Quasi-static indentation characteristics of foam-filled sandwich composite structures with additively manufactured CFRP and GFRP corrugated cores

This paper presents an experimental investigation on the quasi-static indentation performance of polyurethane (PU) foam-filled carbon fibre-reinforced polymer (CFRP) and glass fibre-reinforced polymer (GFRP) corrugated sandwich composite structures (SCSs) under different indenter tip geometries (conical, trapezoidal, hemispherical, pyramidal, and cylindrical shapes). The SCSs were produced using hybrid manufacturing methods: (1) the facesheets were fabricated using the vacuum-assisted resin infusion (VARI) process, (2) the CFRP and GFRP corrugated cores were additively manufactured using the fused filament fabrication (FFF) process, and (3) the self-expanding PU foam-filled the open spaces in the core. The results elucidated that the indenter tip geometry and core material have a large influence on the indentation performance of SCSs. The cylindrical indenter showed the highest peak load, bending stiffness, and damage severity, while the conical indenter offered the lowest peak load, energy absorption, and damage severity. Among different core materials, CFRP corrugated core SCSs exhibited higher peak loads, specific energy absorption, and damage severity compared to ones with GFRP core. The primary damage modes were observed using an optical microscope, showing facesheet rupture, debonding between facesheets and core, core crushing, foam densification, and shear plugging. Shear plugging is a unique failure mode observed with cylindrical indenter tip geometry due to the blunt edges of the indenter, which induced large damages in SCSs. These findings provide new insight into the design and development of lightweight additively manufactured SCSs, which will benefit a wide range of industries and applications.