Background

In ProTOp material regions are not used only to assign the usual material properties. They are also used to assign various other optimization properties to corresponding volume regions.

█ Material region type

The most important optimization property is the region type. ProTOp distinguishes between the following types:

• Free region is the one that can be optimized by removing or restoring material.
• Fixed region is the one that has to remain unchanged and is not optimized.
• Excluded region is the one that is ignored by all FEA and optimization processes; its purpose is to be available for resulting surface export if needed.

The figure below illustrates a model with all three material region types:

• Blue - denotes a free region
• Gray - denotes a fixed region
• Brown - denotes an excluded region

Figure. A part containing all three region types: free, fixed, and excluded.

█ Material model type

The material model type defines the underlying constitutive model and any additional special properties of the material if applicable. The following models are available:

Isotropic models

• ElasticIsotropic is the conventional linearly elastic isotropic material model.
• SemiPlastic is a special isotropic material model that simulates the bilinear elastic-plastic material behavior.
• SemiContact is a special isotropic material model that can be engaged to simulate conditions similar to those found in the vicinity of contacts.

Orthotropic model

• ElasticOrthotropic is the conventional linearly elastic orthotropic material model.

IMPORTANT. The semi-plastic model can only be used in situations with monotonic loading. Structural unloading is not allowed.

IMPORTANT. The semi-contact model can only be used in contact situations with negligible relative motion such as bolt or pin fixing with negligible rotation.

█ Linearly elastic isotropic material properties

These are the conventional properties of a linearly elastic isotropic material. These properties apply to all isotropic material models, including semi-plastic and semi-contact.

• ElaMod is the elastic or Young's modulus.
• PoissR is the Poisson ratio.
• TheExp is the thermal expansion coefficient.

█ Linearly elastic orthotropic material properties

In ProTOp, the linearly elastic orthotropic material properties have to be defined by the conventional engineering constants with respect to the material's principal directions 1, 2, and 3. The constants are as follows:

• E1, E2, E3 are the elastic moduli in the material principal directions 1, 2, and 3.
• Nu12, Nu13, Nu23 are the Poisson's ratios, where NuIJ is physically interpreted as the Poisson ratio that defines the transverse strain in the J-direction, when the material is stressed in the I-direction.
• G12, G13, G23 are the shear moduli associated with the directions 1, 2, and 3.
• A1, A2, A3 are the thermal expansion coefficients in the directions 1, 2, and 3.

These properties apply only to the orthotropic material model.

IMPORTANT. Currently the material's principal directions 1, 2, and 3 must be coincident with the world coordinate system WCS.

█ General material properties

General material properties are additional parameters that are used either for all or only for some special material models.

MasDen
Range: [0.0, ~]
Applies to: all material models
Defines the mass density of the corresponding material.

YStress
Range: [0.0, ~]
Applies to: semi-plastic material model
Defines the initial von Mises yield stress for the special semi-plastic material model.

YHarden
Range: [0.0, 1.0]
Applies to: semi-plastic material model
Defines the yield hardening factor for the special semi-plastic material model.

The yield stress data should be accompanied by a corresponding yield hardening factor, which defines the strain-linear hardening behavior. The yield hardening factor is defined as the ratio between the elastic-plastic and Young's modulus.

Figure. The YHarden defines the relative slope of the post-yield material curve.

TenComRatio
Range: [ > 0.0 ]
Applies to: all material models except semi-contact
Defines the ratio of allowed tension stress to allowed compression stress. This parameter can be used to reinforce tension regions on the account of weaker compression regions, for example, if the used material is more sensitive to tension. To achieve this, set this parameter to less than one.

CSys
Applies to: all material models
Defines the coordinate system associated with this material.

PreStrain1/2/3
Range: [~]
Applies to: all material models
Defines the amount of prescribed normal strain in the direction of the first/second/third axis of the coordinate system associated with this material; the prescribed strain is applied before the structure is loaded by external loads. These parameters can be used to model properly certain situations, for example, bolt fastening.

█ Error and warning conditions

A material data row is flagged by an error status in the following situations:

• The material region type is other than Free, Fixed, or Excluded.
• The material model type is other than ElasticIsotropic, SemiPlastic, SemiContact, or ElasticOrthotropic.
• An elastic orthotropic material is associated with a coordinate system other than WCS.
• The elastic modulus is less than or equal to zero.
• The Poisson ratio is greater than 0.495.
• The mass density is less than zero.
• The yield stress is less than zero.
• The yield stress of a semi-plastic material is less than or equal to zero.
• The yield hardening factor is less than zero.
• The tension to compression ratio is less than or equal to zero.

A material data row is flagged by a warning status in the following situations:

• The Poisson ratio is less than or equal to zero.