Calculating properties of steel

[vtmike]

Hi,

I know the following properties for steel,
Tensile Strength = 135000 psi
Yield Strength = 130000 psi
Elongation in 2 inches = 16% minimum
Reduction in Area = 50% minimum
Hardness (Rockwell C) = 29 - 34Rc

So from above properties I need to calculate the Elastic modulus & Poisson's ratio. This is how I went about it,
1. Calculate strain = change in length/original length = 2.32-2/2 = .16
2. Elastic modulus, E = stress/strain = 135000/.16 = 843750 psi
3. Poissons ratio = lateral strain/axial strain = .16/.5 = .32

Is the above procedure correct? Any help would be appreciated.

Thanks,
Mike

 

[UW_Mechie]

Hi Mike,

A few things-Poisson's ratio and the Elastic Modulus are elastic properties, so you need to calculate them with data from the elastic region. You used the tensile strength to calculate E-the tensile strength is reached in the plastic region for materials with any ductility. Plus, that stress is not the stress that caused the .16 strain (at least nothing in the problem statement states that). The tensile strength is a material property. Does the problem tell you what tensile force or nominal stress that the specimen is being subjected to (F or sigma_o, etc.)? Or give you a stress-strain curve?

If you have a strain-strain curve, you can just use the slope of the linear-elastic region to find E.

Jennifer

 

[FredGarvin]

Keep in mind that ANY steel is going to have a Young's modulus between 26-30 ksi. Your value for Poisson's ratio is right about where it should be. It usually ranges between .28-.32 but I have seen as high as .36 for some steels.