THREE-DIMENSIONAL MICROMECHANICAL FRAMEWORK FOR THE NONLINEAR VISCOELASTIC ANALYSIS OF PULTRUDED COMPOSITES

Abstract eng:
This study introduces a new three-dimensional (3D) micromechanical modeling approach for the nonlinear viscoelastic response of pultruded composites. The pultruded fiber reinforced plastic (FRP) composites under consideration include combinations of roving and continuous filament mat (CFM) reinforcements. The proposed framework can be easily integrated with a finite element (FE) software for the analysis of pultruded structures. The proposed 3D framework consists of three nested and independent models for the roving layers, CFM layers, and a sublaminate model used to generate the overall 3D effective continuum response. The roving layer consists of unidirectional fibers embedded in the matrix; it is idealized as doubly periodic array of fiber with rectangular cross sections. The CFM layer consists of long, swirl, and in-plane randomly oriented filaments. This system is idealized using the average response of two alternating layers with limiting fiber orientations. A 3D nonlinear multi-axial viscoelastic constitutive behavior is formulated using Schapery's integral form. This model is implemented only for the isotropic matrix at the lower level of the nested modeling framework. The fiber medium is considered as transversely isotropic and linear elastic. Stress-update algorithms are needed at all levels of the framework in order to satisfy the nonlinear constitutive and micromechanical relations between the average stresses and strains in the subcells. New iterative numerical algorithms with predictor- corrector type steps are derived to achieve the correct stress and strain states. Experimental tests are performed to calibrate and predict the nonlinear viscoelastic response. These tests include creep and recovery at different loading levels.

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