The dynamic response of blast-loaded monolithic and composite plated structures
Creators: name: McCallef, Karl
Publisher: name: Imperial College London
Year: 2013

description: The scope of the thesis is to investigate the dynamic behaviour of plated structures when subjected to blast loading, focusing in particular on localised blast loading. Two main categories of plated structures are investigated, viz. monolithic plates and composite plates. The thesis includes a literature survey of existing works on the subject, which concludes that there is no available method of describing a localised blast load arising from a given charge size, geometry and stand-off distance from target. The review also investigates analytical methods for predicting displacement of plates subjected to blast, assuming rigid-plastic behaviour and the concept of using dimensionless parameters to predict such displacements. The survey also reviews material models for composites and damage mechanisms for these materials. On the basis of these findings, the thesis proposes a systematic method of mathematically describing the spatial and temporal variations of a localised blast load from a known set of threat parameters (explosive type, quantity, size and stand-off distance). The method is validated by comparison of numerical results using the proposed loading function implemented in a finite element analysis software with experimental results of blast loads on steel plates. This leads to the first study, which focuses on the performance of monolithic plates subjected to a blast load of the form described above. Existing formulations for uniform loading found in the literature are extended to consider this new form of loading. Various plate thicknesses are investigated (thick, moderately thick and thin) and it is found that good correlation is achieved with numerical results, even when the blast load is simplified into an impulsive one. The performance of composite plates under blast loading is also investigated, focusing primarily on a new high-performance composite material (namely, Dyneema HB26). Material characterisation and blast loading tests were carried out and these were used to develop a material model for Dyneema, which is validated using finite element simulations. Its performance is numerically compared with mild and armour (Armox 370T Class 1) steel plates of equal areal density and it is found that Dyneema offers an improvement over mild steel, but armour steel plates lead to the least permanent midpoint deflection. Using dimensionless parameters, a simple design guideline is provided to estimate the deflection for a given plate geometry made of a monolithic or composite material subjected to a specific blast load. The use of this guideline was also illustrated by considering various threats and using the proposed method to recommend various plate thicknesses required for different material systems to meet a specified damage limitation. Furthermore, a numerical-analytical method is proposed to predict the occurrence of Mode I delamination (or separation between the plies) in the early-time response of laminated composite materials, by means of stress propagation analysis.