The National Aerospace Laboratory NLR and Delft University of Technology (TU Delft) in The Netherlands announced on June 10 that they have jointly developed the new AP-PLY fiber architecture with improved damage tolerance for use with a fiber placement machine.
AP-PLY combines the superior mechanical properties of unidirectional laminates with the higher resistance to impact damage of woven fabrics in an automated composites manufacturing process.
Composites are notorious for their poor impact behaviour. Delaminations seriously decrease the compressive strength of this material after impact. Laminates made from woven fabric show in general more beneficial impact behaviour than laminates with unidirectional layers, but their manufacturing process is harder to automate.
Instead of fiber placing parallel fiber bands next to each other, room is left between bands. A second series of interspaced fiber 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 after impact strength and smaller delaminations. Barely visible impact damage is reached at a lower impact energy level.
Manufacturing and testing trials carried out at NLR show that weight reduction of approximately 10 percent seems feasible, compared to a traditional layered structure. Research will continue and the material will be optimized further. As compression after impact strength is an important design driver, it is believed that even greater reductions are possible, ultimately leading to more efficient composite structures in aircraft and other transport applications.
A patent has been applied for the results of this NLR funded research.