Material property sets#

Material property sets define certain aspects of the properties of a material. The attributes described in the following subsections show how you can create and access material property sets in PyACP.

Constant versus variable property sets#

Material property sets can either be constant or variable. Constant property sets are defined by a single value per property. Variable property sets depend on field variables such as temperature and fiber volume content.

Currently, you can only modify the constant property sets with PyACP. Variable property sets can be inspected, but not modified.

Isotropic versus orthotropic property sets#

The following material property sets can be defined as either isotropic or orthotropic:

Whether a material has isotropic or orthotropic properties is determined by its ply type. The isotropic ply types are:

The PlyType.ISOTROPIC_HOMOGENEOUS_CORE ply type has isotropic Engineering Constants, but orthotropic stress and strain limits.

Note

While a material is unstored (see Stored versus unstored objects), the property set does not automatically change from orthotropic to isotropic or vice versa. When storing the material, the backend ensures that its definition is consistent.

Available attributes#

The available attributes for a given property set type change depending on whether the material is isotropic or orthotropic. The following table lists the available attributes for the different property sets in isotropic and orthotropic materials.

Property set

Isotropic attributes

Orthotropic attributes

Engineering constants

E, nu

E1, E2, E3, nu12, nu13, nu23, G12, G13, G23

Stress limits

effective_stress

Xc, Yc, Zc, Xt, Yt, Zt, Sxy, Syz, Sxz

Strain limits

effective_strain

eXc, eYc, eZc, eXt, eYt, eZt, eSxy, eSyz, eSxz

Relation between isotropic and orthotropic property sets#

For stress and strain limits, the isotropic and orthotropic attributes are independently defined. This means that when you change the ply type of a material, you must redefine the stress and strain limits.

For engineering constants, however, the orthotropic and isotropic definitions are interlinked. Therefore, when you change the ply type of a material, the engineering constants are automatically converted. To avoid accidental use of incorrect engineering constants, PyACP enforces conversion and assignment rules, as described later on this page.

Conversion rules#

The following rules apply when changing the ply type of a material:

  • The ply type can always be changed from an isotropic to an orthotropic type.

  • When changing from an orthotropic to an isotropic type, the engineering constants must be consistent with their isotropic counterpart. In particular, the following relations must hold:

    \[\begin{split}E_1 &= E_2 = E_3 \\ \nu_{12} &= \nu_{13} = \nu_{23} \\ G_{12} &= G_{13} = G_{23} = \frac{E_1}{2 \cdot (1 + \nu_{12})}\end{split}\]

Consider the following example:

>>> material = model.create_material(name="New Material")
>>> material
<Material with id 'New Material'>

First, convert to an isotropic ply type. This is allowed since the engineering constants are consistent with an isotropic material.

>>> material.ply_type = pyacp.PlyType.ISOTROPIC
>>> material.engineering_constants.E = 1e9
>>> material.engineering_constants.nu = 0.3

Then convert to an orthotropic material. This is always allowed.

>>> material.ply_type = pyacp.PlyType.WOVEN
>>> material.engineering_constants.E1 = 2e9

Now, the engineering constants are no longer consistent with an isotropic material, so converting back to an isotropic ply type is not allowed.

>>> material.ply_type = pyacp.PlyType.ISOTROPIC
Traceback (most recent call last):
...
ValueError: Invalid argument: Cannot set an isotropic ply type, since the given engineering constants are orthotropic: The G12 value does not match 'E1 / (2. * (1. + nu12))'.

Assignment rules#

Similar rules apply when assigning engineering constants to a material:

  • Isotropic engineering constants can be assigned to both isotropic and orthotropic materials.

  • Orthotropic engineering constants can be assigned to isotropic materials, if their values are consistent with them, and orthotropic materials.

Continuing from the preceding example, you can assign either orthotropic or isotropic engineering constants to the orthotropic material:

>>> material.ply_type
<PlyType.WOVEN: 'woven'>

>>> from ansys.acp.core.material_property_sets import ConstantEngineeringConstants
>>> material.engineering_constants = (
...     ConstantEngineeringConstants.from_orthotropic_constants(
...         E1=1e9,
...         E2=1.1e9,
...         E3=8e8,
...     )
... )
>>> material.engineering_constants = ConstantEngineeringConstants.from_isotropic_constants(
...     E=1e9, nu=0.3
... )

Now you can switch back to an isotropic ply type.

>>> material.ply_type = pyacp.PlyType.ISOTROPIC

Isotropic engineering constants can always be assigned to an isotropic material.

>>> material.engineering_constants = ConstantEngineeringConstants.from_isotropic_constants(
...     E=1.3e9, nu=0.5
... )

Orthotropic engineering constants can be assigned only if the values are consistent with an isotropic material.

>>> material.engineering_constants = (
...     ConstantEngineeringConstants.from_orthotropic_constants(
...         E1=1e9,
...         E2=1e9,
...         E3=1e9,
...         G12=5e8,
...         G23=5e8,
...         G31=5e8,
...     )
... )
>>> material.engineering_constants = (
...     ConstantEngineeringConstants.from_orthotropic_constants(
...         E1=1e9,
...         E2=1.1e9,
...         E3=1.2e9,
...     )
... )
Traceback (most recent call last):
...
ValueError: Invalid argument: Cannot set an isotropic ply type, since the given engineering constants are orthotropic: The G12 value does not match 'E1 / (2. * (1. + nu12))'.