Elastic-plastic deformation and organization analysis for Al 7075 friction stir welding joints based on MXene/SWCNT sensor

In this paper, the health monitoring of Al 7075 friction stir welded structure was carried out, including elastic and plastic deformation during stretching and bending. A thin film sensor composed of MXene and single-walled carbon nanotubes was developed by simple mixing and vacuum filtration. This flexible MXene/SWCNT thin film sensor combining the sensitivity of MXene with the stability of carbon nanotubes and can be pasted on the surface of Al 7075 FSW joints through polyimide encapsulation to achieve structural health monitoring. The experimental results show that the MXene/SWCNT sensors encapsulated in polyimide can effectively capture the micro strain of different areas during stretching and bending. When the strain of the welded structure is less than 3000, only elastic deformation occurs in different regions of the welded structure, and the sensors located in different regions show the same resistance change rate. When the strain is greater than 3000, the resistance change rate of the sensors in the thermal-mechanical affected zone and heat affected zone obviously, and when the external force is released, there is residual resistance, which proves that the plastic deformation occurs in the welded structure at this time. By comparing the resistance change rate of the sensors in different regions, it can be inferred whether plastic deformation occurs. As the strain further increases, the resistance change rate of the sensor further increases and make a stable response until the structure breaks. This sensor can be used to track the whole process monitoring of welded structure before fracture.