Are constitutive models of stress-strain relationships true values or engineering values? 1

[Amyciveng]

Hi I am using a constitutive model of concrete stress strain relationship (fib Model Code/ Eurocode 2) for the concrete damaged plasticity model in ABAQUS.

Are the values I have calculated already true stress/ strain values?

 

[IceBreakerSours]

This is something you should be able to find out for yourself using the documentation that comes with the code. It is an excellent documentation so the sooner you get in to the habit, the better it will be for you.

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[Amyciveng]

I have read the documentation but did not understand it fully, thanks though.

 

[burningDiesel]

Depends on your settings, most notably NLGEOM and your element formulation.
I've dug up the relevant page in the manual for you:

Stress and strain measures


The stress measure used in Abaqus is Cauchy or “true” stress, which corresponds to the force per current area. See “Stress measures,” Section 1.5.2 of the Abaqus Theory Manual, and “Stress rates,” Section 1.5.3 of the Abaqus Theory Manual, for more details on stress measures.

For geometrically nonlinear analysis, a large number of different strain measures exist. Unlike “true” stress, there is no clearly preferred “true” strain. For the same physical deformation different strain measures will report different values in large-strain analysis. The optimal choice of strain measure depends on analysis type, material behavior, and (to some degree) personal preference. See “Strain measures,” Section 1.4.2 of the Abaqus Theory Manual, for more details on strain measures.

By default, the strain output in Abaqus/Standard is the “integrated” total strain (output variable E). For large-strain shells, membranes, and solid elements in Abaqus/Standard two other measures of total strain can be requested: logarithmic strain (output variable LE) and nominal strain (output variable NE).

Logarithmic strain (output variable LE) is the default strain output in Abaqus/Explicit; nominal strain (output variable NE) can be requested as well. The “integrated” total strain is not available in Abaqus/Explicit.

 

[Amyciveng]

Thank you! I am tryig to understand if the stress/strain values I have inputted are true stress/strain rather than the output.