| Περιγραφή: |
High-cycle fatigue is considered as one of the most common failure mechanisms of
steel components in civil and mechanical systems that operate under repeated
(cyclic) loading conditions. Over the last decades, several methodologies have
been proposed for the design and assessment of steel components against highcycle
fatigue, and commercial software p rograms have been developed to assist
engineers predicting the fatigue life of steel components under cyclic loading. The
scope of the present research effort is to revisit the problem of high-cycle fatigue of
steel components and propose a novel numerical methodology for the simulation of crack
growth, based on the “cohesive element” concept.
The dissertation describes the development of a novel and effective numerical
algorithm, capable of predicting the position of crack tip, the direction of crack
propagation and the crack growth rate in steel components. The methodology
combines the use of “cohesive elements” with the calculation of J-integral around the
crack tip, and proposes robust techniques for cyclic skipping and for material
calibration through experimental data. The main research novelties of the
p r e s e n t dissertation can be summarized as follows:
• A modification of existing cohesive element methodology, widely used for
fracture under monotonic loading conditions, has been developed to account
for cyclic (repeated) loading. The proposed algori thm for damage
accumulation is simple and efficient, allowing for automatic and
straightforward calibration of the cohesive law, using the experimental data
from a crack growth rate test (ΔΚ-da/dN) or Paris-law parameters.
• A novel cyclic skipping methodology is proposed, which uses the J-integral
calculation of stress intensity factor and the cohesive element length to
estimate the loading cycles required for the crack to propagate over an
element length within the steel material.
• The developed algorithm is capable of predicting automatically the position
of crack tip, the direction of crack propagation and the crack growth rate,
without re-meshing or consecutive analyses. Furthermore, the crack length is
evaluated at the end of each increment of the analysis.
• The calculation of stress intensity factor is totally automatic. The algorithm is
capable to identify the location of crack tip, and to calculate the appropriate
element paths around the crack tip for J-integral.
• Experimental tests have also been conducted in the laboratory, including
CTOD tests and crack growth r a t e tests, in CT-specimens and in SENBspecimens,
for the efficient calibration of the cohesive law, and
the verification of the developed numerical algorithm.
Δρ. Σπύρος Α. Καραμάνος, Επιβλέπων Καθηγητής |
