Strategies to increase the mechanical performance of long fiber patch preforms

Load path optimized design comes typically with the aim to use as less carbon fiber as possible but still has optimal mechanical properties. Different placement technologies exist which are facing problems when it comes to small radii of curvature. The use of patch placement gives a high flexibility for layup design and therefore offers a high potential in this field. Compared to laminates with continuous fiber, patched laminates suffer from peeling forces in the outer plies under tension force. This leads to premature failure. Since this effect becomes more and more important for laminates with fewer layers a study is presented which investigated the influence of different amount of layers on the mechanical properties and failure behavior. This study shows that for specimens with fewer layers this effect leads to a catastrophic failure while specimens with increasing amount of layers are failing gradually while constantly peeling off plies towards the center of the specimen. To reduce this peeling effect two different overlap designs for the outer plies were investigated. The results show that an overlap of 3 mm already leads to an increase in tensile strength by 5.5 % and therefor is an effective way to increase the performance of patched laminates.