L11 - Failure Of Materials - Metals Flashcards
1
Q
What do ductile fractures look like?
A
- necks down to a point
- cup-cone appearance
2
Q
What do brittle failures look like?
A
- little to no necking
- brittle cleavage across specimen
- clean fracture surface
3
Q
How are cup-cones formed?
A
- initial necking, with stress focussed in neck region
- voids form within matrix as it flows around harder particles
- voids coalesce into a crack
- crack grows across specimen
- failure
4
Q
How can cleavage occur in brittle fracture events?
A
- intergranular cleavage
- cracks propagate along grain boundaries
- more 3D failure surface
- transgranular cleavage
- cracks propagate through grains along particular cleavage planes
5
Q
How much elongation can a brittle material undergo before failure?
A
- <5%
6
Q
How do cracks grow in Griffith Approach?
A
- elastic strain is stored in materials under load
- released when material cracks
- if it is equal to or exceeds the energy required to form a new surface
- results in crack propagating
7
Q
When do cracks grow?
A
- when rate of strain energy release is greater than or equal to rate of change of surface energy with crack length
