ENGINEERING TO TRUE STRESS VS STRAIN DATA 2

[David Browne]

Hello all,

I have a set of mechanical tensile test data in which I wish build material models in ANSYS.

I have Tensile Strain (mm/mm) data and Tensile Stress (MPa) data. These are Engineering Stress/Strain values provided by our testing house (raw data).

I am however looking for True Stress/Strain values to input in to ANSYS.

The tensile strain data only goes up to 2% strain due to limitations of the extensometer.

This therefore results in the tensile strain data going up to 2% strain then no further data is available for the remaining extent of the curve - so no information on the 2% to 100% strain ,or to break off point.

I do however have UTS and break off point information, load, original specimen area and % area reduction, initial and end length of test sample.

I need true stress and strain data for the data when the extensometer is removed to the end point- i.e. from when the data set limits at 0.02 Strain onwards. Could I simply extrapolate the data then convert to true stress/strain?

Thanks in advance.

 

[DrBwts]

You will need to know the changes in cross section to calculate true stress.

 

[rothers]

In the absence of anything better I find the following works well:

True Strain = Ln (1 + Engineering Strain)

True Stress = Engineering Stress ( 1 + Engineering Strain)

 

[David Browne]

Thank you folks.

I managed to calculate true stress and strain using σ = Load/FinalArea and ε = ln(Ao/A) respectively then just interpolated from the last data set to the newly calculated values. Looks like this:

Regards,

David.