PSI - Issue 35

İbrahim Yelek et al. / Procedia Structural Integrity 35 (2022) 51 – 58 Yelek et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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using three-dimensional hexahedron elements. For the region where the deformation is high, the mesh transition zone was made and modelling was done with 8 rows of elements throughout the thickness. For the elements, the /PROP/TYPE17 card was defined and fully integrated element formulation was applied. The contact state between the components was defined with the /INTER/TYPE/7 card and the friction coefficient was taken as 0.15.

Fig. 2. Finite element modelling

Materials were modelled with tabulated material card /MAT/PLAS_TAB for sheet part to represent their hardening behaviour as extracted from tensile tests. On the engineering stress-strain curves, the true stress-strain values were taken from the test device for the part from zero stress to the maximum stress value as seen in the stress-strain graphs in Fig. 4. Then, the part from the maximum stress value to rupture point was iteratively created with the support of FEA by using the inverse method as stated in Zhao et al. (2016). These iterative work results are also shown in force-displacement graphs in Fig. 4. The necking and fracture behavior could not be correctly achieved with the curves generated by using the hardening laws such as Swift (1952) and Voce (1948). The Swift and Voce hardening law parameters are given in Table 1. The Swift hardening law is defined through the Swift (1952) parameters and it is given as [ ̅ ] = ( 0 + ̅ ) (1) where A is material constant, ε 0 is initial strain, n is the strain hardening exponent and ̅ is plastic strain. The Voce hardening law is expressed as the Voce (1948) parameters. They are k 0 is material strength, Q and β are material constants and the Voce hardening law is given as [ ̅ ] = + (1 − [− ̅ ]) (2) Table 1. Swift-Voce hardening law parameter values for materials Swift Voce Specimen ID Yield strength f y (MPa) A ε o n k o Q β Modified S235JR for normal-level DX51D mechanics 272 522.1 0.0094 0.144 265.9 174.4 9.82 Modified S275JR for high-level DX51D mechanics 400 670.2 0.0206 0.131 401.6 168.4 9.66