The paper studies the interrelation between the effective elastic properties and the size of contact areas in the unit cell in modeling a unidirectional hexagonal fiber strand under isostatic and uniaxial pressing in a plastic flow. For a range of relative densities (0.907-1), it is shown that effective Young's modulus and Poisson's ratio correlate well with the integral projection of the contact areas relative to the corresponding cell size. For pore channels with cross-sectional shapes close to a three-beam hypocycloid with unequal beams, the elastic properties in the plane perpendicular to the fiber axis are anisotropic because the cross-sectional projections of the pore channel have different sizes.

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.

UDC 539.4 Mode I and mode II stress intensity factors (SIFs) are determined for a material with parallel pore channels of Y-shaped cross-section with centers at nodes of a regular hexagonal grid and arms aligned with the sides of hexagons. Calculations are performed for a unit cell that includes halves of two adjacent pore channels with an arbitrary length ratio of the arms. The finite-element method is used. It is shown that the SIFs for an equal-arm Y-shaped pore channel depend on the fiber crosssectional radius of curvature. The range of lengths of periodic equal-arm starlike cracks in which they can be regarded as noninteracting is identified.