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Micro - and macro - mechanical properties of aerospace composite structures and their dynamic behaviour

Njuguna, J. A. K. (2006). Micro - and macro - mechanical properties of aerospace composite structures and their dynamic behaviour. (Unpublished Doctoral thesis, City, University of London)


The research presented in this thesis focuses on the micro- and macro-mechanical properties of aerospace composite structures, and their buckling, free vibration, and flutter behaviour. The first part of the thesis concentrates on fundamental experimental research into prediction and enrichment of polymers composites with nanoparticles with particular emphasis on polyurethane and polyaniline. To this end, a conducting thermoplastic elastomer is developed and characterised using physiochemical methods for thermo-mechanical properties. Consequently, a sophisticated new polyurethane nanocomposite elastomer with improved mechanical and thermal properties is developed.

The second part of the thesis is a development of an accurate dynamic stiffness matrix for a three-layered sandwich beam of asymmetric cross-section using the Timoshenko beam theory, Hamiltonian mechanics and symbolic computation. The resulting dynamic stiffness matrix is used to investigate the free vibration characteristics of a number of sandwich beams examples and their results are validated by experiment. Next, a detailed analysis is carried out to establish the rigidity properties (stiffnesses) of fibre reinforced composite structures with particular emphasis on solid rectangular and thin-walled box section. The effect of ply orientation on rigidity properties and the consequent coupling between various modes of deformation is studied. Buckling analysis is carried out to provide an estimate of the stiffnesses. Free vibration investigations on flat and box carbon fibre-reinforced composite beams are then carried out to gain important insights into the material- geometrical coupling effects, and modal interchange in bending-torsion coupled behaviour. Although the dynamic stiffness method is primarily used in the analyses, some complementary finite element analysis and experimental modal analysis using an Impulse Hammer Kit were performed to confirm the predictable accuracy of the dynamic stiffness method. A few carefully designed composite beams were fabricated for the experimental work. Flutter behaviour of swept and unswept wing is also investigated. The results are discussed with significant conclusions drawn. A scope for further work is outlined.

Publication Type: Thesis (Doctoral)
Subjects: Q Science > QA Mathematics
T Technology > TA Engineering (General). Civil engineering (General)
Departments: School of Science & Technology > Engineering
School of Science & Technology > School of Science & Technology Doctoral Theses
Doctoral Theses
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