mechanical properties Flashcards
definition of hardness
the term hardness, as it is used in industry, may be defined as the ability of a material to resist permanent indentation or deformation when in contact with an indenter under
load
tell some hardness tests
✓ Hardness Brinell (HB)
✓ Hardness Vickers (HV)
✓ Hardness Rockwell (HR)
✓ Hardness Knoop (HK)
✓ …and others
describe brinell test
-indenter: 10mm sphere of steel or tungsten carbide
-measurement of indentation diameter
knoop test indenter
diamond pyramid
describe vickers test
-indenter: diamond pyramid
-measurement of indentation diagonal
-load:30kg for macro hardness, 10-2000g for micro hardness, 1mg for nano hardness
describe rockwell test
-indenter: diamond cone for hard materials and steel sphere for soft materials
-measure depth of penentration of the indenter
which are tensile curve important points
- yield strenght
- ultimate tensile strenght (UTS)
- fracture
different materials yield point
- Some metals and alloys show a marked yield point
- Some other metals feature a continuous shift to plasticity (lower slope of the tensile curve) without a definite yield point
how can we determine the yield point if the tensile curve feature a continuous shift to plasticity
drawing a straight line parallel to the initial straight-line portion of the stres-strain curve.
this line is normally offset by a strain of 0.2% (0.002)
def of toughness
Toughness is the ability of a material to absorb energy during deformation.
2 different types of brittle fracture
- intergranular fracture
- transgranular fracture
describe charpy test
The Charpy impact test defines the amount of energy absorbed by a standard notched specimen during high strain-rate
fracture
main factors that promote a brittle transition in metals and alloys
✓ High strain rate
✓ Presence of notch (stress raiser)
✓ Triaxial stress field
✓ Low test temperature
✓ Embrittlement phenomena
