Comparison of interlaminar fracture toughness of filament wound glass/epoxy composites by using MWCNTs or flexible resin

Open Access
Author:
Yoo, Min-Ji
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Charles E Bakis, Thesis Advisor
  • Edward A Smith, Thesis Advisor
Keywords:
  • Interlaminar fracture toughness
  • CNT
  • Mode I
  • II and mixed mode
Abstract:
The objective of this investigation is to evaluate and compare the effectiveness of two approaches for improving the interlaminar fracture toughness (IFT) of wet-filament-wound glass/epoxy composites incorporating multi-walled carbon nanotubes (MWCNTs) into a conventional epoxy matrix material and utilizing flexiblized epoxy resins in selective layers in otherwise rigid-matrix laminates, generally referred to as the layer-wise hybrid (LWH) approach. The Mode I, Mode II, and mixed-mode (I/II) quasi-static interlaminar fracture toughness of the various types of fabricated composites were investigated utilizing double cantilever beam (DCB), end notched flexure (ENF), and single leg bending (SLB) experiments, respectively. Mixed results were obtained when adding MWCNTs to the resin, although the conclusions may be clouded by variations in the void content in the materials, the degree of cure of the flexible epoxy, and the use of old glass fiber. Notwithstanding these complicating factors which require further investigation to be resolved, it was observed that adding MWCNTs improved the Mode I and II IFT values in the case of rigid epoxy and decreased the same IFT values in the case of flexible epoxy. Using a flexible epoxy on one or both sides of the interface increased the Mode I and II IFT values. Adding MWCNTs to either matrix system decreased the mixed-mode IFT. On the other hand, using flexible resin on one or both sides of the fracture plane increased the mixed-mode IFT. Recommendations are provided for resolving the material and process problems in future research.