Treatment of CFRP by IAR method and its effect on the fracture behavior of adhesive bonded CFRP/aluminum composites

It was shown in the previous studies that adhesive shear strength of carbon fiber reinforced plastics (CFRP) to aluminum composites could be improved by the surface treatment of CFRP using Ar⁺ ion irradiation. In the present work, the effect of CFRP treatment by Ar⁺ ion irradiation on the fracture behavior of CFRP/aluminum joint was studied. The aluminum used was 7075-T6 and the CFRP used was multi-directional graphite/epoxy composites whose stacking sequence was [0°/±45°/0°]_3s. The surface of CFRP was treated using Ar⁺ ion irradiation in an oxygen environment. The Ar⁺ ion dose used was 1×10¹⁶ ions cm^-2. Fracture toughness of CFRP/aluminum joint was determined from cracked lap shear specimens using work factor approach. Then, the fracture toughness of ion beam-treated CFRP/aluminum joint was compared with that of untreated CFRP/aluminum joint. The results showed that the fracture toughness of ion beam-treated CFRP/aluminum case was about 72% higher than that of untreated CFRP/aluminum case. X-ray photoelectron spectrometer analysis showed that intensity of hydrophilic bonds, C=O (carbonyl group) and O-C=O (carboxyl group) was increased by the Ar⁺ ion-irradiation in an oxygen environment. Scanning electron microscope examination showed that cohesive failure occurred for ion beam-treated CFRP/aluminum joint while adhesive failure occurred for untreated CFRP/aluminum joint.