The synergistic effect of hybridizing and aligning graphene oxide nanoplatelet (GONP) and multi-walled carbon nanotube (MWCNT) on the mode-I fracture response of glass fiber/epoxy nanocomposite adhesive was studied. Different mixtures of nanofillers with aligned and random orientations and different mixing ratios and weight percentages were used for fabricating the reinforced nanocomposite adhesive joints. The results showed that the hybridization of MWCNTs and GONPs can considerably enhance the fracture behavior of nanocomposite adhesive joints providing that the appropriate hybrid ratio and weight percentage (wt%) were employed. It was found out that hybridizing one-third GONPs and two-thirds MWCNTs with 0.3 total nanofiller wt% caused 90% further improvement in the fracture energy of adhesive compared to the adhesive reinforced with merely MWCNTs at the same total nanofiller wt%. Furthermore, aligning nanofillers with electrical field resulted in more than twice the higher enhancement in the fracture energy of adhesive. Moreover, assessing the fracture surfaces of the unreinforced and reinforced specimens revealed that the type of reinforcement can affect the failure pattern of the adhesive joints.
This study investigates the effect of different surface treatments on the fracture behavior of epoxy-aluminum joints under mode-I loading. Six surface treatments including degreasing, abrasion with varying grit sizes, alkaline etching, acid etching, a combination of alkaline and acid etching, and a combination of abrasion and acid etching were applied to aluminum surfaces before bonding. Surface morphology, roughness parameters, total surface free energy, contact angle, and elemental composition were analyzed. Results showed that the ultimate fracture load and fracture energy initially increased and then decreased with increasing surface roughness. The most effective treatments were found to be acidic etching in combination with alkaline etching and abrasion due to their synergetic effects. These treatments removed the natural oxide layer and created a porous oxide layer, enhancing surface roughness, increasing adhesive-substrate contact areas, and providing more sites for mechanical interlocking. Compared to control joints, significant improvements were observed, including a 40% and 31% increase in maximum fracture load, a 74% and 53% increase in initiation fracture energy, and a 65% and 47% increase in propagation fracture energy, respectively. Etching treatments demonstrated superior effects on the fracture behavior of aluminum adhesive joints compared to abrasion methods, leading to cohesive failure after etching treatments.
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