45713
2018
eng
3395
3400
9
38
article
Elsevier Ltd.
1
--
--
--
3D printing of porcelain by layerwise slurry deposition
The Layerwise Slurry Deposition is a technology for the deposition of highly packed powder layers. A powder bed is achieved by depositing and drying layers of a ceramic suspension by means of a doctor blade. This deposition technique was combined with the binder jetting technology to develop a novel Additive Manufacturing technology, named LSD-print. The LSD-print was applied to a porcelain ceramic. It is shown that it was possible to produce parts with high definition, good surface finish and at the same time having physical and mechanical properties close to those of traditionally processed porcelain, e.g. by slip casting.
This technology shows high future potential for being integrated alongside traditional production of porce-lain, as it is easily scalable to large areas while maintaining a good definition. Both the Layerwise Slurry Deposition method and the binder jetting technologies are readily scalable to areas as large as > 1 m2.
Journal of the European Ceramic Society
0955-2219
10.1016/j.jeurceramsoc.2018.03.014
15.08.2018
Jens Günster
Andrea Zocca
Pedro Lima
W. Acchar
eng
uncontrolled
Binder jetting
eng
uncontrolled
Additive Manufacturing
eng
uncontrolled
3D printing
eng
uncontrolled
Porcelain
Ingenieurwissenschaften und zugeordnete Tätigkeiten
5 Werkstofftechnik
5.4 Multimateriale Fertigungsprozesse
Material
Verlagsliteratur
Datei im Netzwerk der BAM verfügbar ("Closed Access")
Additive Fertigung
45714
2018
eng
1800003-1
1800003-7
5
3
article
Wiley-VCH
Weinheim
1
--
--
--
3D Printing of Self-Organizing Structural Elements for Advanced Functional Structures
A shape evolution approach based on the thermally activated self-organization of 3D printed parts into minimal surface area structures is presented. With this strategy, the present communication opposes currently established additive manufacturing strategies aiming to stipulate each individual volumetric element (voxel) of a part. Instead, a 3D structure is roughly defined in a 3D printing process, with all its advantages, and an externally triggered self-organization allows the formation of structural elements with a definition greatly exceeding the volumetric resolution of the printing process. For enabling the self-organization of printed objects by viscous flow of material, functionally graded structures are printed as rigid frame and melting filler. This approach uniquely combines the freedom in design, provided by 3D printing, with the mathematical formulation of minimal surface structures and the knowledge of the physical potentials governing self-organization, to overcome the paradigm which strictly orrelates the geometrical definition of 3D printed parts to the volumetric resolution of the printing process. Moreover, a transient liquid phase allows local programming of functionalities, such as the alignment of functional particles, by means of electric or magnetic fields.
Advanced Materials Technologies
10.1002/admt.201800003
2365-709X
15.08.2018
Jinchun Chi
Andrea Zocca
Boris Agea Blanco
J. Melcher
M. Sparenberg
Jens Günster
eng
uncontrolled
Additive Manufacturing
eng
uncontrolled
Self-Assembly
eng
uncontrolled
3D-Printing
eng
uncontrolled
Polymeric Materials
Ingenieurwissenschaften und zugeordnete Tätigkeiten
5 Werkstofftechnik
5.4 Multimateriale Fertigungsprozesse
Material
Verlagsliteratur
Datei im Netzwerk der BAM verfügbar ("Closed Access")
Additive Fertigung
47394
2018
eng
lecture
0
--
--
--
3D reconstruction and quantification of dislocation substructures from TEM stereo pairs
Dislocations are the carriers of plastic deformation. As such, their characterization offers important information on the properties they affect. In this contribution, a new tool is presented, which is incorporated in Amira ZIB Edition and allows for three-dimensional (3D) imaging and quantification of dislocations substructures from thick regions an electron-transparent specimen. In the tool, the dislocation segments are traced on diffraction contrast images that are obtained in the transmission electron microscope (TEM). The uncertainties related to the experimental setup and to the proposed method are discussed on the base of a tilt series.
