Materials

Materials are required for the definition of surfaces, cross-sections, and solids. The material properties are incorporated into the stiffnesses of these objects.

Name

You can assign any name to the material. If the designation matches an entry in the library, RFEM reads in the stored material properties. To select the material from the library, click the button at the end of the input line. The transfer of materials is described in the chapter Material Library.

For materials from the library, the 'Basic Material Properties' are fixed and cannot be changed. If you want to use custom material properties, check the Custom Material box in the 'Options' section (see section Custom Material).

Base

The Base tab manages the basic material parameters. It also provides controls for special properties that you can define in additional tabs.

Categories

In this section, you define the material type and the material model.

Material Type

The material type controls which parameters and coefficients are relevant for design. This classification also specifies the material partial safety factors, which are taken into account in design depending on the standard.

For a library material, one of the following material types is preset.

Material Model

The following material models are available in the list:

Isotropic | Linear Elastic

The linear-elastic stiffness properties of the material are independent of direction. They can be described as follows:

The following conditions apply:

• E > 0
• G > 0
• -1 < ν ≤ 0.5 (for surfaces and solids; unlimited upward for members)

The flexibility matrix (inverse of the stiffness matrix) for surfaces is as follows:

Orthotropic | Linear Elastic (Surfaces)

With this material model, stiffness properties can be defined that differ in the two surface directions x and y. This makes it possible, for example, to represent the properties of glass-fiber reinforced plastic, ribbed slabs, or the stress directions of reinforced slabs. The surface axes x and y are perpendicular to each other in the surface plane.

To define different material properties for the x and y directions, activate the Custom Material checkbox in the 'Options' section. In the Orthotropic | Linear Elastic (Surfaces) tab, you can then define the material parameters.

For a positive definite stiffness matrix, the following conditions must be satisfied:

• E_x > 0; E_y > 0
• G_yz > 0; G_xz > 0; G_xy > 0
• $$\left|{\mathrm{\nu }}_{\mathrm{xy}}\right|<\sqrt{\frac{{\mathrm{E}}_{\mathrm{x}}}{{\mathrm{E}}_{\mathrm{y}}}}$$

  Poisson's Ratio

The Poisson's ratio can be defined for both orthotropic directions. The indices for ν_xy and ν_yx are assigned as follows: The first index is the strain in the direction of stress, the second index is the negative strain transverse to the direction of stress.

Orthotropic | Linear Elastic (Solids)

In the three-dimensional orthotropic material model, the elastic stiffnesses can be defined separately in all directions of the solid. To define different material properties for each direction, activate the Custom Material checkbox in the 'Options' section. In the Orthotropic | Linear Elastic (Solids) tab, you can then define the material parameters.

The stiffness matrix elements determined from the input are specified in the 'Orthotropic | Linear Elastic (Solids) - Stiffness Matrix' tab.

Isotropic | Timber | Linear Elastic (Members)

This material model is available for materials of the 'Timber' type. It allows you, for example, to represent the properties of an OSB panel in a member model that captures the different stiffnesses depending on the installation position. You can define the panel orientation in the Isotropic | Timber | Linear Elastic (Members) tab using the two lists.

Orthotropic | Timber | Linear Elastic (Surfaces)

For materials of the 'Timber' type, this material model can be used to control the E-modulus with regard to the load-bearing effect as a wall or slab as well as the shear modulus G_xy: OSB panels, for example, exhibit direction-dependent stiffnesses in the model depending on their installation position.

The stiffness parameters can be defined in the Orthotropic | Timber | Linear Elastic (Surfaces) tab. Standard values are preset for timber materials from the library. To define different material properties for each direction, first activate the Custom Material checkbox in the 'Options' section.

Basic Material Properties

This section of the 'Base' tab lists the key material properties.

Modulus of Elasticity

The E-modulus describes the relationship between normal stress and strain.

Shear Modulus

The shear modulus G, also called sliding modulus, is the second characteristic value for describing the elastic behavior of a linear, isotropic, and homogeneous material. In this case, the deformation is based on shear stress.

Poisson's Ratio

The Poisson's ratio ν, also called Poisson's number, is required to determine lateral contraction. For isotropic materials, the Poisson's ratio is usually between 0.0 and 0.5. From a value of 0.5 onwards (e.g. rubber), it should therefore be assumed that no isotropic material is present.

The relationship between E-modulus, G-modulus, and Poisson's ratio for an isotropic material is described in Equation Poisson's ratio.

If you enter a Custom Material with its isotropic properties, RFEM determines the Poisson's ratio from the E- and G-modulus values. You can change this default setting in the 'Definition Type' list if required.

Definition Type

Specific Weight / Density

The specific weight γ describes the weight of the material per unit volume. This specification is particularly important for the load case "Self-Weight": The automatic self-weight of the model is determined from the specific weight and the cross-sectional areas of the members used or the surfaces and solids.

The density ρ describes the mass of the material per unit volume. This specification is required for dynamic analyses.

Coefficient of Thermal Expansion

The coefficient of thermal expansion α describes the linear relationship between temperature and changes in length (expansion of the material when heated, contraction when cooled).

The coefficient of thermal expansion is relevant for the load types 'Temperature' and 'Temperature Change'.

Options

The checkboxes in this section of the 'Base' tab allow you to influence the material properties. After activating an option, new tabs are added.

Custom Material

For materials from the library, the material properties are fixed and preset. Therefore, they cannot be changed directly in the input fields. To adjust the properties of a material, activate the 'Custom Material' checkbox. This makes the input fields for the basic material properties accessible in the 'Base' tab. You can also modify the design-specific properties in the 'Material Values' tab (see Figure Adjust Material Properties). In the 'Stiffness Modification' tab, it is possible to scale the E- and G-modulus globally by a factor (see Figure Adjust Material Stiffness).

