Mechanical Characterization of Solid Oxide Fuel Cells and Sealants

 
(ISO13124 standard) [122, 123]
. 
Schwickert [124] reported on sealant-metal joints to measure the shear stress. The tests were 
performed in cooperation with the IWM in Freiburg, Germany. The simple shear test specimen is 
shown in 
Figure
3-15
 (
a)
, however, again loading in a combined bending – shear mode can be 
expected.
While not only the shear stress can be determined during the shear test, shear modulus, internal 
stress and viscosity have been also determined on Jülich sealant using a symmetric shear test at 
SOFC operation temperature.[125]. A schematic drawing of the symmetric shear test specimen is 
shown in 
Figure
 3-15
 (
b)
.

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Literature review 
28 
(a)
(b)
Figure 3-15: Schematic drawing of (a) sealant-metal jointed shear test specimen [124];(b) the 
symmetric shear test [125].
A torsion test is considered as an effective way to measure the shear strength [87]. Ferraris et al. 
[123] proposed some modifications of the torsion test and
aiming at a measurement of the pure 
shear strength of the joints [121]. A modified hourglass shaped configuration has been designed. 
The configuration is shown in 
Figure
3-16
. It has been successfully used on SiC and glass-
ceramic materials [121, 123]. However, since their torsion set-up was limited to RT, a new 
torsion set-up has been developed at Jülich, which aims at a measurement of the shear strenght of 
sealants also at high temperatures. In the current work some typical SOFC sealants were tested at 
RT and elevated temperatures.
Figure 3-16: Experimental set-up and specimen for torsion test [122]. 
 

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Literature review 
29 
3.4.3. Fracture toughness 
Ceramic and ceramic composites can have a rather high strength but also a quite low crack 
resistance at the same time [126]. The crack resistance, which is proportional to the fracture 
toughness, is critical for ceramic components as used as cell in SOFCs operating under extreme 
mechanical and thermal loads. Hence, fracture toughness is an important property of advance 
ceramics and is one measure of brittleness and crack resistance [127].
A crack can be loaded three ways, termed mode Ι, II, III as illustrating in 
Figure
 3-17
. Mode Ι is 
an opening mode, while mode П and mode Ш are in-plane and out-of-plane shear mode, 
respectively [128].
Figure 3-17: