Mechanical properties of engineering materials Flashcards
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
