Effects of moisture and temperature on shear strength of resistance welded joints of CF/PEEK composites

In this study, aluminum nitride (AlN) modified carbon fiber heating elements (HE) were used to connect carbon fiber reinforced poly-ether-ether-ketone (CF/PEEK) composites by resistance welding. The effects of AlN content and environmental conditions on the lap shear strength (LSS) of resistance welding composites were investigated by preparing welded joints with different AlN content. The results show that the LSS of the welded joint increases rapidly with the increase of AlN content. When the content of AlN is 5 wt.%, the maximum strength reaches 30.63 MPa. The welded joints were then placed in room temperature (25°C, 50% relative humidity (RH)) and artificial aging chamber (85°C, 90%RH) for 28 days, respectively, and tested in the temperature range of −30°C to 145°C. It is found that with the increase of test temperature, the LSS under the two environmental conditions shows a decreasing trend. High temperature and moisture absorption will have a superimposed negative impact on the LSS of the welded joint. At 145°C, the strength of the sample under elevated temperature wet (ETW) environment is the lowest, which is 21.61 MPa. The SEM analysis of the fracture surface of the joint shows that the main failure mechanism of the joint is the cohesive failure of HE. The main reasons for the degradation of interface bonding properties are wet heat aging and high temperature environment.