Blast resistance of prismatic sandwich structures

Metallic sandwich panels have emerged as candidate blast resistant structures that can be tailored to contain damage from impulsive loads of the type typically generated by explosives.When such panels are impulsively loaded, the stresses imposed by the core on the front face, as well as those transmitted through the core, govern the response metrics: especially the center displacement, the resistance to tearing and the loads transmitted to the supports. Prismatic cores such as I-, X-, Y- and Z- cores differ from other cores, such as foams and trusses, in that they do not exhibit constant dynamic crush strength, enabling collapse to occur in a controlled manner. Establishing relationships between core topology crushing response and panel performance is one of the major goals of this research.For this purpose a gas gun instrumented with high speed photography and direct impact Hopkinson pressure bar was built and used to perform laboratory scale high-speed impact tests. Samples of representative prismatic core unit cells were manufactured and tested in compression at axial velocities ranging from quasi-static to 200m/s. The dynamic strength and deformation (buckling) were measured and used to calibrate the imperfections in a finite element model. The model was then used to validate a constitutive model that can be used to predict the blast resistance of prismatic sandwich structures.This research identifies a simple dual level dynamic strength as a common response in metallic prismatic cores. This is due to the dominant effect of plastic shock generated by dynamic loading. Furthermore, it justifies the use of a simple dynamic axial compression test for calibration of the dynamic strength of the core.An analytical model that accounts for the shock effects in a homogenized core and embodies the dual-level dynamic strength is presented. It is shown to capture the experimental observations and simulated results with acceptable fidelity. This model provides the basis for a constitutive model that can be used to understand the response of sandwich plates subject to impulsive loads.