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FROM:
Edgars Eglitis, Dynamic buckling of composite shells, PhD Thesis, Riga Technical University, Latvia; (2011)
ABSTRACT: This thesis is focused on the investigation of the changes in the buckling behaviour of various composite shells due to dynamic, rapid loading. Currently, the structural design procedures of lightweight structures incorporate assumption of the loads as quasistatic, while maintaining reliability by applying conservative safety coefficients. Different investigations show that in various cases of dynamic loading the buckling loads can be both higher and lower than the static buckling load. Therefore, correct consideration of the load dynamics in the design procedure would lead to safer and more efficient structures. A reliable, experimentally validated analysis approach is required in order to benefit from the weight-saving potential of dynamically loaded composite structures, while maintaining the reliability. However, only few experimental investigations on dynamic buckling of composite structures have been performed because of the complexity of such experiments. In present thesis, the dynamic buckling of composite shells has been investigated experimentally and numerically, and an appropriate experimentally validated modelling approach has been proposed. Chapter 1 gives review of the accumulated knowledge in dynamic buckling of thin-walled structures. The key pioneering research has been reviewed along with the publications describing the current state-of-the-art in the field. It has been revealed that surprisingly few experimental studies have been attempted in dynamic buckling of composite shells, with most researchers resorting to the analytical and numerical investigations only. Chapter 2 contains the relevant information about the experimental and numerical methods used within this thesis. The experimental investigations have been performed on cylindrical composite shells using hydraulically actuated loading frames and a drop tower. The main numerical tool used in this thesis is the ABAQUS/Explicit finite element software. Chapter 3 describes the static buckling behaviour of the selected specimens as a reference for the comparison with the dynamic buckling behaviour. The imperfection sensitivity of the cylindrical shells has been addressed by measuring the geometrical imperfections of the specimens and using this data in the numerical analyses. Chapter 4 contains the results of experimental and numerical investigations of dynamic buckling of composite cylinders. Gradually and suddenly applied loads, as well as half-sine shaped pulse loads have been considered and the influence of the load parameters on the buckling behaviour of the shells has been revealed. Chapter 5 expands the research to stiffened curved composite panels. The results have been obtained for various loading patterns using numerical models validated with the results of static buckling experiments.
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