Effects of knit stretching and matrix crystallinity on the fatigue behaviour of knitted fabric-reinforced GF/PET composites

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Abstract

In this study the tension-tension fatigue behaviour of weft-knitted glass fibre fabric-reinforced polyethylene terephthalate (GF/PET) composites was studied as a function of the stretching ratio of the knit. The knits were stretched prior to consolidation in wale direction in 0, 25, 50 and 73%, respectively, in order to increase the anisotropy and to alter the mechanical properties of the composites. The influence of the matrix morphology (crystalline, amorphous) on the fatigue response was also investigated by using a composite with unstretched knit reinforcement. The results, displayed in normalized maximum fatigue stress vs number of cycles (S-N) diagrams showed that the fatigue endurance limit of the GF/PET composites did not depend either on the knit stretching or the matrix crystallinity. The fatigue endurance limit, normalized to the static tensile strength, was found at ≈27 and ≈50 % for the knitted fabric-reinforced composite sheets tested in wale (W) and course (C) direction, respectively. The damage zone seemed to be localized for 1 and 2 rows of loops in C- and W-directions, respectively. This failure mode reflects the stress transfer and redistribution capability of the plain weft-knit reinforcement.

Original languageEnglish
Pages (from-to)75-79
Number of pages5
JournalAdvanced Composites Letters
Volume6
Issue number3
Publication statusPublished - Jan 1 1997

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Keywords

  • Fatigue
  • GF/PET
  • Knit stretching
  • Matrix morphology
  • Weft knitted reinforced composites

ASJC Scopus subject areas

  • Ceramics and Composites
  • Industrial and Manufacturing Engineering

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