PSI - Issue 81

Jesús Toribio et al. / Procedia Structural Integrity 81 (2026) 558–561

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fractographic mode consisting of a sort of enlarged & oriented cleavage mode, the orientation and enlargement being along the wire axis or cold drawing direction.

Fig. 3. Samples 4A and 6A.

Fig. 4. Samples 4B and 6B

Fig. 5. Sample 6C.

A clearly anisotropic fracture behaviour is observed in the most heavily drawn pearlitic steels, associated with the experimental evidence of the appearance of fracture propagation step deflected 90º in relation to the initial fracture propagation direction in mode I (transverse to the wire). Specimen geometry D (with minimum level of stress triaxiality or constraint) does not exhibit any global 90ª-step, but only local deflections ( embryos of anisotropic fracture). Thus the 90º- step is the signal of strength anisotropy induced in heavily drawn pearlitic steels as a result of the orientation (microstructural) anisotropy generated in the material by the cold-drawing manufacture process. 6. On the role of stress triaxiality (constraint) and microstructural anisotropy/orientation The afore-said anisotropic fracture behaviour of heavily cold drawn pearlitic steels (exhibiting a fracture profile with a 90º step) can be rationalized on the basis of the markedly oriented microstructure of the steel. However, a sufficient level of stress triaxiality ( constraint ) is required in the notched specimens to obtain the afore-said anisotropic fracture behaviour (associated with cracking/fracture path deflection ) with mixed mode propagation and to avoid the otherwise isotropic fracture behaviour for lower levels of stress triaxiality. The limit case of minimum triaxiality (smooth wire) exhibits isotropic fracture behaviour, while that of maximum triaxiality (cracked wire) has a clear anisotropic fracture behaviour (Toribio and Toledano, 2000).