This page is about the material data system in FreeCAD.

Abstract

Since it is hard, or even impossible, to define a fixed or complete set of material properties, we go a more open way. Every object in FreeCAD which has to deal with material will have a Property named "Material", which is a key/value list that can hold an infinite number of material properties. Since this is a very open and extensible way to deal with such data, it also holds the danger of chaos. Therefore this page defines some rules and basic properties for dealing with such material-property-maps.

Rules

Every property set has only one mandatory entry which is "Name". This is the primary key of the material. The rest of the material properties are optional or can be retrieved out of a material DB.

Property names (key) are ordered by strings separated by underscores. The first substring is named by the application or standard, the following can be used to further group the properties. The Values can also be grouped by underscores, e.g. to separate different sorts of steel. Examples:

  • Name=Steel_Cast
  • SpecificWeight=7.85 (at 20° in kg/mm3)
  • EN10027_name = S235JR+AR (steel standard EN 10027-1)
  • FEM_YoungsModulus = xx (in mm−1·kg·s−2)
  • FEM_YoungsModulus_Z
  • FEM_YoungsModulus_X

Each property has a human readably description on this Material page, with links to further information (e.g. Wikipedia).

For each property a unit has to be defined, based on the FreeCAD internal unit mm-kg-s! That allows consistent usage and translation.

The key (name) and the value of the property uses only ASCII characters (7-bit). The keys are written in Camel-Case but interpreted case-insensitive.

The underscores allow later a tree view property editor/viewer which allow folding.

Tools

There are some good resources out there handle materials more easy:

Material Database

Given that above standard is implemented, it would be stupid to store all the properties again and again to objects. Basically we can build up a Material DB with the Name as a primary key. So if you have no special needs for your material, you just define e.g. Name=Steel and FreeCAD can retrieve all properties from that DB. Every additional property you set in the map overrides the one from the DB.

In the future we can host that DB somwhere in the Web and build up a general OpenSource material DB.

At the moment I think of a compiled in mini dataset with a set of "basic" materials and its basic properties and a SQLite based full version.

Material.py

Since handling material-properties is a tedious work we should implement a Python front-end module calls Material.py. This will be the place to implement all kind of helper methods for material handling.

  • Calculation of Mass out of Volume and Density
  • Translation in different unit systems
  • Calculation needed in special application (e.g. FEM)
  • and anything else we don't know yet

The module should be implemented that way it can run in FreeCAD or stand alone on the command line (material-property-map has be given as python map).

The FreeCAD material card file format

Working with materials means often import/export material-definitions. There fore a file format is needed. Since we have only key/value form, we can use a simple and easy to read and parse file format. There fore the ini-file format is chosen. Its standardized and there are already parser available. E.g the Config parser module in python.

Each material definition reside in a file with the ending .FCMat. Some of this files are part of the FreeCAD source and get compiled into the binary. This is to save overhead in distribution and access. But also files can be placed and searched on different places to allow additional non-standard material definitions.

Examples

; last modified 1 April 2001 by John Doe

Name=Steel_Cast
Father=Steel
Source=Some material book everyone knows (or not) ;Some comment
 
[EN10027]
; steel standard EN 10027-1
Name=S235JR+AR      

[Graphic]
Color_Emissiv = 255,255,255

Material properties

Here now the description of agreed material-properties. Feel free to add a subsection for the material-properties of you field of expertise.

General

General material properties
property name Description Unit/Data-Type
Name Unique name of the property, following the rules described above ASCII string 7-bit
Father Name of the material group this material belongs to. If defined this material inherits all the father properties. That means if not defined the father properties will be used. ASCII string 7-bit
Description A placeholder for a longer description of the material ASCII string 7-bit
SpecificWeight The specific weight (also known as the unit weight) is the weight per unit volume of a material. see: Specific_weight kg/mm^3
Vendor Specifies the brand or vendor of the material ASCII string 7-bit
ProductURL An URL where to find more information about the material ASCII string 7-bit
SpecificPrice The price per unit of this material. Units can vary a lot (USD/m³, EUR/piece, etc...) ASCII string 7-bit

ToDos: add some properties with an ordering system for materials (metal, alloy, mineral, wood, ....)

Mechanical

Material properties used in mechanical engineering
property name Description Unit/Data-Type
YoungsModulus Young's modulus, also known as the tensile modulus or elastic modulus, is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. See: Young's modulus kg*mm^-1*s^-2 (kPa)
UltimateTensileStrength Des... N'*mm^-2 (MPa)
Hardness Des...
EN-10027-1 In case of steel material the Steel grade as defined in the European standard No. 10027-1. string ASCII 7-bit

ToDos: further add properties needed for mechanical design.

Graphical

This section defines material-properties which are related to the visual appearance of the material. The

visual appearance
property name Description Unit/Data-Type
AmbientColor Ambient color in the Coin3D color model float,float,float range: 0.0-1.0
DiffuseColor Diffuse color in the Coin3D color model float,float,float range: 0.0-1.0
SpecularColor Specular color in the Coin3D color model float,float,float range: 0.0-1.0
EmissiveColor Emissive color in the Coin3D color model float,float,float range: 0.0-1.0
Shininess Ambient color in the Coin3D color model float range: 0.0-1.0
Transparency Ambient color in the Coin3D color model float range: 0.0-1.0
VertxShader Vertex shader program as defined in GlSl Multi line string ASCII 7-bit
FragmentShader Fragment shader program as defined in GlSl Multi line string ASCII 7-bit


Finite Element Method

ToDos: Build up collection of FEM material properties.

Computational Fluid Dynamics

ToDos: Build up collection of CFM material properties.

Architecture and BIM

Material properties used in architectural design
property name Description Unit/Data-Type
StandardFormat The standard specification system used in this material (ASTM, MasterFormat, CSI, OmniClass, etc...) String ASCII 7-bit
StandardCode The specific code of this material in the above standard format String ASCII 7-bit
FireStandard The fire rating standard used in the material String ASCII 7-bit
FireClass The fire resistance class of the material in the above standard String ASCII 7-bit
ThermalConductivity The thermal conductivity (R or lambda coefficient) that indicates the capacity to transfer heat of a material W/m²K
SoundTransmission The sound transmission coefficient of this material W/m²K
Finish The type of finishing/coating of this material String ASCII 7-bit
Color The color of this material String ASCII 7-bit
UnitsArea The number of units of this material necessary to fill a certain area String ASCII 7-bit

ToDos: add sustainability & LEED properties

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