Biaxial bulge testing of thin films and foils
Miroslav CieslarFaculty of Mathematics and Physics
Charles University, Prague
Czech Republic
J.L. Martin, A. Karimi: EPFL Lausanne, SwitzerlandC. Fressengeas: LPMM, Université de Metz, France
Schedule
• Introduction to small structure testing
• Bulge test
• Applications– Recrystallization of thin foils– Plastic instabilities in Al foils– Plastic deformation of thin metallic films
Most common experimental methods
• Films adhered to substrate– Nanoindentation (hardness, modulus)– Microbeam bending (fatigue, bending)– Wafer curvature (biaxial strain, thermal fatigue)
• Free standing films– Tensile test (difficult sample preparation)– Microbeam bending – Biaxial bulge test
Industrial requirements for reliable biaxial tests
Biaxial bulge test
Testing of membranes in micro- and nano-devices
Finstocks for heat exchangers
Biaxial test with a constant fluid flow-rate
0
20
40
60
80
100
120
0 200 400 600 800 1000 1200 1400 1600
Time [s]
Str
ess [
MP
a]
0.00022 ml/s
0.00130 ml/s
0.00260 ml/s
0.00433 ml/s
Time [s]
Str
ess
[MP
a]
Biaxial test under constant stress-rate
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
3
0 100 200 300 400 500 600 700 800
Time [s]
Str
ess r
ate
[M
Pa/s
]
0.00022 ml/s
0.00130 ml/s
0.00260 ml/s
0.00433 ml/s
Time [s]
Str
ess-
rate
[M
Pa/
s]
Examples
• Thin Al-Fe-Si foils (thickness 8.5 m)
Element Fe Si Cu Mn Mg Zn Ti Al
wt. % 0.51 0.61 0.007 0.020 0.0066 0.022 0.024 bal.
Stress – strain curves obtained from bulge tests during prestraining and after annealing at indicated
temperatures.
Recrystallization of thin foils
Plastic instabilities in Al–Fe-Si foils
0
50
100
150
0 0.8 1.6 2.4 3.2
as received
590 °C
630 °C
stre
ss [
MP
a]
strain [%]
Instabilities after strain rate jump
0
30
60
90
120
0 0.75 1.5 2.25
stre
ss [
MP
a]
strain [%]
as received
TA = 590°C
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Instabilities after an instant increase of stress
by 3 MPa
0
30
60
90
120
0 1 2
TD = R.T.
TD = 120°C
stre
ss [
MP
a]
strain [%]
Thin film plastic deformation
Biaxial plastic deformation of Al thin films
0
40
80
120
160
0 0.2 0.4 0.6
stre
ss [
MP
a]
Strain [%]
0.55 m
1.1 m
4.4 m
TD=R.T.
60
80
100
120
140
160
180
0.4 0.6 0.8 1 1.2 1.4
Rp0.
2 [M
Pa]
d-1/2
[m-1/2
]
Al 5N5
TA = 450 °C
TD = R.T.
Biaxial plastic deformation of Al thin films
Influence of temperature
70
80
90
100
110
120
130
0 50 100 150 200 250
Rp0.
2 [M
Pa]
deformation temperature [°C]
Al 5N5
TA= 450 °C
1.1 m
Biaxial plastic deformation of Al thin films
Creep-fatigue tests
0.2
0.3
0.4
0.5
0.6
0.7
0 20 40 60 80 100 120
stra
in m
ax.
[%]
cycle
Al 5N51.1 m
TD= R.T.
96
100
104
108
112
0.26 0.28 0.3 0.32 0.34
stre
ss [
MP
a]
strain [%]
Al 5N5
TD= R.T.1.1 m
Variation of maximum strain with the number of cycles
Deformation loops received during cycling
Deformation processes in Al-Zn-Mg-Cu thin films
4 m thin films from AA 7075 alloy
0
100
200
300
400
500
600
0 0.5 1 1.5 2
as depositedT
A=350°C, T
D=R.T.
TA=350°C, T
D=120°C
TA=350°C, T
D=160°C
TA=350°C, T
D=200°C
TA=350°C, T
D=280°C
stre
ss [
MP
a]
strain [%]
0
100
200
300
400
500
600
0 50 100 150 200 250 300
Rp
0.2
[M
Pa]
Deformation temperature [°C]
Al-Zn-Mg-Cu
TA = 350 °C