Delamination Behaviour of 3d-textile Reinforced Composites – Experimental and Numerical Approaches

The requirements on aircraft engine design have increased rapidly over the last decades. Future aircrafts engines are expected to be more efficient with lower operation costs and without compromising safety. Concerning the complex requirements for fan systems or fan containments, composite materials are able to fully avail their high potential with regard to a significant weight reduction and an increased efficiency by using their high specific strength and stiffness. However, the insufficient delamination behaviour of 2D-reinforced composites is often opposed to a broad application in impact resistant lightweight structures. In this respect, through thickness reinforcements, e.g. by stitching, are expected to be a very promising way to optimise 2D textile reinforced materials. An experimental investigation approach for 3D reinforced materials under impact loading conditions is presented in this article, which includes the description of the testing procedure as well as the tested material configurations and the experimental results. The focus of the experimental investigation was set on the examination of damage due to delamination failure depending on various stitching configurations using a multi-layered weft knitted fabrics (MKF). Concerning the implementation of the 3D-reinforcement by stitching with the double locked stitch technology, two different stitching thread materials, glass and aramid, were used. In order to compare the stitching configuration effects, different stitch lengths and stitch distances have been investigated as well as unstitched specimens. The laminate specimen plates were subjected to sub-critical impact velocities at an impact-bending-test device. The gained information has been used for numerical investigations to evaluate possibilities of simulating delamination damage in 3D-reinforced structures by the FEM.