Multiscale nonlinear framework for the long-term behavior of layered composite structures

This paper presents an integrated micromechanical-structural framework for local-global nonlinear and time-dependent analysis of fiber reinforced polymer composite materials and structures. The proposed modeling approach involves nested multiscale micromodels for unidirectional and continuous filament mat (CFM) layers. In addition, a sublaminate model is used to provide a three-dimensional (3D) effective anisotropic and continuum response to represent the nonlinear viscoelastic behavior of a through-thickness periodical multilayered material system. The 3D multiscale material framework is integrated with a displacement-based finite-element code to perform structural analyses. The time-dependent responses in the unidirectional and CFM layers are exclusively attributed to their matrix constituents. The Schapery nonlinear viscoelastic model is used with a newly developed recursive-iterative integration method applied for the polymeric matrix. The fiber medium is linear and transversely isotropic. The in situ long-term response of the matrix constituents is calibrated and verified using long-term creep coupon tests. Good prediction ability is shown by the proposed framework for the overall viscoelastic behavior of the layered material. Material and geometric nonlinearities of I-shape thick composite columns, having vinylester resin reinforced with E-glass unidirectional (roving) and CFM layers, are studied to illustrate the capability of the multiscale material-structural framework. Nonlinear elastic behavior and creep collapse analyses of the I-shape column are performed. The recursive-iterative and stress correction algorithms, which are implemented and executed simultaneously at each material scale, enhance equilibrium and avoid misleading convergent states.