CAD/FEA Integration with STEP AP209 Technology and Implementation
Keith A. Hunten, P.E.
IPT Lead - Analysis Tools and Integration
Virtual Product Development Initiative
Lockheed Martin Tactical Aircraft Systems
The Design/Structural Analysis integration problem is typified by the requirement to share
geometric shape and analysis information in an iterative environment. The integration is made more
difficult when composite structures become a part of the problem. Figure 1 illustrates the
interconnectivity that this paper addresses. Most production systems currently employ specific point-to-
point translators to enable this process, and very few analysis systems are able to seamlessly return
geometric shape information to the design shape modeler. With composite structures there are the
additional problems of calculating true fiber directions and ply flat patterns that are shared with the
manufacturing process. All of this information needs to be shared with commercial or in-house detailed
analysis codes such as those for fastened joints and panel buckling.
CompositePly Boundaryand StackingFiniteOptimizationElementModeling
Figure 1. Engineering design, analysis, and manufacturing information interconnectivity.
In large scale industrial settings a standards-based solution to the iterative design/analysis
/manufacturing process is becoming an imperative. Figure 2 illustrates the ‘four-or-more’ problem that is
the major drawback to the point translator approach. If a standard data model (as in the right hand
portion of figure 2) is used to provide information integration there is a significant reduction in the
number of translators and in maintenance. In a large scale system such as that represented in figure 6
there may well be dozens of applications that are required to share information. The ISO 10303-209
STEP Application Protocol (AP) Composite and Metallic Structural Analysis and Related Design has been
developed to address this approach to the Design/Structural Analysis problem.
Figure 2. The ‘four-or-more’ problem.
1 Trademarks are capitalized and listed at the end of this paper Copyright ? 1997 by Lockheed Martin Corporation. All rights reserved.
ISO 10303 STEP (STandard for the Exchange of Product Model Data) is the standard that
provides a complete, unambiguous, computer-interpretable definition of the physical and functional
characteristics of a product throughout its life cycle. The standard has been created by a team of
international experts from disciplines such as aerospace, automotive, shipping, process plants,
CAD/CAE/CAM, academia, and government.
Figure 3 illustrates the various aspects of the STEP standard. The core of the standard is a series
of integrated data models that provide resources for information such as product design, geometric and
topologic representation, and some specialized representations. These data models are all written in
EXPRESS, an implementation-independent computer-sensible language that is also an ISO standard.
There are then Application Protocols (APs) that define application specific views of the integrated
resources in a clearly defined context. Some examples of APs include AP202 Associative Draughting,
AP203 Configuration Controlled Design, and the subject of this paper, AP209 Composite and Metallic
Structural Analysis and Related Design. There are two implementation methods defined within STEP,
the first is a flat ASCII file (Physical File), and the second a standardized application programming
database interface (STEP Data Access Interface (SDAI)). Finally, each AP has an associated set of
Conformance Testing documents to provide a method to test and certify translators and interfaces.
Application specific views of the Integrated Resourcesin a clearly defined context (Not all APs shown)
• Explicit, Associative Draughting
• Configuration Controlled Design (3D Shape)Translatorand• Composite and Metallic Structural AnalysisApplication and Related Design (AP209)Data StructureCertificationDefinition LanguageConformanceIntegrated ResourcesTesting
• Fundamentals of Product DesignEXPRESS• General Concepts• Geometric and Topologic RepresentationWritten in
• Testing• Specialized Representations RequirementsCore Data StructureUsed toImplementation SpecificationsDefinitionsTransferData• Physical File (Flat ASCII File)
• STEP Data Access Interface (Database)
Figure 3. The structure of the STEP standard.
