PSI - Issue 43

Lucie Malíková et al. / Procedia Structural Integrity 43 (2023) 264–269 Lucie Malíková et al. / Structural Integrity Procedia 00 (20 22) 000 – 000

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et al. (2002) or IABSE (2005). For the ongoing experimental campaign, the S460, S690 and S960 steels were selected with the following mechanical properties declared by producers at the room temperature: S460 ( R p0.2 = 486 MPa, R m = 609 MPa), S690 ( R p0.2 = 755 MPa, R m = 833 MPa) and S960 ( R p0.2 = 1040 MPa, R m = 1065 MPa). The own experiments are just at their beginning. Particular parameters of the corrosion pit as well surface cracks are not known yet, but they will be investigated by means of optical microscopes, see an example of a round specimen in Fig. 1c and a detail of a corrosion pit in Fig. 1d.

b)

a) d) Fig. 1. a) Scheme of the cracked bar with a one corrosion pit under tensile loading, b) an example of samples prepared under corrosion conditions, c) an example of a specimen with an initiation of a corrosion pit and d) a detail of the corrosion pit performed on S690. To be able to estimate the influence of the corrosion pit on the further crack propagation, higher-order terms of the Williams expansion for approximation of the stress tensor components in the vicinity of the crack tip were calculated via over-deterministic method. As has been mentioned, the details on the particular methodology can be found in Ayatollahi and Nejati (2011). Ten initial terms of the Williams expansion were determined and then, the requested stress tensor components could be expressed accordingly to the following equation: = ∑ 2 2 −1 =1 ( , ) + ∑ 2 2 −1 =1 ( , ) where i , j  { x , y }. (1) The symbols used in Eq. 1 have the following meaning: • σ ij ... stress tensor components; c)

• A n , B m ... coefficients of the WE corresponding to the loading mode I and II, respectively; • N , M ... number of the WE terms corresponding to the loading mode I and II, respectively; • ( r , θ ) ... coordinates of the polar coordinate system (assuming its origin at the crack tip); • f σ , g σ ... known dimensionless stress functions for loading mode I and II, respectively.

Before the selected fracture criterion was applied, the stress intensity factors had been calculated via an interaction integral method implemented in ANSYS through the command CINT. Let’s not that this command can be used for determination of lots of fracture parameters, such as T -stress, J -integral, C* -integral, material forces, energy-release rate etc. Thus, the correctness of the higher-order terms coefficients could be verified. In the last step of the study presented in this paper, the generalized form of the well-known maximum tangential stress (MTS) criterion, see Erdogan and Sih (1963), was used for estimation of the angle of the further crack