IFMASS10

189

Figure 18: The crack blunting mechanism for striation formation during fatigue crack growth /13/

Figure 19: Fractographs fatigue fracture surface of 7000 aluminium alloys on SEM /14/

9. CONCLUDING REMARKS

he type of fracture caused by load application depends on the stress state on the

crack tip. When the plastic zone on the crack tip is small, as considered in LEFM, a

cleavage fracture occurs, whereas a ductile fracture occurs when the plastic zone on the

crack tip is large, considered in EPFM, producing different fracture morphology.

The width of the stretch zone when testing fracture toughness in EPFM conditions

provides a useful parameter for determination of J integral. The J value obtained by

measuring SZW is considered not to have

ligament size effect.

It must be taken into

account that the slope of the blunting line is sensitive to the microstructure and the

loading rate, and for that it is better to determine both width (SZW) and depth (SZD) of

stretch zone.