Delamination and compression-after-impact properties of z-pinned composite laminates reinforced with circumferentially notched z-pins

The investigations performed here show a positive influence on the properties of z-pin reinforced laminates using circumferentially notches as a defined z-pin surface micro-structuring. In addition to significant improvements of the fracture mechanical properties under Mode-I crack opening loading, effective reductions of the resulting delamination areas that arise during an impact can be achieved. Furthermore, the residual strength properties of pinned laminates are more favourable than those of unpinned ones and can be further improved by the use of circumferentially notched z-pins. The determined values of the Mode-I critical energy release rate G(IC) can be increased by approx. 13% if micro-structured z-pins are used. Laminates reinforced with these z-pins also show reductions in the dimensions of the delamination area depending on the impact energy level. Also the compression-after-impact strength can be increased by 6% for low impact energy of 17 J in z-pinned laminates reinforced with circumferentially notched z-pins, compared to those reinforced with unnotched z-pins. For increasing impact energies the values of the pinned laminates with unnotched as well circumferentially notched z-pins converge. Therefore, it can be concluded that for higher impact energies the effect of a defined micro-structuring of the z-pins surfaces on the delamination area after impact and compression-after-impact properties is negligible.

Automated summary

The investigations conducted in this study demonstrate that the properties of z-pin reinforced laminates can be positively influenced by using circumferentially notches as a defined z-pin surface micro-structuring. The fracture mechanical properties under Mode-I crack opening loading can be significantly improved and the resulting delamination areas that occur during an impact can be effectively reduced. The residual strength properties of pinned laminates are also more favorable and can be further enhanced with the use of circumferentially notched z-pins.