Chapter 8 Failure

Question 1

What is a simple fracture

Answer 1

The separation of a body into two or more pieces

Question 2

Ductile fracture

Answer 2

• slow crack
• fails with warning
• significant plastic deformation

Question 3

Brittle fracture

Answer 3

• Rapid crack
• little or no plastic deformation
• fails without warning

Question 4

cup and cone fracture vs brittle fracture

Answer 4

Question 5

examples of ductile and brittle fractures

Answer 5

Question 6

5 stages of a moderately ductile failure

Answer 6

necking, void nucleation, void growth, crack propagation, fracture

Question 7

principles of fracture mechanics

Answer 7

Question 8

fracture mechanics formula

Answer 8

Question 9

fracture mechanics, stress concentration formula

Answer 9

Question 10

what is crack propagation

Answer 10

a stepwise discontinuous process, which agrees with propagation observed in the field

Question 11

crack propagation and its criteria

Answer 11

Question 12

what is fracture toughness

Answer 12

the measure of a material’s resistance to brittle fracture when a crack is present

Question 13

fracture toughness formula

Answer 13

Question 14

plane fracture toughness

Answer 14

Question 15

What is the difference between fracture toughness and plane strain fracture toughness?

Answer 15

What is the difference between fracture toughness and plane strain fracture toughness?

They are different terms. Toughness is the ability of a material (assumed to be perfect, meaning no cracks) to absorb energy to fracture. It is measured by the area under the stress-strain curve to the point of fracture. Fracture Toughness is the ability of material with pre-cracks to resist fracture by absorbing energy

Question 16

fracture toughness ranges between

metal alloys

ceramics

polymers

composite fibers

Answer 16

Question 17

design against fracture formula and scenarios

Answer 17

Question 18

design example aircraft wing

Answer 18

Question 19

* quick reference *

Example of brittle fracture of ductile materials

Answer 19

Question 20

What is an impact test on ductile materials

Answer 20

the amount of energy absorbed by a material during fracture.

Question 21

what influence does T (temp) have on impact energy

Answer 21

Question 22

what is fatigue failure

Answer 22

is the initiation and propagation of cracks in a material due to cyclic loading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, typically producing striations on some parts of the fracture surface.

Question 23

*quick reference *

Fatigue Failure

Answer 23

Question 24

two types of fatigue behavior

Answer 24

two types of fatigue behavior

Fatigue limit - the highest stress that a material can withstand for an infinite number of cycles without breaking —called also endurance

Fatigue life is defined as the number of cycles that lead to the failure of a structural system

Question 25

\* quick reference \* Fatigue behavior

Answer 25

Question 26

what are the general techniques for improving fatigue life

Answer 26

1) reducing the magnitude of mean stress 2) surface treatments 3) design changes

Question 27

\* Improving Fatigue Life \* 1) reducing the magnitude of mean stress

Answer 27

Question 28

\* Improving Fatigue Life \* 2) surface treatments

Answer 28

Question 29

\* Improving Fatigue Life \* 3) design changes

Answer 29

Question 30

define **creep**

Answer 30

(sometimes called cold flow) is the tendency of a solid material to move slowly or deform permanently under the influence of persistent mechanical stresses.

Question 31

3 stages of creep

Answer 31

Question 32

steady-state creep rate formula

Answer 32

Question 33

prediction of creep rupture lifetime

Answer 33

Question 34

**_Summary of this chapter_**

Answer 34