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Logo: International Research and Training Group IRTG1627/Leibniz Universität Hannover
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Logo: International Research and Training Group IRTG1627/Leibniz Universität Hannover
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Computational Modeling of Fatigue in Solids - General Concepts, State of the Art, Current Research Activities

Lecturer: Prof. Udo Nackenhorst

Institute of Mechanics and Computational Mechanics

Abstract

Fatigue is a phenomenon of degradation of mechanical properties of materials under cyclic
loading. Classical concepts are based on phenomenological descriptions based on standardi-
zed experiments, like S-N-curves etc. This presentation aims on the introduction into more
physical based computational concepts on modeling fatigue of materials and structures;
considering general 3D stress states and arbitrary loading conditions.
Based on the classical balance laws of continuum mechanics the thermodynamic consistent
framework of constitutive theory of materials will be reviewed. For the description of history
dependent material behavior the concept of internal variables will be introduced and esta-
blished computational schemes for the integration of related kinetic equations, which have
been derived from thermodynamic principles, will be presented.
The physical ideas behind damage mechanics will be introduced; however, for simplicity of
this presentation we will restrict ourselves for quasi-isotropic modeling for simplicity. The
challenge for the transition from damage mechanics to fatigue simulation consists in the
efficient numerical treatment of a huge number of load cycles, each of it has to be tackled by
a non-linear finite element computation for a civil engineering structure, lets say a highway
bridge. A further challenge can be identified from the stochastic variability of materials
constitutive behavior, especially in civil engineering buildings (s.o).
Thus, current research activities focus on model reduction techniques for the efficient treat-
ment of huge numbers of load cycles (high cycle fatigue) as well as related techniques to
tackle uncertainties for the prediction of the probability structural lifetime.

Venue: Seminar room 220 (2nd floor of the skyscraper, Appelstrae 9a)
Date: 11-08-2017
Time: 2 pm

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