What is a simple fracture
The separation of a body into two or more pieces
Ductile fracture
- slow crack
- fails with warning
- significant plastic deformation
Brittle fracture
- Rapid crack
- little or no plastic deformation
- fails without warning
cup and cone fracture vs brittle fracture
examples of ductile and brittle fractures
5 stages of a moderately ductile failure
necking, void nucleation, void growth, crack propagation, fracture
principles of fracture mechanics
fracture mechanics formula
fracture mechanics, stress concentration formula
what is crack propagation
a stepwise discontinuous process, which agrees with propagation observed in the field
crack propagation and its criteria
what is fracture toughness
the measure of a material’s resistance to brittle fracture when a crack is present
fracture toughness formula
plane fracture toughness
What is the difference between fracture toughness and plane strain fracture toughness?
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
fracture toughness ranges between
metal alloys
ceramics
polymers
composite fibers
design against fracture formula and scenarios
design example aircraft wing
* quick reference *
Example of brittle fracture of ductile materials
What is an impact test on ductile materials
the amount of energy absorbed by a material during fracture.
what influence does T (temp) have on impact energy
what is fatigue failure
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.
*quick reference *
Fatigue Failure
two types of fatigue behavior
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
* quick reference *
Fatigue behavior
what are the general techniques for improving fatigue life
1) reducing the magnitude of mean stress
2) surface treatments
3) design changes
* Improving Fatigue Life *
1) reducing the magnitude of mean stress
* Improving Fatigue Life *
2) surface treatments
* Improving Fatigue Life *
3) design changes
define creep
(sometimes called cold flow) is the tendency of a solid material to move slowly or deform permanently under the influence of persistent mechanical stresses.
3 stages of creep
steady-state creep rate formula
prediction of creep rupture lifetime
Summary of this chapter