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Special Issue "Syntactic Foams: Microstructural Characterisation and Effective Properties"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: 31 October 2017

Special Issue Editor

Guest Editor
Prof. Dr. Lorenzo Bardella

Department of Civil, Environmental, Architectural Engineering and Mathematics, University of Brescia, Via Branze 43, 25123 Brescia, Italy
Website | E-Mail

Special Issue Information

Dear Colleagues,

Syntactic foams are particulate composites whose filler consists of hollow spherical particles. Such composites are experiencing considerable growth as a result of technological advances. In fact, depending on the employed materials for matrix and filler, syntactic foams find several engineering applications for their high effective specific properties (i.e., macroscopic properties per unit mass) combined with the benefits ensuing from their closed-cell microstructure.

On the one hand, designing the microstructure is a key issue to optimise syntactic foams’ performance. On the other hand, characterising the microstructure is crucial in order to develop accurate predictive models which can also be useful to improve the syntactic foam design.

Of particular interest for this Special Issue is the connection between microstructure and effective properties of syntactic foams, including, but not limited to, nonlinear phenomena, such as mechanical failure.

To this purpose, in addition to the properties and volume fractions of matrix and filler materials, the microstructure characterisation may, for instance, require the determination of the filler polydispersion, in terms of both size and particle wall thickness, the behaviour of the interface between matrix and filler, and the presence of unreinforced voids and matrix regions of varied properties due to manufacturing.

A challenging task is the understanding of how detailed the microstructure characterisation should be in order to accurately model each peculiar effective behaviour relevant in the applications.

This Special Issue also aims at covering research on novel applications, with emphasis on microstructural features. Experimental, theoretical, and computational approaches are welcome, with a special appreciation for multi-disciplinarity.

Prof. Dr. Lorenzo Bardella
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Syntactic foam
  • Effective properties
  • Microstructure
  • Experimental testing
  • Homogenisation methods
  • Computational materials science
  • Filler polydispersion
  • Filler properties
  • Interface
  • Matrix properties
  • Interphase
  • Unreinforced porosity
  • Effective strength
  • Failure modalities

Published Papers (4 papers)

