PSI- Issue 9

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Jesús Toribio / Procedia Structural Integrity 9 (2018) 311–316 Author name / Structural Integrity Procedia 00 (2018) 000–000

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3. Anisotropic fracture behavior and crack path deflection

With regard to yielding and plasticity, anisotropic plastic behavior of cold drawn pearlitic steel was reported by Toribio et al. (2011). In the matter of the anisotropic fracture behavior and the associated crack path deflection and mixed mode state taking place in cold drawn pearlitic steel in the presence of notches (notch-induced anisotropic fracture behavior), large research work was performed by Toribio and Ayaso (2001, 2002a, 2002b, 2003, 2004) on notched samples of progressively cold drawn pearlitic steels with very different notch geometries (Fig. 3) and thus very distinct stress triaxiality (constraint) were analyzed with regard to their role in fracture behavior.

Fig. 3. Notched samples of cold drawn pearlitic steels with very different geometries.

Results demonstrate without any kind of ambiguity that notch-induced anisotropic fracture behavior takes place in the notch type A from the 4 th drawing step, in notch type B from the 3 rd drawing step, in notch type C from the 5 th drawing step and never happens in notch type D, as shown in Fig. 4. The described behavior clearly demonstrates the relevant impact of the colonies and lamellae alignment and orientation on notch-induced fracture, producing anisotropic fracture behavior with its related crack path deflection (or fracture path deviation ).

Fig. 4. Fracture paths in notched samples 4A (4 drawing steps; notch A), 3B (3 drawing steps; notch B) and 5C (5 drawing steps; notch C).

In addition to the explained fracture profiles showing the crack paths as a function of the microstructural anisotropy, the fracture process zone (FPZ) was analyzed by Toribio and Ayaso (2002c). The innovative concept of micro-fracture map (MFM) used by Toribio (1997, 2002a) and by Toribio and Vasseur (1996), was further developed by Toribio and Ayaso (2009), so that MFMs were assembled for the different cold drawing degrees and constraint (triaxiality) levels generated by the corresponding notched geometry.

4. Constraint effects on anisotropic fracture behavior and crack path deflection

With regard to the analysis of constraint (triaxiality) effects on fracture behavior and crack path deflection, the main conclusion of these studies is the a nisotropic fracture behavior of cold drawn pearlitic steel in the presence of notches, although it was proved the necessity of both triaxiality (constraint) and microstructural anisotropy (colonies