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M. Sc. Serhat Aygün

M. Sc. Serhat Aygün Foto von M. Sc. Serhat Aygün

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ORCID iD iconhttps://orcid.org/0000-0001-5267-1015


Education & Professional Experience

since 02/2017 Research Assistant, Institute of Mechanics, TU Dortmund, Germany
04/2015-12/2016 M. Sc. in Mechanical Engineering, TU Dortmund, Germany
Thesis: "Multiscale Modeling of Strain-Induced Crystallization in Polymers"
01/2015-09/2016 Student Assistant, Institute of Mechanics, TU Dortmund, Germany
03/2016-06/2016 Visiting Student Researcher, Structural Engineering, Mechanics and Materials, University of California, Berkeley, Prof. S. Govindjee
10/2011-03/2015 B. Sc. in Mechanical Engineering, TU Dortmund, Germany
Thesis: "Development of a Material Model for Piezoceramics Using Energy Barriers"
05/2014-12/2014 Student Assistant & Trainee, Poynting GmbH, Dortmund, Germany


04/2014-09/2016 Deutschlandstipendium, Wilo-Foundation (scholarship)
11/2015 Martin-Schmeißer-Stipendium, TU Dortmund (research stay)


Supervision of student theses

R. Raveendran
Verhalten von Mikrorissen in Zugproben mit statistisch verteilten Inklusionen
Project Thesis, 2021

X. Hou
Elastische Anisotropie von zweiphasigen Stählen mit verschiedenen Martensitanteilen
Project Thesis, 2020

M. Harnisch
Numerical modeling of cyclic plasticity by using the Armstrong-Frederick kinematic hardening combined with ductile damage
Bachelor Thesis, 2019

A. Möglich
Implementierung einer thermo-mechanisch gekoppelten FE-Formulierung in FEAP
Project Thesis, 2019

M. Harnisch
Modeling of dislocation density in a context of rate-independent plasticity and isotropic hardening
Project Thesis, 2019


Multiscale modeling of calcified polymer hydrogels

Hydrogels, a significant group of highly hydrated polymers, represent the best choice for the potential application to bone fracture regeneration, which goes back to their bioactivity, affinity for biologically active proteins and compatibility with the bone tissue. However, this kind of materials also shows a serious disadvantage, namely, it loses its mechanical strength through swelling. This makes its straightforward usage difficult and motivates the development of different enhancement procedures. One of the most modern techniques for this purpose is calcification or, in a more general sense, mineralization. This method is inspired by the natural process of the bone growth where the enzyme alkaline phosphatase causes mineralization of the bone by cleavage of the phosphate from organic molecules. An analogous process induces homogeneous mineralization of a hydrogel and increases its mechanical strength. Recently, optical and electron microscopy has revealed that calcification yields different types of microstructure dependent on the type of the underlying polymer, and thus has clearly indicated that computational modeling can significantly contribute to the targeted investigation of effective behavior and material parameters. Fracture energy and diffusivity are two particularly important aspects in this context. The former is taken as the main measure of material ductility and represents a weak point of calcified hydrogels. In order to solve this challenging problem, inspiration once more comes from natural materials and their hierarchical microstructure. The study of diffusion in macromolecular solutions is motivated by many biomedical applications as well as by its key role for protein assembly and interstitial transport. The project furthermore studies the design of the mineralization process which includes two essential steps: the understanding of the mechanisms governing the microstructure development and subsequently their optimization. The investigation of the diffusivity and of mineralization requires a profound knowledge on the processes on the nanoscale. This of course strongly substantiates computer simulations, since this kind of processes is yet non-accessible even by the most modern microscopy techniques. The spectrum of applicable methods encompasses the multiscale finite element method, the phase field method, the model reduction strategy and the finite difference method.

