This study presents a new three-dimensional (3D) micromechanics-based nonlinear framework for the analysis of pultruded composite structures. The proposed material modeling framework is a nested micromechanical approach that explicitly recognizes the different composite systems within the cross-section of a pultruded composite member. The 3D lamination theory is used to generate a homogenized nonlinear effective response using a through-thickness representative stacking sequence. Different 3D micromechanical models can be used to represent the composite layers within the repeating stacking sequence, e.g. roving layer, continuous filament mat (CFM), and woven fabrics. The proposed modeling framework is applied for pultruded composite material systems made from roving and CFM. The roving layer is idealized using an existing 3D nonlinear micromechanics model for a unidirectional fiber reinforced material. A simple nonlinear micromechanical model for the CFM layer is introduced and implemented. The overall modeling approach is able to predict both the elastic and nonlinear response of the composite material based on the in-situ properties and response of the fiber and matrix constituents. Experimental data, from off-axis tests of pultruded plates, is used to verify the proposed modeling approach. The 3D modeling framework shows good prediction capabilities for the overall effective elastic constants, as well as the nonlinear multi-axial stress-strain response. In addition, a simple degradation and damage modeling is coupled with the proposed analysis framework. Several applications are performed for the nonlinear analysis of pultruded composite structures, such as progressive failure analysis of notched plates, bending of short beams, and damage analysis of pultruded FRP bolted connections.
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