Detail of the AP-PLY fibre architecture .
Detail of the AP-PLY fibre architecture .
Panel made using AP-PLY.
Panel made using AP-PLY.

According to NLR, the AP-PLY fibre architecture (see pictures) combines the superior mechanical properties of unidirectional laminates with the higher resistance to impact damage of woven fabrics in an automated composites manufacturing process.

As compression strength after impact is an important design driver, NLR believes this research could lead to more efficient composite structures in aircraft and other transport applications.

Impact behaviour

Composites are notorious for their poor impact behaviour, NLR explains. Delaminations seriously decrease the material's compressive strength after impact. Laminates made from woven fabric generally show better impact behaviour than laminates with unidirectional layers, but it is harder to automotive their manufacturing process.

With AP-PLY, instead of fibre placing parallel fibre bands next to each other, room is left between bands. A second series of interspaced fibre bands is placed at an angle with respect to the first series. The remaining gaps are subsequently filled up. Adjacent plies are thus more interconnected and delamination damage is contained in a smaller area. Preliminary test results show significant improvement in compression strength after impact and smaller delaminations. Barely visible impact damage is reached at a lower impact energy level.

AP-PLY manufacturing and testing trials carried out at NLR show that weight reduction of approximately 10% seems feasible, compared to a traditional layered structure.

Research is continuing to optimise the material further.

A patent has been applied for the results of this NLR funded research.

AP-PLY was jointly developed by the National Aerospace Laboratory NLR, the central institute for aerospace research in the Netherlands, and the Faculty of Aerospace Engineering at TU Delft, one of the largest faculties devoted to aerospace engineering in northern Europe.