Damage mechanisms in the CAI failure of thin z-pinned composite laminates

The results of an experimental investigation into the compression after impact (CAI) performance of thin z-pinned carbon-epoxy laminates are reported in this paper. Unpinned and z-pinned [02/902]S and [0/±45/90]S samples were impacted at energies varying between 2 J and 35 J and then subjected to compression loading until failure. The amount and nature of the damage induced by impact and the damage mechanisms leading to CAI failure were characterized by X-radiography and through visual observation of the sample surfaces. The study shows that the effect of z-pins may be beneficial or detrimental to the post-impact strength of the laminates depending on the energy of the impact. The sequence of the main damage mechanisms observed on the laminates during the compression tests is illustrated and discussed to clarify the role of z-pins in controlling the residual strength of the impacted laminates over the full range of examined impact energies.