PSI - Issue 31

Mohammad Reza Khosravani et al. / Procedia Structural Integrity 31 (2021) 105–110 Mohammad Reza Khosravani et al. / Procedia Structural Integrity 00 (2020) 000–000

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3.2. Accelerated thermal ageing procedure

Since structural components might be subjected to di ff erent environmental conditions in their service life, investi gation about the influence of the working conditions on the mechanical behavior of these parts is a necessity (Baragetti et al., 2019; Tavares et al., 2020). In this study, both groups of intact and defected specimens were subjected to accel erated thermal ageing conditions. To this aim, dog-bone shaped specimens were placed in an environmental climate test chamber. In order to provide a reliable simulation of long-term thermal ageing, the temperature of accelerated ageing should not be far from the service temperature. In this respect, the specimens were artificially aged in the temperature range of -5 ◦ C to + 35 ◦ C and each temperature was kept for 5 h. The temperature deviation was ± 0.1 and the ageing cycle was continuously repeated in 10 days. After accelerated thermal ageing process, the specimens were cooled down to room temperature and then tested similar to the unaged specimens. It is noteworthy that the specimens were weighted before and after accelerated ageing procedure. The average of changes in the specimens weight are presented in Table 1.

Table 1. Changes in weight of the 3D-printed specimens before and after thermal ageing. Specimen Original weight ( g )

Weight after ageing ( g )

Changes ( % )

Intact 0 ◦ Intact 90 ◦ Defected 0 ◦ Defected 90 ◦

17.546 17.897 17.125 17.137

17.421 17.786 16.992 16.989

0.71 0.62 0.77 0.86

Prior and after accelerated ageing procedure, length, width and thickness of the specimens were measured precisely and no changes were made. Moreover, an optical microscopy assessment was performed and no type of failure was observed on the aged specimens after thermal ageing process.

3.3. Tensile tests

In order to evaluate the e ff ects of thermal aging and the extent of those e ff ects on the mechanical behavior of 3D printed parts, a series of tensile tests was performed. To this aim, all specimens were tested using a universal testing machine equipped with a 15 kN load cell. In the present study, the tensile tests were conducted with a constant cross-head speed of 5 mm / min. Fig. 3 shows examined specimens after uniaxial tensile test.

Fig. 3. Fractured specimens after tensile tests; intact and unaged (top), defected and aged (bottom).