Micromechanical material models for polymer composites through advanced numerical simulation techniques

Al Kassem, Ghayath; Weichert, Dieter (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2010)
Dissertation / PhD Thesis


In order to reduce laboratory and experiments expenses, one would try to make predictions of a new material’s behavior and response by numerical simulations, with the chief goal being to speed up the trial and error experimental testing and to be able to simulate real phenomena that occur at the micro level of the composites that cannot be accurately implemented in the existing analytical models. The recent dramatic increase in computational power available for mathematical modeling and simulation raises the possibilities that modern numerical methods can play a significant role in the analysis of heterogeneous microstructures. This fact has motivated the work that will be presented in this work, which focuses on the methodology of building up an appropriate finite element material model describing the microstructure of the composite. It contains numerical homogenization practice and theory, as well as micro structural material modeling by using numerical simulation techniques on representative volume elements (RVEs). This work deals with the determination of macroscopic material properties of polymer composites by meso-mechanical numerical modeling. Focus is laid on the methodology how to build up appropriate representative volume elements (RVE) to describe the microstructure of spherical-particles and fibers reinforced composites and how to apply appropriate 3D boundary conditions. This work includes the comparison of the micro structural simulated FE-models with existing empirical and semi analytical formulations like Mori-Tanaka and the interpolative double inclusion (Lielens’ Model) that are used extensively in material modeling. Material characterization experiments are done on a particle reinforced polymer composite and its unfilled matrix to extract the material properties then compared with numerical homogenization applied on our micro material models. Various conclusions and results are discussed for the ‘know how’ in building the appropriate or preeminent representative material model based on the microstructure of the composite. 3D periodic and homogeneous boundary conditions are comprehensively studied, developed and applied to our RVEs. A new approach and technique is established for the 3D periodic boundary conditions. Different cases of numerical homogenization are examined, the isotropic case assumed for the particle filled composites (spherical inclusions) and the transverse isotropic/Orthotropic cases assumed for the fully-aligned/General-Orientation short-fiber reinforced composites (sphero-cylindrical and cylindrical inclusions).