Fatigue strength evaluation of self-piercing riveted cold rolled steel joints under mixed mode loading conditions

Fatigue strength of cross-shaped specimens of SPR joints made of SPCC was evaluated at load angles of 0°, 45°, and 90°. For the static strength at load angles of 0°, 45°, and 90°, the maximum loads were determined to be 4890N, 1969N, and 1611N, respectively. Regarding for the relationship between the load amplitude and the number of cycles (Nf), the results were 014 . 0 3 . 2209 − = f amp N P , 199 . 0 8 . 8610 − = f amp N P , and 149 . 0 3 . 3459 − = f amp N P for the load angle of 0°, 45°, and 90°, respectively. On the basis of the lifetime of 10 cycles, the load amplitudes which correspond to the fatigue limit for load angles of 0°, 45°, and 90° were 38%, 28%, and 29% of the static strength, respectively. The effective stress intensity factor was not found to be appropriate in the evaluation of the fatigue lifetime due to the different fatigue fracture behavior of these specimens.