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@PHDTHESIS{Felder:842201,
author = {Felder, Sebastian},
othercontributors = {Reese, Stefanie and Lion, Alexander},
title = {{M}ultiphysics modeling of polymers and metals :
experimental and numerical investigations},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2022-02286},
pages = {1 Online-Ressource : Illustrationen},
year = {2022},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, Rheinisch-Westfälische Technische
Hochschule Aachen, 2022},
abstract = {Due to the steadily increasing computing power of modern
computers, numerical simulation is nowadays used in all
engineering disciplines. For example, digital twins (i.e.
the virtual representation of physical objects) are employed
in the conception and development phase of products or
processes to analyze, design and optimize them in advance.
In particular, the finite element method (FEM) has
established itself as a well-proven tool for the simulation
of technical (coupled multiphysical) problems. However, the
accuracy and reliability of the predictions made in the
course of finite element analyses are essentially dependent
on the underlying material models. Therefore, new models are
still developed today, in order to represent increasingly
complex phenomena and effects and to achieve predictions
that are as close to reality as possible. In particular, the
modeling of the material behavior in the context of
non-isothermal forming processes (e.g. warm and hot sheet
metal forming and thermoforming of thermoplastics or glass)
represents a complicated task. Here, the following
challenges arise: In general, the materials are formed under
large irreversible deformations. Consequently, only finite
strain constitutive theories lead to reliable results.
Furthermore, complex (time-dependent) inelastic deformation
mechanisms occur. For most materials (such as metals and
polymers), these irreversible processes lead to significant
self-heating of the material, especially at higher forming
rates. In addition, the temperature-dependent mechanical
properties and the formation of residual stresses in the
course of non-isothermal processes must be taken into
account. Moreover, temperature dependent microstructural
phase transformations occur in metals as well as in polymers
during the cooling process, which have a significant
influence on the effective properties of the manufactured
components. Therefore, a complicated coupling of the
mechanical quantities with the temperature and the
corresponding phase transformations arises. If damage and
crack propagation are to be considered in the course of
modeling, the complicating necessity to integrate non-local
damage approaches arises, in order to exclude undesired
mesh-dependent results. For gradient-extended damage
concepts, this leads to the introduction of additional
balance equations, which have to be solved in addition to
the classical balances of energy and linear momentum. The
coupled modeling of these multiple physical phenomena is a
challenging and relevant task, which still requires
fundamental research. This cumulative dissertation aims to
make a valuable contribution in this regards. The
overarching objective of the current work is the development
of coupled multiphysics modeling approaches for polymers and
metals in order to enable more realistic simulations of the
above-mentioned processes in the future. Essentially, this
work comprises a collection of published research articles
by the author (and his co-authors), in the context of the
aforementioned topic. In the introduction, the
research-relevant questions are elaborated in detail. In
addition, an up-to-date literature review is provided. The
subsequent first two publications deal with the experimental
investigation and modeling of semi-crystalline polymers. In
the first paper, extensive experimental data regarding the
mechanical behavior of semi-crystalline polyamide 6 is
collected. Based on this data, a new isothermal continuum
mechanical material model is developed. The underlying
formulation is based on a coupled visco-hyperelastic,
elasto-plastic approach in which nonlinear relaxation and
strain hardening effects are considered. The temperature as
well as the degree of crystallinity serve as constant input
parameters, which significantly influence the effective
material behavior. In the second paper, a
thermo-mechanically coupled extension of the former model is
proposed. The degree of crystallinity is now treated as a
non-constant internal variable, which is dependent on the
temperature history. Thus, the processing induced
microstructural crystallization kinetics and the
corresponding (locally varying) changes in the macroscopic
behavior can be represented. In addition, the heat
generation due to irreversible deformation processes and
exothermic crystal growth is derived from the energy
balance. The predicted mechanical behavior, the heat of
crystallization, as well as the self-heating due to large
irreversible deformations show qualitatively and
quantitatively a good agreement with experiments in
three-dimensional structural examples. The third and last
article in this dissertation deals with the complex
interplay between plastic deformations, damage processes and
temperature, which occurs in metals during e.g. forming
processes. To this end, a gradient-extended
thermo-mechanically coupled constitutive framework is
developed. The modeling of the mechanical behavior is based
on the work of Brepols 2020, where a two-surface damage
plasticity approach is proposed. The heat generation of
these dissipative processes are derived from the energy
balance in a consistent manner. A fully implicit and
monolithic algorithm is presented and discussed in detail
for solving the three global solution fields (i.e.
displacement, temperature, and nonlocal damage variable). In
this way, mesh-objective descriptions of the complex
interactions between the aforementioned phenomena can be
resolved.},
cin = {311510},
ddc = {624},
cid = {$I:(DE-82)311510_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2022-02286},
url = {https://publications.rwth-aachen.de/record/842201},
}
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