A micromechanical constitutive framework for the nonlinear viscoelastic behavior of pultruded composite materials

This study introduces a new three-dimensional (3D) micromechanical modeling approach for the nonlinear viscoelastic behavior of pultruded composites. The studied pultruded composite system consists of vinylester matrix reinforced with E-glass roving and continuous filament mat (CFM) layers. Micromechanical models are introduced for the roving and CFM layers each having a unit-cell with four fiber and matrix subcells. In addition, a sublaminate model is used to provide for a nonlinear equivalent continuum of a layered medium with alternating roving and CFM layers. The roving layer consists of unidirectional fibers embedded in the matrix; it is idealized as doubly periodic array of fiber with square cross-sections. The CFM layer consists of relatively long, swirl, and randomly oriented filaments. This system is idealized using a weighted-average response of two simplified micromodels with fiber and matrix dominated responses. A new iterative procedure is introduced along with a recursive, integration method for the Schapery nonlinear viscoelastic model used for the isotropic matrix subcells of the two micromodels. The fiber medium is considered as transversely isotropic and linear elastic. Incremental micromechanical formulations of the above three micromodels are geared towards the time integration scheme in the matrix phase. New iterative numerical algorithms with predictor-corrector type steps are derived and implemented for the micromodels in order to satisfy the fiber and matrix viscoelastic constitutive relations along with the micromechanical equations in the form of traction continuity and strain compatibility between the subcells. Experimental creep tests are performed with coupons cut from E-glass/vinylester pultruded plate to calibrate and predict the nonlinear viscoelastic response. Three sets of pultruded specimens having off-axis angles: 0degrees, 45degrees, and 90degrees were tested at room temperature under different applied compression stress levels. (C) 2002 Elsevier Science Ltd. All rights reserved.