PSI - Issue 23

Tomáš Oplt et al. / Procedia Structural Integrity 23 (2019) 101–106 Tomáš Oplt / Structural Integrity Procedia 00 ( 2019) 000 – 000

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4. Conclusions

In presented paper was introduced three-dimensional modelling of plasticity induced crack closure of M(T) specimen with straight crack. Settings for numerical model were adopted from previous 2D study (Oplt et al. 2019). Crack was subjected to cyclic loading with constant load range ∆ K = 20 MPa√m advanced for 10 cycles. 1) Numerical results demonstrated that closure levels estimated in the middle of the body were very similar to 2D solution (Oplt et al. 2019) and experimental results (Pokorný et al. 2017) . Presence of crack closure significantly decreases the effective SIF K eff , which promotes the growth. Thus, instead of loading crack by full ∆ K , crack is closed earlier even though global loading is tensile and therefore, crack cannot grow anymore. 2) In reality, fatigue crack does not propagate as a straight line as was assumed in presented paper, but it is always curved. Advantage of 3D modelling is in its ability to describe effects causing the curvature locally, along the whole crack front. One reason for curvature is different singular stress field due to the effect of the free surface. Similarly as K max distribution decreases at the free surface, also crack closure K cl occurs significantly earlier close the free surface. Therefore, when the load asymmetry is low and premature crack closure occurs, both effects are combined together. That leads to lower K eff and crack propagates slower than in the middle of the body. Thus, crack front will be curved more when the crack closure will occur as was also reported experimentally.

Acknowledgements

Financial support was provided by the Grant Agency of the Czech Republic (18-03615S) and infrastructural project m-IPMinfra (CZ.02.1.01/0.0/0.0/16_013/0001823). The equipment base of research infrastructure IPMinfra were used during the research activities.

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