The internal structure of an AP is illustrated in figure 4. The first section of an AP describes
what is in and out of scope for data exchange. There is then an Application Activity Model (AAM) of the
process that the AP enables that is written in the IDEF0 modeling language. The AAM is primarily used
to set the context for the data exchange and to provide a basis for data exchange requirements. The
Application Reference Model (ARM) is an information (data) model of all of the information
requirements of the AP defined in language that an application expert would be familiar. The ARM is the
part of an AP that a reviewer or user would find most useful. Finally there is the Application Interpreted
Model (AIM) that is the result of the mapping of the ARM requirements information model to the STEP
integrated resources information models. The AIM is written in EXPRESS and is useful only for implementers. There are also definitions of conformance classes for applications implementing the AP, and there are associated documents that delineate the test cases/suites for certifying implementations.
Application Protocol ScopeApplication Reference Model (ARM)•In•Information model in- - - - - Application Experts- - - - - Language•Out- - - - -- - - - -
Application Interpreted Model (AIM)
•Maps ARM to STEPENTITY date;Application Activity Model (AAM) Information Model day : day_in_week;•IDEF0•Detailed EXPRESS month : month_in_year; year : INTEGER;END_ENTITY;•Specify Information Requirements andusage/context
Conformance ClassesTest Cases/Suites
•Defines requirements for software•Used to certify software implementationsimplementing the AP
Figure 4. The internal structure of an Application Protocol
The scope of AP209 is illustrated in figure 5. A central theme to the partitioning of information within AP209 is that there are separate product definitions for the analysis and design disciplines. This division is primarily a constraint from the Aerospace industry, however similar requirements were noted from shipping, offshore, and automotive. Both product definitions may be independently configuration controlled, and many aspects of each are subject to approvals. Another crucial concept is that the shape and analysis information is meant to be implemented to enable bi-directional transfer to enable the feedback of information in the iterative design/analysis environment.
The analysis discipline product definitions primarily concern finite element models, analysis controls, and analysis outputs. Loads and boundary conditions may be applied to either mesh or geometry. Linear statics, modes, and frequency analysis types are supported. The scope of the analysis options was decided upon merits of trading addressing all analysis needs versus resources available to develop the standard. Surveys showed that the scope selected typically will address 60 to 90 percent of the analysis needs of an enterprise. It should be noted that AP209 was designed to be easily enhanced to support nonlinear analyses with little or no disturbance to the existing data model. In fact roughly 90 percent of the nonlinear problem is addressed at the present time. The analysis report serves several purposes: first is to document design and analysis decisions such as geometric and material idealizations, and second to reference documents containing text and/or graphical documentation of the model, analysis controls, and results.
The design discipline product definition is primarily concerned with shape representation and assemblies thereof. The geometric shape representations within AP209 are entirely interoperable with
those in AP203 that are currently being implemented by most CAD and CAE vendors. There is one
additional shape representation unique to AP209 that is utilized to represent the shape of composite
constituents such as plies and sandwich cores.
The composite constituents contain geometric information, a variety of laminate stacking tables
definitions, and either an as-laid or as-draped fiber orientation definition. Both part and zone ply table
capabilities are supported. Another important benefit of AP209 is the standardization of an taxonomy of
composite constituents. Definitions and illustrations are given each of the constituents such as ply, core,
and filament laminate.
Material specifications and properties are represented both for composite and homogeneous
(metallic) materials. The specifications and properties may be expressed either at the design level, or
more specialized analysis specifications and properties may be represented.
Analysis Discipline ProductInformation Shared BetweenDefinitionsAnalysis & Design
•Finite Element Analysis•3D Shape Representations–Model (Nodes, Elements, Properties,...)•Composite Constituents–Controls (Loads, Boundary•Material Specifications & PropertiesConstraints,...)•Part Definitions–Results (Displacements, Stresses,...)
•Ply Boundaries, SurfacesDesign Discipline Product Definition•Laminate Stacking Tables•Shape Representations•Reinforcement Orientation•Assemblies
Material Specifications &Configuration Control, ApprovalsProperties•Part, product definitions•Composites•Finite element analysis model, controls, and•Homogeneous (metallics)results
3D Shape Representation
•AP202/203 Commonality Plus Composite Specific3D Shapes–Advanced B-Representation–Faceted B-Representation–Manifold Surfaces With Topology–Wireframe & Surface without Topology–Wireframe Geometry with Topology–Composite Constituent Shape Representation
Figure 5. AP209 scope.