AVIZO / AMIRA User Meeting
Berlin, Germany
14.11.2018
14.11.2018
false
true
0
Leonardo Agudo Jácome
eng
uncontrolled
Dislocation
eng
uncontrolled
Diffraction contrast
eng
uncontrolled
Scanning transmission electron microscopy (STEM)
Analytische Chemie
5 Werkstofftechnik
5.1 Materialographie, Fraktographie und Alterung technischer Werkstoffe
Chemie und Prozesstechnik
Datei im Netzwerk der BAM verfügbar ("Closed Access")
Präsentation
48399
2018
eng
lecture
0
--
--
--
A continuum damage model for the simulation of concrete under cyclic loading
A continuum damage model for concrete is developed with a focus on fatigue under compressive stresses. This includes the possibility to model stress redistributions and capture size effects. In contrast to cycle based approaches, where damage is accumulated based on the number of full stress cycles, a strain based approach is developed that can capture cyclic degradation under variable loading cycles including different amplitudes and loading frequencies. The model is designed to represent failure under static loading as a particular case of fatigue failure after a single loading cycle. As a consequence, most of the material parameters can be deduced from statictests. Only a limit set of additional constitutive parameters is required to accurately describe the evolution under fatigue loading. Another advantage of the proposed model is the possibility to directly incorporate other multi-physics effects such as creep and shrinkage or thermal loading on the constitutive level. A multiscale approach in time is presented to enable structural computations of fatigue failure with a reduced computational effort. The damage rate within the short time scale corresponding to a single cycle is computed based on a Fourier based approach. This evolution equation is then solved on the long time scale using different implicit and explicit time integration schemes. Their performance and some limitations for specific loading regimes is discussed.
https://euro-c.tuwien.ac.at/home/
Computational Modelling of concrete and concrete Structures Euro-C, March 1st 2018
Bad Hofgastein, Austria
26.02.2018
false
true
0
Vitaliy Kindrachuk
eng
uncontrolled
Continnum damage model
eng
uncontrolled
Simulation of concrete
eng
uncontrolled
Under cyclic loading
Ingenieurbau
5 Werkstofftechnik
5.2 Metallische Hochtemperaturwerkstoffe
5.5 Materialmodellierung
7 Bauwerkssicherheit
Infrastruktur
Datei im Netzwerk der BAM verfügbar ("Closed Access")
Präsentation
7.7 Modellierung und Simulation
48400
2018
eng
155
164
2018
conferenceobject
CRC Press, Taylor & Francis Group
Leiden, The Netherland
1
--
--
--
A continuum damage model for the simulation of concrete under cyclic loading
A continuum damage model for concrete is developed with a focus on fatigue under compressive stresses. This includes the possibility to model stress redistributions and capture size effects. In contrast to cycle based approaches, where damage is accumulated based on the number of full stress cycles, a strain based approach is developed that can capture cyclic degradation under variable loading cycles including different amplitudes and loading frequencies. The model is designed to represent failure under static loading as a particular case of fatigue failure after a single loading cycle. As a consequence, most of the material parameters can be deduced from statictests. Only a limit set of additional constitutive parameters is required to accurately describe the evolution under fatigue loading. Another advantage of the proposed model is the possibility to directly incorporate other multi-physics effects such as creep and shrinkage or thermal loading on the constitutive level. A multiscale approach in time is presented to enable structural computations of fatigue failure with a reduced computational effort. The damage rate within the short time scale corresponding to a single cycle is computed based on a Fourier based approach. This evolution equation is then solved on the long time scale using different implicit and explicit time integration schemes. Their performance and some limitations for specific loading regimes is discussed.
Computational Modelling of Concrete and Concrete Structures (EURO-C 2018)
https://euro-c.tuwien.ac.at/home/
978-1-315-18296-4
978-1-138-74117-1
Euro-C, March 1st 2018
Bad Hofgastein, Austria
26.02.2018
01.03.2018
03.07.2019
false
true
Vitaliy Kindrachuk
eng
uncontrolled
Continnum damage model
eng
uncontrolled
Simulation of concrete
eng
uncontrolled
Under cyclic loading
Ingenieurbau
5 Werkstofftechnik
5.2 Metallische Hochtemperaturwerkstoffe
5.5 Materialmodellierung
7 Bauwerkssicherheit
Infrastruktur
Verlagsliteratur
Datei im Netzwerk der BAM verfügbar ("Closed Access")
7.7 Modellierung und Simulation
47999
2018
eng
155
164
conferenceobject
CRC Press, Taylor & Francis Group
Boca Raton, Lodon, New York, Leiden
1
--
--
--
A continuum damage model for the simulation of concrete under cyclic loading
Lifetime aspects including fatigue failure of concrete structures were traditionally only of minor importance. Because of the growing interest in maxing out the capacities of concrete, its fatigue failure under compression has become an issue. A variety of interacting phenomena such as e.g. loss of prestress, degradation due to chemical reactions or creep and shrinkage influence the fatigue resistance. Failure due to cyclic loads is generally not instantaneous, but characterized by a steady damage accumulation. Therefore, a reliable numerical model to predict the performance of concrete over its lifetime is required, which accurately captures order effects and full three-dimensional stress states.
