Characterization and Modeling of Low Twist Yarn Mechanics in Tubular Braided Composites

• Author / Creator

  Cheung, Benjamin

• Twisted yarns are commonly used in traditional textiles applications, such as in apparel manufacture, but their study and use in composite textiles is limited, especially in the case of continuous multifilament yarns. In textiles applications, small amounts of twist have shown to increase the strength of yarns, yet the increase in fiber obliquity contributes to a decrease in effective stiffness of the yarn. A specific emphasis on low levels of twist exists since higher levels of twist are not practical or feasible. It is proposed that including twist in the manufacturing process for textile composites can have a positive impact on the mechanical performance of tubular braided composites (TBCs), due to their strong correlation of performance to manufacturing parameters. The use and analysis of twisted yarns in TBCs was systematically approached by building up from single textile yarns to single composite strands and eventually up to TBCs. This approach allowed for the impact of twist to be observed at each scale of testing. Dry textile yarns were tested to determine the impact of twist and confirmed what was noted in existing literature; that is, an increase in strength and a decrease in effective stiffness. It was also shown that existing yarn twist models do not accurately capture the stiffness response of low twist yarns. Following this, composite strands were tested under the same twist levels and it was determined that yarn twist has much less of an impact when in the presence of a composite matrix. Finally, TBCs were manufactured with yarn twist to determine the impact at the scale of a composite textile and tested under tension. Digital image correlation (DIC) is used for these experiments in order to capture the full field strain behaviour. The presence of twisted yarns in the TBCs is found significantly increase yield strength without negatively impacting the stiffness response. This increase in stress capacity is then modeled by means of the Ramberg-Osgood equation, which accounts for both an increase in strength as well as a change in plastic strain behaviour. Throughout this thesis, two different yarn materials are used for each study. The first, Kevlar 49, is a traditional choice for composite reinforcement due to its high stiffness to weight ratio, and there is much literature on the mechanical behaviour of Kevlar 49 as a composite constituent. As well, a more novel cellulose-derived multifilament yarn BioMid was also used in parallel. Using two different types of continuous multifilament yarns also confirms whether or not the effects observed are specific to the material used.

• Subjects / Keywords

  • Yarn
  • Twist
  • Composites
  • Braids
  • Textiles
  • Braided

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-139v-mv78

• License

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