Research on the joining of three-layer sheets by flat bottom riveting process

With the widespread application of lightweight materials in aerospace and automotive industries, higher demands are placed on the joining technology of lightweight materials, and the flat bottom riveting process is proposed as new technology. In this study, the material flow of three-layer sheets during the flat bottom riveting process was investigated using experimental methods. The failure modes of the sheets under different loading methods were discussed in tensile and shear tests. The results showed that a double mechanical interlock structure was created among the three-layer sheets. The first mechanical interlock between the upper and middle sheets has higher tensile and shear loads than the second mechanical interlock between the middle and lower sheets. The double mechanical interlock structure has higher joint strength compared to the single mechanical interlock structure formed by two-layer sheets of flat bottom riveting process. In addition, the tensile and shear load application methods can cause different modes of failure of the sheet. Tensile failures and pull-off failures occur with higher tensile loads and shear failures and mixed failures occur with higher shear loads. The first mechanical interlock has a stronger failure energy absorption capacity.