Lecture 11- properties and applications of materials

Question 1

What is the difference in appearance between 2 specimens after fracture in tensile testing if one has a higher fracture toughness than the other?

Answer 1

more fracture toughness= necking and plastic deformation

low fracture toughness= specimen just breaks in the same diameter

Question 2

how is fracture toughness tested?

Answer 2

3-point bending at a low strain rate for notched or cracked sample

Question 3

what are the 3 modes of crack opening?

Answer 3

tension
shear
tearing

Question 4

What is a critical crack length?

Answer 4

a measure of damage tolerance of a material

Question 5

what happens to cracks from the moment of testing till fracture?

Answer 5

they grow until critical crack length is reached, causing fracture

Question 6

whats the relationship between fracture toughness and critical crack length

Answer 6

the greater the citral crack length the grater, the fracture toughness

Question 7

Are systems designed to leak before breaking, or the opposite? What kind of failure do we want?

Answer 7

leak before breaking
ductile failure