PSI - Issue 17

Liting Shi et al. / Procedia Structural Integrity 17 (2019) 355–362 Liting Shi/ Structural Integrity Procedia 00 (2019) 000 – 000

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Tensile shear specimens were tested at a displacement rate of 3 mm/min using an MTS load frame until fracture, i.e. full material separation. The fractured specimens were collected for fracture modes assessment. Pull out and interfacial fracture were used to define the fracture modes.

3. Determination of critical weld nugget diameter ensuring pull out fracture mode

An empirical formula to determine the critical weld nugget diameter recommended by AWS is shown as follows, = 4√ (1) where t is thickness of sheet where pull out fracture occurs in mm. From Fig. 1, it can be observed that to ensure fracture occurring in the HAZ and not at the interface, we have, ≥ (2) and ≤ (3) where is shear stress around the HAZ, = ( (1 − )) ⁄ and are shear stress at IMC layer, = 4 ( 2 ) ⁄ . and are the shear strength of HAZ and IMC layer. Further, d is the weld nugget diameter, is the thickness reduction rate of the aluminum sheet, and t is the aluminum sheet thickness. From inequalities (2) and (3), we can obtain the critical weld nugget size, as follows, ≥ 4 (1 − ) (4) where the shear strength ratio, β = ⁄ (5) For the aluminum stack-ups, a new formula for critical weld nugget diameter calculation was previously developed (Shi et al. (2019)) as follows, ≥ 4 (1 − ) (6) where is the ratio of shear strength of HAZ to weld nugget. The predicted fracture load is calculated as = (1 − ) (7)

4. Results and discussion

The experimental results including sheet thickness reduction, weld nugget diameter, fracture load, and shear strengths of the HAZ, aluminum weld nugget, and IMC are provided in Table 3.

Table 3 Experimental results of aluminum and aluminum-steel stack-ups. The standard error is also listed..