Study of foam density variations in composite sandwich panels under high velocity impact loading

• Foam density variation in a sandwich panel under ballistic impact is investigated.
• Specific energy absorption showed better performance for low density foam.
• Morphological study showed cell wall thickness and strut play vital role.
• Foam density affects projectile yawing and back face fracture pattern.

This study investigates the effect of foam density variations in sandwich structure under high velocity impact loadings. The structure consists of composite facing made from glass fiber woven roving reinforced unsaturated polyester resin and rigid polyurethane foam core with density of 37, 49, 70, 95, 105 and 240 kg/m3. Smooth bore gas gun in velocity range of 100–150 m/s and 10.7 g semi-spherical tip steel projectile was used for high velocity impact tests. Results showed 49 kg/m3 foam density attained highest performance in term of ballistic limit velocity and energy absorption for fully perforated specimens. Optimized foam core density resulted in projectile yawing and side impact to back face and higher energy absorption. SEM analysis and morphological study revealed, low ballistic performance in low density foam core (below 40 kg/m3) in the sandwich structure may be associated with foam's low cell wall thickness and strut. Similar analysis for the 40–70 kg/m3 foam core densities showed increase in foam's cell wall thickness with no significant change for the strut and also highest strut thickness for the above 70 kg/m3 foam density with no change in cell wall thickness.

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