Experimental investigations on 3D reinforced multilayer weft knitted fabric laminates under impact loading conditions
Werner Hufenbach*, Nikica Petrinic**, Andreas Hornig***, Albert Langkamp***, Jens Wiegand**** *Technische Universität Dresden, Institut für Leichtbau und Kunststofftechnik, 01062 Dresden **Oxford University, Department of Engineering Science ***Technische Universität Dresden, Institut für Leichtbau und Kunststofftechnik, 01062 Dresden ****Oxford University, Department of Engineering Science
Quarterly No. 4, 2006 pages 14-18
DOI:
keywords: 3D reinforcement, crash and impact test, stitching, composites
abstract 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. In this respect, the almost unexplored field of through thickness reinforced structures is 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 test results. Two layers of multi-layered weft knitted fabrics were used to manufacture the laminates using the Bakelite L1000 epoxy resin in a resin transfer moulding process. For fabrication of stitched laminates by the double locked stitch technology two different stitching thread materials, glass and aramid, were used. In order to compare stitching configuration effects, the lengths from 1.0 to 4.8 st/10 mm and stitch distances of 5 and 10 mm were used as well as unstitched specimens. The laminates were subjected to a subcritical impact velocity of 8 m/s at the impact-bending-test device, which is explained in detail here. The damage was characterised with the focus on delamination and matrix cracking through computer tomography, optical, x-ray and ultrasonic inspections. The results of the study indicate that the used testing device is capable to evaluate the influence of the stitching pattern on the damage resistance, where particular stitching setups tend to result in higher delamination resistance.