influence of loading history on plasticity induced closure

Influence of loading history on plasticity induced closure and shape of a
fatigue crack: comparison between experiments and numerical modeling
Introduction.
This subject is part of the studies concerning the degradation due to thermal fatigue of structural parts
in nuclear power plants. These numerous studies were decided after an incident that has occurred in
the French Civaux nuclear power plant (located only 30km from our institute) in May 1998: a fatigue
crack was detected in the cooling system of the reactor.
In this context, the laboratory has, in a first step, brought its contribution in modeling the propagation
of a physically short crack (short in the depth, but relatively long on the surface) as this geometry is
widely observed in thermal crack network: the propagation of such a bidimensional short crack has
been carefully studied taking into account the plasticity induced crack closure in an austenitic 304L
stainless steel.
Scientific background.
These first three-dimensional finite element calculations realized with the Abaqus software, with the
progressive reconstruction of the plastic wake at the origin of closure, were based on the assumption
of a linear crack front shape. The conditions of arrest (or not) of the propagation of a single crack
have then been defined with a good correlation between the numerical prediction and the experimental
characterization of opening kinetics related to a variation in the compliance. Nevertheless, these results
were not in agreement with a constant amplitude of the stress intensity factor range ∆Keff at the crack
tip, and consequently with the concept of a propagation governed by this ∆Keff amplitude: this was
contradictory this results of numerous authors following initial works of Elber.
In order to go further, numerical simulations aiming at taking into account the shape of real crack have
been done. First, tests conducted alternatively under air and vacuum environment have allowed
characterizing precisely the crack shape for a loading corresponding to a constant value of the stress
intensity factor range ∆K. through a simplified approach consisting in considering arc of circle
geometrical shapes, an important influence of the crack front shape on the closure phenomena has
been demonstrated: the curvature seems to standardize the ∆Keff amplitude along the crack front. In
order to characterize more precisely the description of the crack shape, additional work has been done
in order to introduce an automated numerical remeshing aiming at predicting the change in crack front
shape during crack propagation. A PhD is under progress (ending at the end of 2014) on this topic in
the limited frame of propagation under a constant value of the stress intensity factor range. The
obtained results are very promising, and support the assumption that the crack curvature can be
controlled by a constant value of the effective stress intensity factor range ∆Keff. Nevertheless, the
complexity of the problem (propagation under mechanical cycling in mode I, plastic behavior law
combining isotropic and kinematic hardening, evolution of crack closure throughout test, remeshing at
each step) implies a detailed study of the possible influence of different parameters on crack evolution,
particularly in the case of loading conditions close to industrial ones.
Objectives of the PhD.
The objectives of the proposed PhD are to continue the development of the numerical tool of the
previous PhD, in order to obtain an automatic configuration of the crack front in agreement with crack
fronts resulting from tests made under different loading conditions with resulting plastic wakes
depending on loading history : propagation under constant load (increasing ∆K), threshold test
(decreasing ∆K), different load ratio R, variable amplitude (single overload, repeated overloads,
change in level (low-high, high-low). The final aim is to obtain a numerical tool integrating concepts
allowing to describe fatigue crack propagation in a structure in loading conditions close to real ones.
References of the supervisors concerning this subject.
Published paper in an international review with peer review
Vor, K., C. Gardin, et al. (2013). "Wake length and loading history effects on crack closure of
through-thickness long and short cracks in 304L: Part I - Experiments." Engineering
Fracture Mechanics 99(February 2013): 266-277.
Vor, K., C. Gardin, et al. (2013). "Wake length and loading history effects on crack closure of
through-thickness long and short cracks in 304L: Part II - 3D numerical simulation."
Engineering Fracture Mechanics 99: 306-323.
Fiordalisi, S., C. Gardin, et al. (2013). "Influence of crack shape on 3D numerical modeling of
plasticity-induced closure of short and long fatigue cracks." Key engineering materials
577-578: 213-216.
Vor, K., C. Gardin, et al. (2010). "Evolution de la contribution de la fermeture pour les
fissures courtes 2D dans un acier inoxydable 304L." Revue de Métallurgie - Cahiers
d'Informations techniques 107(1): 21-26.
Vor, K., C. Sarrazin - Baudoux, et al. (2009). Prestrain influence on fatigue crack propagation
in a 304L stainless steel. 2009 ASME Pressure vessels and piping conference, july
2009, Prague, Czech Republic.
International conferences
Gardin, C., S. Fiordalisi, et al. (2014). 3D numerical study on how the local effective stress
intensity factor range can explain the fatigue crack front shape. 11th International
Fatigue Congress, published in Advanced Materials research, vol. 891-892,
Melbourne, Australia.
Gardin, C., C. Sarrazin - Baudoux, et al. (2013). Numerical approach of the influence of crack
front shape on plasticity-induced crack closure in 304L steel. ESIS TC1 Spring
Meeting 2013, Workshop on “Crack Closure Effects in Fatigue Crack Propagation”
Porto, Portugal.
Gardin, C., K. Vor, et al. (2012). Three-dimensional modelling of plasticity-induced crack
closure in a 304L stainless steel : influence of crack length and crack shape. 19th
European Conference on Fracture (ECF19), Kazan, Russia.
Sarrazin - Baudoux, C., C. Gardin, et al. (2010). History effect on closure of short and long
fatigue crack in 304L stainless steel. International Conference on Fatigue Damage of
Structural Materials VIII, September 2010, Hyannis, USA.
Vor, K., C. Sarrazin - Baudoux, et al. (2010). Wake history effect on closure of short and long
fatigue crack in 304L stainless steel. Fatigue 2010, Prague.
Vor, K., C. Sarrazin - Baudoux, et al. (2009). Effect of short crack on closure behavior in a
304L austenitic stainless steel. International Conference of Fracture 12, Ottawa.
National conferences
Arzaghi, M., C. Gardin, et al. (2011). Modélisation sous Abaqus de la fermeture de fissures
courtes dans un acier inoxydable 304L. Congrès Français de Mécanique, Besançon,
France.
Vor, K., C. Gardin, et al. (2009). Evolution de la contribution de la fermeture pour les fissures
courtes 2D dans un acier inoxydable austénitique. Mesures et suivi de
l'endommagement en fatigue, Paris, mai 09, SF2M.
Vor, K., C. Sarrazin-Baudoux, et al. (2009). Effet de fissure courte sur la fermeture dans un
acier inoxydable 304L. CFM’09 XIXème congrès Français de Mécanique, Marseille,
août 2009.
Vor, K., C. Sarrazin - Baudoux, et al. (2008). Effect of prestrain on the fatigue crack
propagation in a 304L stainless steel. proc. 26èmes Journées de Printemps de la
SF2M, Paris.
Contractual reports
Vor, K., C. Gardin, et al. (2008). Etude de la propagation en fatigue de fissures courtes en
stade II : influence du mode de sollicitation et de la taille de la zone plastifiée initiale,
rapport final du contrat CQN01812 EDF- LMPM ENSMA.
PhD
Vor, K. (2009). Etude expérimentale et modélisation numérique de la fermeture de fissures
longues et courtes dans un acier inoxydable 304L. Ecole doctorale : Sciences pour
l'Ingénieur et Aéronautique - section de recherche : Mécanique des Solides, des
Matériaux, des Structures et des Surfaces. Poitiers Chasseneuil, Poitiers Ensma.