dc.description.abstract |
Functionally graded materials (FGM) are composite materials with microstructure
gradation optimized for the functioning of engineering components. For the case of
fibrous composites, the fibre density is varied spatially, leading to variable material
properties tailored to specific optimization requirements. There is an increasing demand
for the use of such intelligent materials in space and aircraft industries. The current
preferred methods to study engineering components made of FGM are mainly
modelling particularly those that are finite element (FE) based as experimental methods
have not yet sufficiently matured. Hence this thesis reports the development of a new
Mindlin-type element and new Reissner-type element for the FE modelling of
functionally graded composite (FGC) structures subjected to various loadings such as
tensile loading, in-plane bending and out-of-plane bending, buckling and free vibration.
The Mindlin-type element formulation is based on averaging of transverse shear
distribution over plate thickness using Lagrangian interpolation. Two types of Mindlintype
element were developed in this report. The properties of the first Mindlin-type
element (i.e. Average Mindlin-type element) are computed by using an average fibre
distribution technique which averages the macro-mechanical properties over each
element. The properties of the second Mindlin-type element (i.e. Smooth Mindlin-type
element) are computed by using a smooth fibre distribution technique, which directly
uses the macro-mechanical properties at Gaussian quadrature points of each element.
The Reissner-type element formulation is based on parabolic transverse shear
distribution over plate thickness using Lagrangian and Hermitian interpolation. Two
types of Reissner-type element were developed in this report, which include the
Average and Smooth Reissner-type elements.
There were two types of non-linearity considered in the modelling of the composite
structures, which include finite strain and material degradation. The composite
structures considered in this paper are functionally graded in a single direction only, but
the FE code developed is capable of analysing composite structures with multidirectional
functional gradation. This study was able to show that the structural
integrity enhancement and strength maximisation of composite structures are achievable
through functional gradation of material properties over the composite structures. |
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