Fracture Fatigue

Question 1

What is ductile fracture?

Answer 1

Deformation accompanied by significant plastic deformation

Question 2

What is brittle fracture?

Answer 2

• Little or no plastic deformation
• Catastrophic
• Intergranular: between grains
• Intragranular: within grains

Question 3

What are flaws?

Answer 3

-Stress concentrators hence a smaller sample has a greater yield strength as they contain a lesser number of faults

Question 4

What are the modes of crack tip deformation (LEFM)?

Answer 4

• Opening (vertical)
• Sliding (backwards)
• Tearing (sideways)

Question 5

What is fatigue?

Answer 5

• Failure under cyclic stress
• The number of cycles to failure at any stress level is called the fatigue life
• considered high at >10^4 cycles

Question 6

How can we extend fatigue life?

Answer 6

-Polish the surface to remove stress amplification sites
-Reduce the number of internal defects
-Impose a compressive stress surface
-Remove stress concentrators
-Shot peening

Question 7

What is simple fracture?

Answer 7

• Occurs by crack propagation
• Ductile fracture: some plastic deformation – slow crack propagation
• Brittle fracture: no plastic deformation – fast crack propagation
• Fracture surfaces – different for ductile and brittle

Question 8

What is the fracture toughness of a material?

Answer 8

Measurement of a materials resistance to fracture