Use of STEP AP 209

What is AP 209
Do I have to read AP 209?
AP 209 viewer
AP 209 implementation and testing

What is AP 209?

A STEP Application Protocol (AP) specifies how the STEP integrated resource parts are used in a particular business application. Two STEP APs of particular interest to engineering analysis are:

AP 203, Configuration controlled design: This AP supports product configuration management, product assembly structure and 3D shape. The AP was published in 1994, and is now in daily use, especially within the automotive and aerospace industries.
AP 209, Composite and metallic structural analysis and related design: This AP encompasses all of AP 203 and also supports composite lay-up information and finite element analysis. The AP was published in 2001, and industry implementation is being lead by the PDES Inc. engineering analysis team.

NOTE - Although AP 203 is a subset of AP 209, both APs will continue to be used. Some software accepts AP 203 files, but not AP 209 files.

Key features of AP 209 are as follows.

The AP supports different versions of a product design and different versions of an analysis model, with links between analysis versions and design versions. An AP 209 implementation can be used to add configuration management data to analysis data. This will enable analysis data to be linked to design data within a PDM system.
The AP supports both CAD geometry and finite element data, with links between:
- geometric features; and
- elements, faces or edges of elements, and nodes.
Boundary conditions and loadings can be defined with respect to either geometric features, or elements ad nodes. A finite element pre-processor can use these links to generate finite element input data. A finite element post-processor can use these links to relate finite element results back to product design geometry.

Information about the business drivers behind STEP AP 209, is contained in 'Open systems for Engineering Analysis - made possible by a standard', an extract from an article in the NAFEMS journal 'Benchmark'.

Do I have to read AP 209?

No. AP 209 import/export should be:

just another button on your CAD/CAE system; or
a software utility that translates between AP 209 and a CAD/CAE system native format.

Practicing engineers do not need to know more. But when purchasing software, you should be familiar with the scope of AP 209. The standard has a broad scope, so what you want to do may be supported by the standard, but not yet implemented by your vendor.

Key documents

ISO 10303-209:2001, Composite and metallic structural analysis and related design: This defines the AP itself. It references part 104 for its finite element analysis capabilities (see below) and other integrated resource parts for configuration management, assembly structure, and geometry and topolpgy.
ISO 10303-104:2000, Finite element analysis: This is the integrated resource that defines the finite element capabilities used within AP 209.

You have to get these documents from your national standards body (e.g. ANSI, DIN, AFNOR, BSI) or from ISO. They are not on the web.

AP 209 viewer

Finite element model and results data in AP 209 format can be viewed free of charge at MSC Software. Subscribers to the MSC Internet service can also manipulate and analyse AP 209 data.

Product geometry in AP 203 format can be viewed free of charge at STEP Tools Inc..

AP 209 implemention and testing

In order to implement AP 209, you do have to read the standard. It is heavy going, but there are two (complementary) supporting documents which will help:

Recommended practices for AP 209: This document was produced by PDES Inc. to assist AP 209 implementors.
Guidelines for the instantiation of AP 209: This document was produced by NAFEMS to define good practice in the use of AP 209 for the publication of benchmarks (and incidentally for other purposes).

AP 209 implementations can be tested using the published AP 209 files for the NAFEMS benchmarks.

STEP is designed to ensure high quality data exchange.

How STEP works

The STEP AP contains a 'long form schema' defined using the EXPRESS language

This schema specifies the structure of the data in an exchange file, and imposes constrains on the consistency and completeness of the data.

NOTE - EXPRESS is defined by ISO 10303-11. EXPRESS is similar to UML, but with a powerful capability for imposing constraints on data.
The format of an exchange file (known as a 'part 21 file') is defined by algorithm from the EXPRESS schema.

NOTE - The algorithm for creating an exchange file is defined by ISO 10303-21.
Software can compile the EXPRESS schema, and then check that an exchange file has the correct structure and satisfies the constraints.

NOTE - The constraints in the AP 209 schema are very extensive, so that an AP 209 exchange file that complies with the schema is almost certainly a complete and consistent set of finite element analysis data.

The correctness of a STEP exchange file can be checked using public domain software, as follows:

AP 209 long form schema: This is the complete EXPRESS schema for AP 209
NOTE - Unlike the AP 209 text which has to be purchased, the EXPRESS schema is freely available.
EXPRESSO toolkit: This toolkit was written by NIST in the USA to assist STEP implementation.