Enhancing the bonding of CFRP adhesive joints through laser-based surface preparation strategies

  • Ran Tao

Student thesis: Doctoral Thesis

Abstract

Nowadays, Carbon Fiber-Reinforced Polymers (CFRPs) have been widely applied in the aerospace and automotive industries. Secondary adhesive bonding, instead of using rivets or bolts in conventional mechanical fastenings, is promising in joining CFRPs because it is simple and applicable for cured parts, widely applied for repairing structures, and of light weight. However, the mechanical performance of secondary bonding is very sensitive to the treatment of CFRP parts. Besides, another concern arises from the fact that secondary bonded specimen often prematurely fails due to delamination and leads to a catastrophic structural collapse. While enhancing the joint strength and toughness is important, limiting the progression of damage is crucial, to ensure confidence in the design and allow enough time for maintenance and repair. Therefore, it is significant to introduce a crack arrest feature into the joints, to slow down (or even stop) the crack growth and achieve progressive failure. In this thesis, we employ advanced surface preparation strategies to enhance the strength, toughness, and safety of adhesively bonded CFRP joints. Globally uniform surface pretreatments, using conventional mechanical abrasion, peel-ply, and pulsed CO2 laser irradiation, are employed at first to improve the mechanical responses of adhesively bonded CFRP joints. Then, to better understand damage mechanisms and guide the joint design, characterizations of surface chemistry, surface energy, and surface morphology are correlated with obtained strength and toughness. Next, trench patterns, ablated by pulsed CO2 laser irradiation, are applied to CFRP substrate to further analyze the role of surface roughness on increased mode I energy release rate. Finally, a novel surface patterning strategy is proposed to achieve superior toughness enhancement in adhesively bonded CFRP joints to improve the joint safety. Such surface preparation strategy is assessed through 2D numerical models and realized experimentally by patterning of pulsed CO2 laser irradiation, illustrating its potential in toughening the joint and successfully delaying the crack propagation.
Date of AwardNov 2020
Original languageEnglish (US)
Awarding Institution
  • Physical Science and Engineering
SupervisorGilles Lubineau (Supervisor)

Keywords

  • Adhesive joints
  • CFRP
  • CO2 laser irradiation
  • patterned interface
  • crack-arrest feature
  • toughening strategy

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