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Mixed boundary conditions for FFT-based homogenization at finite strains

: Kabel, M.; Fliegener, S.; Schneider, M.


Computational mechanics 57 (2016), No.2, pp.193-210
ISSN: 0178-7675
ISSN: 1432-0924
Deutsche Forschungsgemeinschaft DFG
Technologies for Multifunctional Lightweight Structures
Journal Article
Fraunhofer ITWM ()
Fraunhofer IWM ()
composite materials; finite deformation; LippmannSchwinger equation; FFT

In this article we introduce a Lippmann-Schwinger formulation for the unit cell problem of periodic homogenization of elasticity at finite strains incorporating arbitrary mixed boundary conditions. Such problems occur frequently, for instance when validating computational results with tensile tests, where the deformation gradient in loading direction is fixed, as is the stress in the corresponding orthogonal plane. Previous Lippmann-Schwinger formulations involving mixed boundary can only describe tensile tests where the vector of applied force is proportional to a coordinate direction. Utilizing suitable orthogonal projectors we develop a Lippmann-Schwinger framework for arbitrary mixed boundary conditions. The resulting fixed point and Newton-Krylov algorithms preserve the positive characteristics of existing FFT-algorithms. We demonstrate the power of the proposed methods with a series of numerical examples, including continuous fiber reinforced laminates and a complex nonwoven structure of a long fiber reinforced thermoplastic, resulting in a speed-up of some computations by a factor of 1000.