Mechanical Properties of Materials Flashcards
What is the difference between engineering stress and true stress?
Engineering stress considers only the initial area under load, true stress would account for the actual area at any point in time.
What causes elastic deformation?
Stretching of interatomic bonds
When is elastic deformation not linear? How is it’s modulus calculated?
In certain metals, ceramics, and polymers. You find the tangent modulus instead.
What is anelasticity? Which materials exhibit high anelastic behavior?
Elastic behavior that is not instantaneous, so it regains its shape over a period of time. Polymers are highly anelastic.
What is poissons ratio? What is a typical range of ratios?
v = -ex/ey
0.25-0.35
What causes plastic deformation?
Atomic bonds breaking.
If there are two distinct yield points on a stress strain curve, which is considered the average yield strength?
The lower one.
What is ductility? How is it practically measured? In what range is a material considered brittle?
% elongation to fracture or % reduction in area to fracture.
% elongation = deltaL/L0 x 100
less than 5% is considered brittle.
Define resilience.
A material’s ability to absorb elastic energy, and have this energy removed on unloading. It is equal to the area under the elastic part of the stress strain curve.
To be resilient you want high yield strength and low E.
Define toughness
A material’s ability to absorb plastic energy before fracture. It is equal to the area under the stress-strain curve. A tough material must have high strength and ductility.
