Abstract:
This Thesis focuses on the influence of bimodularity on the strength and the
fracture behaviour of nuclear grade graphite. A new analytical hypothesis includes
bimodular effect to characterize the strength and the fracture parameters have
been proved with the help of experimental and numerical analogy. Weibull
statistical approach has been used to evaluate the effective volume and effective
surface area. The effective volume and effective area are the key step in
estimating reliability of ceramic component life cycle. The most common tests
performed to assess the strength and reliability of components made from nuclear
grade graphite is flexural tests on rectangular and cylindrical cross-sectioned
beam, and C-ring specimen under diametrical compressive and tensile loads. The
ASTM closed form solutions for the effective volume and area exists for these
specimen geometries has been improved for more general bimodular field, which
are based on classical theories with underlying assumptions. In general the closed
form expressions are valid for limited specimen geometry bounds. But, the
alternative numerical approach based on finite element has been utilized to
calculate the effective volume and area for any type of ceramic test specimens.
The results obtained through the use of the numerical approach are compared with
the analytical closed form solutions and these comparisons leads to the conclusion
that the effect of bimodularity has been significant.
The influence of bimodularity on fracture behaviour of graphite specimens has
been studied with the help of fracture toughness (KIc), critical J-integral (JIc) and
critical strain energy release rate (GIc). The crack characterizing parameters
critical stress intensity factor and critical strain energy release rate have been
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estimated with the help of Weibull distribution plot between peak loads versus
cumulative probability of failure. Experimental and Computational fracture
parameters have been compared qualitatively to describe the significance of
bimodularity.
A universal path independent integral
u
J
that represents the energy release rate or
flux during crack extension in a homogeneous and isotropic material, has been
derived for straight and curved crack subjected to multiple loads including
magnetostriction. These integrals are widely applicable in the interacting thermomagneto-elastic problems for aerospace, avionics and nuclear reactor components.
Keywords: Weibull Effective volume, Effective area, Size effect, Bimodularity,
Bimodular 3D J-integral, Contour integral, Fracture toughness, Graphite, Strain
energy release rate, Bimodular FE analysis, Reliability analysis.
