An improved design methodology for modeling thick-section composite structures using a multi-scale approach
Date
2010
Authors
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Publisher
University of Delaware
Abstract
Material nonlinearity and progressive ply failure are important considerations in the finite element modeling of thick section composite structures. Ply-level anisotropic nonlinearity and ply-based failure criteria require ply-level stresses and strains, but discretely modeling individual plies in a large scale, thick section composite structure with hundreds of plies is not computationally feasible. A method was developed [1-4] to model the material nonlinearity and progressive ply failure of composite laminates using finite element software without explicitly simulating individual plies. In this method, the multiple plies of a laminate are treated as a homogenous, or smeared, material with equivalent material properties. Ply-level material nonlinearity and progressive failure analysis are incorporated by dehomogenizing, or unsmearing, the laminate. The LAMPATNL program integrated this method into a finite element environment [4]. Improvements to this program are documented and discussed in this work. Also, the LAMPATNL user material is validated against both the linear and nonlinear material point models. In this work, a standardized process for designing composite structures with the LAMPATNL user material is developed. The design methodology uses newly formulated output parameters, stiffness ratios, to analyze the nonlinear response and progressive failure of the composite structure. These new parameters greatly improve the visualization of critical design information of the structure. An example comparing the original outputs of LAMPATNL to the new outputs is provided to illustrate the contributions of the stiffness ratio parameters. Two case studies, an open-hole sample under multi-axial loading and a compressive shear sample, are evaluated using the design methodology. Changes to the layups of the laminates in these cases are made using the insights gained from the design methodology. Coupling LAMPATNL with a design methodology and new stiffness ratio parameters demonstrates the utility of progressive failure and nonlinear analysis when applied to composite structures. The straightforward visualization of critical design information creates a unique approach to analyzing the design of thick section composites. This methodology represents a unique contribution to the modeling of composite structures that is not matched by any current composite model.