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Influence Of Stress-Free Aging On Modulus And Strength Of 2d Kevlar® Tubular Braided Composites
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Braiding is a manufacturing technique in which material yarns are repeatedly interlaced to create a preform. The preform is impregnated with a polymer matrix to create a braided composite. Several studies have investigated the tensile, compressive and torsional behaviour of braided composites and characterized their mechanical properties. The results of these studies have often displayed large variations between like specimens. One potential explanation of this variation is uncontrolled manufacturing parameters, including the stress-free aging time post cure for these materials. The objective of this study was to experimentally investigate the influence of stress-free aging on the stiffness and strength of tubular braided composites (TBCs). Samples were manufactured from Kevlar-49 (DEN 1420) using a maypole braider at three-braid angles (35o , 45o and 55o ). EPON 826 and Lindau LS-81k were used to cure the sample following the manufacturer data sheet. Manufactured TBCs were left to age for three different times (0 weeks, 2 weeks and 6 weeks). Post aging, quasi-static tensile testing of the samples was conducted following ASTM standard D3039 at a loading rate of 1 mm/min. To measure strain, Digital Image Correlation (DIC) was used. Images were taken every 2 seconds for the duration of the tensile test and processed in imaging software DaVis®. Results from the study were mixed for the different braid angles. For 35o and 45o , there was no statistically significant change in the longitudinal modulus, yield strength and failure strain for the different aged samples. For the 55o samples, there was an 8.43% increase in Young’s Modulus and a 15.04% increase in ultimate tensile strength. Due to the architecture of the braids, at higher braid angles, the transverse properties of the resin are more pronounced. The increased strength and stiffness of the resin post aging results in an overall increase in the strength and stiffness of the higher angle composites, confirming the changes in properties of thermosets documented in literature. Further investigation over a larger braid angle range and for longer post-cure times are crucial to confirm findings.
Part of Proceedings of the Canadian Society for Mechanical Engineering International Congress 2022.
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- Date created
- 2022-06-01
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- Article (Published)