The Anisotropic Yield Surface of Cellular Materials

The fabrication process of cellular materials, such as foaming, usually leads to cells elongated in one direction, but equiaxed in a plane normal to that direction. This study is aimed at understanding the elasto-plastic behaviour of transversely isotropic cellular materials with inner gas pressure. An idealised ellipsoidal-cell face-centred-cubic foam that is filled with gas was generated and modelled to obtain the uniaxial stress–strain relationship, Poisson’s ratio and multiaxial yield surface. The effects of the elongation ratio and gas pressure on the elasto-plastic properties for a relative density of 0.5 were investigated. It was found that an increase in the elongation ratio caused increases in both the elastic modulus and yield stress for uniaxial loading along the cell elongation direction, and led to a tilted multiaxial yield surface in the mean stress and Mises equivalent stress plane. Compared to isotropic spheroidal-cell foams, the size of the yield surface of the ellipsoidal-cell foam is smaller for high-stress triaxiality, but larger for low-stress triaxiality, and the yield surface rotates counter-clockwise with the Lode angle increasing. The gas pressure caused asymmetry of the uniaxial stress–strain curve (e.g., reduced tensile yield stress), and it increased the nominal plastic Poisson’s ratio for compression, but had the opposite effect for tension. Furthermore, the gas pressure shifted the yield surface towards the negative mean stress axis with a distance equal to the gas pressure. The combined effects of the elongation ratio and gas pressure are complicated, particularly for the elasto-plastic properties in the plane in which the cells are equiaxed.

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The effect of doubly tapered strut morphology on the plastic yield surface of cellular materials

International Journal of Mechanical Sciences ◽

10.1016/s0020-7403(02)00066-8 ◽

2002 ◽

Vol 44 (8) ◽

pp. 1559-1581 ◽

Cited By ~ 18

Author(s):

H.S Kim ◽

S.T.S Al-Hassani

Keyword(s):

Yield Surface ◽

Cellular Materials ◽

Plastic Yield

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Flat embeddment of monolayer cells, tissue sections, and other cellular materials attached onto glass substrate

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100161394 ◽

1990 ◽

Vol 48 (3) ◽

pp. 766-767

Author(s):

Jeffrey P. Chang ◽

Jaang J. Wang

Keyword(s):

Present Report ◽

Cellular Materials ◽

Cover Glass ◽

Tissue Sections ◽

Embedding Technique ◽

Exfoliated Cells ◽

Black Paper ◽

Cell Concentrations ◽

Flat Embedding

Flat embeddment of certain specimens for electron microscopy is necessary for three classes of biological materials: namely monolayer cells, tissue sections of paraffin or plastics, as well as cell concentrations, exfoliated cells, and cell smears. The present report concerns a flat-embedding technique which can be applied to all these three classes of materials and which is a modified and improved version of Chang's original methodology.Preparation of coverglasses and microslides. Chemically cleaned coverglasses, 11 × 22 mm or other sizes, are laid in rows on black paper. Ink-mark one coner for identifying the spray-side of the glass for growing cells. Lightly spray with Teflon monomer (Heddy/Contact Inductries, Paterson, NO 07524, U.S.A.) from a pressurized can. Bake the sprayed glasses at 500°F for 45 min on Cover-Glass Ceramic Racks (A. Thomas Co. Philadelphia), for Teflon to polymerize.Monolayer Cells. After sterilization, the Teflon-treated coverglasses, with cells attached, are treated or fixed in situ in Columbia staining dishes (A. Thomas Co., Philadelphia) for subsequent processing.

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