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Engineering Vs. True stress strain curve in nonlinear analysis

Engineering Vs. True stress strain curve in nonlinear analysis

Engineering Vs. True stress strain curve in nonlinear analysis

(OP)
Hi,

When doing a non-linear analysis, I know that I should insert the true stress and strain curve to the material model (regular metal plasticity model using ANSYS for instance). The data I get from the material manufacturer (Young's modulus, yield point) is based on the engineering stress strain curve.

As I understand the yield point should be the same (engineering Y.P = true Y.P) so is the data before the yield point.

In Ansys the stress-strain curve first point is the yield point and from there on I should insert the true stress - strain data is this correct? the curve data is from the true stress-strain and the parameters (yield point, young's modulus) is based on the engineering data because up to the yield point true and engineering should be almost the same?

RE: Engineering Vs. True stress strain curve in nonlinear analysis

If you convert your engineering (nominal) stress-strain data to true stress-strain using the formulas below you will see how the values for both measures differ depending on the stress/strain level:

ε_true = ln(1+ε_eng)
σ_true = σ_eng(1+ε_eng)

You should notice that the difference becomes visible starting from the yield point.

Depending on the software you may also have to convert total strain to plastic strain:

ε_pl = ε_tot - (σ/E)

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