Multiscale Modeling of Strain-Induced Crystallization in Polymers

The present project treats a polymer affected by the strain induced crystallization (SIC) as a heterogeneous medium consisting of regions with the different degree of network regularity. Such a concept allows depicting the nucleation and the growth of crystalline regions as well as the change of effective material parameters depending on the level of the strain applied. The model proposed is thermodynamically consistent. It is based on the assumptions for the free Helmholtz energy and dissipation. Both of them primarily include bulk- and surface terms due to the deformation and crystallization. The external variables are deformations and temperature, whereas the inelastic deformations and degree of the network regularity are internal variables. Their evolution equations are derived according to the principle of maximum of dissipation. The influences of latent heat and of temperature change are implemented in order to simulate thermal effects. The explained framework is advantageous for several reasons. First, it is suitable to answer the crucial question of which process predominantly influences SIC: the nucleation of new crystalline regions or the growth of already existing ones. Secondly, the proposed model is ideal for a direct implementation within the standard multiscale finite element concept. This numerical homogenization procedure is compatible with the theory of finite strains and is applicable for modeling the cases where the ratio of characteristic lengths of scales tends to zero. Both of these features are necessary for the effective modeling of SIC. The project also includes a study of stochastic aspects of the process, where a distribution function for the observable variables is introduced to express the expectation value of relevant quantities. The necessary evolution equation is derived by considering the effective energy of a control volume. The main goals here are to study nucleation and to evaluate the average size of the regions with different regularities of the network. The solution of the tasks itemized will make it possible to achieve the final project goal: the advanced simulations of SIC which can significantly contribute to the more efficient designing and usage of polymers. This is especially motivated by the fact that SIC has to be understood as a kind of reinforcement already successfully applied for some rubber materials. The proposed concepts are of general nature and can be taken as a basis for the modeling of similar processes involving the evolution of the internal microstructure.



S. Aygün, T. Wiegold and S. Klinge
Coupling of the phase field approach to the Armstrong-Frederick model for the simulation of ductile damage under cyclic load
International Journal of Plasticity,
143, 103021, 2021

S. Aygün and S. Klinge
Thermomechanical Modeling of Microstructure Evolution Caused by Strain-Induced Crystallization
12, 11, 2575, 2020

S. Aygün and S. Klinge
Continuum mechanical modeling of strain-induced crystallization in polymers
International Journal of Solids and Structures,
196-197, 129-139, 2020

S. Klinge, S. Aygün, R. P. Gilbert and G. A. Holzapfel
Multiscale FEM simulations of cross-linked actin network embedded in cytosol with the focus on the filament orientation
International Journal for Numerical Methods in Biomedical Engineering,
34, 7, e2993, 2018


S. Klinge, T. Wiegold, S. Aygün, R. P. Gilbert, and G. A. Holzapfel
On the mechanical modeling of cell components
20, 1, e202000129, 2021

S. Aygün and S. Klinge
Study of stochastic aspects in the modeling of the strain-induced crystallization in unfilled polymers
20, 1, e202000031, 2021

S. Aygün and S. Klinge
Coupled thermomechanical model for strain-induced crystallization in polymers
19, 1, e201900342, 2019

S. Aygün and S. Klinge
Modeling the thermomechanical behavior of strain-induced crystallization in unfilled polymers
Proceedings of the 8th GACM Colloquium on Computational Mechanics,
151-154, 2019

S. Klinge, S. Aygün and M. Bambach
Extended Simulations of the Roll Bonding Process
18, 1, e201800257, 2018

S. Aygün and S. Klinge
Study of the microstructure evolution caused by the strain‐induced crystallization in polymers
18, 1, e201800224, 2018

T. Wiegold , S. Klinge, S. Aygün, R. P. Gilbert and G. A. Holzapfel
Viscoelasticity of cross‐linked actin network embedded in cytosol
18, 1, e201800151, 2018

S. Aygün, S. Klinge and S. Govindjee
Continuum Mechanical Modeling of Strain-Induced Crystallization in Polymers
Proceedings of the 7th GACM Colloquium on Computational Mechanics,
579-582, 2017

S. Aygün and S. Klinge
Mechanical Modeling of the Strain-Induced-Crystallization in Polymers
17, 1, 389-390, 2017

S. Klinge, S. Aygün, J. Mosler and G. A. Holzapfel
Cross-linked actin networks: Micro- and macroscopic effects
16, 1, 93-94, 2016


Thermomechanical and multiscale modeling of polymeric materials with complex microstructures
91st GAMM Annual Meeting, Kassel, Germany, March 15-19, 2021

Modeling the thermomechanical behavior of strain-induced crystallization in unfilled polymers
8th GACM Colloquium on Computational Mechanics, Kassel, Germany, August 28-30, 2019

Coupled thermomechanical model for strain-induced crystallization in polymers
Young Researchers' Minisymposia, 90th GAMM Annual Meeting, Vienna, Austria, February 18-22, 2019

Study of the microstructure evolution caused by the strain-induced crystallization in polymers
89th GAMM Annual Meeting, Munich, Germany, March 19-23, 2018

Continuum Mechanical Modeling of Strain-Induced Crystallization in Polymers
7th GACM Colloquium on Computational Mechanics, Stuttgart, Germany, October 11-13, 2017

Multiscale Modeling of Strain-Induced Crystallization in Polymers
88th GAMM Annual Meeting, Weimar, Germany, March 6-10, 2017