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SEM fractographs for AS4PB-2S with (a) FPC and (b) notch. Similar images for AS4PB-1S with (c) FPC and (d) notch. Crack growth direction is vertically upwards.
Source publication
Fatigue pre-cracked four-point bend specimens of a rolled AZ31 Mg alloy are loaded asymmetrically and their mixed-mode (I and II) fracture behaviour is contrasted with pre-notched samples. In-situ mapping of displacement and strain fields is performed through optical imaging coupled with digital image correlation analysis. The fracture surface morp...
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... Figure 2, SEM images of the fracture surface for the FPC and the notched specimens pertaining to M e (M p ) of 0.85 (0.49) and 0.71 (0.33) are presented. The FPC samples display elongated grooves or step-like ridges (locations C and D in Figure 2a and H in Figure 2c). ...
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... Figure 2, SEM images of the fracture surface for the FPC and the notched specimens pertaining to M e (M p ) of 0.85 (0.49) and 0.71 (0.33) are presented. The FPC samples display elongated grooves or step-like ridges (locations C and D in Figure 2a and H in Figure 2c). Such quasi-brittle features, observed for all FPC specimens, have been reported earlier only under mode I loading [3,11,21]. ...
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... Figure 2, SEM images of the fracture surface for the FPC and the notched specimens pertaining to M e (M p ) of 0.85 (0.49) and 0.71 (0.33) are presented. The FPC samples display elongated grooves or step-like ridges (locations C and D in Figure 2a and H in Figure 2c). Such quasi-brittle features, observed for all FPC specimens, have been reported earlier only under mode I loading [3,11,21]. ...
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... the other hand, for notched AS4PB-2S (Figure 2b), ductile fracture features, consisting of large, rounded dimples (e.g. location E) with some enclosing inclusions (e.g. ...
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... morphology was seen for notched S4PBS. The notched AS4PB-1S (see Figure 2d) exhibits a hybrid mechanism consisting of elongated dimples (e.g. I) and step-like ridges (e.g. ...
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... using the corresponding J c values (Table 1), the average evolution rates of f tt with respect to J for the above two specimens are estimated to be 0.0052 and 0.0012 mm/N. Thus, a faster TT accumulation rate near the tip occurs for the FPC sample, which triggers twin-induced quasi-brittle failure (Figure 2a). For the notched sample, this mechanism is suppressed owing to sluggish evolution of TTs near the tip giving rise to dimple fracture. ...
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... a drop in near-tip triaxiality caused by a reduction in M e is expected to retard it [17]. Interestingly, large, rounded voids are perceived in Figure 2b which pertains to M e = 0.85 (M p = 0.49), whereas few elongated voids are seen in Figure 2d which corresponds to M e = 0.71 (M p = 0.33). This is possibly caused by more TT development for the latter as suggested by CPFE simulations [27]. ...
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... a drop in near-tip triaxiality caused by a reduction in M e is expected to retard it [17]. Interestingly, large, rounded voids are perceived in Figure 2b which pertains to M e = 0.85 (M p = 0.49), whereas few elongated voids are seen in Figure 2d which corresponds to M e = 0.71 (M p = 0.33). This is possibly caused by more TT development for the latter as suggested by CPFE simulations [27]. ...
Citations
... It was attributed to the ductile failure by microvoid growth and coalescence during the test at the blunt notch, while profuse ET occurred in the region ahead of the notch. They [37,39] concluded that profuse ET activation enhances plastic energy dissipation, geometric hardening, strengthening through ET-ET and ET-slip interactions, and grain boundary strengthening, thereby, FT. A lower FT was obtained on fatigue pre-cracked notched four-point bend hot-rolled AZ31 specimen [39]. ...
... They [37,39] concluded that profuse ET activation enhances plastic energy dissipation, geometric hardening, strengthening through ET-ET and ET-slip interactions, and grain boundary strengthening, thereby, FT. A lower FT was obtained on fatigue pre-cracked notched four-point bend hot-rolled AZ31 specimen [39]. ...
Anisotropic fracture toughness (FT) in a hot-rolled Mg-3Al-0.5Ce magnesium alloy has been investigated using fatigue pre-cracked compact tension (CT) specimens with the notch (a n)‖ to the rolling direction (RD) and transverse direction (TD). During testing, notable non-linear load-displacement behavior before peak load indicated significant crack tip plasticity. Thus, elastic-plastic FT (J IC) was evaluated and found to be 20.7N/mm and 15.8N/mm for a n ‖ to RD and TD, respectively. Long-aligned Al 11 Ce 3 precipitates were present in this alloy within the elongated grain boundaries along RD. During FT testing, profuse {1012}〈1011〉 extension twins (ET) with c-axis almost ‖ and lamellae morphology almost ⊥ to RD formed between these elongated precipitates, irrespective of the notch, a n ‖ to RD or TD. The ET lamellae ⊥ and ‖ to crack path lead to trans and inter lamellar crack for a n ‖ to RD and TD, respectively. Translamellar crack in a n ‖ to RD leads to comparatively high strain hardening, dislocation density, geometrically necessary boundaries, and grain refinement, indicating larger plastic energy dissipation and thereby has higher J IC than in a n ‖ to TD with interlamellar crack.
... It is expected that the role of these factors would be equally crucial under mixed-mode loading as well, especially since the near-tip stress state changes dramatically as loading transitions from mode I to II [22]. In a recent study, Baruah et al. [23] contrasted the fracture response exhibited by fatigue pre-cracked asymmetric 4PB specimens of rolled AZ31 Mg alloy against the notched samples studied earlier by Vaishakh et al. [21] at RT. They noted a pronounced reduction in J c , irrespective of mode mixity in the former compared to the latter. ...
... These images are then analyzed using the Digital Image Correlation (DIC) software VIC-2D to ascertain the surface deformation and strains. The parameters employed in the above analysis are the same as those reported by Baruah et al. [23]. The variations of bending moment M and shear force V at the notched section versus specimen rotation (θ) and notch mouth sliding displacements (δ s ), respectively, are employed to estimate the mode I and mode II contributions to the energy release rate [25]. ...
... These two components are added to get the total energy release rate J. The crack initiation stage and associated critical value of J (referred to, in the sequel, as J c ) is ascertained from careful visual examination of the optical images and/or by using one of the other methods described by Baruah et al. [23]. ...
