PSI - Issue 75

Okan Yılmaz et al. / Procedia Structural Integrity 75 (2025) 435 –441 O. Yılmaz and D. Van Hoecke / Structural Integrity Procedia 00 (2025) 000–000

440

6

UHSS-B component

r/t=3

UHSS-A component

r/t=2

r/t=1

r/t=0.5

2000

2000

1000

1000

P RAM damage parameter (MPa)

P RAM damage parameter (MPa)

100

100

1E+2

1E+3

1E+4

1E+5

1E+6

1E+2

1E+3

1E+4

1E+5

1E+6

Cycles

Cycles

Fig. 4. Fatigue initiation life of the tested UHSS-A (left) and UHSS-B (right). Component Wo¨hler curves constructed for the test geometry have the probability of failure of 2.5%.

Defective (UHSS-A)

Smooth (UHSS-A)

Smooth (UHSS-B)

bend

bend

bend

1E+7

0.5*N

UNSAFE

2*N

1E+6

1E+5

1E+4

1E+3

Calculated cycles

1E+2

SAFE

1E+1

1E+1 1E+2 1E+3 1E+4 1E+5 1E+6 1E+7

Experimental cycles

Fig. 5. Cross comparison of tested fatigue initiation life with the calculated values. A design space is defined using 0 . 5 N − 2 N scatter band.

Fracture surfaces resulting from defective and smooth bending surfaces are illustrated in Figure 6. In both cases, fatigue crack surfaces revealed multiple initiation points. For the defective bended surface, crack surface starts with a rough patch, which manifests from the initial bending defects propagating in the first cycles upon loading. On the contrary, for smooth bending operation, there was no rougher crack surface in the first millimetre and the entire crack surface showed typical fatigue crack characteristics.

5. Conclusions

The objective of this study was to develop a method that considers the complex e ff ect of cold forming in predicting number of cycles of a formed part so that the materials for fatigue-critical applications using cold-formed profiles could be assessed for quality. We developed a test methodology that can reproduce the e ff ect of bending and surface parameters and using the calculation routine proposed by the non-linear FKM guideline (Fiedler et al., 2019) that only includes stress concentration e ff ects and approximating the flow curve, a useful separator for quality assessment was