Coupling between diffusion of biodiesel and large deformation in elastomers: from experimental investigation to constitutive modeling / Ch'ng Shiau Ying
Due to the concern of limited fossil fuel reserve and stringent emission regulations, there is a tremendous increase in the demand for renewable energy in Malaysia. The introduction of biodiesel is by far considered as the most promising solution. Nevertheless, particular composition of biodiesel...
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| Format: | Thesis |
| Published: |
2014
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| Subjects: | |
| Online Access: | http://studentsrepo.um.edu.my/7591/4/sy_thesis.pdf http://studentsrepo.um.edu.my/7591/ |
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| Summary: | Due to the concern of limited fossil fuel reserve and stringent emission regulations,
there is a tremendous increase in the demand for renewable energy in Malaysia. The
introduction of biodiesel is by far considered as the most promising solution. Nevertheless,
particular composition of biodiesel leads to material compatibility issue especially
in industrial applications involving elastomeric materials. Indeed, it is established that
the exposure of elastomers to biodiesel yields to a material degradation which reduces
their performance. When elastomeric components are subjected to fluctuating mechanical
loading and simultaneously are exposed to aggressive solvent such as biodiesel, two
important aspects may contribute to the material degradations: diffusion of solvents resulting
to swelling and fluctuating mechanical loading leading to fatigue failure. Since the
interactions between the above aspects are not fully understood, it is crucial to investigate
and to model the corresponding coupled diffusion-mechanical deformation phenomenon
for durability analysis of the components. The first part of this thesis focuses on the experimental
investigation on the swelling of elastomers in biodiesel in the absence and in
the presence of static mechanical deformations. The former and the latter are referred
to as free swelling and constrained swelling respectively. To this end, original devices
and specimens are developed so that swelling tests can be conducted on the elastomers
while they are simultaneously subjected to various deformation modes: simple extension,
simple torsion and simultaneous extension/torsion. It is observed that the presence of
static mechanical loading affects significantly the swelling characteristics of elastomers
in biodiesel. Moreover, it is found that when a swollen elastomer is subjected to cyclic
loading conditions, inelastic responses such stress-softening due to Mullins effect, hysteresis
and permanent set decrease as the degree of swelling increases. The second part
of this thesis deals with the continuum mechanical modeling of swelling. First, the theiii
oretical framework of the model consistent with the second law of thermodynamics is
established. More precisely, the proposed model is based on the multiplicative decomposition
of the deformation gradient tensor along with the concept of strain amplification
factor to account for the effect of carbon black filler. Using this theoretical framework,
two particular cases are considered: (1) modeling the Mullins effect in swollen elastomers
and (2) prediction of the equilibrium swelling of elastomers in biodiesel in the absence
and in the presence of static mechanical deformation. It is observed that the model gives
a qualitatively good agreement with experimental observations. Finally, the model for
predicting the equilibrium swelling is implemented as a user-supplied subroutine in the
finite element package ABAQUS to analyze the complex phenomena which occur during
coupled biodiesel diffusion-mechanical deformations in elastomers. |
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