PSI - Issue 68

Niklaas Becker et al. / Procedia Structural Integrity 68 (2025) 776–781 Niklaas Becker / Structural Integrity Procedia 00 (2024) 000–000

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2.3. Residual stress

Residual stress measurements were performed using high X-ray di ff raction at beamline P07B at PETRA III at DESY (Deutsches Elektronen Synchrotron, Hamburg, Germany). The line measurements were carried out in trans mission with 1.0 mm of measuring point distance passing through the center of the spot weld, see Figure 1 a). The Al (311) reflection was used to determine the horizontal (Y-axis) and vertical (X-axis) strains using the FIT2D software from Hammersley et al. (1994). A stress-free specimen was used as a reference.

2.4. Hardness

The hardness measurement was carried out 14 days after welding on a Struers Duracan using the HV0.2 method with an indenter opening angle of 136°. Three rows were measured with a vertical distance of 0.5 mm and a distance between the measuring points of 0.5 mm, Figure 1 a).

3. Results

Figure 2 shows the temperature distribution within the spot weld as a function of the plunge time of: 0.8 sec, 1.5 sec and 3.5 sec. It can be seen that the maximum temperature in the center of the spot weld is always reached shortly after the plunge time is achieved and increases with increasing plunge time. The kink in the temperature curves indicates the welding tool leaving the surface of the welding object. As the plunge time increases, the maximum temperature also increases at all other measuring points.

Plunge time 0.8 sec

600

Center

500

2.5 mm

400

5.0 mm

300

10.0 mm

200

100

Temperatur [°C]

0

0.0

2.5

5.0

7.5

10.0

12.5

15.0

Time [s]

Plunge time 1.5 sec

600

Center

500

2.5 mm

400

5.0 mm

300

10.0 mm

200

100

Temperatur [°C]

0

0.0

2.5

5.0

7.5

10.0

12.5

15.0

Time [s]

Plunge time 3.5 sec

600

Center

500

2.5 mm

400

5.0 mm

300

10.0 mm

200

100

Temperatur [°C]

0

0.0

2.5

5.0

7.5

10.0

12.5

15.0

Time [s]

Fig. 2. Temperature as a function of plunge time measured in the center and at 2.5 mm, 5.0 mm and 10.0 mm distance from the weld center.

In Figure 3 the in-plane residual stresses σ xx and σ yy for the di ff erent welding parameter are shown. The stresses in y-direction are purely positive, i.e. tensile stresses. The stresses increase in the direction towards the spot weld and reach their maximum within the spot weld. The slope of the σ yy stress curve decreases with the increase in energy input, i.e. larger Pt. In contrast, σ xx show some tensile and compression regions. In the direction towards the spot weld,