PSI - Issue 68

Ilia Nikitin et al. / Procedia Structural Integrity 68 (2025) 24–31 I. Nikitin et al. / Structural Integrity Procedia 00 (2025) 000–000

30

7

(a)

(b)

(c)

(d)

Fig. 3. (a) Results of laser track numerical simulation with not-melt volumes and (b) corresponding VHCF fracture pattern; (c) numerical simulation of re-melt volumes during SLM and (d) corresponding microstructure.

As a result of the heat transfer problem simulation, different types of defects and their distribution were predicted depending on the laser beam parameters and scanning rates. Low power or high scanning rates produce defects in the form of not-melt zones. These zones have weak links between neighboring layers that can be simulated as a local area with low elastic moduli. High power and low scanning rates produce defects in the form of re-melt zones. Such defects lead to significant strain incompatibility due to limited plasticity and can be simulated as a zone with elevated elastic moduli. Moreover, the results of the heat transfer simulations provide information about the size and distribution of the corresponding defects. The structural integrity simulations under cyclic loading were performed for a typical VHCF specimen with an hourglass shape. A series of internal defects were introduced into the 3D specimen model according to the previous heat conduction simulation, with corresponding defect shapes and spacing. The simulations were conducted for different deviations in the elastic moduli of the defects. The local Young’s moduli vary from near-zero values (non melt voids) to double the value (multiple re-melt zones). The results of the fatigue life simulation for SLM material with different types of defects (non-melt and re-melt volumes) are as follows: 2 ⁄ =0.01 (near to pore state of the internal defect) = =2.11 ∙ 10 > cycles 2 ⁄ =0.5 (the weak melting bound) = =1.08 ∙ 10 ? cycles 2 ⁄ =1 (homogeneous material without internal defects) = =4.36 ∙ 10 ? cycles 2 ⁄ =1.10 (re-melt defects with coarse grain formation) = =2.78 ∙ 10 ? cycles 2 ⁄ =1.15 (re-melt defects with coarse grain formation) = =1.87 ∙ 10 ? cycles where E 2 is the elastic modulus of regular material, E is the modulus of defect. Based on the results of numerical simulations, the presence of non-melt volumes in the SLM material decreases the fatigue life by up to 10 times, while the presence of re-melt volumes has a lower impact on fatigue life (fatigue life reduction is about 1.5 times).