PSI - Issue 79

Ibrahim T. Teke et al. / Procedia Structural Integrity 79 (2026) 17–25

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3.2. Single-Lap Joints (SLJ) Table 2 reveals a dramatic overestimation in life when prestress is omitted for dissimilar Mg – Al SLJs. For example, at 2.7 kN, the experimental fatigue life was 7691 and 8793 cycles, while the non-prestressed model predicted over 104 million cycles, clearly unrealistic. However, the prestressed model predicted 6061 cycles, aligning well with the physical behavior and emphasizing the necessity of thermal stress consideration in dissimilar joints with mismatched thermal expansion coefficients. Table 2. Mg-Al dissimilar spot-welded SLJ life prediction capability with prestress.

Load (kN) 4.05 4.05

Without Prestress Prediction

Experimental Prediction

Study

1767 1317 3070 2173 3052 3857 7691 8793

957 957

3,886,700 3,886,700 9,628,400 9,628,400 17,961,000 17,961,000 104,290,000 104,290,000 698,700,000 698,700,000

Sun et al. (2016) Sun et al. (2016) Sun et al. (2016) Sun et al. (2016) Sun et al. (2016) Sun et al. (2016) Sun et al. (2016) Sun et al. (2016) Sun et al. (2016) Sun et al. (2016)

3.6 3.6

1360 1360 2914 2914 6061 6061

3.33 3.33

2.7 2.7 1.8 1.8

37170 40054

21497 21497

3.3. SLJ Joints with Steel – Steel Combinations The results in Table 3 further validate the importance of prestress integration. At 2.76 kN, the experimental life was 37,964 cycles, the pre-stress prediction was 27,774, and the non-prestressed model yielded 232,510 cycles — more than 6× the experimental v alue. This overprediction trend persisted at lower loads, particularly in the high-cycle regime, where residual stress distributions play a dominant role in fatigue crack nucleation. Table 3. Steel-steel dissimilar spot-welded SLJ life prediction capability with prestress.

Load (kN) 3.36 2.76 2.17 1.58

Without Prestress Prediction

Experimental Prediction

Study

11,933 37,964 151,674

9723

73,257

Asati et al. (2022) Asati et al. (2022) Asati et al. (2022) Asati et al. (2022)

27,774 232,510 117,750 1,117,900

1,162,417 1,132,500 11,805,000

3.4. Modified Tensile-Shear (MTS) Joints For similar DIN 1623 steel MTS specimens (Table 4), the effect of prestress was less pronounced but still non negligible. At 2.1 kN, the experimental life was 433,452 cycles, while the pre-stressed model estimated 218,420 and the non-prestressed model gave 225,420. In this case, both models slightly underestimated fatigue life, but the pre stress model captured life evolution more accurately in mid-cycle ranges (e.g., 2.4 – 3.0 kN). The results indicate that in similar material joints, prestress improves accuracy but is not as critical as in dissimilar interfaces.