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Title: Structural behaviour of blast loaded hybrid systems
Author: Yang, Yang
ISNI:       0000 0004 2696 4844
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2011
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Currently, in the military and civilian fields, there is an increasing demand for using hybrid systems, which are manmade structural systems combining two or more distinct materials. By carefully studying and designing such kind of structural systems, one can take advantage of heterogeneity of the structure, thus significantly improving the overall structural performance. Hence, the demand for robust analytical and numerical models to predict blast performance of such system has become more important. The primary aim of the present research is to investigate and understand the structural behaviour of several hybrid systems under extreme dynamic loads and to propose concepts for optimisation. Three types of hybrid systems have been studied, improved and their performance has been validated. They are the metal-to-composite hybrid joints, sandwich panels, and the metamaterial. Analytical, numerical and experimental studies have been conducted to analyse the structural behaviour of hybrid joints and sandwich panels under transient high intensity dynamic loading, in order to ensure these systems possess the desired capacity, designed strength, and robustness. Therefore, they are able to resist not only static loadings but also shocks induced by various explosions. For frequency analysis purposes, the perforated hybrid joints and metamaterials have been considered as a 2D lattice. The primitive cell (unit cell) of the lattice is formulated in the Fourier space (k-space) and studied using the Floquet-Bloch’s principle to investigate the attenuation-free shock response characteristics. Plane wave propagation in the hybrid system is thus investigated by constructing the first Brillouin zone and extracting the band structure diagram. As another case for a hybrid system, the structural performance of a circular sandwich panel with symmetric through-thickness architecture subjected to a pulse loading of arbitrary temporal and spatially uniform distribution (UDL) has been investigated by using the third order shear deformation theory. Based on the Hamilton’s principle, the governing partial differential equations (PDE’s) are derived. By applying the weak form Galerkin’s method of weighted residuals, the PDE’s are transformed into ODE’s. By solving the ODE’s with their boundary and initial conditions, results show that there is a strong correlation with finite element results obtained from ABAQUS 6.9. The third-order shear deformation theory allows for accurate assessment of out-of -plane shear in the core where the failure usually occurs. Due to the fact that core of a sandwich panel is more often to be the weakest link, a remedy must sought, e.g. employing additional core layers, to improve its performance. Dynamic response of four circular sandwich panel constructions with different proposed core designs under global and local blast loading conditions has been investigated. Numerical finite element (FE) models have been set up to study the effect of additional core inter-layers on blast resistance enhancement of these sandwich panels. A ductile elastomeric layer of polyurea, and a fairly compressible Divinycell-H200 foam layer have been selected as the additional core inter-layers and have been placed in different arrangements to protect the core of the standard sandwich panels, and maximise overall blast resistance. Comparison of specific kinetic and strain energies shows the effect of additional core layers on blast energy absorption of a sandwich system. The study shows the improvement in shear failure prevention in the core as a result of the use of additional core layers. One qualitative 2DoF system with a viscoelastic spring element representing the integral effects of sacrificial additional core inter-layers and a nonlinear spring representing the stiffness of the conventional sandwich system; and a similar qualitative SDoF model of a conventional sandwich panel have been developed for dynamic analysis. The conclusions drawn from the numerical tests are confirmed by the output of this analysis. The results of this research work give a better understanding of the performance of some generic hybrid systems under blast, which allows the optimised hybrid system to be more confidently designed and should be able to fill the gap in the currently growing demand for high strength, light weight, reliable hybrid systems in various civilian and military industries.
Supervisor: Louca, Luke Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral