Yield stress, proof stress, toughness, Young's modulus, Hooke's law.

Hooke's Law

* "Stress is proportional to strain up to the PROPORTIONAL LIMIT (1)"

* This means that any increase in stress will bring about a proportional increase in strain up to the proportional limit.

* Written mathematically, the formula of Hooke's Law is:

(1)

E=σ ε

* E is a constant. (Young's Modulus[see below])

* σ is stress (Pa)

* ε is strain

Young's Modulus

* Young's Modulus is a measure of the stiffness of a material.

* It is also known as the Modulus of Stiffness/Elasticity

* This is the constant that is represented in Hooke's Law (see above)

Proportional Limit

* This is when an increase in stress no longer has a linear relationship with an increase in strain.

* Sometimes this is known as the elastic limit.

Resilience

* This is the ability of a material to retain its shape after being deformed.

* It can be found through the area under the curve up to the proportional limit.

Yield Stress

* This is the Stress Value at the Progressive Yield Point (3).

* This is when there is no relationship between an increase in stress and an increase in strain.

* Is a useful value as the UTS point occurs after some deformation where this only begins to deform.

Proof Stress

* An approximation for the Yield point/Elastic limit for materials that don't have a definite one due to their structure.

* To find the approximation, a tangent is produced from the Proportional Limit. The points of intersection between the graph and the tangent defines the Proof Stress of the material.

* The line may be moved slightly to accommodate for certain materials.

* Examples are 0.1%/0.2% Proof Stress, where the tangent is produced from a point slightly (0.001) to the right of the Proportional Limit.

Toughness

* "A material's ability to absorb energy"

* This is sometimes known as impact strength.

* This can be found by...