Lecture 8

Question 1

What are the properties of cracks?

Answer 1

• No volume
• Move without diffusion
• Can move fast

Question 2

What are some microstructural defects?

Answer 2

• Inclusions
• Precipitates
• Substitutional atoms
• Interstitial atoms
• Vacancies
• Dislocations

Question 3

What assumptions are applied in LEFM?

Answer 3

It’s a homogeneous, isentropic, elastic continuum

Question 4

What does LEFM stand for?

Answer 4

Linear Elastic Fracture Mechanics

Question 5

What is K1/ what does it represent?

Answer 5

It is the mode 1 stress intensity factor

It represents the severity of the stress singularity

Question 6

What are the three modes of fracture?

Answer 6

Mode I: Opening
Mode II: Shear
Mode III: Antiplane Shear

Question 7

Give examples for each of the fracture modes

Answer 7

Mode I: the normal response of equi-axed material
Mode II: often observed in materials with definite planes weakness
Mode III: Shafts loaded in torsion

Question 8

How do different elastic cracks compare?

Answer 8

The pattern of stress and displacement is identical near the tip
The only difference between cracks is the value of K

Question 9

What is the stress intensity factor equation?

Answer 9

K = Ysigmasqrt(pi*a)

Question 10

What is Y?

Answer 10

A dimensionless calibration function which deals with geometrical details