PSI - Issue 52

Tomáš Vražina et al. / Procedia Structural Integrity 52 (2024) 43 – 51 Tomáš Vražina et. al/ Structural Integrity Procedia 00 ( 2022) 000 – 000

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to the increase in dislocation density as a consequence of the imposed strain amplitude. The relatively high dislocation density tends to complicate interactions between dislocations, resulting in the formation of planar tangled structures that impede dislocation movement. Additionally, dislocation annihilation becomes more pronounced with the activation of a secondary slip system. Once the total dislocation density reaches equilibrium and the maximum stress amplitude is attained, further cycling triggers rearrangements within the dislocation structure, resulting in the production of walls and channels. The low concentration of dislocations in channels makes dislocation movement easier, leading to softening of a material.

Fig. 4 Fatigue hardening/softening curves a) HR material b) LPBF material.

The cyclic stress-strain curves in the dependence of the stress amplitude vs plastic strain amplitude presented in Fig. 5 reveal that the cyclic behavior at the half-life of HR material is shifted slightly to higher stress amplitudes. However, it has to be noted that both materials are within statistical scatter interchangeable. Experimental data are fitted with the following equation (5) and the parameters of this dependence for LPBF and HR material are shown in Table 3. log = ′ log +log ′ (5)

Fig.5 Cyclic stress-strain curves of LPBF and HR material.

Table 3 Calculation of cyclic stress-strain curves parameters of 699 XA. LPBF

HR

′

´ (MPa)

950 ± 50

980 ± 170

(-)

0.12 ± 0.01

0.13 ± 0.02