Thu 2020-05-07 14.15

Location: Live-streaming: https://kth-se.zoom.us/j/66552079402, Stockholm (English)

Subject area: Engineering Mechanics

Doctoral student: Luca Manzari , Strömningsmekanik och Teknisk Akustik

Opponent: Associate Professor Mathieu Aucejo, Laboratoire de Mécanique des Structures et des Systèmes Couplés

Supervisor: Peter Göransson, Farkostteknik, VinnExcellence Center for ECO2 Vehicle design; Jacques Cuenca, ; Ines Lopez Arteaga, VinnExcellence Center for ECO2 Vehicle design

Abstract

This thesis proposes an experimental method for observing and characterizing the viscoelastic properties of anisotropic media using high-speed white light stereo imaging. The method uses short-time video recordings of a specimen undergoing forced harmonic motion.The three-dimensional displacement field of the specimen is then resolved using digital image correlation.Measuring for a short time has multiple advantages: it minimizes the conditioning of the specimen, and gives meaningful results when true stationary conditions are inaccessible (e.g. because of relaxation processes, or changes in the environmental conditions that cannot be accounted for).Moreover, it enables a reduction of the data storage needs and the computational costs associated with the image acquisition and processing.To overcome the intrinsic limitations of a Fourier-based approach for short time records, an optimization algorithm is used to determine the point-wise amplitude, phase and frequency of the full-field harmonic motion.This approach maximizes signal-to-noise ratio, is suitable for the identification of non-linear behaviors and tolerates data records that are non-uniformly spaced in time (e.g. because of momentary data losses and failure of the image matching algorithms).The measurement accuracy is increased by proposing a method to extract the frame of reference of the specimen on a per-frame bases, and express the measured displacement field therein.A cube of melamine foam and a pantographic sheet have been observed using the proposed method, and the measured data compared with the outcome of linear viscoelastic numerical models.The added information obtained about the melamine is believed to improve the accuracy of the characterization of its viscoelastic behavior, and the observation of the pantographic sheet represents and absolute first in the experimental studies of its dynamics.

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