Quiz 4 Flashcards
Fatigue Strength
Stress after 10^7 cycles
Fatigue life
of cycles required to cause a failure for a given applied load
Fatigue Limit
The stress at or below the fatigue limit is not significant to internally damage the material. In theory the material can serve for a very long time. Where curve platos.
How will the surface of a fracture look?
Due to the cyclic nature of loading a material fracture surface will have riges.
How if fatigue damage initiated?
Fatigue damage is initiated at imperfections in the material. Ie machined surface finish, porosity, threads.
Enhance Fatigue Life
Eliminate sharp corners (fillet to remove stress concentrations)
Compressive residual stress (“springs” shot peening similar to sand blasting )
Surface treatment (diffusion hardening)
Creep Definition
Plastic deformation of a material over a long time at elevated temperature
Primary Creep
Initial rapid deformation
Secondary Creep
“Steady state”. The strain rate is constant therefore it is predictable
Tertiary Creep
Accelerated deformation leading to rupture and failure
Time to Rupture
Time to reach failure at a given temperature and load condition.
Material failure
a material will lose its strength and fully or partially separate. Failure can happen due to many parameters:
- tension
-compression
-shear
-torsion
-heat
-pressure
Ductile Fracture
A material experiences a lot of plastic deformation. It can neck or form coleuses and dimples.
Brittle Fracture
Very little plastic deformation. Fracture happens rapidly and without warning. Can be inter-granular or trans granular
Brittle Fracture
Very little plastic deformation. Fracture happens rapidly and without warning. Can be inter-granular or trans granular
