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Previous studies have shown that while stainless-steel sandwich panels with pyramidal truss cores have a superior blast resistance to monolithic plates of equal mass per unit area, their ballistic performance is similar to their monolithic counterparts. Here, we explore concepts to enhance the ballistic resistance without changing the volumetric efficiency of the panels by filling the spaces within the core with combinations of polyurethane, alumina prisms, and aramid fiber textiles. The addition of the polyurethane does not enhance the ballistic limit compared with the equivalent monolithic steel plate, even when aramids are added. This poor performance occurs because the polymer is penetrated by a hole enlargement mechanism which does not result in significant projectile deformation or load spreading and engagement of the steel face sheets. By contrast, ceramic inserts deform and erode the projectile and also comminute the ceramic. The ceramic communition (and resultant dilation) results in stretching of both steel face sheets and leads to significant energy dissipation. The ballistic limit of this hybrid is about twice that of the equivalent monolithic steel plate. The addition of a Kevlar fabric to the ceramic hybrid is shown to not significantly change the ballistic limit but does reduce the residual velocities of the debris.

Public reporting burden for this collection of information is estimated to average 1 bour per response, iiKluding the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, SPONSOR/MONITOR'S ACRONYM(S) SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release; distribution is unlimited. SUPPLEMENTARY NOTES♦Christian is a research associate for the Oak Ridge Institute for Science and Technology, Oak Ridge, TN. ABSTRACTPhase-toughened epoxy/dicyandiamide adhesives were loaded with magnetic particle filler and then cured by induction processing. The effect of induction field magnitude and exposure time on bonding strength of the loaded adhesives was characterized. At low magnetic field amplitudes, bond strength increased significantly with exposure time, with the highest strength bonds occurring after 60-min exposures. At high magnetic field amplitudes, bond strength increased only slightly with exposure time, so that significant bond strength was reached after 15 min of exposure. In general, the induction-cured adhesives exhibited lower bond strengths than comparable oven-cured adhesives. All of these strength trends were likely due to processinduced variations in the adhesive degree of cure, toughening phase development, or thermal degradation. SUBJECT TERMSinduction curing, phase-toughened adhesive, dicyandiamide, magnetic powders, epoxy, magnetic susceptor, DICY