Abstract

In this paper, a mechanism-based lamina level modeling approach is used as the basis for developing a macroscopic (lamina level) model to capture the mechanisms of kink banding. Laminae are modeled as inelastic degrading homogenized layers in a state of plane stress according to Schapery Theory (ST). However, the principal orthotropic material axes are allowed to rotate as a function of deformation. In ST, each lamina degrades as characterized through laboratory scale experiments. In the fiber direction, elastic behavior prevails; however, in this work, the phenomenon of fiber microbuckling leading to kink banding, which is responsible for the sudden degradation of the axial lamina properties under compression, is explicitly accounted for by allowing the fiber rotation at a material point to be a variable in the problem. These features are built into a user-defined material subroutine that is implemented through the commercial finite element (FE) software ABAQUS. Thus, in this model we eschew the notion of a fixed compressive strength of a lamina and instead use the mechanics of the failure process to provide the in situ compression strength of a material point in a lamina, the latter being dictated strongly by the current local stress state, the current state of the lamina transverse material properties, and the local fiber rotation. The inputs to this model are laboratory scale, coupon level test data (at the lamina level) that provide information on the lamina transverse property degradation (that is, appropriate, measured, strain-stress relations of the lamina transverse properties), the elastic lamina orthotropic properties and the geometry of the lamina. The validity of the approach advocated is demonstrated through numerical simulations of unidirectional lamina with initial fiber imperfections. The predictions of the simulations reported in this paper are compared against previously reported results from micromechanical analyses. Good agreement between the present macroscopic modeling approach and the previous micromechanical observations are reported.

Keywords

fiber kinking, fiber rotation, matrix damage, progressive failure analysis, compressive response

Authors