Many constitutive models for concrete are currently available, which are applicable for specific loading regimes, different time scales and different resolution scales.
However, a key limitation of those models is that they generally do not address issues related to fatigue on a structural level. Very few models can be found in the literature that reproduce deterioration of concrete under repeated loading-unloading cycles. This is due to the computational effort necessary to explicitly resolve every cycle which exceeds the currently available computational resources. The limitation can only be overcome by the application of multiscale methods in time.
The objective of the paper is the development of numerical methods for the simulation of concrete under fatigue loading using temporal multiscale methods.
First, a continuum damage model for concrete is developed with a focus on fatigue under compressive stresses [1]. This includes the possibility to model stress redistributions and capture size effects. In contrast to cycle based approaches, where damage is accumulated based on the number of full stress cycles, a strain based approach is developed that can capture cyclic degradation under variable loading cycles including different amplitudes and loading frequencies. The model is designed to represent failure under static loading as a particular case of fatigue failure after a single loading cycle. As a consequence, most of the material parameters can be deduced from static tests. Only a limit set of additional constitutive parameters is required to accurately describe the evolution under fatigue loading. Another advantage of the proposed model is the possibility to directly incorporate other multi-physics effects such as creep and shrinkage or thermal loading on the constitutive level.
Second, a multiscale approach in time is presented to enable structural computations of fatigue failure with a reduced computational effort. The damage rate within the short time scale corresponding to a single cycle is computed based on a Fourier based approach [2]. This evolution equation is then solved on the long time scale using different implicit and explicit time integration schemes. Their performance and some limitations for specific loading regimes is discussed.
Finally, the developed methods will be validated and compared to experimental data.
[1] Vitaliy Kindrachuk, Marc Thiele, Jörg F. Unger. Constitutive modeling of creep-fatigue interaction for normal strength concrete under compression, International Journal of Fatigue, 78:81-94, 2015
[2] Vitaliy Kindrachuk, Jörg F. Unger. A Fourier transformation-based temporal integration scheme for viscoplastic solids subjected to fatigue deterioration, International Journal of Fatigue, 100:215-228, 2017
Computational modelling of concrete structures
978-1-138-74117-1
10.1201/9781315182964-19
Conference on Computational Modelling of concrete and concrete structures (EURO_C 2018')
Bad Hofgastein, Austria
26.02.2018
01.03.2018
16.05.2019
Vitaliy Kindrachuk
Thomas Titscher
Volker Hirthammer
Jörg F. Unger
eng
uncontrolled
Fatigue
eng
uncontrolled
Concrete
eng
uncontrolled
Damage
Ingenieurbau
5 Werkstofftechnik
5.2 Metallische Hochtemperaturwerkstoffe
5.5 Materialmodellierung
7 Bauwerkssicherheit
Infrastruktur
Verlagsliteratur
Datei im Netzwerk der BAM verfügbar ("Closed Access")
7.7 Modellierung und Simulation
48001
2018
eng
lecture
0
--
--
--
A continuum damage model for the simulation of concrete under cyclic loading
Lifetime aspects including fatigue failure of concrete structures were traditionally only of minor importance. Because of the growing interest in maxing out the capacities of concrete, its fatigue failure under compression has become an issue. A variety of interacting phenomena such as e.g. loss of prestress, degradation due to chemical reactions or creep and shrinkage influence the fatigue resistance. Failure due to cyclic loads is generally not instantaneous, but characterized by a steady damage accumulation. Therefore, a reliable numerical model to predict the performance of concrete over its lifetime is required, which accurately captures order effects and full three-dimensional stress states.
Many constitutive models for concrete are currently available, which are applicable for specific loading regimes, different time scales and different resolution scales.
However, a key limitation of those models is that they generally do not address issues related to fatigue on a structural level. Very few models can be found in the literature that reproduce deterioration of concrete under repeated loading-unloading cycles. This is due to the computational effort necessary to explicitly resolve every cycle which exceeds the currently available computational resources. The limitation can only be overcome by the application of multiscale methods in time.
