Effective stiffness and strength properties of cellular materials in the transverse plane

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School of Engineering | Doctoral thesis (article-based) | Defence date: 2013-12-13
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70 + app. 45
Aalto University publication series DOCTORAL DISSERTATIONS, 181/2013
In recent years, with growing interest in the energy efficient material processing, and the robust and light-weight product fabrication, cellular materials have found their way into various engineering applications. For the efficient use of these materials, a profound understanding of the relationship between their mechanical and geometrical properties in the transverse plane is necessary. Hence, in order to contribute to the fields of the cellular material modeling and testing, the present study comprising physical and simulation experiments was conducted. The physical experiments were conducted to determine the effective stiffness properties of the cellular materials in the transverse plane. In these experiments, two different cellular materials, Nomex honeycombs and Norway spruce (Picea abies), were investigated. The experimental data were obtained through the proposed experimental method which involves testing of specimens of different material orientations relative to the loading direction. A benefit of the method is its ability to combine the anisotropic linear elasticity with the physical experiments. Hence, in addition to the effective in-plane elastic moduli and Poisson's ratios, the shear modulus and coefficients of mutual influence characterizing the coupling between the shearing and normal stresses were also determined. The simulation experiments of the present study were carried out to quantify the effects of the cell geometry, the variations related to the cell wall height and cell wall thickness and the scale on the effective stiffness and strength properties in the transverse plane. For this aim, a statistical simulation model which uses the cell wall mechanical and geometrical properties was introduced. The model was validated through a comparative study based on the results of the physical and simulation experiments on Nomex honeycombs. The results of the physical and simulation experiments on the effective stiffness properties in the transverse plane imply that the stiffness properties are influenced by the geometrical properties and variations of the cellular structure. Besides, the simulation experiments on the in-plane strength properties reveal that both the scale and cell wall height variations have impact on the cellular material strength.
Supervising professor
Tuhkuri, Jukka, Prof., Aalto University, Department of Applied Mechanics, Finland
Thesis advisor
Freund, Jouni, Docent, Aalto University, Department of Applied Mechanics, Finland
cellular material, transverse plane, Nomex honeycomb, Norway spruce, cell wall height, cell wall thickness, scale, effective stiffness, strength
Other note
  • [Publication 1]: A. Karakoç, J. Freund. Experimental studies on mechanical properties of cellular structures using Nomex honeycomb cores. Composite Structures 2012; 94: 2017-2024.
    DOI: 10.1016/j.compstruct.2012.01.024. View at publisher
  • [Publication 2]: A. Karakoç, P. Tukiainen, J. Freund, M. Hughes. Experiments on the effective compliance in the radial-tangential plane of Norway spruce. Composite Structures 2013; 102: 287-293.
    DOI: 10.1016/j.compstruct.2013.03.013. View at publisher
  • [Publication 3]: A. Karakoç, K. Santaoja, J. Freund. Simulation experiments on the effective in-plane compliance of the honeycomb materials. Composite Structures 2013; 96: 312–320.
    DOI: 10.1016/j.compstruct.2012.09.021. View at publisher
  • [Publication 4]: A. Karakoç, J. Freund. A statistical failure initiation model for honeycomb materials. Composite Structures 2013; 95: 154-162.
    DOI: 10.1016/j.compstruct.2012.07.001. View at publisher