Dynamic Failure of Blast-Resistant Structures Subjected to Impulsive LoadingSungsoo Lee, Ph.D., Northwestern University, 2005.
Major Professor: Dr. Horacio D. Espinosa.
The compressive behavior of open-cell aluminum foams, stainless steel woven textile core materials, and stainless steel pyramidal truss core materials have been investigated at three different deformation rate regimes. Quasi-static compression tests were performed using a miniature loading frame, intermediate rates were achieved using a stored-energy Kolsky bar, and high strain rate tests were performed using a light-gas gun. This thesis provides a quantification of load-deformation response and associated failure modes across the sample as captured optically in real time. In all the cores, the differences in failure modes were more dramatic for the gas gun experiments, where a shock wave is generated at the impact surface. The woven textile materials exhibited moderate dependence of strength on the deformation rate compared to open-cell foam materials. In the pyramidal truss cores, the rate effect on the strength surpassed those of the other cores tested. In this case, the inertia associated with the bending and buckling of truss struts played a significant role.
This thesis proposes a novel experimental methodology to study dynamic deformation of blast-resistant structures subjected to underwater blast loading. The experimental setup embodied real fluid-structure interaction and the impulsive loading similar to a blast was generated by a flyer plate impacting water. An analysis of scaling-down was performed to make a laboratory-scale apparatus which is analogous to large-scale naval applications. Calibration experiments and corresponding simulations proved the experimental setup to be functional as designed.
Different concepts of blast-resistant structures were tested using the newly-developed FSI experimental setup to validate the performance of the structures and to assess the failure mechanisms. As a reference, stainless steel monolithic plates were tested and analyses of the dynamic deformation behavior were performed by measurements of the impact velocity of the flyer, the pressure wave in the water, and the deformation field on the plates by shadow Moiré. Sandwich plates with square honeycomb cores and pyramidal truss cores provided similar improvements in reduction of deflection, which was more than that provided by polymer-coated plates. We envisioned that improvement can be enhanced by more elaborated designs of the sandwich plates and polymer coatings.