Sandwich composites are of interest in marine applications due
to their high strength-to-weight ratio and tailorable mechanical properties, but their resistance to air blast loading is not well understood. Full-scale 100 kg TNT equivalent air blast testing at a 15 m stand-off distance was
performed on glass-fibre reinforced polymer (GFRP) sandwich panels with
polyvinyl chloride (PVC); polymethacrylimid (PMI); and styrene acrylonitrile
(SAN) foam cores, all possessing the same thickness and density. Further testing
was performed to assess the blast resistance of a sandwich panel containing
a stepwise graded density SAN foam core, increasing in density away from the
blast facing side. Finally a sandwich panel containing compliant polypropylene
(PP) fibres within the GFRP front face-sheet, was subjected to blast loading
with the intention of preventing front face-sheet cracking during blast. Measurements
of the sandwich panel responses were made using high-speed digital image correlation (DIC), and post-blast damage was assessed by sectioning the
sandwich panels and mapping the damage observed. It was concluded that all
cores are effective in improving blast tolerance and that the SAN core was
the most blast tolerant out of the three foam polymer types, with the DIC results
showing a lower deflection measured during blast, and post-blast visual
inspections showing less damage suffered. By grading the density of the core it
was found that through thickness crack propagation was mitigated, as well as
damage in the higher density foam layers, thus resulting in a smoother back
face-sheet deflection profile. By incorporating compliant PP fibres into the
front face-sheet, cracking was prevented in the GFRP, despite damage being
present in the core and the interfaces between the core and face-sheets.