The objective of the paper is the development of numerical methods for the simulation of concrete under fatigue loading using temporal multiscale methods.
First, a continuum damage model for concrete is developed with a focus on fatigue under compressive stresses. This includes the possibility to model stress redistributions and capture size effects. In contrast to cycle based approaches, where damage is accumulated based on the number of full stress cycles, a strain based approach is developed that can capture cyclic degradation under variable loading cycles including different amplitudes and loading frequencies. The model is designed to represent failure under static loading as a particular case of fatigue failure after a single loading cycle. As a consequence, most of the material parameters can be deduced from static tests. Only a limit set of additional constitutive parameters is required to accurately describe the evolution under fatigue loading. Another advantage of the proposed model is the possibility to directly incorporate other multi-physics effects such as creep and shrinkage or thermal loading on the constitutive level.
Second, a multiscale approach in time is presented to enable structural computations of fatigue failure with a reduced computational effort. The damage rate within the short time scale corresponding to a single cycle is computed based on a Fourier based approach. This evolution equation is then solved on the long time scale using different implicit and explicit time integration schemes. Their performance and some limitations for specific loading regimes is discussed.
Finally, the developed methods will be validated and compared to experimental data.
Conference on Computational Modelling of concrete and concrete structures (EURO_C 2018')
Bad Hofgastein, Austria
26.02.2018
01.03.2018
false
true
0
Jörg F. Unger
spa
uncontrolled
Fatigue
eng
uncontrolled
Concrete
eng
uncontrolled
Damage
Ingenieurbau
5 Werkstofftechnik
5.2 Metallische Hochtemperaturwerkstoffe
5.5 Materialmodellierung
7 Bauwerkssicherheit
Infrastruktur
Datei im Netzwerk der BAM verfügbar ("Closed Access")
Präsentation
7.7 Modellierung und Simulation
44008
2018
eng
196
214
2
114
article
Wiley
1
--
--
--
A Fourier transformation-based method for gradient-enhanced modeling of fatigue
A key limitation of the most constitutive models that reproduce a Degradation of quasi-brittle materials is that they generally do not address issues related to fatigue. One reason is the huge computational costs to resolve each load cycle on the structural level. The goal of this paper is the development of a temporal Integration scheme, which significantly increases the computational efficiency of the finite element method in comparison to conventional temporal integrations.
The essential constituent of the fatigue model is an implicit gradient-enhanced formulation of the damage rate. The evolution of the field variables is computed as amultiscale Fourier series in time.On a microchronological scale attributed to single cycles, the initial boundary value problem is approximated by linear BVPs with respect to the Fourier coefficients. Using the adaptive cycle jump concept, the obtained damage rates are transferred to a coarsermacrochronological scale associated with the duration of material deterioration. The performance of the developedmethod is hence improved due to an efficient numerical treatment of the microchronological problem in combination with the cycle jump technique on the macrochronological scale. Validation examples demonstrate the convergence of the obtained solutions to the reference simulations while significantly reducing the computational costs.
International journal for numerical methods in engineering
10.1002/nme.5740
1097-0207
0029-5981
29.03.2018
Vitaliy Kindrachuk
Thomas Titscher
Jörg F. Unger
eng
uncontrolled
Accelerated temporal integration
eng
uncontrolled
Fourier series
eng
uncontrolled
Gradient-enhanced fatigue model
Ingenieurwissenschaften und zugeordnete Tätigkeiten
5 Werkstofftechnik
5.2 Metallische Hochtemperaturwerkstoffe
5.5 Materialmodellierung
7 Bauwerkssicherheit
Material
Degradation von Werkstoffen
Verlagsliteratur
Datei im Netzwerk der BAM verfügbar ("Closed Access")
7.0 Abteilungsleitung und andere
46975
2018
eng
lecture
0
--
--
--
A novel computational method for efficient evaluation of structural fatigue
The methods of computational damage mechanics are well-established for the description of degradation of materials under monotone loading. An extension to structural damage induced by cyclic loading is however significantly limited. This is due to enormous computational costs required to resolve each load cycle by conventional temporal incremental integration schemes while a typical fatigue loading history comprises between thousands and millions of cycles. Despite the permanent increase of computational resources and algorithmic performance, a successful approach is rather based on the development of novel multiscale in time integration schemes.
