Experimental studies of the low velocity impact and compression-after-impact behaviors of foam core sandwich composites with a focus on the evolution and effects of indentation

This study presents an investigation in the low-velocity impact and compression-after-impact behaviors of foam core sandwich structures. A series of low-velocity impact tests involving different impactor shapes and energies have been performed on the sandwich specimens. The results indicate that for a given impact energy, the flat impactor creates slight matrix cracking but a barely visible indentation, whilst a hemispherical impactor results in significant local damage and finally a conical impactor perforates the upper skin of the specimen. Compression after impact (CAI) tests were conducted to investigate the relationship of indentation depth, impact damage area and residual strength. The experimental results show that residual strength decreases linearly with increasing impact energy for the hemispherical impactor, whereas there is no significant change following impact using the flat impactor over the range of impact energies considered. For the conical impactor, the lower energy required for the upper skin perforation reduces the indentation depth. The paper also investigates the damage tolerance and develops a relationship between the impact indentation and residual strength of the impacted sandwich structures.