TY - BOOK

T1 - Nonlinear material modeling and simulation of thermoplastics

AU - Morak, Matthias M.

N1 - embargoed until 01-07-2024

PY - 2019

Y1 - 2019

N2 - Short fiber-reinforced thermoplastics are increasingly used in almost all industrial sectors. Finite element simulations are used to simulate the material behavior under mechanical stress in order to minimize the cost and time intensive testing of components. Due to the many different influencing factors, conventional material models, which were mostly developed for metals, reach their limits when it comes to precisely describing the correct response of plastics to mechanical stress. Within the scope of this work, both a standard isochoric isotropic elasto-viscoplastic material model developed for steel and an anisotropic elasto-viscoplastic material model, which takes into account the fiber orientation via a micromechanical approach and was developed especially for the simulation of plastics, are investigated and evaluated. The material considered in this thesis is a polyamide 6 with a glass fiber content of 30 wt.%. For the model calibration numerous experiments have to be carried out to determine the material behavior at different strain rates, stress states and fiber orientations. The material behavior is investigated in the quasi-static as well as in the dynamic deformation range. The influence of temperature and humidity on the mechanical behavior is neglected in this thesis for the time being. Since during the injection molding process of short fiber-reinforced thermoplastics a certain orientation of the fibers occurs, which is primarily defined by the geometry and the injection molding process itself, injection molding simulations are carried out to determine this orientation distribution in the components under consideration. In addition, the empirical parameters of the material model used for the injection molding simulation are optimized in order to obtain the most accurate information possible regarding the anisotropy. Based on the results of the experimental characterization of the material and the injection molding simulation, the material parameters are calculated and the models calibrated accordingly. The failure parameters and the material parameters of the anisotropic model are adjusted by nonlinear optimization based on the experimental data. Finally, both models, the isotropic and the anisotropic one, are checked and evaluated by means of a component simulation.

AB - Short fiber-reinforced thermoplastics are increasingly used in almost all industrial sectors. Finite element simulations are used to simulate the material behavior under mechanical stress in order to minimize the cost and time intensive testing of components. Due to the many different influencing factors, conventional material models, which were mostly developed for metals, reach their limits when it comes to precisely describing the correct response of plastics to mechanical stress. Within the scope of this work, both a standard isochoric isotropic elasto-viscoplastic material model developed for steel and an anisotropic elasto-viscoplastic material model, which takes into account the fiber orientation via a micromechanical approach and was developed especially for the simulation of plastics, are investigated and evaluated. The material considered in this thesis is a polyamide 6 with a glass fiber content of 30 wt.%. For the model calibration numerous experiments have to be carried out to determine the material behavior at different strain rates, stress states and fiber orientations. The material behavior is investigated in the quasi-static as well as in the dynamic deformation range. The influence of temperature and humidity on the mechanical behavior is neglected in this thesis for the time being. Since during the injection molding process of short fiber-reinforced thermoplastics a certain orientation of the fibers occurs, which is primarily defined by the geometry and the injection molding process itself, injection molding simulations are carried out to determine this orientation distribution in the components under consideration. In addition, the empirical parameters of the material model used for the injection molding simulation are optimized in order to obtain the most accurate information possible regarding the anisotropy. Based on the results of the experimental characterization of the material and the injection molding simulation, the material parameters are calculated and the models calibrated accordingly. The failure parameters and the material parameters of the anisotropic model are adjusted by nonlinear optimization based on the experimental data. Finally, both models, the isotropic and the anisotropic one, are checked and evaluated by means of a component simulation.

KW - short-fiber reinforced polyamide

KW - isochoric isotropic elasto-viscoplastic material model

KW - anisotropic elasto-viscoplastic material model

KW - material characterization

KW - injection molding model parameter optimization

KW - integrative simulation

KW - Kurzglasfaserverstärktes Polyamid

KW - Charakterisierung

KW - Isochor-isotrope elasto-viskoplastische Materialmodellierung und -kalibrierung

KW - Anisotrope elasto-viskoplastische Materialmodellierung

KW - Spritzgussmodellparameteroptimierung

KW - Integrative Simulation

M3 - Doctoral Thesis

ER -