An important feature of AP209 is the sharing of information between the design and analysis
product definitions. The shape information is shared at the lowest level allowing locations for nodes to be
the same as points defining curves, surfaces, and solids. Additional associativities between nodes and
elements may be forged to geometric aspects such as curves and surfaces to facilitate processes such as
mesh generation. Both disciplines may also share composite constituents, material properties, and
material specifications. A final crucial concept is that both disciplines share the same product structure
ISO Status of AP209
The AP209 standard passed the ISO Committee Draft (CD) international ballot in October 1996 with
thirteen of eighteen P-members voting. Eleven countries agreed, and two disagreed. AP209 has also been
part of a focused effort to ensure the maximum degree of interoperability (data sharing) between STEP
APs. Issues regarding AP interoperability were submitted as CD ballot comments. No substantial
technical issues were raised against the CD document, and resolution of all ballot comments is complete.
The AP209 document is currently being prepared for distribution as a Draft International Standard (DIS),
with a target release date for international DIS balloting beginning in June 1997.
Information Integration with AP209
The integration of tools (applications) in a large-scale system is illustrated in figure 6. There are
five major groups of applications represented: CAD-based shape design, composite producibility and
optimization, analysis model creation and post-processing, a configuration control and archival
management system to enable the use of many different Finite Element Analysis (FEA) tools, and detail
analysis tools such as the panel analysis applications illustrated. AP209 technology is utilized throughout
to provide bi-directional sharing of information.
The CAD-based shape design tools today often have at least some level of functionality of Finite
Element Model (FEM) generation capability. The use of AP209 provides a standardized format so that
the mesh information and any related geometric associativities created in the CAD tool may be shared
with each of the other processes in figure 6. The composite shape and structure information may also be
associated and shared. This combination of associated shape, mesh, and composites information enables
applications such as automated composite analysis material property generation for finite elements, that is
a task previously impossible without the information integration offered by AP209. A typical automated
property routine would loop though all composite plies associated with an element and use the ply
thickness, orientation, and material property information to calculate elastic response matrices.
Pro / ECATIAUnigraphicsFiberSim
CAD ToolProducibilityPANDAWrappersTool WrappersPATRANP3
Feature-basedPly Stacking Panel AnalysisSDRCCost and DesignSequence andTool WrappersSimulationIDEASBoundary OptimizationModeling ToolTool WrappersWrappersMaterials
AP209 Archival, ConfigurationControl, and FE AnalysisTool Wrappers
Figure 6. Large scale system integration with AP209.
Composites producability and optimization tools stand to benefit most from AP209 technology as
the ability for the tools to share ply shape and structure table information in a standardized format has not
been available before. There are two paradigms for composite structure and shape representation within
AP209: ply by ply stacking to define the entire part, and zones of constant laminates (either at a point or
over an area on a surface). A part may be described by both methods to maximize flexibility in the
composite product development process. An example of the need for dual representation is designing and
analyzing a part by area zones, and then deriving the ply boundaries for manufacturing, and then the flat
patterns for a fabric cutting machine.
An area of information management that has long been neglected is the configuration control and
management of FEA. The combination of product structure, work authorization, and configuration
management data structures in AP209 offer the capability to manage a wide variety of CAD/CAE
information. An application to manage and archive AP209 information provides the engineer with more
options than may be available with current generation point-tot-point translators. An example of this
utility would be SPAM (Stiffened Panel Analysis Modeler), that was originally written to output
ABAQUS information. Engineers at a different corporate site wanted to use SPAM, but only had
ANSYS available. Conversion of SPAM to AP209 in combination with the management and translation
application would allow the use of the tool with a wider variety of solvers without further modification of
the detail analysis tool providing a significant resource and maintenance cost savings.
Having a standardized shape, analysis, and composites database enables other processes than
those that have been classically involved in the Design/Analysis process. An example of this is composite
failure analyses that require analysis, shape, and detail analysis input to perform the task.
