PSI - Issue 4

Stefan Kolitsch et al. / Procedia Structural Integrity 4 (2017) 95–105 Stefan Kolitsch/ Structural Integrity Procedia 00 (2017) 000 – 000

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In order to describe the fracture mechanism for short cracks, the constraint effect is considered via the Q-stress. Thus the critical J-integral J c can be calculated by an potential function depending on the Q-stress and the material parameter J mat (FITNET 2008),



    p Q a

.

(2)

J J 

    1

c

mat

Here J mat is estimated from the fracture toughness K IC assuming a plane strain condition.   E ν J K 2 2 Ic mat 1    .

(3)

The dependence of the Q-stress on the crack length has been found to be quite accurately described by a potential function,   k Q a D a    . (4)

In Fig. 1 the calculated limiting curves for four different materials are plotted against the flaw size in a double logarithmic scale and compared with the experimental data.

Fig. 1. Failure assessment diagram for the fracture strain depending on the flaw size. Comparison of the experimental results and the predicted failure strain [Kolitsch et al 2017]. Additionally typical strains are displayed for the bending process and when a train is passing the switch.