PSI - Issue 57

Matthias Hecht et al. / Procedia Structural Integrity 57 (2024) 581–588 Matthias Hecht et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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3. Results 3.1. Fatigue behavior

The bowl specimens failed cohesively in the adhesive layer at the most highly stressed location. The results of the cyclic tests are shown in Fig. 3. Where the ratio between the vertical loading force ̅ a,Ax and the horizontal loading force ̅ a,M is ̅ a,Ax =0. ∙ ̅ a,M . (5) This ratio was chosen so that the two uniaxial loads lead approx. to the same fatigue life. Whereby care was taken to ensure that at the highest stressed locations under combined loading, both force channels have a significant effect on the stress.

Fig. 3 Experimental result of the fatigue test under pure vertical loading, pure horizontal loading, and combined loading with and without phase shift under variable amplitudes The Gassner lines were determined using the Maximum-Likelihood method according to [17]. The parameters of the Basquin equation are shown in Table 1. The scatter under uniaxial load cases is slightly higher than the one under combined load with and without phase shift. The scatter and slopes under combined loading with and without phase shift are similar to the ones under uniaxial loading.

Table 1 Statistically determined parameters of the Gassner lines

Slope ̅ a,Ax Slope ̅ a,M ̅ a,Ax

or ̅ a,M in kN at ̅ f =2∙ 0 6 Cycles ̅ a,Ax =3. 9 ̅ a,M =7.28

Scatter : ̅ a,Ax Scatter : ̅ a,M

Loading

4.93 − 3.94 4.29

− .79

: .24 −

− : .22

Pure vertical

Pure horizontal Combined, φ = 0° Combined, φ = 90° 4. 4 ̅ a,Ax =2.47 , ̅ a,M = .09 : . 4 : . . 9 ̅ a,Ax =2.97 , ̅ a,M = .78 : . :. .09 The fatigue strength under combined loading without phase shift is 31 % lower compared to pure vertical loading for a lifetime of N = 2 ∙ 10 5 cycles. A phase shift of φ = 90° leads to a 17 % higher fatigue strength compared to proportional loading at a fatigue life of N = 2 ∙ 10 5 cycles. Compared to past published experimental results under constant and variable amplitude [18,19], no strong influence in the scatter could be observed, but the slopes are slightly steeper here.