Mécanique linéaire élastique de la rupture (rupture fragile) tridimensionnelle: de la théorie à la pratique Three-dimensional linear elastic fracture mechanics (brittle fracture): from theory to practice Habilitation à Diriger des Recherches Véronique Lazarus Laboratoire FAST, UPMC Univ Paris 6 Tuesday 6th of July 2010 1
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Mécanique linéaire élastique de la rupture (rupture fragile)tridimensionnelle: de la théorie à la pratique
Three-dimensional linear elastic fracture mechanics (brittlefracture): from theory to practiceHabilitation à Diriger des Recherches
Véronique Lazarus
Laboratoire FAST, UPMC Univ Paris 6
Tuesday 6th of July 2010
1
CV
1991-1994 Engineering degree.Ecole Nationale Supérieure de Techniques Avancées.
1994 DEA (Postgraduate degree)in Mechanical Engineering (University of Paris 6).
1994-1997 PhD in Mechanical engineering at the Laboratoire deModélisation en Mécanique (Paris 6).Advisor: J.-B. Leblond.“Some three-dimensional problems of brittle fracturemechanics”.
1997–98 ATER at University of Paris 6.1998– Associate professor at University Paris 6.
2
Teaching
Almost 2200 teaching hours.60% practical (TD), 20% numerical work (TP num), 20% Lab work (TP exp),20% courses.
I Continuum thermomechanics.I Solid mechanics.I Fluid mechanics.I Mathematics.I History of sciencesI Computer science.
3
Research
1994–2006 Laboratoire de Modélisation en Mécanique (LMM),incorporated in 2007 into the Institut Jean Le Rondd’Alembert (IJLRDA, UMR 7190).Mechanics of Solids and Structures Team.
2006–2008 Institut Jean Le Rond d’Alembert and FASTlaboratoryduring teaching sabbatical leave (3 X 6 months, CRCT,Delegation CNRS).
2008– Laboratoire Fluides, Automatique et SystèmesThermiques (FAST, UMR 7108).Porous and Fractured Media Team.
4
Publications
I 21 articles in peer-reviewed journals(7 J Mech Phys Solids, 4 Int J Solids Struct, 3 Cr Acad Sci II B, 2 Int JFracture, 1 Phys Rev E, 1 EPL-Europhys Lett, 1 Langmuir, 1 J ApplMech-T ASME, 1 Reflets de la Physique).
I 13 articles in International Conference proceedings.I 2 successful ANR and 2 successful Triangle de la Physique funding
requests.
5
PhD students
I On 3D LEFM theory with J.B. Leblond:09/2001-10/2005 Elie FAVIER.09/2005-07/2009 Nadjime PINDRA .09/2008– Laurène LEGRAND.
I On drying of colloidal suspensions with L. Pauchard:2007 Cécile BOUSQUET. Industrial PhD, CEA
Marcoule.10/2007– Mourad CHEKCHAKI.
6
Brittle Fracture mechanics (LEFM): History
I Starting point: Cracked Liberty ship (second World War).I Griffith 20’s→ Irwin 50’s (Naval research Laboratory).I Failure occurs for small strains and negligible plasticity.
(glass, metal at low temperatures, rocks...).
7
Brittle Fracture mechanics: the aims
Take an elastic loaded body:
1. Will a crack appear?
2. If yes, can we predict its shape? Can we predict the number of radialcracks?
3. If cracks are present, will they propagate, over which distance? until thetotal breakdown of the body?
4. Can we predict the crack front shape?
8
Brittle Fracture mechanics: the aims
JL Prensier
Take an elastic loaded body:1. Will a crack appear?2. If yes, can we predict its shape? Can we predict the number of radial
cracks?3. If cracks are present, will they propagate, over which distance? until the
total breakdown of the body?4. Can we predict the crack front shape?
8
Brittle Fracture mechanics: the aims
JL Prensier
Take an elastic loaded body:1. Will a crack appear?2. If yes, can we predict its shape? Can we predict the number of radial
cracks?3. If cracks are present, will they propagate, over which distance? until the
total breakdown of the body?4. Can we predict the crack front shape?
