Effect of atmospheric pressure plasma modification on surface temperature and Mode-I fracture toughness of carbon fiber reinforced polymer

Atmospheric pressure plasma modification has been commonly applied to improving the adhesive bonding performance of carbon fiber reinforced polymer (CFRP). However, plasma modification generally induces a high temperature on material surface, and causes thermal deformation, internal stress, and even damage to the CFRP. Therefore, it is necessary to further optimize the process parameters of plasma modification effects to meet the requirements of engineering application. This article uses air as the source of atmospheric pressure plasma to study surface temperature of CFRP under different process parameters. The functional relationship was established between surface temperature, nozzle height, and scanning speed, achieving accurate prediction for plasma-induced surface temperature (root mean square error of 2.7℃, maximum deviation of 5.4℃). Then, the scanning path of plasma modification was further optimized to reduce the cumulative effect of heat during the modification process. Based on the test results of plasma modification on the bonding performance of CFRP, the optimal process parameters were determined for plasma modification to control the surface treatment temperature less than 150℃, i.e., a nozzle height of 16 mm, a scanning speed of 45 mm/s, and a scanning spacing of 16 mm, where the surface temperature of CFRP is measured as 143.9℃. Consequently, the Mode-I fracture toughness is increased to 425 J/m² (approximately 534.3% higher than the original state), and the failure mode is improved from interface to mixed failure. The research results aim to find the optimal process of parameters plasma modification with consideration of surface temperature and adhesive bonding performance, which provides valuable and practical information to the engineering application of plasma modification processes for CFRP materials.