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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the bulge test carried out in the study of Yadav (2008). The stress ratio, r-values of the material and the determined coefficients of the yield function are shown in Table 1 and 2, respectively.

Ͳ (-) Ͷͷ (-) ͻͲ (-) „ (-) 1.000 0.9468 0.9795 0.9611

Table 1. Plastic properties of the material (Sener et al. 2021). Material

r 0

r 45

r 90

AISI 304

0.461 0.865 0.863

Table 2. The parameters of the yield function. (Sener et al. 2021). Material ƒ ͳ ƒ ʹ a 3 a 4 a 5 AISI 304 1.000 -1.2631 2.3616

a 6

a 7

a 8

a 9

-2.0126 1.0861 5.5580 -4.2162 6.9908 10.4084

Planar anisotropy (the yield stress ratios and r-values) variations of were predicted, and yield locus contour was computed by the determined coefficients, and they were compared to the experimental findings given in Table 1 to validate the material model. The comparisons of the predicted results with experiments are shown in Fig. 1.

Fig. 1. (a) yield stress ratio; (b) r-value; (c) yield locus.

As it is seen from the Fig.1, the anisotropic behavior of the material was effectively defined by the determined material constants in the yield function. 2.2. Determination of the critical damage indicator with different mechanical tests In this study, a damage model considering the plastic work was used. In this model, the fracture initiation is predicted based on the stored distortional energy value until the failure. The formulation of the fracture model is given in Eq. (2) (Freudental, (1950), Clift et al. (1990)). ( ) eqv f  (2) Where C denotes the critical damage indicator, and it is determined by computing the area under true stress-true plastic strain curve. The criterion was adopted by Clift et al. (1990) to predict the fracture initiation in three different forming operations: strip compression and tension, axisymmetric extrusion, and simple upsetting. Generalized plastic work criterion provided successful agreements. Recently, Akşen et al. (2022) also implemented this failure model to predict the stretch flanging performance of TWIP940 steel and the stroke at which the fracture initiates and the hole expansion ratio were accurately predicted. This criterion is a practical phenomenological ductile fracture model that 0 f eqv eqv C d   = 