PSI - Issue 54

Martin Matušů et al. / Procedia Structural Integrity 54 (2024) 135 – 142 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

140

6

Two different specimens from platform n°1 and n°3 were analysed in Figure 4. The difference between is mainly visible in the central part of the specimen where the surface of the core section seems to have much higher roughness. Crack from the surface of a specimen for both cases as can be seen in Figure 4 with marked crack initiation. High porosity is visible in Figure 2 b) as so as the crack initiation from a notch on a surface (microscopic image was taken on SEM microscope).

ĂͿ

ďͿ

Fig. 4. a) Series T240 n°1 platform at amplitude of stress 100MPa and N f = 170 031 cycles with red mark indicating crack initiation b) Series T240 n°3 platform at amplitude of stress 70MPa and N f = 105 156 cycles with red mark indicating crack initiation 3. Temperature monitoring As part of the experimental setup, thermal cameras Flir A315 and Fluke RSE600 were used to measure the surface temperature of the tested specimens. The goal was to identify any variations in the thermal response during cyclic loading between various printed platforms. To assess the relationship between stress amplitude and stabilized temperature during fatigue testing, a step-test was devised. Load levels during each block (refer to Figure 5b) were applied for a period ranging from 3,500 to 10,000 cycles, depending on the stress level. The stabilized temperature was evaluated for stress levels ranging from 30 MPa to 130 MPa. Stabilized temperature plays a crucial role in temperature measurements during fatigue testing, as it represents the temperature range in which the specimen, be it aluminium [2] or steel [5; 6; 7; 8], spends the majority of its service life. The measurement of temperature relies on the self-heating effect that naturally occurs when cyclic loading is applied to different materials. Stabilized temperature typically manifests during the second phase of temperature evolution (see Figure 5a). The level of stabilized temperature is affected by the stress level, frequency, and the material being tested [9; 10; 11]. To ensure the focus remained on the self-heating effect, a reference non-loaded specimen was positioned near the tested specimen. This arrangement filters out the ambient temperature variations or the drift of the thermal camera. The primary objective of this paper was to investigate differences between specimens from individual platforms with the key focused parameter being the stabilized temperature increase  . Figure 6 shows the output of the observations. As regards the differences between the individual self-heating curves, it is obvious that the HTs performed at higher temperatures (T240 and T300), which affect the ductility and the disintegration of the silicon network, lead to higher observed temperature increases in the stress levels above the fatigue limit. On the contrary, the T200 heat treatment similar with artificial aging decreases the role of plastic strains and it decreases the thermal response as well.