Improvement of Interlaminar Bonding in EPDM/CFRP Joints via Controlled Laser Micromachining

In this study, a nanosecond-pulsed ultraviolet laser surface processing technique was used to create periodic microgroove matrix structures on the surface of an ethylene propylene diene monomer (EPDM) substrate for interfacial strengthening with carbon fiber-reinforced composites (CFRP). The effects of surface modification on the mechanical properties of the bonding interface were systematically investigated via mechanical tests combined with multiscale characterization methods. The experimental results demonstrated that laser surface treatment reduced the contact angle of the EPDM surface by 67.8% and increased the surface roughness (S_a) to 26.21 μm. These changes significantly enhanced the material surface wettability and mechanical interlocking effect. Fourier-transform infrared spectroscopy analysis confirmed that the laser treatment increased the prevalence of hydrophilic groups on the EPDM surface. Single-lap shear strength tests revealed that the maximum shear strength of the EPDM/CFRP joint reached 4.84 MPa, which was 325% higher than that of the untreated specimen. In addition, the failure mode shifted from adhesive failure to substrate failure. This study provides a substantial theoretical and experimental basis for optimizing the EPDM/CFRP bonding interface.