Temperature-Dependent

To define a linear elastic material with temperature-dependent stress-strain properties, activate the 'Custom' and 'Temperature-Dependent' checkboxes. You can then define the temperature-dependent material properties in the Temperature-Dependent tab.

Cost Estimation

For the determination of costs, the materials assigned to the individual objects are used. You can define the unit costs and units of the objects in the Cost Estimation tab.

Estimation of CO₂ Emissions

The estimation of CO₂ emissions is also based on the materials assigned to the individual objects. You can define the unit emissions and units in the Estimation of CO₂ Emissions tab.

Custom Texture

With a custom texture, you can assign a surface structure to the material. The objects are then displayed very realistically in the rendering. In the 'Custom Texture' tab, select an existing entry or define a new texture using the button (see chapter Textures).

Material Values

The Material Values tab lists all material properties that are relevant for the static analysis and for design in the add-ons.

Stiffness Modification

The Stiffness Modification tab is displayed if you have checked the Custom Material option in the 'Base' tab. Here, you can globally adjust the stiffness of the material, for example to take safety factors or reduced material properties into account.

Two options are available in the 'Modification Type' list:

• Division factor for E- and G-modulus
• Multiplication factor for E- and G-modulus

Enter the factor by which the material stiffness is to be adjusted in the 'Parameters' section.

If a material with orthotropic properties is present, the E- and G-modulus as well as the Poisson's ratios can be adjusted in the Orthotropic | Linear Elastic tab (see Figure Stiffness Matrix). If you activate the 'Set Stiffness Matrix Elements' option in the Orthotropic | Linear Elastic | Stiffness Matrix tab, you can also define the stiffness matrix elements manually.

Temperature-Dependent

The Temperature-Dependent tab is displayed if you have checked the Custom Material and Temperature-Dependent options in the 'Base' tab. Here, you can describe the temperature-dependent material properties. The temperature-dependent material properties are taken into account for objects subjected to thermal loads due to temperature or temperature change. When calculating temperature loads, the final temperature of the respective step is applied.

Select a material property, for example the E-modulus, in the 'Temperature-Dependent Property' list. Then create the required table rows using the button so that you can enter the temperatures with the corresponding values row by row. The button can also be used to import the data from an Excel table.

The 'Reference Temperature' defines the stiffnesses for the objects that are not subjected to temperature loads. For a reference value of, for example, 300 °C, the reduced E-modulus at this point of the temperature curve is applied to all members and surfaces.

Custom Material Library

You can save a custom material in a library as a template. This saves you from defining the material properties again in further projects.

Save Material

To save the current material as a custom material, click the button after defining the material properties in the lower section 'Basic Material Properties'.

The 'New Custom Material' dialog appears.

Enter the name of the material in the 'Name' field. If necessary, you can still adjust the material properties. Clicking OK saves the custom material in the library.

Import Material

To import a custom material from the library, click the button in the 'Basic Material Properties' section.

The 'Edit Custom Material' dialog appears. In this library with your saved materials (see Figure Dialog 'New Custom Material'), you can select the appropriate entry and then transfer it with OK.

If you have imported a custom material and want to change the properties in general, you can adjust the material properties in the library using the button (in the 'Basic Material Properties' section).

Define Library Location

By default, the library with the custom material is stored in the user_library_material.dbm file in the directory of the user configurations. You can check this directory in the Program Options.

Select the User Material Library entry in the Database category (1). Then display the folder of the user_library_material.dbm file using the button (2). If you want to use another material library located on a network drive of your company, define the directory of the file and click 'Save'. However, you can also transfer your file to another computer and set the storage path appropriately there in the same dialog.

Cost Estimation

The Cost Estimation tab is displayed if you have checked the Cost Estimation option in the 'Base' tab.

For the structural objects 'Members', 'Surfaces', and 'Solids', select which material property is relevant for the cost estimation in each case: weight, volume, or area, etc.

Enter the value in the 'Unit Cost' column that one unit of the material costs. Various options for the unit costs are available in the list of the 'Unit' column.

The program directly determines the proportionate costs from the unit costs and the properties of the structural objects assigned to the material.

The 'Total Weight' at the end of the table shows the mass resulting from the sum of all activated partial masses of the material. Furthermore, the proportion of the total weight that this material accounts for in the mass of all materials activated for the cost estimation is displayed.

The 'Total Costs' show the price resulting from the sum of all activated partial costs of the material. Furthermore, the proportion of the costs that this material accounts for in the total price of all materials activated for the cost estimation is displayed.

The 'Overall Costs' are the sum of the total costs of all materials activated for the cost estimation.

Estimation of CO₂ Emissions

The Estimation of CO₂ Emissions tab is displayed if you have checked the Estimation of CO₂ Emissions option in the 'Base' tab.

For the structural objects 'Members', 'Surfaces', and 'Solids', select which material property is relevant for the estimation of CO₂ emissions in each case: weight, volume, or area, etc.

Enter the value in the 'Unit Emission' column that one unit of the material causes in terms of CO₂. Various emission units for CO₂ equivalents are available in the list of the 'Unit' column.

The program determines the proportionate CO₂ emissions from the unit emissions and the properties of the structural objects assigned to the material. The calculation is thus performed directly and not, as in other add-ons, via a separate function.

The 'Total Emission' shows the CO₂ equivalents resulting from the sum of all activated partial emissions of the material. Furthermore, the proportion of emissions that this material accounts for in the total emissions of all materials activated for the estimation is displayed.

The 'Overall Emission' is the sum of the total emissions of all materials activated for the estimation of CO₂ emissions.