CH 8 - Mechanical Failure Flashcards
1
Q
What is ductile fracture?
A
- fracture accompanied by significant plastic deformation
- more desirable
- one piece with a large deformation
2
Q
What is brittle fracture?
A
- fracture with little or no plastic deformation
- many pieces with small deformations
3
Q
What are the failure stages of a ductile fracture?
A
necking -> void nucleation -> void growth & coalescence -> shearing at surface -> fracture
4
Q
Define intergranular
A
between grains
5
Q
Define transgranular
A
through grains
6
Q
What is the criterion for crack propagation?
A
crack propagates if crack-tip stress exceeds a critical stress
7
Q
Which cracks in a material will grow first?
A
largest, most highly stressed cracks
8
Q
What is the ductile-to-brittle transition temperature (DBTT)?
A
- Temp where material transitions from being ductile to brittle
- EX: titanic
9
Q
What is fatigue?
A
- failure under applied cyclic stress
- can cause partial failure
- responsible for about 90% of mechanical engineering failures
10
Q
What is the fatigue limit?
A
- point where additional cycles do not affect stress amplitude
- flat part on stress amp vs cycles to failure curve
- does not exist for all materials
11
Q
What are ways to improve fatigue life?
A
- impose compressive surface stresses to suppress surface cracks from growing
- remove stress concentrators (round vs sharp corners)
12
Q
What is creep?
A
deformation at a constant stress over time
