Unstable
1.2
a, εp =1.3%
σr = 20 M
Pa, ε =1
.1%
p
1
0.8
Stable
Normalized Strain Energy Release Rate
σr = 20 MP
σr = 20 MPa
, εp=0.65%
0.6
0.4
0.2
0
2
σr = 20 MPa, ε =0
p
σr = 0, εp=0
4
6
8
Adherend Thickness - H [mm]
10
Fig. 1. The directional stability of cracks in DCB specimens predicted using
the energy balance model in reference [12]. The strain energy available is
normalized to Gc = 310 J/m2
136
P
L = 200 mm
F
Adherend
s
Adhesive
t = 0.5 mm
H = 4.8 mm
F
a0 = 100 mm
P
r
θ
Adhesive
Mesh around the crack-tip
y
Fig. 2. The DCB specimen geometry used in the finite element analysis to determine the crack
propagation behavior after the kinking occurred. The insert is the mesh around the crack-tip.
x
137
Phase Angle – Ψ [degree]
5
s/t
1
2
3
4
-5
-15
α = 0.97
α = 0.92
α = 0.84
α = 0.74
-25
Fig. 3. The phase angle at the crack tip versus the normalized kinked crack length s/t
for different materials combinations obtained from the parametric study.
5
138
4.0 t
3.0 t
Adherend
Adhesive
Adherend
2.2 t
1.7 t
Initial kink
α = 0.97
t
0.92
0.84
0.74
2-3t
3-4t
3.5 - 5 t
4.5 - 6 t
Fig. 4. The crack trajectories of directionally unstable crack propagation for different materials systems
predicted using the finite element analysis.
139
1 m/s
b
Fig. 5. The failure surfaces of the DCB specimens prepared using acetone wipe (a) and P2
etch (b), respectively. The
indicates the areas where XPS analyses were conducted.
10-5 m/s
10-5 m/s
1 m/s
1 m/s
1 m/s
10-5 m/s
10-5 m/s
a
140
Acetone wiped side
Top view
P2 etched side
Acetone wiped side
Side view
P2 etched side
Direction of crack propagation
Fig. 6. The failure surfaces and the crack trajectory of the DCB specimen with asymmetric surface
preparation. The
indicates the areas where XPS and Auger analyses were conducted.
141
Fracture Toughness - Gc [J/m2]
400
300
200
100
0
A
0% rubber
B
4.1% rubber
C
8.1% rubber
D
15% rubber
Fig. 7. The fracture toughness of the DCB specimens using adhesives with different levels of rubber
concentrations. Error bars represent ± 1 standard deviation.
142
(a)
A (0% rubber)
(b)
B (4.1% rubber)
(c)
C ( 8.1% rubber)
(d)
E (15.0% rubber)
Fig. 8. The failure surfaces of the as-produced DCB specimens prepared using different adhesives.
143
(a)
B (4.1% rubber)
(b)
C (8.1% rubber)
(c)
E (15.0% rubber)
144
Fig. 9. The failure surfaces of the DCB specimens prepared using different adhesives. All the specimens
contained 1.1% plastic deformation in the adherends