Evaluation of the Effect of Thermal Oxidation and Moisture on the Interfacial Shear Strength of Unidirectional IM7/BMI Composite by Fiber Push-in Nanoindentation

T. Xu, H. Luo, Z. Xu, Z. Hu, M. Minary-Jolandan, S. Roy, H. Lu

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

Fiber push-in nanoindentation is conducted on a unidirectional carbon fiber reinforced bismaleimide resin composite (IM7/BMI) after thermal oxidation to determine the interfacial shear strength. A unidirectional IM7/BMI laminated plate is isothermally oxidized under various conditions: in air for 2 months at 195 °C and 245 °C, and immersed in water for 2 years at room temperature to reach a moisture-saturated state. The water-immersed specimens are subsequently placed in a preheated environment at 260 °C to receive sudden heating, or are gradually heated at a rate of approximately 6 °C/min. A flat punch tip of 3 μm in diameter is used to push the fiber into the matrix while the resulting load-displacement data is recorded. From the load-displacement data, the interfacial shear strength is determined using a shear-lag model, which is verified by finite element method simulations. It is found that thermal oxidation at 245 °C in air leads to a significant reduction in interfacial shear strength of the IM7/BMI unidirectional composite, while thermal oxidation at 195 °C and moisture concentration have a negligible effect on the interfacial shear strength. For moisture-saturated specimens under a slow heating rate, there is no detectable reduction in the interfacial shear strength. In contrast, the moisture-saturated specimens under sudden heating show a significant reduction in interfacial shear strength. Scanning electron micrographs of IM7/BMI composite reveal that both thermal oxidation at 245 °C in air and sudden heating induced microcracks and debonding along the fiber/matrix interface, thereby weakening the interface, which is the origin of failure mechanism.

Original languageEnglish (US)
Pages (from-to)111-123
Number of pages13
JournalExperimental Mechanics
Volume58
Issue number1
DOIs
StatePublished - Jan 1 2018
Externally publishedYes

Keywords

  • Carbon fibers
  • Cohesive shear traction separation law
  • Environmental degradation
  • Finite element analysis
  • Interfacial strength
  • Polymer-matrix composites

ASJC Scopus subject areas

  • Aerospace Engineering
  • Mechanics of Materials
  • Mechanical Engineering

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