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Vibro-acoustic modelling of anisotropic poroelastic materials: characterisation of the anisotropic properties
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present-day challenges in the transport industry, steered by the increasing environmental awareness, necessitate manufacturers to take measures to reduce emissions related to the movements of goods and humans. In particular, the measures aiming at a reduced mass or higher load capacity to increase fuel efficiency,  generally deteriorate the noise and vibration insulation properties of their products. In order to comply with the regulations and customer demands, modern vehicles increasingly move towards a multifunctional integrated design approach, if possible for all subcomponents involved. Such a multifunctional design approach is an iterative process, evaluating the proposed solutions in every stage, and is therefore best performed in a virtual testing environment. \\Poroelastic materials are interesting to include in a multifunctional design, offering reasonably good vibro-acoustic insulation properties at a low weight penalty. These materials can also be combined in multilayer arrangements to further enhance the overall performance. \\In order to achieve an accurate modelling of the vibro-acoustic behaviour of poroelastic materials, the input data describing the material properties should be of a high quality. Two characteristics inherent to these materials encumber a precise characterisation with traditional techniques. Poro-elastic aggregates are anelastic due to the constituent material used, and anisotropic as a consequence of the production process. Characterisation techniques allowing for an accurate determination of the material properties need to take these intrinsic characteristics into account.\\The objective in this thesis is to enable the characterisation of a constitutive material model for poroelastic materials which is as general as possible, and includes the inherent material anelasticity and anisotropy. For this purpose, a set of advanced characterisation techniques has been developed to characterise the anisotropic flow resistivity tensor and the anisotropic dynamic Hooke's tensor. \\These advanced characterisation techniques are based on an inverse estimation procedure, used consistently throughout the work, and includes both experiments and numerical predictions. The property to characterise is isolated in a specially designed set-up such that it can be modelled by physics solely involving this property. The obtained experimental and numerical data then serve as the input to an optimisation, which returns the material properties for which the difference between both is as small as possible. These methods have been successfully applied to melamine foam, which is found to be both anisotropic and anelastic, confirming the need for such advanced characterisation techniques.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , xiv, 58 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2013:67
National Category
Fluid Mechanics and Acoustics Textile, Rubber and Polymeric Materials
Identifiers
URN: urn:nbn:se:kth:diva-137809ISBN: 978-91-7501-983-3 (print)OAI: oai:DiVA.org:kth-137809DiVA: diva2:679713
Public defence
2014-01-20, sal F3, KTH, Lindstedtsvägen 26, Stockholm, 13:15 (English)
Opponent
Supervisors
Funder
EU, European Research Council, MRTN-CT-2006-035559
Note

QC 20131219

Available from: 2013-12-19 Created: 2013-12-16 Last updated: 2013-12-19Bibliographically approved
List of papers
1. Identification of the full anisotropic flow resistivity tensor for multiple glass wool and melamine foam samples
Open this publication in new window or tab >>Identification of the full anisotropic flow resistivity tensor for multiple glass wool and melamine foam samples
2013 (English)In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 134, no 6, 4659-4669 p.Article in journal (Refereed) Published
Abstract [en]

The flow resistivity tensor, which is the inverse of the viscous permeability tensor, is one of the most important material properties for the acoustic performance of porous materials used in acoustic treatments. Due to the manufacturing processes involved, these porous materials are most often geometrically anisotropic on a microscopic scale, and for demanding applications, there is a need for improved characterization methods. This paper discusses recent refinements of a method for the identification of the anisotropic flow resistivity tensor. The inverse estimation is verified for three fictitious materials with different degrees of anisotropy. Measurements are performed on nine glass wool samples and seven melamine foam samples, and the anisotropic flow resistivity tensors obtained are validated by comparison to measurements performed on uni-directional cylindrical samples, extracted from the same, previously measured cubic samples. The variability of flow resistivity in the batch of material from which the glass wool is extracted is discussed. The results for the melamine foam suggest that there is a relation between the direction of highest flow resistivity, and the rise direction of the material.

Keyword
Inverse Estimation, Fibrous Materials, Absorption, Frame
National Category
Aerospace Engineering Applied Mechanics Vehicle Engineering Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-133593 (URN)10.1121/1.4824841 (DOI)000328654900009 ()2-s2.0-84890155492 (Scopus ID)
Funder
EU, European Research Council, MRTN-CT-2006-35559
Note

QC 20140121

Available from: 2013-11-06 Created: 2013-11-06 Last updated: 2017-12-06Bibliographically approved
2. On the influence of frequency-dependent elastic properties in vibro-acoustic modelling of porous materials under structural excitation
Open this publication in new window or tab >>On the influence of frequency-dependent elastic properties in vibro-acoustic modelling of porous materials under structural excitation
2014 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 333, no 24, 6560-6571 p.Article in journal (Refereed) Published
Abstract [en]

The aspects related to the frequency dependence of the elastic properties of porous materials have been largely neglected in the past for several reasons. For acoustic excitation of porous materials, the material behaviour can be quite well represented by models where the properties of the solid frame have little influence. Only recently has the importance of the dynamic moduli of the frame come into focus. This is related to a growing interest in the material behaviour due to structural excitation. Two aspects stand out in connection with the elastic-dynamic behaviour. The first is related to methods for the characterisation of the dynamic moduli of porous materials. The second is a perceived lack of numerical methods able to model the complex material behaviour under structural excitation, in particular at higher frequencies. In the current paper, experimental data from a panel under structural excitation, coated with a porous material, is used in correlation with numerical predictions, involving a frequency-dependent material model for the stiffness properties of the porous material. The results suggest that the frequency dependence is of importance for a correct prediction of the response of trim installations. The change in material behaviour due to the frequency-dependent properties is illustrated in terms of the propagation of the slow wave and the shear wave in the porous material.

