Mechanical properties of engineering materials Flashcards
(14 cards)
Describe the poisson ratio?
The ration between the lateral and axial strain
What is the relationship between shear and elastic module for isotopic materials?
E=2G(1+v)
E = elastic modulus
G= shear modulus
Define isotropic and anisotropic
Isotopic - grains are spherical and randomly orientated
Anisotropic- after rolling it flattens the fibres and grains out to make them all point in the same direction
Define hardness
A measure of a materials resistance to localised plastic deformation
Name hardness testing techniques
Brinnel
Vickers
Knoop
Rockwell
For most metals hardness and tensile strength are proportional. What is this proportionality?
TS=3.45*HB
Define and give an example of a ductile material
Ductile materials plastically deform when they fail and give warning prior to doing so. E.g copper
Define a brittle material and give an example
Brittle material will fail without deformation under stress e.g glass
Define fatigue
Progressive and localised structural damage that occurs when a material is subjected to cyclic loading
What is the effect of grain size on fatigue?
Stress and grain size are inversely proportional
Stress ~ 1/sqrt(d)
Define. Creep
Tendency of a solid material to slowly move or deform permanently under the influences of stresses. Creep increases with temperature
What is the critical temperature for creep?
40% of the melting temperature in K
What are the three stages of creep?
Primary creep - period of decelerating strain rate, as time passes under constant stress the rate of strain reduces.
Secondary creep- extended period of slow almost steady deformation
Tertiary creep - strain rate rapidly accelerates and the material fails
What is the significance of grain structure on creep deformation?
Lots of crystals in a random structure will have a low creep resistance
Directionally solidified structure will have increased resistance
Single crystal will have the most resistance