A Fourier transformation-based temporal integration (FTTI) is represented, which takes advantage of temporal scale separation incorporated into the cycle jump method. The response fields are approximated by a Fourier series whose coefficients undergo the evolution on a long-time scale. This is correlated with the evolution of the history variables, including damage, by means of the adaptive cycle jump method of various orders. The necessary extrapolation rates are obtained from the underlying solution of a short-time scale problem, which results from the oscillatory boundary condition and fulfills the global equilibrium of the Fourier coefficients. In this way, a remarkable speedup is achieved because the number of cycles to be fully integrated dramatically decreases.
The key idea behind the FTTI method is that the global in space equilibrium problem is linear since it is decoupled from the evolution equations. The latter are solved in the quadrature points under response fields prescribed throughout the whole load cycle. Consequently, integration of a single load cycle is much more efficient than the conventional single scale integration where the global equilibrium iteration and the local iteration of the evolution equations are coupled. This results in an additional speedup of the FTTI method.
The performance of the FTTI technique is demonstrated for two different constitutive behaviors: a viscoplastic model with a damage variable governed by the local equivalent viscoplastic strain; a quasi-brittle response where the damage variable is driven by a non-local equivalent strain. The latter is implicitly introduced as proposed by Peerlings. Both, the explicit and implicit extrapolation schemes are validated. The FTTI solutions agree very well with the reference cycle-by -cycle solutions, while significantly reducing the computational costs. The adaptive determination of the jump length can properly recognize the particular responses throughout the fatigue loading history (stationary fatigue, acceleration of fatigue damage when approaching failure) as well as stress redistribution phenomena.
International Fatigue International Fatigue International Fatigue International Fatigue International Fatigue International Fatigue Congress Congress Congress 2018
Poitiers, France
27.05.2018
01.06.2018
0
Vitaliy Kindrachuk
eng
uncontrolled
Fatigue
eng
uncontrolled
Accelerated integration scheme
Ingenieurwissenschaften und zugeordnete Tätigkeiten
5 Werkstofftechnik
5.2 Metallische Hochtemperaturwerkstoffe
5.5 Materialmodellierung
7 Bauwerkssicherheit
Material
Degradation von Werkstoffen
Datei im Netzwerk der BAM verfügbar ("Closed Access")
Präsentation
7.0 Abteilungsleitung und andere
46973
2018
eng
lecture
0
--
--
--
A numerical approach to model high-temperature creep behaviour of Ni-base superalloys from microstructural morphology to grain size scales
A constitutive model for the mechanical behaviour of single crystal Ni-base superalloys under high temperature conditions has been developed in the framework of a Cooretec project in cooperation with Siemens AG, MTU Aero Engines AG and University Bayreuth. In addition to the conventional material properties e.g. elastic constants, the model requires the parameters of the initial microstructure as an input. Thus, the γ’-precipitate size and the channel width of the γ-matrix were obtained from SEM micrographs. The model uses the slip system theory and describes the movement, multiplication and annihilation of dislocations in the channels. Furthermore, the cutting of precipitates is another mechanism contributing to the plastic flow. The evolution of the morphology due to rafting and its effects on the deformation have been implemented according to. The kinematic hardening is introduced as a stress tensor to realistically represent the strain hardening of arbitrary oriented single crystals.
The mechanical behaviour of single crystal specimens has been experimentally investigated in tension tests at different strain rates and in creep tests under various loads. The constitutive model has been calibrated based on the experimental data for temperatures of 950°C and 850°C and the [001] and [111] crystallographic orientations.
Finally, a micromechanical model was created to simulate the creep response of additive manufactured polycrystalline structures. An EBSD image is taken to obtain the grain geometry and their respective orientation. The grain boundaries are discretised using cohesive elements, whereas the single crystal model was applied to each grain in the representative volume. The polycrystal model is generated using Dream3D, NetGen and other software previously developed at the BAM.
6th European Conference on Computational Mechanics (ECCM 6)
Glasgow, UK
11.06.2018
15.06.2018
0
Fabian Czediwoda
eng
uncontrolled
Nickel-base superalloy
eng
uncontrolled
Creep
eng
uncontrolled
Rafting
eng
uncontrolled
Viscoplasticity
eng
uncontrolled
EBSD
eng
uncontrolled
Grain boundaries
Ingenieurwissenschaften und zugeordnete Tätigkeiten
5 Werkstofftechnik
5.2 Metallische Hochtemperaturwerkstoffe
5.5 Materialmodellierung
Material
Degradation von Werkstoffen
Datei im Netzwerk der BAM verfügbar ("Closed Access")
Präsentation