(UnstructuredTHERMOSERVICESMECHANICALFinite Element,(Unstructured and(StandardSUB-SYSTEMSComposite shapestructured gridmaterials,and tables)(Control Laws,Finite Difference)allowables,?State Analyses)
STEP Integrated Engineering Analysis Core
Application Reference Model (EA C-ARM)
Figure 7. Engineering Analysis Core ARM architecture.
Future Engineering Analysis Development
There is currently a new work item (NWI) being initiated in the ISO Engineering Analysis (EA)
committee to build upon AP209 to create a suite of EA APs. An EA Core ARM is being developed that
will unify various analysis disciplines (figure 7). The requirements model in the EA C-ARM will be
completely mappable to that in AP209 assuring interoperability with other disciplines. To date three other
APs have been scoped for implementation within the EA Suite. The first will be a material services AP
that will provide a standard to represent properties and allowables for materials, adhesives, and standard
fasteners. A second AP will be created to represent structured and unstructured finite difference
aerodynamic and thermodynamic information. The last AP will be created to represent information to
perform the electro-mechanical sub-systems integration and analysis tasks such as control laws and state
space analyses. The intent is to provide an interoperating suite of EA APs that will share information in a
To date there have been three successful pilot implementations of AP209, and two more are
underway. The pilots completed to date were performed by three teams of companies: one under the
auspices of the PDES, Inc. consortium, another under a contract from the US Airforce Manufacturing
Technologies Directoriate’s PDES Application Protocol Suite for Composites (PAS-C) program, and the
third under contract from the US Army Tank Command (TACOM). Subsequently two more efforts are
underway: a Phase two pilot under PDES, Inc., and the Defense Advance Research Program
Administration (DARPA) MADE (Manufacturing Development) Integrated Product Data Environment
(IPDE) program being worked at Boeing. The successes of these pilots have proven the effectiveness and
accuracy of the AP209 data exchange standard.
ShapeSum of Plies
Figure 8. Shape representations from the TACOM AP209 pilot.
The initial PDES, Inc. FEA pilot team included participants from Boeing, Ford, General Motors
International Technegroup Incorporated (ITI-OH), Lockheed Martin, MacNeal Schwendler Corporation,
and Northrop Grumman. The exchanges centered upon the analysis of a metallic automotive engine
crankshaft. A solid model of the crankshaft was transferred from ComputerVision (CV) to PATRAN
where an idealized analysis shape and the derived analysis model were created. The model was
subsequently analyzed in MSC/NASTRAN, and also written out in AP209 format and read into CV
Stresslab where an identical analysis was performed. During each step in the demonstration information
was appended to an AP209 Physical File repository and displayed in an AP209 Visualizer application
created by ITI-OH. Note that the AP209 visualizer had support from the TACOM and PAS-C pilots as
well. Thus at the end of the cycle there were analysis results available in CV Stresslab, PATRAN, and in
the AP209 visualizer demonstrating the sharing of analysis information. A video documenting this project is available from PDES, Inc.
The TACOM pilot concentrated on the design and analysis of a composite upper hull of an armored vehicle. The participants included South Carolina Research Authority (SCRA), Lockheed Martin, and MacNeal Schwendler Corporation. Figure 8 illustrates the various shape representations of the nose of the composite armored vehicle (CAV) that were represented in a single AP209 repository throughout the life cycle of the pilot. The solid model of the nose CAV was transferred out of Intergraph and into PATRAN, as were the surface/wireframe representations of the ply boundaries. The ply boundaries were also put through a ply merger and appended to an AP209 repository of the solid model shape. A finite element model of the nose was then made in PATRAN, and output to AP209 format and appended to the AP209 repository. An application developed under the pilot was then run to automatically generate the material response matrices from the plies and elements that were then passed back to PATRAN. The analysis was then performed in ABAQUS, translated back into PATRAN, and then into AP209 format and appended to the repository. The completed repository was then read back into Intergraph. In the end there were three applications able to visualize the analysis output: PATAN, Intergraph, and the AP209 visualizer.
