Effect of notch acuity on the fracture behavior of AZ31 Mg alloy

Fracture mechanism and toughness of a rolled magnesium alloy under dynamic loading

“…The latter are far more numerous close to the initial crack front (Fig.8(a)). Thus, a brittle to ductile transition seems to have occurred with crack extension in the static experiment, which was also reported by Prasad et al [15] in their static fracture tests with fatigue pre-cracked four-point specimens. On the other hand, the fractographs pertaining to the dynamic tests continue to show dimples far ahead of the initial crack front as well (Fig.9(b), (c)).…”

“…They reported elongated stripes or grooves on the fracture surface and concluded that these form by intersection of twins (of another variant) on the fracture surface. Similar groove-like features on the fracture surface were also noted in [12,15] from static fracture tests using fatigue pre-cracked specimens and by Kondori and Benzerga [3] from cylindrical tensile specimens with fine circumferential notches of AZ31 Mg alloy. By contrast, far few dimples were observed on the fracture surfaces of the statically loaded specimen.…”

“…They noted that a significant contribution to toughness (roughly 70%) arises from profuse tensile twinning in the background plastic zone which corroborates with [13]. Further, a strong enhancement in J c with notch size was also noticed in [15] accompanied by a brittle-ductile transition. The complex interplay between stress triaxiality level (varied by changing the notch size) and plastic anisotropy has been found to influence ductility and failure mechanism in notched cylindrical AZ31 Mg alloy bars under tensile loading [3].…”

“…the fracture surface morphology near the initial crack front can be perceived between the static and dynamic tests. Thus, the fracture surface pertaining to the former (Fig.8(a)) is decorated predominantly with quasi-brittle features like elongated grooves or flutes such as those labeled as "A", "B" and "C", which are believed to be induced by tensile twins [3,12,13,15]. These features, which are quite different from the shallow striation-like impressions seen in the fatigue pre-crack region (below the white dashed line in Fig.8(a)), were labeled as Cleavage 3 regime in the fracture mechanism maps pertaining to Mg alloys by Gandhi and Ashby [50].…”

“…The fracture behaviour of Mg alloys under static loading has been extensively investigated [2,[11][12][13][14][15][16][17][18][19][20][21][22]. Somekawa et al [2,11,12] observed an increase in K IC and decrease in tensile twinning as grain size is refined, along with a change in fracture mechanism from twin-induced crack propagation to ductile void growth and coalescence.…”