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Modeling Fiber Kinking at the Microscale and MesoscaleA computational micromechanics (CMM) model is employed to interrogate the assumptions of a recently developed mesoscale continuum damage mechanics (CDM) model for fiber kinking. The CMM model considers an individually discretized three dimensional fiber and surrounding matrix accounting for nonlinearity in the fiber, matrix plasticity, fiber/matrix interface debonding, and geometric nonlinearity. Key parameters of the CMM model were measured through experiments. In particular, a novel experimental technique to characterize the in situ longitudinal compressive strength of carbon fibers through indentation of micropillars is presented. The CDM model is formulated on the basis of Budiansky's fiber kinking theory (FKT) with a constitutive deformation-decomposition approach to alleviate mesh size sensitivity. In contrast to conventional mesoscale CDM models that prescribe a constitutive response directly, the response of the proposed model is an outcome of material nonlinearity and large rotations of the fiber direction following FKT. Comparison of the predictions from the CMM and CDM models shows remarkable correlation in strength, post-peak residual stress, and fiber rotation, with less than 10% difference between the two models in most cases. Additional comparisons are made with several fiber kinking models proposed in the literature to highlight the efficacy of the two models. Finally, the CMM model is exercised in parametric studies to explore opportunities to improve the longitudinal compression strength of a ply through the use of nonconventional microstructures.
Document ID
20180007919
Document Type
Technical Publication (TP)
Authors
Herraez, Miguel (Universidad Politecnica de Madrid Madrid, Spain)
Bergan, Andrew C. (NASA Langley Research Center Hampton, VA, United States)
Gonzalez, Carlos (Universidad Politecnica de Madrid Madrid, Spain)
Lopes, Claudio S. (IMDEA Materials Institute Madrid, Spain)
Date Acquired
November 29, 2018
Publication Date
October 1, 2018
Subject Category
Composite Materials
Report/Patent Number
NF1676L-31270
NASA/TP-2018-220105
L-20964
Funding Number(s)
WBS: WBS 826611.04.07.01
Distribution Limits
Public
Copyright
Public Use Permitted.

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