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@PHDTHESIS{Poggenpohl:961281,
author = {Poggenpohl, Lukas Martin},
othercontributors = {Reese, Stefanie and Simon, Jaan-Willem and Wulfinghoff,
Stephan},
title = {{M}odeling micromorphic damage in long carbon fiber
reinforced plastics at different scales},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2023-06739},
pages = {1 Online-Ressource : Illustrationen, Diagramme},
year = {2023},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, Rheinisch-Westfälische Technische
Hochschule Aachen, 2023},
abstract = {Composites have been used for a long time in the history of
mankind. Already in the times of the pharaohs, clay and
straw were combined to build houses out of this material. In
general, composites are used to combine the positive
properties of the various components and produce materials
with extreme properties or properties tailored to the
application needs. Nowadays, composites made from a
combination of epoxy resin with glass fibers (so-called
glass fiber reinforced plastics or GFRPs) or carbon fibers
(so-called carbon fiber reinforced plastics or CFRPs) are
used primarily in lightweight construction. The latter offer
particularly high stiffness and strength combined with low
density, making them an ideal material for lightweight
construction applications. CFRPs are manufactured either
from layers of parallel fibers laid on top of each other in
different directions or from woven fabrics with different
weave structures, which are usually filled with an epoxy
resin. Due to the complex microstructure, even simple load
cases lead to complex stress states within the material. In
addition, CFRP exhibits brittle material failure with
significant scatter in material parameters, leading to high
factors of safety in applications. A more accurate
prediction of the material behavior, especially in the area
of material damage, would lead to a reduction of the safety
factors and thus to a better design of CFRP structures. This
cumulative dissertation aims to contribute to a better
understanding of the damage behavior of carbon fiber
reinforced plastics. It consists mainly of three previously
published scientific papers from the author and several
co-authors. The aim of the publications was the simulation
of the damage behavior of CFRPs both at the scale of the
components and at the microscopic scale of the laminates and
fabrics. Here, the material model used for brittle damage,
without considering plasticity, is similar for all three
publications. In the material model, gradient-extended (or
micromorph) damage is used to produce mesh size-independent
results.The dissertation begins with an introduction to
illuminate the research-relevant questions and to present
the current state of research. This is followed by the first
of a total of three scientific publications. Here, an
isotropic material model for large deformations was extended
by an anisotropic component in order to simulate the
material behavior of CFRP on a macroscopic level. Both the
isotropic and anisotropic portions were given their own
scalar damage variable to distinguish between damage to the
epoxy matrix (isotropic part) and damage to the carbon fiber
(anisotropic extension). A tension-compression asymmetry was
also introduced for both parts to account for the effect of
crack closure. In addition, an anisotropy was introduced in
the gradient term of the isotropic material part to account
for the direction dependence of the crack propagation.
Finally, the material parameters of the numerical model were
fitted to experimental results of unidirectional CFRP and
the performance of the material model was evaluated.In the
second publication, the material behavior of CFRP was
investigated on the microscale. Since a geometric
distinction between fiber and matrix is possible on the
microscale, only the isotropic part of the previously
implemented material model was used. The aim of the
publication was to develop a new homogenization approach
with and without consideration of the interface between
epoxy matrix and carbon fiber. The homogenization approach
was based on the so-called failure zone averaging and aimed
at deriving a material behavior for the next larger scale
from simulations of the microscale. The approach took into
account the energetic components from both the mechanical
part of the model and the micromorphic extension. An
examination of the power components showed that the
micromorphic power is non-zero in the case of failure zone
averaging, and even shows power peaks that exceed those of
the mechanical power. However, in terms of the total energy
dissipated in the system, it was shown that the energy
dissipated by the micromorphic components is negligible. The
publication concluded with simulations that included the
interface between fiber and matrix. Here, a generally
reduced strength with simultaneously increased dissipated
energy was observed. In the last publication, the previously
presented homogenization method was applied to the load
cases of simple shear, pure shear and mixed mode loading. It
was shown that different load-deformation curves formed
depending on the type of load, the geometry and whether the
tension-compression asymmetry is activated. In particular,
the orientation of the failure zone had a significant
influence here. The publication again concluded with
simulations that took into account the interface between
fiber and matrix. Here, as before, an increased dissipation
with simultaneously reduced strength was shown.The
dissertation concludes with an outlook on research-relevant
questions arising from the results of the three published
papers for future work in this area of research.},
cin = {311510},
ddc = {624},
cid = {$I:(DE-82)311510_20140620$},
pnm = {DFG project 404502442 - Experimentelle und numerische
Untersuchung von geschichteten, faserverstärkten
Kunststoffen bei Crash-Beanspruchungen (404502442) / DFG
project 286076101 - Scherschneiden
kohlenstofffaserverstärkter Kunststoffe.
Fertigungstechnologie und numerische Modellierung
(286076101)},
pid = {G:(GEPRIS)404502442 / G:(GEPRIS)286076101},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2023-06739},
url = {https://publications.rwth-aachen.de/record/961281},
}
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