Crack Paths 2012

certain slope regarding the cross section of the bolt in such a way that the angle formed

increases when the applied load decreases (bottom of Fig. 7 and Fig. 8), due to the

location and directionality of the maximumprincipal stresses [13].

(a)

(b)

(c)

Figure 7. Fatigue fracture surface.

(a) 'V=600MPa, R=0and Nf=6056 cycles.

(b) 'V=486MPa, R=0and Nf=16475 cycles.

(c) 'V=172MPa, R=0and Nf=820321 cycles.

Figure 8. Initial propagation of the fatigue crack.

After the fatigue surface, the region associated with critical cracking (fracture regime)

appears. It presents a quasi-plane shape whose size diminishes when the depth of the

fatigue fracture increases, almost disappearing for small (Fig. 7c), and a ductile edge

which corresponds to the final fracture where the thread breaks longitudinally. This last

region has a slope of 45º in its section located towards the first thread’s loaded side.

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