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=

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

is stress (Pa)

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 tangentdefines 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 finding the Area under the ENTIRE curve.

Hooke's LawYoung's ModulusProportional LimitResilienceYield StressProof StressToughness