Nickel-titanium alloy has increased flexibility over stainless steel. How does the modulus of elasticity for nickel-titanium compare to that for stainless steel? two times that of stainless steel one -fourth to one-fifth that of stainless steel half that of stainless steel similar to stainless steel

The modulus of elasticity, also known as Young´s Modulus is a physical quantity that measures the ability of a material to deform elastically when a stress is applied on it.

This number comes from a laboratory tension test where a material probe of certain known geometry is pulled until it deforms and finally breaks, and its formula is:

[tex]E = \frac{Stress}{Strain}[/tex]

Stress is the force per unit area of the probe and strain is the change in elongation occurred during deformation. It can be deducted from the formula that for a same value in stress, an increasing value of strain will yield a lower value of the modulus of elasticity. This means that for the same value of stress, the more the material elongates the more flexible it is and the less modulus of elasticity it has. Having a high modulus of elasticity will make the material stiffer.

Knowing that Nickel-titanium alloy (Nitinol) is more flexible than Stainless Steel and using what we know now about Modulus of elasticity we can easily deduct that Nitinol´s modulus of elasticity is lower than that of stainless steel.

For reference:

Nitinol´s Young Modulus ranges from 28GPa to 41 GPa when it has martensite internal structure and it´s approximately 83GPa when it is austenitic. Compared to Stainless Steel which has a Young Modulus of approximately 190GPa in both martensitic and austenitic forms. (This quantities are for reference only, Young modulus, especially in Nitinol, changes considerably with temperature)