Texture and Fatigue Crack Growth

Term paper presentation

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

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