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Research

Open AccessArticle A Continuum Damage Mechanics Model for the Static and Cyclic Fatigue of Cellular Composites
Materials 2017, 10(8), 951; doi:10.3390/ma10080951
Received: 24 May 2017 / Revised: 7 August 2017 / Accepted: 8 August 2017 / Published: 15 August 2017
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Abstract
The fatigue behavior of a cellular composite with an epoxy matrix and glass foam granules is analyzed and modeled by means of continuum damage mechanics. The investigated cellular composite is a particular type of composite foam, and is very similar to syntactic foams.
[...] Read more.
The fatigue behavior of a cellular composite with an epoxy matrix and glass foam granules is analyzed and modeled by means of continuum damage mechanics. The investigated cellular composite is a particular type of composite foam, and is very similar to syntactic foams. In contrast to conventional syntactic foams constituted by hollow spherical particles (balloons), cellular glass, mineral, or metal place holders are combined with the matrix material (metal or polymer) in the case of cellular composites. A microstructural investigation of the damage behavior is performed using scanning electron microscopy. For the modeling of the fatigue behavior, the damage is separated into pure static and pure cyclic damage and described in terms of the stiffness loss of the material using damage models for cyclic and creep damage. Both models incorporate nonlinear accumulation and interaction of damage. A cycle jumping procedure is developed, which allows for a fast and accurate calculation of the damage evolution for constant load frequencies. The damage model is applied to examine the mean stress effect for cyclic fatigue and to investigate the frequency effect and the influence of the signal form in the case of static and cyclic damage interaction. The calculated lifetimes are in very good agreement with experimental results. Full article
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Open AccessArticle Influence of Partially Debonded Interface on Elasticity of Syntactic Foam: A Numerical Study
Materials 2017, 10(8), 911; doi:10.3390/ma10080911
Received: 26 June 2017 / Revised: 2 August 2017 / Accepted: 3 August 2017 / Published: 8 August 2017
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Abstract
The effect of interfacial bonding of glass hollow microspheres and a polymer matrix on the elastic properties of syntactic foam was investigated using representative volume element (RVE) models, including partially debonded interfaces. Finite element analysis, with models having different debonding geometries, was performed
[...] Read more.
The effect of interfacial bonding of glass hollow microspheres and a polymer matrix on the elastic properties of syntactic foam was investigated using representative volume element (RVE) models, including partially debonded interfaces. Finite element analysis, with models having different debonding geometries, was performed to numerically estimate the elastic behavior of the models. The models consisted of bonded and debonded regions of interfaces; the bonded region was treated as the perfectly bonded interface, while the Coulomb friction model was used to describe the debonded region with a small friction coefficient. The changes in the tensile and compressive moduli of the foams were investigated in terms of the degree of interfacial debonding and debonding geometry. Full article
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Open AccessFeature PaperArticle Effect of Fly-Ash Cenospheres on Properties of Clay-Ceramic Syntactic Foams
Materials 2017, 10(7), 828; doi:10.3390/ma10070828
Received: 19 June 2017 / Revised: 19 June 2017 / Accepted: 11 July 2017 / Published: 19 July 2017
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Abstract
A low-density clay ceramic syntactic foam (CSF) composite material was successfully synthesized from illitic clay added by fly ash cenospheres (CS) using the semi-dry formation method. The content of CS varied in the range of 10, 30, 50 and 60 vol %. Furthermore,
[...] Read more.
A low-density clay ceramic syntactic foam (CSF) composite material was successfully synthesized from illitic clay added by fly ash cenospheres (CS) using the semi-dry formation method. The content of CS varied in the range of 10, 30, 50 and 60 vol %. Furthermore, reference samples without cenospheres were produced for property comparison. The materials comprising different amount of the additives were fired at temperatures of 600, 950, 1000, 1050, 1100, 1150 and 1200 °C. Firing times were kept constant at 30 min. Processing characteristics of the materials were evaluated in terms of density achieved and shrinkage observed as functions of both the CS content and the sintering temperature. The compressive strength and water uptake were determined as application-oriented properties. Except for the reference and the low CS level samples, the materials show an increase in strength with the increase in firing temperature, and a decrease of mechanical reliability with a decrease in density, which is typical for porous materials. Exceptions are the samples with no or low (10 vol %) content of cenospheres. In this case, the maximum strength is obtained at an intermediate sintering temperature of 1100 °C. At a low density (1.10 and 1.25 g/cm3), the highest levels of strength are obtained after sintering at 1200 °C. For nominal porosity levels of 50 and 60 vol %, 41 and 26 MPa peak stresses, respectively, are recorded under compressive load. Full article
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Open AccessFeature PaperArticle Water Impact of Syntactic Foams
Materials 2017, 10(3), 224; doi:10.3390/ma10030224
Received: 22 January 2017 / Revised: 7 February 2017 / Accepted: 13 February 2017 / Published: 23 February 2017
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Abstract
Syntactic foams are particulate composite materials that are extensively integrated in naval and aerospace structures as core materials for sandwich panels. While several studies have demonstrated the potential of syntactic foams as energy absorbing materials in impact tests, our understanding of their response
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Syntactic foams are particulate composite materials that are extensively integrated in naval and aerospace structures as core materials for sandwich panels. While several studies have demonstrated the potential of syntactic foams as energy absorbing materials in impact tests, our understanding of their response to water impact remains elusive. In this work, we attempt a first characterization of the behavior of a vinyl ester/glass syntactic subject to slamming. High-speed imaging is leveraged to elucidate the physics of water impact of syntactic foam wedges in a free-fall drop tower. From the images, we simultaneously measure the deformation of the wedge and the hydrodynamic loading, thereby clarifying the central role of fluid–structure interaction during water impact. We study two different impact heights and microballoon density to assess the role of impact energy and syntactic foam composition on the slamming response. Our results demonstrate that both these factors have a critical role on the slamming response of syntactic foams. Reducing the density of microballoons might help to reduce the severity of the hydrodynamic loading experienced by the wedge, but this comes at the expense of a larger deformation. Such a larger deformation could ultimately lead to failure for large drop heights. These experimental results offer compelling evidence for the role of hydroelastic coupling in the slamming response of syntactic foams. Full article
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