Modeling the formation of internal boundaries in an unidirectional fiber strand compacted in plastic state

Abstract

The formation of internal boundaries in a unidirectional fiber strand during isostatic and uniaxial pressing in plastic state is studied. The process is modeled using the finite-element method (FEM). An ideal contact elastoplastic problem for a hexagonal fiber strand undergoing plane deformation is solved taking into account friction at the boundaries. For angles of 0°, 30°, 60°, and 90° between the normal to the contact area and the pressing direction, the contact area width, change in the contact area slope, and the radius vector of the cross-sectional boundary of the fiber inside the pore channel as functions of density are determined for the friction coefficient at the boundaries of fibers equal to 0 and 0.5.

Modeling the effective elastic properties of materials pressed from a unidirectional hexagonal fiber strand

“…The geometrical parameters of the cell depend on pressing type (uniaxial or isostatic) and relative density of a material [12,13]. Under isostatic pressing, the cross-section of the pore channel resembles a hypocycloid with equal beams.…”

“…Figure 2b shows that the curves corresponding to the elastic modulus ratio toward the pressing direction (E ax and E by ) and fiber axis (E z ) almost completely match. The ratios with E ay and E bx moduli do not match at minimal relative densities, which is obviously due to the error of determining the sizes of interfiber contact areas whose normal lines are sloped at wide angles to the pressing direction [12,13]. Recall that the cited paper used the same FE mesh to model pressing to the different final relative densities.…”

“…The papers [12,13] modeled a unidirectional hexagonal fiber strand under isostatic and uniaxial pressing in a plastic flow to determine the geometrical characteristics of unit cells for different relative densities. These cells ( Fig.…”

“…Tables 1 and 2 summarize the relative sizes of the cell (L x and L y ) and cross-sectional projections of pore channels (w x and w y ). [12,13] ϑ L x L y 2 w x(y) /L x(y) The objective of this paper is to assess the interrelation between the effective elastic properties and geometry of the structure represented by unit cells in modeling fibers under isostatic and uniaxial pressing [12,13]. Ideal contact [14] at the boundaries is considered.…”

“…Relative Sizes of the Unit Cell and Pore Channels Determined in Modeling a Unidirectional Hexagonal Fiber Strand under Uniaxial Pressing in a Plastic Flow[12,13] …”