Bienvenue

1
An experimental investigation of mixed-mode
crack growth process in orthotropic viscoelastic
material
() Frédéric Dubois, () Octavian Pop, ()
Rostand Moutou Pitti, () Nicolas Sauvat, ()
Christophe Petit, () Valery Valle
()GEMH, University of Limoges Egletons, France
()LMS, University of Poitiers, France
() Heterogeneous Material Research Group Civil
Engineering and Durability Team
frederic.dubois_at_unilim.fr
() Laboratory of Solid Mechanics
2
An experimental investigation of mixed-mode
crack growth process in orthotropic viscoelastic
material

• Scientific context
• Mixed mode crack growth (2MCG) specimen
• Numerical optimization by the Mq Integral
• Material and experimental setup
• Experimental results
• Conclusions and perspectives

3
Scientific context

• Crack growth process during timber structure live

?
Crack propagation during creep loading
Crack process in joints

• Complex loading
• Viscoelastic behavior

?
Differed mixed mode configuration around the
crack tip
4
Scientific context

• Objectives

Long term loading or creep effects Viscoelastic
effects Shrinkage/swelling effects Mechano-sorptiv
e effects
5
Scientific context

• Crack growth stability G / crack length
  representation

Energy release rate G
Crack growth initiation
Viscoelastic energy
Crack length a
6
Mixed mode crack growth (2MCG) specimen

• New 2MCG specimen crack growth stability for
  mixed mode configuration

7
Mixed mode crack growth (2MCG) specimen

• New 2MCG specimen crack growth stability for
  mixed mode configuration

8
Numerical optimization by the Mq Integral

• Formalism

y
1
x
1
W
9
Numerical optimization by the Mq Integral

• Physical interpretation

10
Numerical optimization by the Mq Integral

• Crack growth stabilization

Virtual displacements for the Mq integral
Open mode
11
Numerical optimization by the Mq Integral

• Crack growth stabilization

Virtual displacements for the Mq integral
Shear mode
12
Numerical optimization by the Mq Integral

• G1 versus crack length in pure open mode

13
Numerical optimization by the Mq Integral

• G1 and G2 versus crack length in mixed mode
  (angle of loading 45)

14
Material and experimental setup

• 2MCG Specimen

• Beech specimen

• Douglas fire specimen

15
Material and experimental setup

• Experimental setup

LVDT sensor
Zwick testing machine with a displacement control
mobile arcan
CCD camera
fixed arcan
16
Material and experimental setup

• Crack tip and marker follow-up

Scale calibration with image analysis and LVDT
response
d
Detection of the crack tip advance
17
Experimental results

• Results in terms of force/displacement

open mode configuration
F
d
crack growth process
18
Experimental results

• Results in terms of force/displacement

mixed mode configuration (b 45)
F
crack growth process
d
19
Experimental results

• Results in terms of force/crack length

Open mode
Mixed mode 45
800
3500
700
3000
600
2500
500
2000
F (N)
400
F(N)
crack stability zone
1500
300
1000
200
500
100
0
0
30
40
50
60
70
80
90
a (mm)
20
and
Conclusions
perspectives

• Validation of the 2MGC specimen design
• Validation of the crack growth stability for
  mixed mode configurations
• Use of the image analysis in the crack advance
  follow-up

• Energy release rate evaluation during the crack
  growth test
• Experimental strain analysis using the image
  correlation method
• Introduce viscoelastic behavior in the
  experimental analysis

21
and
Conclusions
perspectives

• Strain analysis by image correlation

22
An experimental investigation of mixed-mode
crack growth process in orthotropic viscoelastic
material
() Frédéric Dubois, () Octavian Pop, ()
Rostand Moutou Pitti, () Nicolas Sauvat, ()
Christophe Petit, () Valery Valle
Thanks for your attention
()GEMH, University of Limoges Egletons, France
()LMS, University of Poitiers, France
() Heterogeneous Material Research Group Civil
Engineering and Durability Team
frederic.dubois_at_unilim.fr
() Laboratory of Solid Mechanics