Material

Overview

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". This is comprised of 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 disorganization and 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 readable 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:

Units calculator to get your material information in the Unit needed for FreeCAD
http://www.matweb.com/ free of charge Material database with thousands of material values

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 called {{FileName|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. Therefore 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. Therefore 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 resides in a file with the ending {{FileName|.FCMat}}. Some of these 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.

Example .FCMat file

 ; 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]
 EmissiveColor = 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.