The Effect of Packing Type on the Equivalent Modulus and Stress Concentrations of Unidirectional Composites

A representative volume element (RVE) with 11 uniform fiber packings is studied. The effective modulus of RVE corresponding to the different packing types is evaluated using the finite-element modelling and a semianalytical multistep rule of mixtures. The equivalent modulus of the RVE depends on the packing type. The elongated triangular packing type was closest to the random packing type. All the packing types displayed a strong transverse isotropy with less than a 1% variation in equivalent modulus in the two transverse directions. The multistep rule of mixtures could allow for changes in the moduli due to the different packing types. However, this method consistently underpredicted the equivalent modulus compared with full FE results. The effective modulus for the random packing closest to that of the elongated triangular packing type. The stress distribution in the interface varied strongly with packing type and loading direction. The sparsest packing type, i.e., the truncated hexagonal one led to both the highest equivalent modulus and the highest stress concentrations in the interface. The densest packing type, i.e., the triangular packing, led to the lowest modulus and lowest radial stress concentrations.