PSI - Issue 38

Kimiya Hemmesi et al. / Procedia Structural Integrity 38 (2022) 401–410 Author name / Structural Integrity Procedia 00 (2021) 000 – 000

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Fig. 3. Summary of the staircase tests for notched specimen from 42CrMoS4, at OL 1.

a)

b)

Fig. 4. S-N curves for notched specimens: a) 42CrMoS4, b) EN AW-6082.

3. Notch root strain measurements During the overload cycles, the notch root strain history was monitored by means of the digital image correlation (DIC) technique using a 3D system ARAMIS by GOM. The system consists of two digital cameras and an evaluation software which allows for an accuracy of displacement measurements of 0.01 %. The results reported below are based on a gauge length of 0.54 mm positioned ±0.27 mm with respect to the notch root. Fig. 5 shows the force and axial (longitudinal) strain records for a 42CrMoS4 (a) and an EN AW-6082 (b) specimen during five overload cycles. The latter were applied under force control, starting towards the tensile regime and ending with unloading from the compressive regime. In contrast to OL 1 (see Fig. 5a and Fig. 5c), the strain signal due to OL 2 exhibits a considerable non-linear behaviour for both materials (see Fig. 5b and Fig. 5d). This indicates that pronounced strain hardening occurs at OL 2, while this effect is of minor significance at OL 1. Another experimental finding is that, after five overload cycles and subsequent unloading to force = 0 kN, remaining compressive strains were measured in all cases, being especially pronounced for the both materials at OL 2 and for the aluminium alloy at OL 2.