Understanding stress-strain yield stress input for Samcef

When you define a Simcenter Samcef Elastoplastic Material, you must define the Stress-Strain (H) Yield stress law in an Isotropic, Orthotropic or Anisotropic material.

This law is driven by two properties:

• The Stress-Strain Input Data Type, which defines the Stress-Strain (H) law type. You can select:Engineering Stress-Strain.Engineering-Plastic Strain.True Stress-Log Strain.True Stress-Plastic Strain.Undefined.

• The Stress-Strain (H), which defines the law values.

The Yield stress can be constant, can be a strain-dependent field, or can be a temperature-dependent and strain-dependent field.

Depending on the Stress-Strain Input Data Type value, some conversion may be performed to fit Samcef stress-strain data law requirements.

Simcenter Samcef stress-strain measures laws

Stress measure	Strain measure	Samcef law type name
Biot	Biot	Biot
Cauchy	Natural	Cauchy
2nd Piola Kirchoff	Green Lagrange	Kirchoff
Kirchoff	Natural	Loki

For more information, see the definition of stress-strain measures page in the Simcenter Samcef solver documentation..

Simcenter Samcef vs Pre/Post stress measures

Samcef stress measure	Pre/Post stress measure
Biot Stress.	Engineering Stress
Cauchy Stress	True Stress
2nd Piola Kirchoff	n/a
Kirchoff	n/a

Samcef vs Pre/Post strain measures

Strain measure	Pre/Post strain measure
Biot	Engineering Strain
Natural	True Strain
Green Lagrange	n/a

Law types and related conversion rules

Simcenter Samcef stress-strain laws in materials use plastic strains. The following table describes the conversion process.

Pre/Post stress-strain Law Type	Match a Samcef law ?	Output to Samcef law...
Engineering Stress-Strain	This law has no equivalent in Samcef.	Stress-strain data are converted to the Samcef Biot law
Engineering-Plastic Strain	This law matches the {Biot stress, Biot strain} Samcef Biot law.	Stress-strain data are written out as specified in the material data without conversion to a Samcef Biot
True Stress-Log Strain	This law has no equivalent in Samcef.	Stress-strain data are converted to the Samcef Cauchy law
True Stress-Plastic Strain	This law matches the {Cauchy stress, Natural strain} Samcef Cauchy law.	Stress-strain data are written out as specified in the material data without conversion to a Samcef Cauchy law
Undefined type	Unknown law	Stress-strain data are written out as specified in the material data without conversion to a Samcef Kirchoff law

For more information, see the Simcenter Samcef documentation.

Young modulus and conversion rules

The conversion process requires the Young's modulus to be defined in the material.

Note:

Temperature-Dependent stress-strain law

If the stress-strain law varies with temperature, the conversion process is performed for each given temperature value. The Young's modulus will be evaluated at every temperature value that is required when evaluating the stress-strain law.

Note:

Temperature-Independent stress-strain law

If the stress-strain law does not vary with temperature, but the Young's modulus does vary with temperature, the Young's modulus value will be evaluated at the given Temperature (TREF) material reference temperature. If this reference temperature is not specified, a 20C° default is used.

Stress-strain law dependency fields and Samcef out-of-bounds computation

If the yield stress law only depends on the plastic strain and if the computed strains go outside the strains definition range, Simcenter Samcef will compute the field value by using the extreme value of the given plastic strains range definition.

If the yield stress law depends both on plastic strain and temperature,

• if the computed strains go outside the strain definition range, Simcenter Samcef will evaluate the field by using the extreme value of the given plastic strain range definition.

• if the computed temperature goes outside the temperature definition range, an error is issued when Simcenter Samcef tries to evaluate the field.

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Understanding stress-strain yield stress input for Samcef, Simcenter 3D 2021.1 Series

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