Carbon Fiber-Reinforced Polymers (CFRPs) have been widely applied in the aerospace and automotive industries to achieve unprecedented weight reductions. However, major challenges need to be solved in order to exploit their full potential, especially in the design of full composite primary structure, making then a vital part of the mobility and energy revolution.
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 lightweight. 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 work, the objective is to enhance the strength, toughness, and safety of adhesively bonded CFRP joints, through advanced surface preparation strategies. Globally uniform surface pretreatments, using conventional mechanical abrasion, peel-ply, and pulsed CO2 laser irradiation, are employed at first to improve the mode I energy release rate (ERR) of adhesively bonded CFRP DCB 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 mode I ERR. 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 ERR.
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.
Ran Tao joined KAUST as a master student in 2013 and completed a master thesis in 2015. After that, he continued as a PhD student with Professor Gilles Lubineau in COHMAS Laboratory, the Structural Composite Lab at KAUST. His topic is adhesive bonding of CFRP materials.
Committee Chair: Prof. Sigurdur Thoroddsen
Committee Member: Prof. Gilles Lubineau
Committee Member: Prof. Paul Martin Mai
Committee Member: Dr. Carlos González
Committee Member: Dr. Nikhil Verghese
Zoom link for this Ph.D. defense: