PSI - Issue 53

Reza Ahmadi et al. / Procedia Structural Integrity 53 (2024) 97–111 Author name / Structural Integrity Procedia 00 (2019) 000–000

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distribution exhibited dynamic changes as the load was applied: initially, upon loading, the detection of the hottest area likely indicated the initiation of damage, possibly stemming from the part with high stress concentration for full bodies and from notches for notched specimens (Figures 9,11,15). Subsequently, intermittent flashes of intense brightness, symbolizing the release of energy during the formation of damage, were observed. In the final phase of testing, a uniform temperature increases across the specimen surface became evident, attributed to the propagation of damage throughout the specimen. These thermal observations provided a vivid depiction of the evolving damage mechanisms and their associated thermal signatures. Based on figure 8 the outcomes of the comprehensive thermal analysis conducted on the entire full specimens, the calculated average value for the damage stress is determined to be 27.2. This value represents the threshold at which damage initiation occurs within the material. In the case of specimens with a single hole and two holes (Figure 10,14), the average result stands at 22.2 and 19.4 MPa, which is lower compared to the results obtained for full specimens. The decrease in the damage stress threshold from 27.2 for full specimens to 22.2 for specimens with a single hole and 19.4 for specimens with two holes highlights the importance of considering the geometry and features of structural components in mechanical and thermal analyses, because stress concentrations tend to occur at the edges of holes or notches, potentially reducing the damage stress of the specimen with two holes compared to the un-notched specimen. It also emphasizes the significance of stress concentrations and their impact on material behaviour. These results suggest that the presence of a single hole or two holes in the specimens has reduced their damage stress threshold compared to the full specimens. In other words, the material is more sensitive to damage initiation in the presence of holes. This observation is consistent with the general understanding that stress concentration effects near geometric irregularities, such as holes or notches, can lead to earlier damage initiation. Broken specimens are shown in figures 12,13.

Figure 10. Temperature evolution vs applied stress during static tensile test for notched specimens with one hole.