effect of material texture on fatigue crack growth and fracture toughness
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Crystallography and Local Failure
Transgranular fracture:● RSS on slip systems in A● gA w.r.t. stress state
Intergranular fracture● boundary plane w.r.t stress
state((nAB and nAC)● misorientation between the
grains(ΔgAB and ΔgAC)
Effect of Macro-Texture
● AZ61 Mg alloy● avg. Grain Size = 20 micron
Sajuri, Zainuddin Bin et al. "Effects of Mn content and texture on fatigue properties of as-cast and extruded AZ61 magnesium alloys." International journal of mechanical sciences 48.2 (2006): 198-209
Slip bands present in 45o sample
● texture only affects short crack growth rates
● difference in crack growth behaviour, threshold SIF range is due to crack closure behaviour for each orientation and crack size.
● TiAl6V4: 50% αp(hcp) and 50% (αs in β) grains
● avg. grain size: 15 microns● macrozones: mm size clear and dark
areas in optical microscopes
● Macozones display strong alpha phase texture
● Neighbouring macrozones display no crystallographic relationship
● Slip occurs in basal or prismatic plane depending upon RSS
● Crack density proportional to RSS
Le Biavant, K, S Pommier, and C Prioul. "Local texture and fatigue crack initiation in a Ti‐6Al‐4V titanium alloy." Fatigue & Fracture of Engineering Materials & Structures 25.6 (2002): 527-545.
[a] microstructure [b] macrozones
Fatigue Crack Growth
● In different macrozones, different amount of crack coalescence occurs depending upon minor crack density
Crack Trajectory
Azar, Amin S, Lars-Erik Svensson, and Bård Nyhus. "Effect of crystal orientation and texture on fatigue crack evolution in high strength steel welds." International Journal of Fatigue 77 (2015): 95-104.
● GROD: Grain Reference Orientation Distribution: angular deviation of each point relative to a reference orientation
● GOS: Grain Orientation Spread: Distribution of orientation spread within a grain