The PAS-C program AP209 pilot was performed with AP232 (Technical Data Packaging Core Information and Exchange) to show how the two APs cooperated in performing a configuration controlled design and analysis modification to a horizontal stabilizer skin of an airlifter. Both AP209 and AP232 were primarily developed under the PAS-C program. The PAS-C pilot began with a metallic horizontal stabilizer skin native CAD (Unigraphics) and AP209 files with related configuration control information being transmitted to a subcontractor via AP232. The subcontractor then took the AP209 shape of the metallic skin and used it as a basis to create a hat-stiffened composite replacement skin design. The composite design was first created using a zone composite description, and then converted to a ply description. The shape information was shared with PATRAN to create a finite element model, and the zone descriptions paired with the finite element model used to automatically create the skin elastic response matrices. The analyses of the metallic skin (again in AP209 format) was used as a basis for loads and boundary conditions to analyze the replacements composite skin. The composite shape, FEM, composite plies and zones, and analysis information was aggregated in an AP209 repository in a similar fashion to the last two pilots. Analysis results were viewed both in PATRAN and the AP209 visualizer. Finally the revised versions of the shape and analysis models were packaged in AP232 format and returned to the prime contractor. A video documenting this pilot is currently in production.
The Phase two PDES, Inc. EA pilot has been underway since October 1997. The scope of the pilot is to expand the richness of AP209 implementations completed in the Phase one FEA pilot, and to extend the implementations to include panel and finite difference aerodynamic information. The aero data will then be coupled with structural data to enable a loosely coupled un-trimmed aeroelastic analysis. The participants include Boeing (including the MADE IPDE work related in the next paragraph), Lockheed Martin, MacNeal Schwendler, and NASA Lewis.
The DARPA/Boeing MADE IPDE contract is to provide an AP209 based coupling between
structural and aerodynamic analysis. The team includes Boeing, Arizona State University, and MacNeal Schwendler Corporation. The structural tools involved include MSC/PATRAN and MSC/NASTRAN, and the aerodynamic tool is the Boeing A502 panel aerodynamic application. The project includes both Physical File and SDAI data sharing implementations, and includes an innovative approach to integrating applications with multiple APs. A typical analysis iteration involves reading in the AP209 file of A502 panels and pressures into MSC/PATRAN, reading in the AP209 file of FEM and analysis results into MSC/PATRAN, mapping the pressures from the A502 model onto the structural model, analyzing the FEM with MSC/NASTRAN, mapping the deflections back onto the A502 mesh in PATRAN, and writing out the A502 panel model in an AP209 file for another aerodynamic analysis with A502. To date the AP209 Physical File based implementation has successfully demonstrated five iterations to a converged aeroelastic analysis of a composite VTOL aricraft wing.
The ISO 10303 STEP AP209 emerging standard has received widespread review during the last six years since the inception of the project. Many pilot implementations have proven that AP209 capabilities are mature enough for large scale commercial implementations. Current efforts underway will ensure that AP209 will function interoperably within a suite of EA APs that address the multi-disciplinary analysis problems that are increasingly facing engineers. Work with AP232 and other AP interoperability projects have ensured data sharing with many other STEP APs. Finally, it is clear that the scope of AP209 provides an effective standards-based solution to the majority of the iterative structural Design/Analysis integration problems.
NASTRAN is a registered trademark of NASA. MSC/NASTRAN is an enhanced, proprietary version developed and maintained by MacNeal Schwendler Corporation.
PATRAN is a registered trademark of the MacNeal Schwendler Corporation.
Unigraphics is a registered trademark of the Electronic Data Corporation.
Computervision is a registered trademark of the Computervision Corporation.
Stresslab is a registered trademark of the Computervision Corporation.
Intergraph is a registered trademark of the Intergraph Corporation.
STEP, Standard for the Exchange of Product Model Data
AP, Application Protocol
ARM, Application Reference Model
AIM, Application Interface Model
FEA, Finite Element Analysis
SPAM, Stiffened Panel Analysis Modeler