8
Brittle Fracture mechanics: the aims
J Tignon
Take an elastic loaded body:1. Will a crack appear?2. If yes, can we predict its shape? Can we predict the number of radial
cracks?3. If cracks are present, will they propagate, over which distance? until the
total breakdown of the body?4. Can we predict the crack front shape?
8
Outline
1. Bases (Irwin 1950-)
If cracks are present, will they propagate, over which distance? until thetotal breakdown of the body?
2. Deformation of the crack front (Rice 1985-)
Can we predict the crack front shape?
3. Crack initiation (2000’s)
Will a crack appear?If yes, can we predict its shape? Can we predict the number of radialcracks?
9
Traditional LEFM approach
~up
∂Ωt
∂Ωu
~T p
s~e2(s)
~e1
F
~e3(s)
E , ν
Linear Elastic material. Condition of crack propagation?
10
Definition of the Stress Intensity Factors
~e12
~e2
31
process zone
rM
Westergaard (1938), Williams (1952), Leblond and Torlai (1992):
The stationnary shape is nearly elliptical with:ab
= (1− ν)ββ+1
ab
= (1− ν) if β 1 (G = Gc)
Favier, Lazarus, Leblond (IJSS, 2006)
24
The configuration stability problem
x
y
z
I Problem: circular, straight cracks are often used in engineering, is itsafe?
I If the crack front is perturbed, will the perturbation increases (instable) ordecreases (stable) in time?
This stability problem has been studied byI Rice and Gao (1985-1990) for circular and half-plane cracksI Lazarus and Leblond (1998) for the interfacial half-plane crackI Leblond, Favier, Pindra, Lazarus, Mouchrif, Perrin (1996-) for
tunnel-cracks
25
Straight front stability in mode 1: unperturbed problem
x
y
z
K = cst , α = 0
z
x
y
a
−σ
σ
K = 2q
2πσa1/2, α = 1/2
z
x
y
aP
−P
K =q
2πPa−1/2, α = −1/2
K (a) = kaα
I if α > 0,dK (a)
da> 0 : instable propagation at constant loading.
I if α < 0,dK (a)
da< 0 : stable propagation at constant loading.
26
Model problems: SIF along the perturbed configuration
x
y
z
a
δ(z)
δK (z)
K (a)= α
δ(z)
a+
12π
PVZ ∞−∞
δ(z′)− δ(z)
(z′ − z)2 dz′
In Fourier transform along z−axis:
δbK (k)
K (a)=
„α− ka
2
« bδ(k)
ak wavenumber
27
Stability of the crack shape. Case α < 0,dK (a)
da< 0.
Then α− ka2< 0 whatever the value of k .
Since,δbK (k)
K (a)=
„α− ka
2
« bδ(k)
a
it implies that any perturbation disappears.
B
Aλ
a
λ aK (A) < K (B)
a λ
A
B
λ aK (A) < K (B)
28
Stability of the crack shape. Case α > 0,dK (a)
da> 0.
λ aK (A) < K (B)
B
Aλ
a
λ aK (A) > K (B)
a λ
A
B
29
Stability of the crack shape. Case α > 0.
Stabilityλ < λc
K (A) < K (B)
B
Aλ
a
Bifurcationλ = λc = λ∗c aK (A) = K (B)
where
λ∗c =π
α
Instabilityλ > λc
K (A) > K (B)
a λ
A
B
Since λc = λ∗c a with a, ultimately any perturbation tends to disappear.If :
I The first order approach remains validI The fracture properties are homogeneous...
30
Crack propagation in heterogeneous media
Crack front shape such as K (x , z) = Kc(x , z), ∀(x , z) ∈ F?For slightly toughness heterogeneities:Kc(z, x) = Kc(1 + ∆Kc(z, x)), |∆Kc | 1:
δ(k , a) = −ad∆Kc(k , a)ka2− α
Meaningless if α ≥ 0 due to the existence of a bifurcation
⇒ α < 0 in the sequel.
