PSI - Issue 61

Toros Arda Akşen et al. / Procedia Structural Integrity 61 (2024) 260 – 267 Toros Arda Akşen, Bora Şener, Emre Esener, Mehmet Firat / Structural Integrity Procedia 00 (2019) 000 – 000

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As it is seen from Fig. 6 that tearing was observed in the cup corner in both FE analysis. The higher die displacement value (96 mm) was predicted with the CDI value obtained from the bulge test than that of uniaxial tension test (61 mm). In addition, the fracture initiation region and its propagation were compared with the experimental result, and it was noticed that the proposed numerical model, which the critical damage indicator is procured from the bulge test could well predict propagation path of the crack (Fig. 8). Fig. 8 illustrates the ratio of plastic work distribution to critical damage indicator as percentage.

Fracture initiation

Crack propagation

Fig. 8. Fracture initiation and its propagation.

The crack paths were also similar for the critical damage indicator from the bulge test and the uniaxial tension test; however, the punch strokes at fracture initiation were different. In Fig. 8, the legend shows the fracture initiation. When the region re ached 1, the fracture was assumed to begin. The fracture initiated at the blank’s region interacted with the punch’s corner radius in both experiment and simulations. In the study of Şener and Kurtaran (2016), the blank was drawn by 80 mm without tearing. In this study, the blank was drawn 120 mm under identical conditions, and a major fracture was observed (Fig. 8). In the numerical approach, the critical damage indicator from the bulge test predicted higher fracture stroke than 80 mm, whereas critical damage value from the uniaxial tensile test predicted lower fracture stroke that is not accurate. Considering the magnitude of the tearing, and the blank was drawn under same conditions by 80 mm without tearing, the fracture may be initiated slightly higher than 80 mm. In this regard, the critical damage value determined from the bulge test provided plausible approximation. 5. Conclusions In this manuscript, the effect of the mechanical tests adopted to adjust the ductile fracture model on the fracture initiation prediction was investigated. A model considering material anisotropy and ductile fracture was developed and it was applied to predict the fracture in the rectangular cup drawing process. Material anisotropy was identified with the fourth-order homogeneous polynomial yield function and plastic work criterion was used to predict tearing in the process. The CDI was calibrated with uniaxial tensile and biaxial bulge tests and the process was separately simulated with the determined critical damage values. Fracture initiation was predicted at higher die displacement value with damage indicator value obtained from the bulge test and the predicted value was closer to the experiment. This is explained with the suppression of the diffuse necking in the bulge test. In the bulge test, equi-biaxial stress state occurs, and diffuse necking is delayed during the test. Therefore, the higher critical failure index is determined, and the higher fracture displacement (die displacement) is predicted in the analysis. From these results, it can be concluded that a convenient mechanical test leading to similar stress state with the fracture region of the forming