This thesis investigates the nonlinear dynamic response of the steel monolithic square plated structures due to localised blast loads, such as those emanating from close-in charges. Such target plates are assumed to be made of novel high strength ARMOX steel material types manufactured by SSAB® as well as conventional mild steel.
A detailed review of earlier works in the literature is presented on the experimental, numerical and theoretical methods of analysis to predict the response of beams, circular and quadrangular plates subject to blast and impact loads. The large scatter of data from the above analyses has been cast in dimensionless forms to correlate between the methods of predicting the response. The review concludes that, the choice of material type as well as the intrinsic complexity associated with the load type make the response of the structure inherently different to those of plated elements made of more conventional grade metals.
Based on the state-of-the-art Digital Image Correlation experimental testing conducted in the Blast Impact and Survivability Research Unit in University of Cape Town, various proposed numerical models have been validated. These include advanced techniques to model the fluid structure interactions. This led to discerning the parameters that influence the plastic response. Empirical relations in dimensionless form have been proposed which pass through most scattered data from numerical and experimental results. A prompt observation is that assessing the plastic response of the structures to localised blasts necessitates understanding the underlying patterns and laws of plastic response. Such understanding is gained by theoretical methods with idealisations of the material or the structural response.
This leads to theoretical studies using the principles of virtual velocities assuming constitutive framework of limit analysis, i.e. rigid, perfectly plastic behaviour. While appreciating the limitations of current theoretical models, a comprehensive approach is undertaken to explore the response of the plates of various boundary conditions, distinguished in terms of their thicknesses, i.e. thick, moderately thick and thin plates. Furthermore, the nonlinear elastic response of the plates has been examined, leading to a unified theoretical solution of elastic-perfectly plastic systems.
On the basis of the existing work in the literature, a method to mathematically describe the parameters that characterise the blast load itself and the structure impacted whereupon with a given charge geometry, stand off and material type is presented and validated with numerical models. Based on the dimensionless study, single parameters to predict the rupture impulse has been determined.