A macroscopic model for kink banding instabilities in fiber composites

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.

In-Plane Fracture of Laminated Fiber Reinforced Composites with Varying Fracture Resistance: Experimental Observations and Numerical Crack Propagation Simulations

“…For instance, in compression failure of unidirectional composites, micromechanical models have successfully shown the initiation and evolution of fiber micro-buckling leading to kink banding failure. 42 This lack of objectivity in fracture resistance at first seems to rule out a predictive capability for failure of these materials. However as shown in Section IV(B) average estimates of fracture resistance, R avg , significantly reproduce the observed failure response.…”

Progressive damage and failure response of hybrid 3D textile composites subjected to flexural loading, part I: Experimental studies

“…The kink bands progressively develop on the compressive side of the specimen with further deformation, limiting the maximum load capacity of this class of materials. Compressive failure due to kink banding has been extensively investigated in the past, resulting in a series of important studies on kinking (Budiansky and Fleck, 1993;Kyriakides et al, 1995;Lee and Waas, 1999;Feld et al, 2011;Prabhakar and Waas, 2013a,b;Schultheisz and Waas, 1996;Waas and Schultheisz, 1996;Basu et al, 2006;Feld et al, 2012;Allix et al, 2014;Zidek and Völlmecke, 2014;Davidson and Waas, 2014). It is established that kink band formation is due to both geometric nonlinearity (fiber misalignment) and material nonlinearity (matrix degradation) in fiber reinforced composites.…”

Progressive damage and failure response of hybrid 3D textile composites subjected to flexural loading, part II: Mechanics based multiscale computational modeling of progressive damage and failure

“…The nonlinear progression can be dictated through a nonlinear constitutive law, such as Schapery theory (Schapery, 1990) or Hill's anisotropic plasticity theory (Hill, 1948). The direct implementation of the lamina level nonlinear constitutive relations within a FE framework to predict the kind band formation has been reported by Basu et al (2006), Song et al (2009) andZhang et al (2012). The key in these models is to allow the principal orthotropic material axis to rotate as a function of deformation.…”