Material/de

Diese Seite erklärt das Materialdatensystem in FreeCAD.

Diese Seite befindet sich noch in der Übersetzung!

Überblick
Weil es schwierig bis unmöglich ist, einen festes oder komplette Bestand an Materialeigenschaften festzulegen, wählen wir einen offeneren Weg. Jedes Objekt in FreeCad das mit Materialien zu tun hat, hat eine Eigenschaft die mit "Material" benannt ist und eine Schlüssel/Wert-Liste ist, die eine unendliche Zahl an Materialeigenschaften enthalten kann. Weil dieser Weg mit solchen Daten umzugehen sehr offene und erweiterbar ist, besteht auch die Gefahr von Chaos. Deswegen beschreibt diese Seite einige Regeln und grundsätzlichen Eigenschaften um mit solchen Materialeigenschaften-Listen umzugehen.

Regeln
Jeder Eigenschaftssatz hat nur einen notwendigen Eintrag der "Name" benannt ist. Die ist der primäre Schlüssel des Materials. Die restlichen Materialeigenschaften sind optional oder können aus einer Materialdatenbank bezogen werden.

Eigenschaftsnamen (Schlüssel) nach Wörtern getrennt durch Unterstriche geordnet. The first substring is named by the application or standard, the following can be used to further group the properties.

Die Werte können durch Unterstriche gruppiert werden, z.B. um verschiedene Stahlsorten zu unterscheiden. Beispiel:
 * 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:
 * Units calculater to get your material information in the Unit needed for FreeCAD
 * http://www.matweb.com/ free 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 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
ToDos: add some properties with an ordering system for materials (metal, alloy, mineral, wood, ....)

Mechanical
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

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
ToDos: add sustainability & LEED properties