MSE 175 Exam 1 Combined

radial cleavage, macro

chevron cleavage, macro

river cleavage, micro

tongue cleavage, micro

feather cleavage, micro

river cleavage & deformation twins

wallner cleavage, micro

quasi-cleavage

transgranular interaction with grains?

goes through the grain

intergranular interaction with grains?

goes along grain boundaries

• faceted fracture surface

• usually because impurity segregation

• weakened forces at grain boundaries

brittle intergranular fracture

• crack growth along favored crystallographic planes

• (river, feather, tongues, wallner, herring)

brittle cleavage/transgranular fracture

• macroscopically flat

• fracture surface is shiny to the naked eye (metals)

• fracture supersedes any sizable plastic deformation

brittle fracture

intergranular fracture by impurity segregation

intergranular fracture by over heating

What is K_IC?

fracture toughness, material property

What is K_I?

Stress intensity factor

Brittle fracture occurs when..

K_I >= K_IC

Modes of fracture mechanics

1. Opening

2. Shear

3. Tearing / aAnti-plane sheare

Cup-and-Cone Ductile Rupture

Ductile Rupture - Skewed Dimples

Silicate Inclusions in Carbon Steel

Ductile Rupture (Steel Wire, Fibrous Fracture) —> On the flat horizontal surface (dimples) & vertically the elongated grain boundaries are visible

Fatigure - Macroscopic Beach Marks

Low Cycle Fatigue - Microcracks in the External Surface (Microcracks & Slip Bands - extrusion/ intrusion pairs)

Fatigue: Crack Origin

Fatigue: Crack Origin

Fatigue: Slip Lines

Fatigue: Slip Lines

Fatigue: Feather Pattern

Fatigue: River Pattern

Fatigue: Striations

Fatigue: Striations (transitions in load amplitude)

Fatigue: Brittle Cracking (titanium alloy casting)

Fatigue: Brittle Cracking (pearlitic cast iron)

Fatigue: Brittle Cracking (continuous alumina fiber reinforced Mg alloy) & Visible Fiber Pullout

Ductile Rupture

• Facilitated by microvoid growth and coalescence

• Microvoids tend to nucleate at particulates

• Fracture surface is characterized by dimples with shear ridges

• Height of the ridges is indicative of the ductility of the material

• Orientation of the ridges is indicative of the stress state

Fatigue Failure

Four stages:

1) crack initiation (may be circumvented by preexisting defect)

2) Stage I crack growth along a slip band (may be circumvented by pre-existing defect)

3) Stage II crack growth by alternating slip that produces striations.

4) Catastrophic fracture (ductile rupture or quasi- cleavage)