# Youngs modulus vs Ultimate tensile strength

## Main Question or Discussion Point

In case FEA we consider ultimate tensile strength to decide whether component will fail OR pass why ultimate tensile strength is lesser than youngs modulus? Example for copper UTS is 245 MPa n youngs moduls 131000MPa. Why it is like this?

Regards,
Amlesh

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rock.freak667
Homework Helper
The UTS is the stress at which the component/material will fracture.

The Modulus of Elasticity or Young's modulus is the ratio of the stress to strain for the elastic region of the stress-strain curve of the material.

Where did you get those values for copper?

Rock,

By the way, I got this coper value from one of our vendor.

The compressive strength and young modulus are different quantities, measuring different properties. They do have the same unit but they are still different. So comparing their values is a little meaningless.
Like saying that the torque of a given force (in Nm) is less (or more) than the work done by the force over a given distance (also in Nm).

I am not saying that is not interesting to look at the values, as long as you know their meaning.
Actually the so called theoretical strength of many metals was found to be between E/20 and E/5, (if I remember correctly) where E is Young's modulus. These are calculated from crystal structure and bond strength, for a perfect crystal. So it seems that there is a general tendency to have UTS "less" than E, in value.
The measured UTS values are a lot less than predicted by this rule of thumb, due to defects in structure.

Last edited:
AlephZero
Homework Helper
So it seems that there is a general tendency to have UTS "less" than E, in value.
You can think of Young's Modulus as the elastic stress when the strain is 1 (i.e. the length of the object has doubled). Not many materials can double in length and remain perfectly elastic, so the UTS of most materials is numerically less than E.

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Dear All,