Analysis of Braided Composites Structures and Yarns for Compression Loading and Design for First Bending Mode

Abstract

The open architecture composite structures team at Auburn University has developed prototypes of strong, ultra-lightweight braided lattice structures for primary application in the aerospace sector. This research focuses on experimentally finding the compression failure loads of a 48K-core braided carbon-fiber composite cord-preg yarn #6. Different compression test fixtures such as Spherical-end, Hex-end, Cap-nut-end fixtures were designed and developed for testing the yarn specimen. Specimens of yarn #6 with varying span-lengths in the range of 7 mm to 90 mm were experimentally tested for compressive strength and the loads at which buckling occurred were found to be in span-lengths exceeding 35 mm. The results of this work provide design parameters for structures with yarn #6 to improve the axial and helical yarn count, helical angle and span-length of axial yarns in the structure. Finite element analysis was used to find the 1st bending frequency of the largest OACS tubes designed and manufactured by the Auburn University team and its potential application as an RF transparent antenna support on communication satellites. Finite Element (FE) models of small OACS tubes with 45 mm diameter and 300 mm length, and full-scale OACS tubes with 250 mm diameter and 900 mm length were designed to exceed 100 Hz., 1st bending frequency - a design requirement for the satellite application. The modelling involved, OACS tubes with all-carbon yarns, all-glass yarns and carbon-glass hybrid structures. Effects of changes to the geometrical shapes such as conical and cylindrical OACS tubes on the full-scale models have also been studied. This study concludes that an OACS tube 250 mm in diameter and 900 mm in length with the set design and boundary conditions will achieve the design requirement of 1st bending mode of 100 Hz., and this will be achieved by using, a 4 mm diameter all-carbon-fiber yarn architecture (approximately 324K carbon tows) comprising of, 48 axial yarns, 8 clockwise helical and 8 counter-clockwise helical yarns with a 45 degree braid angle.