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Prabhakar P.,320 Beal Avenue | Waas A.M.,320 Beal Avenue
54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference | Year: 2013

A new finite element formulation that can seamlessly model the transition from a continuum to a non-continuum (through fracture) is introduced in this paper. In-plane fiber-matrix fracture (also referred to as splitting) is frequently observed in tensile failure of fiber reinforced polymer matrix composites (FRPC). This mechanism is modeled through the development of a continuum-decohesive finite element (CDFE) by considering a single lamina. The transition from a continuum to a non-continuum in the CDFE method is modeled directly (physically) without resorting to enrichment of the shape functions of the element, as is done in other methods, such as the variational multiscale cohesive method (VMCM) or through nodal enrichment as in extended finite element method (XFEM). The CDFE is a natural merger between cohesive elements and continuum elements. Predictions using the CDFE method were found to be in very good agreement with corresponding experimental data for open hole tension tests of fiber reinforced lamina. © 2013 by Pavana Prabhakar. Source


Prabhakar P.,320 Beal Avenue | Waas A.M.,320 Beal Avenue
Computational Materials Science | Year: 2013

Analyzing failure mechanics of fiber-reinforced media that correspond to different length scales with the goal of up-scaling is addressed in this paper with respect to compressive kinking instability in fiber reinforced laminae. Using the concentric cylinder model (CCM) as a representative element of a lamina, J2 deformation theory along with Hill's anisotropic plasticity theory is used to extend the constitutive model for the fiber-matrix cylinder, and hence the lamina, into the nonlinear regime. The model requires the elastic properties of fiber and matrix, the fiber volume fraction and the nonlinear shear response of the polymer matrix. An 8-layer laminate is up-scaled using this method by homogenizing the off-axis laminae and retaining micro-mechanics in the 0° laminae, and results are compared against a discrete fiber-matrix micro-mechanical model of the laminate. The effect of homogenizing the laminae on the compressive response of the laminate is investigated. © 2011 Elsevier B.V. All rights reserved. Source


Prabhakar P.,320 Beal Avenue | Waas A.M.,320 Beal Avenue
Composites Part A: Applied Science and Manufacturing | Year: 2013

Computational models to predict the compressive strength of carbon fiber reinforced polymer matrix composites are proposed here, motivated by the failure mechanisms observed in compression tests. Delamination, fiber kink-banding and their interaction are seen to dominate the failure response. An upscaled semi-homogenized laminate model is developed to predict the observed compressive response of multidirectional laminates. A generalized 2-D formulation is presented to determine the interfaces most susceptible to delamination. Subsequently, cohesive elements are added along these interfaces to introduce delamination capability in the model. Predictions of the model are compared against experimental data, and are found to be in agreement with respect to compressive strength and failure modes. Further, the effect of stacking sequence on the compressive strength and failure mode is investigated. © 2013 Elsevier Ltd. Source


Prabhakar P.,320 Beal Avenue | Waas A.M.,320 Beal Avenue
Composites Science and Technology | Year: 2013

A new finite element to seamlessly model the transition from a continuum to a non-continuum (through fracture) is introduced in this paper, motivated by the variational multi-scale cohesive (VMCM) method. In-plane fiber-matrix fracture (also referred to as splitting) is frequently observed in tensile failure of fiber reinforced polymer matrix composites (FRPCs). By considering a single lamina, this mechanism is modeled through the development of a continuum-decohesive finite element (CDFE). In the CDFE method, the transition from a continuum to a non-continuum is modeled directly (physically) without resorting to enrichment of the shape functions of the element, as is done in other methods, such as the VMCM or through nodal enrichment, as is done with the extended finite element method (XFEM). The CDFE is a natural merger between cohesive elements and continuum elements. The predictions of the CDFE method were found to be in very good agreement with corresponding experimental data. © 2013 Elsevier Ltd. Source


Heinrich C.,320 Beal Avenue | Heinrich C.,HIGH-TECH | Waas A.M.,320 Beal Avenue | Waas A.M.,Imperial College London
Computers, Materials and Continua | Year: 2013

The smeared crack approach (SCA) is revisited to describe post-peak softening in laminated composite materials. First, predictions of the SCA are compared against linear elastic fracture mechanics (LEFM) based predictions for the debonding of an adhesively bonded double cantilever beam. A sensitivity analysis is performed to establish the influence of element size and cohesive strength on the load-deflection response. The SCA is further validated by studying the in-plane fracture of a laminated composite in a single edge bend test configuration. In doing so, issues related to mesh size and their effects (or non-effects) are discussed and compared against other predictive computational techniques. Finally, the SCA is specialized to orthotropic materials. The application of the SCA is demonstrated for failure mechanics of the open hole tension test, where fiber/matrix fracture is predominant and predicted well by the present approach. Copyright © 2013 Tech Science Press. Source

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