Application to
1. Crack trapping by obstacles
2. Crack propagation in disordered medium
31
Application to the crack trapping
y
z
Kc
Kc(1 + ∆Kc)
1. Gao and Rice (1989, 1991)
2. Dalmas, Barthel, Vandembroucq (2009)
3. ANR MEPHYSTARTheory: S. Patinet, postdoc with V. Lazarus D. Vandembroucq.Experiments: L. Alzate (PhD D. Dalmas, St Gobain)
32
Application to disordered medium.
δ(k , a) = −ad∆Kc(k , a)ka2− α
I Power spectrum of the crack front fluctuations:
|δ(k , a)|2 = a2 |d∆Kc(k)|2„|α|+ ka
2
«2
as a function of |d∆Kc(k)|2 power spectrum of the toughness fluctuations∆Kc .
I If |d∆Kc(k)|2 = cst = bK0 (white noise), one obtains:
|δ(k , a)|2bK0a2=
1„|α|+ ka
2
«2
which corresponds to a Family-Viscek (1985) scaling ζ = 0.5 and τ = 1.
33
Application to disordered media. Other results
I Interfacial/homogeneous: minor influence.
Pindra, Lazarus, Leblond, JMPS 2008.I Mode mixity: minor influence
Pindra, Lazarus, Leblond, JMPS 2010I Tunnel-crack/half-plane crack: minor influenceI Loading α: MAJOR influenceI Irwin/Paris law: MAJOR influence with a memory effect
bδ(k , a) =
Z a
a0
»exp(−ka/2)
exp(−ka′/2)
–2β “ aa′”βcδc(k , a′) da′,
Lazarus and Leblond (2002); Favier, Lazarus and Leblond (JMPS, 2006).
Statistical physics approach:Daguier, Bouchaud and Lapasset (1995), Schmittbuhl, Maloy et al.(1995-2010), Ramanatha, Fisher, Ertas (1997), Krauth and Rosso (2002),Hansen et al. (2003), Roux, Vandembroucq, Hild, (2003), Katzav etAdda-Bedia (2006), Ponson (2007), Bonamy (2009)...
34
Interaction between several cracks
I Interaction between two tunnel-cracks:
I Determination of Wij for two-tunnel cracks (Pindra, Lazarus, Leblond, 2010)
I Bifurcation wavelength λc = λ∗a when a (Legrand, Leblond, 2010).
2a2b 2b
σ
I Extension of the code PlaneCracks for two cracks (PhD of L. Legrand).
35
Comparison of PlaneCracks with experiments
Lazarus (2003) Dupeux et al. (1998)
Collaboration envisaged with Muriel Braccini (SIMAP, Grenoble).One crack, interaction of two cracks (L. Legrand).
36
Heterogeneous media: comparison with experiments
D. Dalmas and D. VandembroucqANR Mephystar J. Schmittbuhl et al.
37
Outline
Bases of the LEFM approach
Deformation of the crack front shape
Crack initiation
Conclusion
38
JL Prensier
1. Will a crack appear?
2. If yes, can we predict its shape?
39
Variational approach to fracture.Bourdin, Francfort and Marigo (1998-2008)
PrincipleF cracks such as Etot (F) ≡ Eelastic(F) + Gc length(F) is minimum.
I Identical to the traditional approach if a crack is still present.I Applicable only if an “idea” of the crack shape.
Regularized form: Non-local damage modelα(M) damage field such as Etot (α) ≡ Eelastic(α) + Gc f (α, `) is minimum.
where f (α, `) chosen such as lim`→0 f (α, `) = length(F).I Convergence toward the initial principle for `→ 0.I Suitable for numerical purposes.
40
Directional drying in capillary cells
Gauthier, Lazarus and Pauchard(Langmuir 2007, EPL 2010)
silica particles (diameter ∼ 10 nm).I Drying from the single bottom open edge.I Contraction prevent by adhesion⇒ tensile stresses⇒ vertical star-shaped cracks.
I Variation of the drying conditions⇒various number n of radial cracks