Place, publisher, year, edition, pages
Elsevier, 2014
National Category
Textile, Rubber and Polymeric Materials Aerospace Engineering Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-137743 (URN)10.1016/j.jsv.2014.07.032 (DOI)000342547500017 ()2-s2.0-84907486439 (Scopus ID)
Note

Updated from submitted to published.

QC 20141105

Available from: 2013-12-16 Created: 2013-12-16 Last updated: 2017-12-06Bibliographically approved
3. A general methodology for inverse estimation of the elastic and anelastic properties of anisotropic open-cell porous materials-with application to a melamine foam
Open this publication in new window or tab >>A general methodology for inverse estimation of the elastic and anelastic properties of anisotropic open-cell porous materials-with application to a melamine foam
2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 8, 084904- p.Article in journal (Refereed) Published
Abstract [en]

This paper proposes an inverse estimation method for the characterisation of the elastic and anelastic properties of the frame of anisotropic open-cell foams used for sound absorption. A model of viscoelasticity based on a fractional differential constitutive equation is used, leading to an augmented Hooke's law in the frequency domain, where the elastic and anelastic phenomena appear as distinctive terms in the stiffness matrix. The parameters of the model are nine orthotropic elastic moduli, three angles of orientation of the material principal directions and three parameters governing the anelastic frequency dependence. The inverse estimation consists in numerically fitting the model on a set of transfer functions extracted from a sample of material. The setup uses a seismic-mass measurement repeated in the three directions of space and is placed in a vacuum chamber in order to remove the air from the pores of the sample. The method allows to reconstruct the full frequency-dependent complex stiffness matrix of the frame of an anisotropic open-cell foam and in particular it provides the frequency of maximum energy dissipation by viscoelastic effects. The characterisation of a melamine foam sample is performed and the relation between the fractional-derivative model and other types of parameterisations of the augmented Hooke's law is discussed.

Keyword
Anisotropy, Energy dissipation, Estimation, Porous materials, Stiffness matrix
National Category
Textile, Rubber and Polymeric Materials Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-137747 (URN)10.1063/1.4865789 (DOI)000332619600090 ()2-s2.0-84896794683 (Scopus ID)
Funder
EU, European Research Council, MRTN-CT-2006-035559
Note

QC 20140508. Updated from submitted to published

Available from: 2013-12-16 Created: 2013-12-16 Last updated: 2017-12-06Bibliographically approved
4. A method for characterisation of the static elastic properties of the porous frame of orthotropic open-cell foams
Open this publication in new window or tab >>A method for characterisation of the static elastic properties of the porous frame of orthotropic open-cell foams
2015 (English)In: International Journal of Engineering Science, ISSN 0020-7225, E-ISSN 1879-2197, Vol. 86, 44-59 p.Article in journal (Refereed) Published
Abstract [en]

This paper proposes a method to identify the static, fully relaxed elastic Hooke's matrix of a porous open-cell material. The moduli are estimated through an inverse estimation method, by performing a fit of a numerical model on the measured displacements on the faces of the porous material. These displacements are obtained from a static compression along each of the three coordinate axes. The material is modelled as an orthotropic equivalent solid, of which the principal directions are not necessarily aligned with the orthonormal coordinate system in which the experiments are conducted. The angles of relative orientation accounting for the misalignment are among the properties to be estimated. The focus in this paper is on the methodology itself, and its validity is verified by applying the method to four artificial materials with different levels of anisotropy. In addition, the robustness of the method to perturbations on the input data is investigated.

Keyword
Anisotropy, Hooke's tensor, Inverse estimation, Open-cell foams, Porous materials
National Category
Textile, Rubber and Polymeric Materials Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-137749 (URN)10.1016/j.ijengsci.2014.10.005 (DOI)000346459200005 ()2-s2.0-84909994477 (Scopus ID)
Funder
EU, European Research Council, MRTN-CT-2006-035559
Note

QC 20150220. Updated from submitted to published.

Available from: 2013-12-16 Created: 2013-12-16 Last updated: 2017-12-06Bibliographically approved
5. A method for inverse estimation of the static elastic properties of anisotropic poroelastic foams - with application to a melamine foam
Open this publication in new window or tab >>A method for inverse estimation of the static elastic properties of anisotropic poroelastic foams - with application to a melamine foam
2013 (English)Report (Refereed)
Abstract [en]

The paper presents a method for the characterisation of the static, fully relaxed elastic properties of poroelastic materials. The approach is based on full field measurements of the 3D displacements in a number of points on the faces of the compressed material sample. These are used as targets in an inverse estimation to fit a model of the material to experimental data. In the current work, the material is modelled as an orthotropic equivalent solid, of which the principal directions are not necessarily aligned with the orthonormal coordinate system in which the experiments are conducted. The angles of relative orientation accounting for the misalignment are among the properties to be estimated. In addition, the proposed model considers the region of reduced stiffness close to material discontinuities, which has been identified in previous investigations. The method presented is verified for an artificial material, and its robustness is studied. A characterised melamine foam is found to have an orthotropic symmetry, and its lowest stiffness in the direction parallel to the rise direction of the material.

National Category
Textile, Rubber and Polymeric Materials Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-137750 (URN)
Funder
EU, European Research Council, MRTN-CT-2006-035559
Note

QC 2013

Available from: 2013-12-16 Created: 2013-12-16 Last updated: 2013-12-19Bibliographically approved

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