h1

TY  - THES
AU  - Gillner, Karl
TI  - Ermittlung der Zeitfestigkeit und zyklischen Rissfortschrittsgeschwindigkeit eines AFP-Stahls aus Mikrostruktursimulationen
VL  - 8/2018
PB  - RWTH Aachen University
VL  - Dissertation
CY  - Aachen
M1  - RWTH-2018-231614
SN  - 978-3-84406232-8
T2  - Berichte aus dem Institut für Eisenhüttenkunde
SP  - 1 Online-Ressource (xxi, 148 Seiten) : Illustrationen
PY  - 2018
N1  - Druckausgabe: 2018. - Auch veröffentlicht auf dem Publikationsserver der RWTH Aachen University 2019
N1  - Dissertation, RWTH Aachen University, 2018
AB  - The experimental determination of fatigue material properties is elaborate. A solution might be given by numerical models. Here in this study, a multiscale numerical approach is presented. The approach correlates the statistical distribution of microstructural properties and their microdeformation behavior with the material's macroscopic fatigue behavior. The solution is used to calculate the high cycle fatigue strength and the cyclic crack propagation rate at different loading ratios. The microstructural properties are modeled with statistically equivalent representative volume elements (RVEs) of the microstructure. Their generation requires statistical distribution functions of the grain size and grain shape as well as the phase fraction of the different phases. The mechanical behavior is modeled for each phase separately. A crystal plasticity (CP) constitutive material model with combined isotropic and kinematic hardening is used to calculate the mechanical response of each grain in dependency of its crystallographic orientation. The crystal plasticity parameter set is inversely calibrated on strain controlled low cycle fatigue tests. The simulation of only few loading cycles with the RVEs and the CP-model are required to obtain local strain fields which can be evaluated for the highest value of grain size averaged accumulated plastic strain. The spot where the highest value of this indicator occurs is evaluated to be the most likely to initiate a lifetime determining fatigue crack. Simulating a large number of these statistically equivalent, although, in detail different RVEs, the indicators are distributed after an extreme value distribution function. The indicator and the parameters of the function are then used to calculate the basis equation, which calculates the number of cycles for crack initiation, and the extrapolation equation, which extrapolates the basis equation to match experimental findings of fatigue properties. In this thesis, the ferritic-pearlitic steel 38MnSiV5 has been used for the generation of the RVEs and the calibration of the CP-model. The validation of the model's outcome has been conducted on high cycle fatigue properties and cyclic crack propagation rates at different loading ratios. The numerically obtained results match the experiments in a very good agreement.
LB  - PUB:(DE-HGF)11 ; PUB:(DE-HGF)3
DO  - DOI:10.18154/RWTH-2018-231614
UR  - https://publications.rwth-aachen.de/record/751774
ER  -