PSI - Issue 81

Vitalii Mocharskyi et al. / Procedia Structural Integrity 81 (2026) 31–34

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3. Results and discussion Analysis of tensile stress-strain curves of nitinol showed that after laser treatment, the relative elongation of the samples decreased by approximately 10% compared to the untreated material, while σ u (ultimate tensile strength) decreased by more than 8% (Fig.3).

Fig. 3. Tensile stress-strain curves of nitinol before and after laser processing Scanning electron microscopy images showed that the surface of the processed nitinol after static tensile test (Fig. 4). is radically different from the surface of the untreated nitinol (Fig. 5), a large number of microcracks are formed. Fracture fractograms showed that the cracks are formed on the surface and then propagate into the material (Fig. 6).

a b Fig. 4. SEM images of the surface of processed nitinol samples after tensile testing: a - magnification x50, b - magnification x500

The appearance of a large number of microcracks can be explained by the increase in the amount of martensite in the surface layers after laser processing due to ultrafast heating and cooling, which has a lower relative elongation than austenite. The increase in the amount of martensite, the number of surface cracks after laser treatment, and their growth are the reasons for the decrease in the relative elongation of the samples, as well as the decrease in σ u (the ultimate tensile strength) compared to the original material.