Enhancing the dynamic performance and fracture resistance of steel plates under impulsive loads has always been of great interest to the researchers and scientists. A convenient technique to enhance the energy absorption capability of steel plates is to spray-cast a layer of polyurea onto the plates. Since polyurea readily adheres to metallic surfaces and has a short curing time, the technique may be used to retrofit existing metallic structures to improve their blast resistance. We have examined the effectiveness of this approach, focusing on the question of the significance of the relative position of the polyurea layer with respect to the loading direction; i.e. , we have explored whether the polyurea layer cast on the front face (the impulse-receiving face) or on the back face of the steel plate would provide a more effective blast mitigating composite. In addition we have studied the effects of the thickness of the polyurea layer and the steel-polyurea interface bonding strength.

The experimental results suggest that the polyurea layer can have a significant effect on the response of the steel plate to dynamic impulsive loads, both in terms of failure mitigation and energy absorption, if it is deposited on the back face of the plate. And, remarkably, when polyurea is placed on the front face of the plate, it may actually enhance the destructive effect of the blast, promoting the failure of the steel plate, depending on the interface bonding strength between the polyurea and steel layers and the polyurea layer thickness. These experimental results are supported by our computational simulations of the entire experiments. In addition, SEM and optical microscopy is performed to examine the microstructure of the failed samples, and also understand the fracture and necking patterns, and the underpinning mechanisms of failure. Based on the micrographs, finite-element models are developed that are capable of predicting the fracture process of the steel plates.

An independent chapter completes this dissertation. In Chapter 7, we report the results of an experimental and numerical investigation of dynamic and quasi-static compressive response of single and hex-arrayed thick aluminum tubes.