PSI - Issue 21

E.F. Akbulut Irmak et al. / Procedia Structural Integrity 21 (2019) 190–197 E. F. Akbulut Irmak et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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In the current study, characterization and modeling of the anisotropy of the material were carried out by Cazacu Barlat yield function, which can describe the yielding asymmetry between tension and compression. Cazacu et al. (2006) introduced the yield criterion in the form = (| 1 | − 1 ) + (| 2 | − 2 ) + (| 3 | − 3 ) (1) where , i =1,…,3 are the principal values of the stress deviator. The exponent a is considered as a positive degree of homogeneity of the yield function, k is a material constant. The size of the yield locus either constant or function of the accumulated plastic strain is given by F symbol. According to the criterion, the ratio of tensile to compressive uniaxial yield stress is given by Cazacu et al. (2006) = { ( 2 3 ∗(1+ )) +2∗( 1 3 ∗(1− )) ( 2 3 ∗(1− )) +2∗( 1 3 ∗(1+ )) } 1 (2) To clarify, if the yield stresses in tension and compression are equal, then k =0. In particular, for k =0 and a =2, the yield criterion reduces to the Von Mises yield criterion, Plunkett et al. (2008). Homogeneity exponent is significant to capture the material’s response . According to a study carried out by Plunkett et al. (2008), the exponent was determined by evaluating the entire data set as a =4 for magnesium alloy, a =5 for medium alloy carbon steel and, a =12 for aluminum alloy sheet metal, respectively. For the material used in the current study, the degree of homogeneity of the yield function was determined as a =12. Homogeneity exponent was adjusted until good approximation of the data was obtained. Cazacu-Barlat yield locus parameters were determined in accordance with the experimental results. In order to describe hardening behavior of the material, Hockett-Sherby hardening law was calibrated with respect to the uniaxial tensile test in 0-degree and implemented in the numerical models. As a material model, *MAT_233 (*MAT_CAZACU_BARLAT) was implemented. Yield locus and the hardening model are seen in Figure 4.

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Figure 4. a) Yield locus and b) Hockett-Sherby hardening law

Fracture surfaces of the specimens were investigated with two different types of specimens. When the fracture surfaces of the deformed specimens are examined carefully, brittle-ductile fracture features can be observed.