PSI - Issue 79

Daniel Hofferberth et al. / Procedia Structural Integrity 79 (2026) 313–321

317

Based on the information for each type of specimen with its individual geometry, the stress concentration factors were calculated by using FEA and the analytical equation (2), as well as the V 90% , calculated by using the FEA method, Table 1.

Table 1: Results of the FEA and analytical (K t,a ) calculations

Specimen type

ISO 2740

ISO 3928 R30

ISO 3928 R09

Analysis

FEA 1.06

analytical FEA

analytical FEA

analytical

Stress concentration factor K t,a Highly stressed volume V 90% [mm³]

1.08

1.06 15.4

1.07

2.51 0.13

2.49

840

For the assessment approaches, the FEA results will be applied. 4. Fatigue assessment

Fatigue tests under alternating (R = -1) and pulsating tensile loading (R = 0) were performed at room temperature. The ageing at office conditions was used as reference for the comparison with the different elevated temperatures with lower humidity (40°C/10% and 60°C/10%). The results of the fatigue tests of the individual specimen geometries were shown as S-N curves in double-log diagrams. The evaluation was performed by applying the MLM method. Since only a small influence of aging conditions was observed during the fatigue test evaluation, and the number of test points for each individual condition was limited to 4, all fatigue tests were statistically evaluated independently of the aging conditions. The fatigue test results for the different ageing (storage) conditions are shown in the S-N curves in Fig. 4. Based on this common investigation of the fatigue test results, in total six S-N curves were determined in the range between 10 2 < N ≤ 1 ꞏ 10 6 load cycles at ambient temperature. Based on the MLM evaluation, the slope k, the endurable stress amplitude for a probability of survival of P s = 50 % of each S-N curve were determined. The scatter band T σ , based on the Gaussian log-normal distribution, was estimated, too.

Fig. 4: Common evaluation of the individual results ISO 3928 R30

With the knowledge of the small impact of the aging conditions, the common evaluation was performed consistently, Fig. 5 and Fig. 6.