Micromechanical and finite element investigation of the influence of microvoid distribution on the transversely isotropic viscoelastic behavior of fiber-reinforced composites

Microvoids are unavoidable in the manufacturing of unidirectional fiber-reinforced polymer composites (UDFRPs). Qualified products retain a void volume fraction below 5%, yet conventional homogenization schemes adopt this fraction as the sole descriptor and therefore project the morphological information onto a single scalar, leaving the differential influence of fiber-adjacent and inter-matrix microvoids unresolved. The present work develops a distribution-resolved multiscale framework through three coordinated advances. A Spatially Controlled Reduction Method introduces a void distribution parameter that partitions voids between the matrix interior and the fiber interfaces. Pair correlation, Ripley's K, and Besag's L functions confirm that this parameter spans the full range of the spatial descriptor, of which the Random Reduction Method samples only the central region. A Constrained Seed Growth algorithm couples the distribution parameter with a cluster-number control and reproduces representative morphologies observed in actual processing. Volume-weakening factors derived from the asymmetric disruption of interfacial stress transfer are embedded in the Bridging, Mori–Tanaka, composite cylinders assemblage, and generalized self-consistent schemes. The four schemes reproduce the numerical response with median relative error within 6% for void volume fractions up to 6% across fiber volume fractions from 20% to 60%. The generalized self-consistent scheme gives the smallest error, with a median within 2.3%. Two complementary user-material subroutines (UMATs) verified under harmonic loading provide a morphology-resolved entry point for engineering-scale viscoelastic analyses. The algorithms are released in the open-source Abaqus plugin "RVE Builder (UDFRPs)", available at https://github.com/YuhaoMeng/RVE_Builder.