Mechanical Characterization of Solid Oxide Fuel Cells and Sealants

Dislocation creep mechanisms 
Dislocation glide climb, climb controlled 
4-5 
Lattice 
Dislocation glide climb, glide controlled 
3 
Lattice 
Dislocation of dislocation loops 
4 
Lattice 
Dislocation climb without glide 
3 
Lattice 
Dislocation climb by pipe diffusion 
5 
Dislocation core 
Diffusion creep mechanisms 
Vacancy flow through grains 
1 
Lattice 
Vacancy flow through boundaries 
1 
Grain boundary 
Interface reaction control 
2 
Lattice/ Grain boundary 
Grain boundary sliding mechanisms 
Sliding with liquid 
1 
Liquid 
Sliding without liquid ( diffusion control) 
1 
Lattice/grain boundary 
(2) Bending tests
Cell materials for SOFCs are nowadays normally produced by tape-casting to obtain thin layers. 
This shape of the materials makes it difficult to carry out compressive or tensile creep test. 
Hence, flexure bending tests, such as four-bending test are considered as an effective method to 
study the creep of ceramics [153]. They are easy to perform and avoid problems of alignment 
and fixing for the brittle materials. However, creep deformation can be different in tension and 
compression leading to problems in deriving creep data of ceramics from bending tests. 
Hollenberg 
et al.
[154] derived a relationship between creep strain and loading-point deflection 
for steady-state creep with the assumption that the neutral axis passed through the centre of 
cross-sectional area of the specimen. Snowden and Mehrtens [155] modified the expression 
related to the center deflection of specimen, which made the data analysis and experiment 
measurement more simple and convebending.

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Literature review 
37 
Figure 3-24: Schematic of the partly circular bent beam [156]. 
The strain 
𝜀
𝑐
at the center of beam and the relation between the strain 
𝜀
𝑚
in the outer beam and 
the load-point deflection, respectively, can be expressed as [154, 156] :
𝜀
𝑐
=
−ℎ
(
𝑛
𝑛 + 2) (
𝐿 − 𝑎
2 )
2
−
𝐿
2
4
∙ 𝑦
𝑐
(3-12) 
𝜀
𝑚
=
2ℎ (𝑛 + 2)
(𝐿 − 𝑎)[𝐿 + 𝑎(𝑛 + 1)]
∙ 𝑦
𝐿
(3-13) 
where 
𝑦
𝑐 
,